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Default C-Audio Power Amp Head ...

Does anyone have a set of schematics for the C-Audio RA3001 that they could
let me have fairly urgently please ?

The links to the service manual on the supposed C-Audio 'website', just seem
to take you round in ever decreasing circles via other third party vendors
of everthing you can imagine.

TIA

Arfa


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Arfa Daily wrote:

Does anyone have a set of schematics for the C-Audio RA3001 that they could
let me have fairly urgently please ?


It's not a 'head', it's a 19" rack mounting pro power amp with line level
inputs. What do you want to know btw ? They are notoriously unreliable. First
job is to replace all the PSU caps that have been cooked by the hot exhaust air.
Then check how many mosfets are open.

I know an awful lot about it, having rejected it as an ODM product for
Studiomaster. I think it was that model.


The links to the service manual on the supposed C-Audio 'website', just seem
to take you round in ever decreasing circles via other third party vendors
of everthing you can imagine.


Harman UK bought them. And I could tell you a story about that too ! Ask there.
Except it's not Harman any more it seems but google that for starters. They've
moved to Letchworth. I think most of the C-Audio parts ended up shuffled into a
corner (I could tell another story) so they might be willing to get rid of some
unwanted and unloved bits. Unless they already put them in a skip (dumpster for
USAans)

Graham

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Default C-Audio Power Amp Head ...


"Eeyore" wrote in message
...


Arfa Daily wrote:

Does anyone have a set of schematics for the C-Audio RA3001 that they
could
let me have fairly urgently please ?


It's not a 'head', it's a 19" rack mounting pro power amp with line level
inputs. What do you want to know btw ? They are notoriously unreliable.
First
job is to replace all the PSU caps that have been cooked by the hot
exhaust air.
Then check how many mosfets are open.

I know an awful lot about it, having rejected it as an ODM product for
Studiomaster. I think it was that model.


The links to the service manual on the supposed C-Audio 'website', just
seem
to take you round in ever decreasing circles via other third party
vendors
of everthing you can imagine.


Harman UK bought them. And I could tell you a story about that too ! Ask
there.
Except it's not Harman any more it seems but google that for starters.
They've
moved to Letchworth. I think most of the C-Audio parts ended up shuffled
into a
corner (I could tell another story) so they might be willing to get rid of
some
unwanted and unloved bits. Unless they already put them in a skip
(dumpster for
USAans)

Graham


The guy who owns the shop where all this stuff comes from, and who is a
musician himself with 'many years in', tends to call anything that's rack
mount, line input and 'power', a "head", as opposed to an "amp" for an
instrument level standalone unit like a Marshall, or a "combo" for the same
thing with speakers built in like an AC30 or Fender Twin. I just follow his
lead, and call them the same. What do you describe as a "head"?

Anyways, as to what's wrong with it. The "A" channel has an *extremely*
asymmetric output. On a sine wave, looks like the output from a half wave
reccy with no filter cap on the end. It also 'bounces' in amplitude when the
input level, or front panel level, is varied. The problem is right up the
front end somewhere. There are pukka sine waves around the TL074 input amp,
but soon after, the signal has taken on this asymmetry, which is then
faithfully amplified by the output stage. The "B" channel works perfectly,
so I guess I can start comparing between the two. Just would have been a lot
easier with a set of schematics to see where exactly the signal goes. It's
got that nasty 'feel' about it, that says it's going to be something like an
o/c resistor, which looks perfect to the naked eye ...

I see a couple of bunches of four TO92 transistors, so I think that may be a
good place to start looking.

Arfa


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Arfa Daily wrote:

"Eeyore" wrote in message
Arfa Daily wrote:

Does anyone have a set of schematics for the C-Audio RA3001 that they
could let me have fairly urgently please ?


It's not a 'head', it's a 19" rack mounting pro power amp with line level
inputs. What do you want to know btw ? They are notoriously unreliable.
First job is to replace all the PSU caps that have been cooked by the hot
exhaust air. Then check how many mosfets are open.

I know an awful lot about it, having rejected it as an ODM product for
Studiomaster. I think it was that model.

The links to the service manual on the supposed C-Audio 'website', just
seem to take you round in ever decreasing circles via other third party
vendors of everthing you can imagine.


Harman UK bought them. And I could tell you a story about that too ! Ask
there. Except it's not Harman any more it seems but google that for

starters.
They've moved to Letchworth. I think most of the C-Audio parts ended up

shuffled
into a corner (I could tell another story) so they might be willing to get

rid of
some unwanted and unloved bits. Unless they already put them in a skip
(dumpster for USAans)


The guy who owns the shop where all this stuff comes from, and who is a
musician himself with 'many years in', tends to call anything that's rack
mount, line input and 'power', a "head", as opposed to an "amp" for an
instrument level standalone unit like a Marshall, or a "combo" for the same
thing with speakers built in like an AC30 or Fender Twin. I just follow his
lead, and call them the same. What do you describe as a "head"?


A 'head' has preamp level inputs. A guitar head has sensitive Hi-Z inputs for
guitars, a 'PA' head has mic inputs. The old name for what an RA3001 type amp is
a 'slave amp'.


Anyways, as to what's wrong with it. The "A" channel has an *extremely*
asymmetric output.


Typical C-Audio !


On a sine wave, looks like the output from a half wave
reccy with no filter cap on the end. It also 'bounces' in amplitude when the
input level, or front panel level, is varied. The problem is right up the
front end somewhere. There are pukka sine waves around the TL074 input amp,
but soon after, the signal has taken on this asymmetry, which is then
faithfully amplified by the output stage. The "B" channel works perfectly,
so I guess I can start comparing between the two. Just would have been a lot
easier with a set of schematics to see where exactly the signal goes. It's
got that nasty 'feel' about it, that says it's going to be something like an
o/c resistor, which looks perfect to the naked eye ...

I see a couple of bunches of four TO92 transistors, so I think that may be a
good place to start looking.


Unlikely.

Do you know how to test Hitachi lateral mosfet output devices ? Not much
different from any mosfet except they made true complements.

Remove them all. I expect they're TO-3 so easy to get them out and test. You
will find a fair few are totally open. Replace these and you're good to go but
DO replace the reservoir caps too. They will have been roasted by the searingly
hot air passing over the heatsink. Don't even think of using 85C types.

One of the worst laid out designs I've ever seen in my entire life.

In tests I measured 150C *on the HEATSINK*. God knows what the junction temp
was. Your trouble will be getting genuine Hitachi replacements as they stopped
making them and the Semelab/Magnatec and Exicon replacements aren't exactly
identical.. I may have a few but you WILL pay megabucks for them.

Graham

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Default C-Audio Power Amp Head ...


"Eeyore" wrote in message
...


Arfa Daily wrote:

"Eeyore" wrote in message
Arfa Daily wrote:

Does anyone have a set of schematics for the C-Audio RA3001 that they
could let me have fairly urgently please ?

It's not a 'head', it's a 19" rack mounting pro power amp with line
level
inputs. What do you want to know btw ? They are notoriously unreliable.
First job is to replace all the PSU caps that have been cooked by the
hot
exhaust air. Then check how many mosfets are open.

I know an awful lot about it, having rejected it as an ODM product for
Studiomaster. I think it was that model.

The links to the service manual on the supposed C-Audio 'website',
just
seem to take you round in ever decreasing circles via other third
party
vendors of everthing you can imagine.

Harman UK bought them. And I could tell you a story about that too !
Ask
there. Except it's not Harman any more it seems but google that for

starters.
They've moved to Letchworth. I think most of the C-Audio parts ended up

shuffled
into a corner (I could tell another story) so they might be willing to
get

rid of
some unwanted and unloved bits. Unless they already put them in a skip
(dumpster for USAans)


The guy who owns the shop where all this stuff comes from, and who is a
musician himself with 'many years in', tends to call anything that's rack
mount, line input and 'power', a "head", as opposed to an "amp" for an
instrument level standalone unit like a Marshall, or a "combo" for the
same
thing with speakers built in like an AC30 or Fender Twin. I just follow
his
lead, and call them the same. What do you describe as a "head"?


A 'head' has preamp level inputs. A guitar head has sensitive Hi-Z inputs
for
guitars, a 'PA' head has mic inputs. The old name for what an RA3001 type
amp is
a 'slave amp'.


Anyways, as to what's wrong with it. The "A" channel has an *extremely*
asymmetric output.


Typical C-Audio !


On a sine wave, looks like the output from a half wave
reccy with no filter cap on the end. It also 'bounces' in amplitude when
the
input level, or front panel level, is varied. The problem is right up the
front end somewhere. There are pukka sine waves around the TL074 input
amp,
but soon after, the signal has taken on this asymmetry, which is then
faithfully amplified by the output stage. The "B" channel works
perfectly,
so I guess I can start comparing between the two. Just would have been a
lot
easier with a set of schematics to see where exactly the signal goes.
It's
got that nasty 'feel' about it, that says it's going to be something like
an
o/c resistor, which looks perfect to the naked eye ...

I see a couple of bunches of four TO92 transistors, so I think that may
be a
good place to start looking.


Unlikely.

Do you know how to test Hitachi lateral mosfet output devices ? Not much
different from any mosfet except they made true complements.

Remove them all. I expect they're TO-3 so easy to get them out and test.
You
will find a fair few are totally open. Replace these and you're good to go
but
DO replace the reservoir caps too. They will have been roasted by the
searingly
hot air passing over the heatsink. Don't even think of using 85C types.

One of the worst laid out designs I've ever seen in my entire life.

In tests I measured 150C *on the HEATSINK*. God knows what the junction
temp
was. Your trouble will be getting genuine Hitachi replacements as they
stopped
making them and the Semelab/Magnatec and Exicon replacements aren't
exactly
identical.. I may have a few but you WILL pay megabucks for them.

Graham


Well, if that's the case, it ain't gonna get done, as he only sold it a
couple of weeks ago as a cheapy second hand job. As a matter of interest,
does the circuit employ feedback to the front end then ? I wasn't expecting
this to be an output issue, as the waveform seems to distort quite early in
the chain, but now you suggest this, I guess it makes some sense of the way
that the amplitude of the waveform 'bounces' a couple of times before
settling, when the level is adjusted, externally or front panel.

Arfa




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Default C-Audio Power Amp Head ...

On Nov 24, 7:25*pm, "Arfa Daily" wrote:
"Eeyore" wrote in message

...







Arfa Daily wrote:


Does anyone have a set of schematics for the C-Audio RA3001 that they
could
let me have fairly urgently please ?


It's not a 'head', it's a 19" rack mounting pro power amp with line level
inputs. What do you want to know btw ? They are notoriously unreliable.
First
job is to replace all the PSU caps that have been cooked by the hot
exhaust air.
Then check how many mosfets are open.


I know an awful lot about it, having rejected it as an ODM product for
Studiomaster. I think *it was that model.


The links to the service manual on the supposed C-Audio 'website', just
seem
to take you round in ever decreasing circles via other third party
vendors
of everthing you can imagine.


Harman UK bought them. And I could tell you a story about that too ! Ask
there.
Except it's not Harman any more it seems but google that for starters.
They've
moved to Letchworth. I think most of the C-Audio parts ended up shuffled
into a
corner (I could tell another story) so they might be willing to get rid of
some
unwanted and unloved bits. Unless they already put them in a skip
(dumpster for
USAans)


Graham


The guy who owns the shop where all this stuff comes from, and who is a
musician himself with 'many years in', tends to call anything that's rack
mount, line input and 'power', a "head", as opposed to an "amp" for an
instrument level standalone unit like a Marshall, or a "combo" for the same
thing with speakers built in like an AC30 or Fender Twin. I just follow his
lead, and call them the same. What do you describe as a "head"?

Anyways, as to what's wrong with it. The "A" channel has an *extremely*
asymmetric output. On a sine wave, looks like the output from a half wave
reccy with no filter cap on the end. It also 'bounces' in amplitude when the
input level, or front panel level, is varied. The problem is right up the
front end somewhere. There are pukka sine waves around the TL074 input amp,
but soon after, the signal has taken on this asymmetry, which is then
faithfully amplified by the output stage. The "B" channel works perfectly,
so I guess I can start comparing between the two. Just would have been a lot
easier with a set of schematics to see where exactly the signal goes. It's
got that nasty 'feel' about it, that says it's going to be something like an
o/c resistor, which looks perfect to the naked eye ...

I see a couple of bunches of four TO92 transistors, so I think that may be a
good place to start looking.

Arfa- Hide quoted text -

- Show quoted text -


On the western side of the big pond, "head" can mean what you folks on
the eastern side, I believe, call the "Loo". Think it comes from
nautical background when the in-ship toilet was at the front/head of
the ship/boat.

Bob H
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Default C-Audio Power Amp Head ...


"hr(bob) " wrote in message
...
On Nov 24, 7:25 pm, "Arfa Daily" wrote:
"Eeyore" wrote in message

...







Arfa Daily wrote:


Does anyone have a set of schematics for the C-Audio RA3001 that they
could
let me have fairly urgently please ?


It's not a 'head', it's a 19" rack mounting pro power amp with line
level
inputs. What do you want to know btw ? They are notoriously unreliable.
First
job is to replace all the PSU caps that have been cooked by the hot
exhaust air.
Then check how many mosfets are open.


I know an awful lot about it, having rejected it as an ODM product for
Studiomaster. I think it was that model.


The links to the service manual on the supposed C-Audio 'website', just
seem
to take you round in ever decreasing circles via other third party
vendors
of everthing you can imagine.


Harman UK bought them. And I could tell you a story about that too ! Ask
there.
Except it's not Harman any more it seems but google that for starters.
They've
moved to Letchworth. I think most of the C-Audio parts ended up shuffled
into a
corner (I could tell another story) so they might be willing to get rid
of
some
unwanted and unloved bits. Unless they already put them in a skip
(dumpster for
USAans)


Graham


The guy who owns the shop where all this stuff comes from, and who is a
musician himself with 'many years in', tends to call anything that's rack
mount, line input and 'power', a "head", as opposed to an "amp" for an
instrument level standalone unit like a Marshall, or a "combo" for the
same
thing with speakers built in like an AC30 or Fender Twin. I just follow
his
lead, and call them the same. What do you describe as a "head"?

Anyways, as to what's wrong with it. The "A" channel has an *extremely*
asymmetric output. On a sine wave, looks like the output from a half wave
reccy with no filter cap on the end. It also 'bounces' in amplitude when
the
input level, or front panel level, is varied. The problem is right up the
front end somewhere. There are pukka sine waves around the TL074 input
amp,
but soon after, the signal has taken on this asymmetry, which is then
faithfully amplified by the output stage. The "B" channel works perfectly,
so I guess I can start comparing between the two. Just would have been a
lot
easier with a set of schematics to see where exactly the signal goes. It's
got that nasty 'feel' about it, that says it's going to be something like
an
o/c resistor, which looks perfect to the naked eye ...

I see a couple of bunches of four TO92 transistors, so I think that may be
a
good place to start looking.

Arfa- Hide quoted text -

- Show quoted text -


On the western side of the big pond, "head" can mean what you folks on
the eastern side, I believe, call the "Loo". Think it comes from
nautical background when the in-ship toilet was at the front/head of
the ship/boat.

Bob H

That is exactly correct, Bob. The toilets on board a British naval vessel
are also known as "The Head" or sometimes "Heads", and when a cadet, I was
taught that it was because of them being at the front of the ship, which in
the days of wooden sailing vessels, was as far from the captain's quarters
at the stern, as they possibly could be. Don't know if the same terminology
is used on merchant vessels.

Arfa


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Arfa Daily wrote:

"Eeyore" wrote in message


snip

One of the worst laid out designs I've ever seen in my entire life.

In tests I measured 150C *on the HEATSINK*. God knows what the junction
temp was. Your trouble will be getting genuine Hitachi replacements as they
stopped making them and the Semelab/Magnatec and Exicon replacements aren't
exactly identical.. I may have a few but you WILL pay megabucks for them.


http://cgi.ebay.co.uk/2SK175-Transis...QQcmdZViewItem

http://cgi.ebay.co.uk/2SJ56-Transist...QQcmdZViewItem

Probably cheaper to remove all the Hitachis (and sell them ?) and replace all
with Exicon or Semelab.

http://www.profusionplc.com/pro/gex/...eral%20mosfet#

http://uk.farnell.com/jsp/search/bro...questid=473126

You need the 'BUZ' parts.


Well, if that's the case, it ain't gonna get done, as he only sold it a
couple of weeks ago as a cheapy second hand job. As a matter of interest,
does the circuit employ feedback to the front end then ?


Oh yeah.


I wasn't expecting
this to be an output issue, as the waveform seems to distort quite early in
the chain, but now you suggest this, I guess it makes some sense of the way
that the amplitude of the waveform 'bounces' a couple of times before
settling, when the level is adjusted, externally or front panel.


It 'might' be something else. You'll only tell by removing the output devices
(thankfully easy enough) and testing them but C-Audio have a reputation for
eating them. And will do so again if driven hard into 4 ohms.

Graham

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"Meat Plow" wrote in message
...
On Tue, 25 Nov 2008 06:00:02 +0000, Eeyore
wrote:



Arfa Daily wrote:

"Eeyore" wrote in message
Arfa Daily wrote:

Does anyone have a set of schematics for the C-Audio RA3001 that they
could let me have fairly urgently please ?

It's not a 'head', it's a 19" rack mounting pro power amp with line
level
inputs. What do you want to know btw ? They are notoriously
unreliable.
First job is to replace all the PSU caps that have been cooked by the
hot
exhaust air. Then check how many mosfets are open.

I know an awful lot about it, having rejected it as an ODM product for
Studiomaster. I think it was that model.

The links to the service manual on the supposed C-Audio 'website',
just
seem to take you round in ever decreasing circles via other third
party
vendors of everthing you can imagine.

Harman UK bought them. And I could tell you a story about that too !
Ask
there. Except it's not Harman any more it seems but google that for
starters.
They've moved to Letchworth. I think most of the C-Audio parts ended
up
shuffled
into a corner (I could tell another story) so they might be willing to
get
rid of
some unwanted and unloved bits. Unless they already put them in a skip
(dumpster for USAans)

The guy who owns the shop where all this stuff comes from, and who is a
musician himself with 'many years in', tends to call anything that's
rack
mount, line input and 'power', a "head", as opposed to an "amp" for an
instrument level standalone unit like a Marshall, or a "combo" for the
same
thing with speakers built in like an AC30 or Fender Twin. I just follow
his
lead, and call them the same. What do you describe as a "head"?


A 'head' has preamp level inputs. A guitar head has sensitive Hi-Z inputs
for
guitars, a 'PA' head has mic inputs. The old name for what an RA3001 type
amp is
a 'slave amp'.


Anyways, as to what's wrong with it. The "A" channel has an *extremely*
asymmetric output.


Typical C-Audio !


On a sine wave, looks like the output from a half wave
reccy with no filter cap on the end. It also 'bounces' in amplitude when
the
input level, or front panel level, is varied. The problem is right up
the
front end somewhere. There are pukka sine waves around the TL074 input
amp,
but soon after, the signal has taken on this asymmetry, which is then
faithfully amplified by the output stage. The "B" channel works
perfectly,
so I guess I can start comparing between the two. Just would have been a
lot
easier with a set of schematics to see where exactly the signal goes.
It's
got that nasty 'feel' about it, that says it's going to be something
like an
o/c resistor, which looks perfect to the naked eye ...

I see a couple of bunches of four TO92 transistors, so I think that may
be a
good place to start looking.


Unlikely.

Do you know how to test Hitachi lateral mosfet output devices ? Not much
different from any mosfet except they made true complements.

Remove them all. I expect they're TO-3 so easy to get them out and test.
You
will find a fair few are totally open. Replace these and you're good to go
but
DO replace the reservoir caps too. They will have been roasted by the
searingly
hot air passing over the heatsink. Don't even think of using 85C types.

One of the worst laid out designs I've ever seen in my entire life.

In tests I measured 150C *on the HEATSINK*. God knows what the junction
temp
was. Your trouble will be getting genuine Hitachi replacements as they
stopped
making them and the Semelab/Magnatec and Exicon replacements aren't
exactly
identical.. I may have a few but you WILL pay megabucks for them.

Graham


Ran into the Hitachi mosfet issue years ago after acquiring a Sound
Code Systems (SCS) rack mount power amp. Had the 2SJ49/2SK134 pairs
inside if I recall correctly. I replaced them with J50/K135 devices
which at the time were still available. Now adays there are
replacements but with a little modification since they are not in a
TO3 package. I've had that amp now for 15 years after repair and
used it for 5 years as a bass guitar amp strapped mono. Now adays it
is the PA amp for my home studio. I've only seen one SCS amp and this
is it.




IIRC, the C-Audio RA series commonly used BUZ Mosfets, both T03 and T0247,
which are still easily available.

http://uk.farnell.com/jsp/search/bro...estid=48642 0



Gareth.




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"Meat Plow" wrote in message
...
On Tue, 25 Nov 2008 18:54:01 -0000, "Gareth Magennis"
wrote:

IIRC, the C-Audio RA series commonly used BUZ Mosfets, both T03 and T0247,
which are still easily available.

http://uk.farnell.com/jsp/search/bro...estid=48642 0



Gareth.




Good to know when the old J50's and K135's decide to check out.



Well, I didn't say the BUZ were replacements for those, but C-audio did use
a selection of different devices throughout the years they were in
production.

Some of the amps were rather prone to RF oscillations, burning out their
Zobel networks - attributed to various things like heatsink/ground bonding
or layout design, depending on who you talked to and what opinion they had,
or how much bull**** they liked to talk.

I replaced quite a few BUZ's, and they were expensive back then, about the
same as Farnell charge now. Can't remember changing many, if any, reservoir
capacitors though.




Gareth.




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"Gareth Magennis" wrote in message
news

"Meat Plow" wrote in message
...
On Tue, 25 Nov 2008 18:54:01 -0000, "Gareth Magennis"
wrote:

IIRC, the C-Audio RA series commonly used BUZ Mosfets, both T03 and
T0247,
which are still easily available.

http://uk.farnell.com/jsp/search/bro...estid=48642 0



Gareth.




Good to know when the old J50's and K135's decide to check out.



Well, I didn't say the BUZ were replacements for those, but C-audio did
use a selection of different devices throughout the years they were in
production.

Some of the amps were rather prone to RF oscillations, burning out their
Zobel networks - attributed to various things like heatsink/ground
bonding or layout design, depending on who you talked to and what opinion
they had, or how much bull**** they liked to talk.

I replaced quite a few BUZ's, and they were expensive back then, about the
same as Farnell charge now. Can't remember changing many, if any,
reservoir capacitors though.




Gareth.



Oh, and the worst problem they suffered from was (allegedly) smoke fluid (in
club installs) being deposited on the PCB behind the fan intake. This would
eventually corrode lots of fine tracks running along the board, the most
common victim being part of the Protect/Speaker Relay circuit, so the amp
would stay in Protect forever.

Annoyingly, the corrosive substance would creep under the Speaker relays and
eat the tracks under them as well, so repairing these amps properly was
either very time consuming and expensive, or just plain uneconomical.

And, the 47 ohm 10 Watt ceramic Soft Start resistors would very often need
replacing.


These had their fair share of design problems, that's for sure.




Gareth.


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Gareth Magennis wrote:

IIRC, the C-Audio RA series commonly used BUZ Mosfets,


Not originally.


both T03 and T0247, which are still easily available.


But best not to mix them I imagine.

Graham

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Gareth Magennis wrote:

"Gareth Magennis" wrote
"Meat Plow" wrote in message
"Gareth Magennis" wrote:

IIRC, the C-Audio RA series commonly used BUZ Mosfets, both T03 and
T0247, which are still easily available.

http://uk.farnell.com/jsp/search/bro...estid=48642 0

Good to know when the old J50's and K135's decide to check out.



Well, I didn't say the BUZ were replacements for those, but C-audio did
use a selection of different devices throughout the years they were in
production.

Some of the amps were rather prone to RF oscillations, burning out their
Zobel networks - attributed to various things like heatsink/ground
bonding or layout design, depending on who you talked to and what opinion
they had, or how much bull**** they liked to talk.

I replaced quite a few BUZ's, and they were expensive back then, about the
same as Farnell charge now. Can't remember changing many, if any,
reservoir capacitors though.


Surprised at that. C-Audio's stance was they were a 'service item'. Like the mosfets presumably !


Oh, and the worst problem they suffered from was (allegedly) smoke fluid (in
club installs) being deposited on the PCB behind the fan intake. This would
eventually corrode lots of fine tracks running along the board, the most
common victim being part of the Protect/Speaker Relay circuit, so the amp
would stay in Protect forever.

Annoyingly, the corrosive substance would creep under the Speaker relays and
eat the tracks under them as well, so repairing these amps properly was
either very time consuming and expensive, or just plain uneconomical.

And, the 47 ohm 10 Watt ceramic Soft Start resistors would very often need
replacing.

These had their fair share of design problems, that's for sure.


Which is why I didn't approve them to be sold under the Studiomaster badge and went on to design the much loved D Series.
http://cgi.ebay.co.uk/ws/eBayISAPI.d...MEWA:IT&ih=011

Siemens ODM'd the RA3001 though IIRC.

Graham

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"Eeyore" wrote in message
...


Arfa Daily wrote:

"Eeyore" wrote in message


snip

One of the worst laid out designs I've ever seen in my entire life.

In tests I measured 150C *on the HEATSINK*. God knows what the junction
temp was. Your trouble will be getting genuine Hitachi replacements as
they
stopped making them and the Semelab/Magnatec and Exicon replacements
aren't
exactly identical.. I may have a few but you WILL pay megabucks for
them.


http://cgi.ebay.co.uk/2SK175-Transis...QQcmdZViewItem

http://cgi.ebay.co.uk/2SJ56-Transist...QQcmdZViewItem

Probably cheaper to remove all the Hitachis (and sell them ?) and replace
all
with Exicon or Semelab.

http://www.profusionplc.com/pro/gex/...eral%20mosfet#

http://uk.farnell.com/jsp/search/bro...questid=473126

You need the 'BUZ' parts.


Well, if that's the case, it ain't gonna get done, as he only sold it a
couple of weeks ago as a cheapy second hand job. As a matter of interest,
does the circuit employ feedback to the front end then ?


Oh yeah.


I wasn't expecting
this to be an output issue, as the waveform seems to distort quite early
in
the chain, but now you suggest this, I guess it makes some sense of the
way
that the amplitude of the waveform 'bounces' a couple of times before
settling, when the level is adjusted, externally or front panel.


It 'might' be something else. You'll only tell by removing the output
devices
(thankfully easy enough) and testing them but C-Audio have a reputation
for
eating them. And will do so again if driven hard into 4 ohms.

Graham


You are right. One whole bank of FETs is o/c - hence the very asymmetric
output. There has been a further development. I rang the shop to tell him
the bad news that a set of twelve devices was going to set him back 100
quid, with the possibility of there being some o/c on the other channel (a
couple of them seem very cool under drive conditions, compared to their
neighbours, so a good indication that they may well be open as well) and
then the possibility of some smoothers as well. Turns out that when he sold
the guy this one as a s/h unit, he picked up the wrong one. This example was
sitting waiting to come to me for checking, so he has now given the customer
the right one, and is writing this one off, for the time being at least.
Thanks for the useful pointer to the FETs, anyway.

Arfa


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"Gareth Magennis" wrote in message
...

"Meat Plow" wrote in message
...
On Tue, 25 Nov 2008 06:00:02 +0000, Eeyore
wrote:



Arfa Daily wrote:

"Eeyore" wrote in message
Arfa Daily wrote:

Does anyone have a set of schematics for the C-Audio RA3001 that
they
could let me have fairly urgently please ?

It's not a 'head', it's a 19" rack mounting pro power amp with line
level
inputs. What do you want to know btw ? They are notoriously
unreliable.
First job is to replace all the PSU caps that have been cooked by the
hot
exhaust air. Then check how many mosfets are open.

I know an awful lot about it, having rejected it as an ODM product
for
Studiomaster. I think it was that model.

The links to the service manual on the supposed C-Audio 'website',
just
seem to take you round in ever decreasing circles via other third
party
vendors of everthing you can imagine.

Harman UK bought them. And I could tell you a story about that too !
Ask
there. Except it's not Harman any more it seems but google that for
starters.
They've moved to Letchworth. I think most of the C-Audio parts ended
up
shuffled
into a corner (I could tell another story) so they might be willing
to get
rid of
some unwanted and unloved bits. Unless they already put them in a
skip
(dumpster for USAans)

The guy who owns the shop where all this stuff comes from, and who is a
musician himself with 'many years in', tends to call anything that's
rack
mount, line input and 'power', a "head", as opposed to an "amp" for an
instrument level standalone unit like a Marshall, or a "combo" for the
same
thing with speakers built in like an AC30 or Fender Twin. I just follow
his
lead, and call them the same. What do you describe as a "head"?

A 'head' has preamp level inputs. A guitar head has sensitive Hi-Z inputs
for
guitars, a 'PA' head has mic inputs. The old name for what an RA3001 type
amp is
a 'slave amp'.


Anyways, as to what's wrong with it. The "A" channel has an *extremely*
asymmetric output.

Typical C-Audio !


On a sine wave, looks like the output from a half wave
reccy with no filter cap on the end. It also 'bounces' in amplitude
when the
input level, or front panel level, is varied. The problem is right up
the
front end somewhere. There are pukka sine waves around the TL074 input
amp,
but soon after, the signal has taken on this asymmetry, which is then
faithfully amplified by the output stage. The "B" channel works
perfectly,
so I guess I can start comparing between the two. Just would have been
a lot
easier with a set of schematics to see where exactly the signal goes.
It's
got that nasty 'feel' about it, that says it's going to be something
like an
o/c resistor, which looks perfect to the naked eye ...

I see a couple of bunches of four TO92 transistors, so I think that may
be a
good place to start looking.

Unlikely.

Do you know how to test Hitachi lateral mosfet output devices ? Not much
different from any mosfet except they made true complements.

Remove them all. I expect they're TO-3 so easy to get them out and test.
You
will find a fair few are totally open. Replace these and you're good to
go but
DO replace the reservoir caps too. They will have been roasted by the
searingly
hot air passing over the heatsink. Don't even think of using 85C types.

One of the worst laid out designs I've ever seen in my entire life.

In tests I measured 150C *on the HEATSINK*. God knows what the junction
temp
was. Your trouble will be getting genuine Hitachi replacements as they
stopped
making them and the Semelab/Magnatec and Exicon replacements aren't
exactly
identical.. I may have a few but you WILL pay megabucks for them.

Graham


Ran into the Hitachi mosfet issue years ago after acquiring a Sound
Code Systems (SCS) rack mount power amp. Had the 2SJ49/2SK134 pairs
inside if I recall correctly. I replaced them with J50/K135 devices
which at the time were still available. Now adays there are
replacements but with a little modification since they are not in a
TO3 package. I've had that amp now for 15 years after repair and
used it for 5 years as a bass guitar amp strapped mono. Now adays it
is the PA amp for my home studio. I've only seen one SCS amp and this
is it.




IIRC, the C-Audio RA series commonly used BUZ Mosfets, both T03 and T0247,
which are still easily available.

http://uk.farnell.com/jsp/search/bro...estid=48642 0



Gareth.



Yes, they are BUZ's and yes, they are in the Farnell book, allbeit with a
different suffix letter to what is actually fitted now, but with six N's and
six P's in the equation, at 8 quid + VAT a pop, that's 100+ quidsworth trade
in devices for one channel, before we even start looking at the other
channel to see if any are open there as well.

Shop owner has deemed it uneconomic for the moment, so it will go back up
the corner to await its ultimate fate ... :-(

Talking of Farnell, do you order much from them ? Have you noticed how much
they seem now to be rationalising 'on the shelf' stock ? It used to be
*very* rare to ever catch them out of stock on any catalogue item. Now,
there seems to be something on every order. Also, have you noticed how you
get one order in two shipments ? One parcel comes from Leeds, and the other,
often something like a single transistor, comes in a box the size of your
head, by UPS, from Belgium. Surely, this can't make economic sense, let
alone (God forgive me for using the "e" word) ecological sense ?

Arfa




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"Eeyore" wrote in message
...


Gareth Magennis wrote:

IIRC, the C-Audio RA series commonly used BUZ Mosfets,


Not originally.


both T03 and T0247, which are still easily available.


But best not to mix them I imagine.

Graham


This one that I had on the bench used BUZ's, and the soldering on them looks
original

Arfa


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Arfa Daily wrote:

"Eeyore" wrote

It 'might' be something else. You'll only tell by removing the output
devices (thankfully easy enough) and testing them but C-Audio have a reputation
for eating them. And will do so again if driven hard into 4 ohms.


You are right. One whole bank of FETs is o/c - hence the very asymmetric
output. There has been a further development. I rang the shop to tell him
the bad news that a set of twelve devices was going to set him back 100
quid, with the possibility of there being some o/c on the other channel (a
couple of them seem very cool under drive conditions, compared to their
neighbours, so a good indication that they may well be open as well)


That's what happens. The weakest or hottest fail first (open) and the relatively large ON resistance for these devices causes assymmetry in the delevered peak
voltage to the load.

Graham

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Meat Plow wrote:

Eeyorewrote:
Gareth Magennis wrote:
"Gareth Magennis" wrote
"Meat Plow" wrote in message
"Gareth Magennis" wrote:

IIRC, the C-Audio RA series commonly used BUZ Mosfets, both T03 and
T0247, which are still easily available.

http://uk.farnell.com/jsp/search/bro...estid=48642 0

Good to know when the old J50's and K135's decide to check out.


Well, I didn't say the BUZ were replacements for those, but C-audio did
use a selection of different devices throughout the years they were in
production.

Some of the amps were rather prone to RF oscillations, burning out their
Zobel networks - attributed to various things like heatsink/ground
bonding or layout design, depending on who you talked to and what opinion
they had, or how much bull**** they liked to talk.

I replaced quite a few BUZ's, and they were expensive back then, about the
same as Farnell charge now. Can't remember changing many, if any,
reservoir capacitors though.


Surprised at that. C-Audio's stance was they were a 'service item'. Like the mosfets presumably !


Oh, and the worst problem they suffered from was (allegedly) smoke fluid (in
club installs) being deposited on the PCB behind the fan intake. This would
eventually corrode lots of fine tracks running along the board, the most
common victim being part of the Protect/Speaker Relay circuit, so the amp
would stay in Protect forever.

Annoyingly, the corrosive substance would creep under the Speaker relays and
eat the tracks under them as well, so repairing these amps properly was
either very time consuming and expensive, or just plain uneconomical.

And, the 47 ohm 10 Watt ceramic Soft Start resistors would very often need
replacing.

These had their fair share of design problems, that's for sure.


Which is why I didn't approve them to be sold under the Studiomaster badge and went on to design the much loved D Series.
http://cgi.ebay.co.uk/ws/eBayISAPI.d...MEWA:IT&ih=011

Siemens ODM'd the RA3001 though IIRC.


I own a Studiomaster 700D and would like to replace the quad set of
mains filters. These are low profile, I know there is a specific name
for them. The tops of these all seem to bubble upwards but when I
picked that part off it was just a cover of sorts for the real
container both overshod with heat shrink. I don't think they are bad,
haven't removed them but the amp works however I'm worried about it
being in service as my bass guitar amp.


NEVER seen that myself but those amps are getting old now. Original spec parts were Samwha (forget which series but the plastic film was dark
green) 3300uF/63V (yes they're overvolted off load @ 67V but we checked that for reliability with Samwha and they sent us detailed info to say
it's basically OK, the leakage current just increases very marginally at ~ 5% overvoltage and no load).

The alternative part was IIRC, Panasonic (again forget which series). Dumpy little black cans. Looked absurdly small. I expect that's what
you've got.

I specced the ripple current per cap at ~ 2.7-3A IIRC. You'll find something in Farnell that'll do fine. Use 105C caps if you want to continue
using it forever.

I assume you're driving a 4 ohm load btw ?

Want some more Oomph ? Fit 4700s. It'll reduce the dynamic headroom though.

What do you think of the amp btw ?

Graham

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Meat Plow wrote:

I'm also looking for a new speaker binder set as one is broken off.


You must have a US model. Those weren't sourced in the UK. That means you have an Indian built one. Can't tell you what they used sadly.


Currently I'm using Spec-on connectors. I bought this amp used at a thieves price.


They go on ebay for 'reasonable' prices. I just bought one on behalf on my local music pub client for £72. 10 years old and looked almost new
inside. Just had some 'rack rash'.


Is there a place here in the US for factory parts or do i have to get
them from GB?


Not at all. I gave data in my other post. Don't scrimp on the ripple current btw. Use good brand caps. I found Samwha to be excellent btw at a
reasonable price. My second preference is Panasonic.

Graham


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Meat Plow wrote:

Is there a place here in the US for factory parts or do i have to get
them from GB?


I'm fairly certain the original spec is the Samwha HC series 3300uF 63V.

Yes, this pdf includes the data sheet. The ripple current is in fact 3A.
http://www.rapidonline.com/netalogue/specs/11-3100e.pdf

Now ask me how I remember that after over 15 years ago.

You'll easily find replacements.

Graham




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"Arfa Daily" wrote in message
...

"Eeyore" wrote in message
...


Gareth Magennis wrote:

IIRC, the C-Audio RA series commonly used BUZ Mosfets,


Not originally.


both T03 and T0247, which are still easily available.


But best not to mix them I imagine.

Graham


This one that I had on the bench used BUZ's, and the soldering on them
looks original

Arfa


Often C Audio would put little pink or green dots on the transistors,
presumably after testing them prior to production. Not the kind of thing a
repairshop would do, so this may indicate if they are the originals or not.

I often used to find only one or two devices not working or clamping at high
voltages, you may not have to replace the lot at all.




Gareth.


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IIRC, the C-Audio RA series commonly used BUZ Mosfets, both T03 and
T0247, which are still easily available.

http://uk.farnell.com/jsp/search/bro...estid=48642 0



Gareth.



Yes, they are BUZ's and yes, they are in the Farnell book, allbeit with a
different suffix letter to what is actually fitted now, but with six N's
and six P's in the equation, at 8 quid + VAT a pop, that's 100+ quidsworth
trade in devices for one channel, before we even start looking at the
other channel to see if any are open there as well.

Shop owner has deemed it uneconomic for the moment, so it will go back up
the corner to await its ultimate fate ... :-(

Talking of Farnell, do you order much from them ? Have you noticed how
much they seem now to be rationalising 'on the shelf' stock ? It used to
be *very* rare to ever catch them out of stock on any catalogue item. Now,
there seems to be something on every order. Also, have you noticed how you
get one order in two shipments ? One parcel comes from Leeds, and the
other, often something like a single transistor, comes in a box the size
of your head, by UPS, from Belgium. Surely, this can't make economic
sense, let alone (God forgive me for using the "e" word) ecological sense
?

Arfa



I order just about all my stuff from Farnell. They don't tend to have much
in the way of unusual or older transistors, these I can usually find at
Cricklewood Electronics.
http://www.cricklewoodelectronics.co...ewood/home.php

I get my stuff next day without fail from both Farnell and Cricklewood,
nothing is usually out of stock or comes from Belgium.

I'm in Leeds, so is Farnell, so maybe that might have something to do with
it, but shouldn't really. What kind of stuff is coming from Belgium?
Chocolate screwdrivers?



Cheers,



Gareth.


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Gareth Magennis wrote:

I'm in Leeds, so is Farnell, so maybe that might have something to do with
it, but shouldn't really. What kind of stuff is coming from Belgium?
Chocolate screwdrivers?


I've seem multiple deliveries from them. Simple explanation. They don't hold all stock in a single place.

Graham

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"Gareth Magennis" wrote in message
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IIRC, the C-Audio RA series commonly used BUZ Mosfets, both T03 and
T0247, which are still easily available.

http://uk.farnell.com/jsp/search/bro...estid=48642 0



Gareth.



Yes, they are BUZ's and yes, they are in the Farnell book, allbeit with a
different suffix letter to what is actually fitted now, but with six N's
and six P's in the equation, at 8 quid + VAT a pop, that's 100+
quidsworth trade in devices for one channel, before we even start looking
at the other channel to see if any are open there as well.

Shop owner has deemed it uneconomic for the moment, so it will go back up
the corner to await its ultimate fate ... :-(

Talking of Farnell, do you order much from them ? Have you noticed how
much they seem now to be rationalising 'on the shelf' stock ? It used to
be *very* rare to ever catch them out of stock on any catalogue item.
Now, there seems to be something on every order. Also, have you noticed
how you get one order in two shipments ? One parcel comes from Leeds, and
the other, often something like a single transistor, comes in a box the
size of your head, by UPS, from Belgium. Surely, this can't make economic
sense, let alone (God forgive me for using the "e" word) ecological sense
?

Arfa



I order just about all my stuff from Farnell. They don't tend to have
much in the way of unusual or older transistors, these I can usually find
at Cricklewood Electronics.
http://www.cricklewoodelectronics.co...ewood/home.php

I get my stuff next day without fail from both Farnell and Cricklewood,
nothing is usually out of stock or comes from Belgium.

I'm in Leeds, so is Farnell, so maybe that might have something to do with
it, but shouldn't really. What kind of stuff is coming from Belgium?
Chocolate screwdrivers?



Cheers,



Gareth.


Seems like just about anything I order now can come from the Belgian
warehouse. To be fair, it usually comes the next day, as the stuff from
Leeds does, but how much must it be costing them to process, pack and ship
from Belgium, just one item out of an order of perhaps 10 items ? They also
seem to employ no rhyme or reason with determining how exactly the orders
are shipped by default. One day, they will deliver a transformer weighing a
couple of pounds, in a Jiffy bag, by regular post. The next day, a packet of
transistors will arrive in a box a foot square, conveyed by UPS, who don't
usually get to me until late afternoon. One thing about UPS *really*
irritates me (must be my age). After having got it to the right address, and
asked me to sign for it, and after the same bloke delivering the same sorts
of packets to me from the same company, for a long time, he still says every
time after I finish signing "What's the surname, please ?" Aaaaarrghhh !!!

I haven't used Cricklewood for a while. I also hadn't used Grandata for a
while until a few weeks ago. They have really gone down the toilet compared
to what they were. I needed an STK, and a couple of power transistors for an
amp, as well as a few other bits and pieces - fuses and so on. All items
showed as in stock on the website, so I went ahead and placed the order,
credit card payment and all that. The next day, I was extremely annoyed to
get an e-mail informing me that half the stuff was on 3 to 10 day back
order. It has actually taken a total of about 5 weeks to finally get
everything that was on the order, the last transistor arriving just
yesterday ...

Arfa


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Arfa Daily wrote:

Seems like just about anything I order now can come from the Belgian
warehouse. To be fair, it usually comes the next day, as the stuff from
Leeds does, but how much must it be costing them to process, pack and ship
from Belgium, just one item out of an order of perhaps 10 items ? They also
seem to employ no rhyme or reason with determining how exactly the orders
are shipped by default. One day, they will deliver a transformer weighing a
couple of pounds, in a Jiffy bag, by regular post. The next day, a packet of
transistors will arrive in a box a foot square, conveyed by UPS, who don't
usually get to me until late afternoon.


Why do you think they charge the price they do ?

The use of 'satellite warehouses' is well established. Someone must have done the sums. You can bet UPS don't get their standard fee for such
an operation.


Graham



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Arfa Daily wrote in message
...

"Gareth Magennis" wrote in message
...


IIRC, the C-Audio RA series commonly used BUZ Mosfets, both T03 and




I haven't used Cricklewood for a while. I also hadn't used Grandata for a
while until a few weeks ago. They have really gone down the toilet

compared
to what they were. I needed an STK, and a couple of power transistors for

an
amp, as well as a few other bits and pieces - fuses and so on. All items
showed as in stock on the website, so I went ahead and placed the order,
credit card payment and all that. The next day, I was extremely annoyed to
get an e-mail informing me that half the stuff was on 3 to 10 day back
order. It has actually taken a total of about 5 weeks to finally get
everything that was on the order, the last transistor arriving just
yesterday ...

Arfa



Grandata must have dumped or auctioned-off their back catalog when moving
address from Wembley to Ruislip and trading name to Thumbs Up , actually
thumbs down, earlier this year

A few totals of
IC types in 2000 Grandata catalog, 2008 "Thumbs Up"
TDA... 760 136
TEA.... 120 14
L.... 370 55
M.... 234 10

Anyone ever get to the Pike auctions in Nottingham?
Or is there any other electronic component auctions around since that one in
Stroud Gloucester closed down ?


BTW yesterday I passed a Maplins store as a pallet load of returns was being
tail-lifted on a lorry, well wrapping tape had Returns Centre printed all
over it. Does that turn up at Pikes with all the other returns ?


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/







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"Eeyore" wrote in message
...


Arfa Daily wrote:

Seems like just about anything I order now can come from the Belgian
warehouse. To be fair, it usually comes the next day, as the stuff from
Leeds does, but how much must it be costing them to process, pack and
ship
from Belgium, just one item out of an order of perhaps 10 items ? They
also
seem to employ no rhyme or reason with determining how exactly the orders
are shipped by default. One day, they will deliver a transformer weighing
a
couple of pounds, in a Jiffy bag, by regular post. The next day, a packet
of
transistors will arrive in a box a foot square, conveyed by UPS, who
don't
usually get to me until late afternoon.


Why do you think they charge the price they do ?

The use of 'satellite warehouses' is well established. Someone must have
done the sums. You can bet UPS don't get their standard fee for such
an operation.


Graham


Farnell don't charge me shipping, and to be honest, I've never felt that
their prices are excessive, given the stockholding that they have, and the
normal efficiency of their service.

Arfa


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"Arfa Daily" wrote in message
...

"Eeyore" wrote in message
...


Arfa Daily wrote:

Seems like just about anything I order now can come from the Belgian
warehouse. To be fair, it usually comes the next day, as the stuff from
Leeds does, but how much must it be costing them to process, pack and
ship
from Belgium, just one item out of an order of perhaps 10 items ? They
also
seem to employ no rhyme or reason with determining how exactly the
orders
are shipped by default. One day, they will deliver a transformer
weighing a
couple of pounds, in a Jiffy bag, by regular post. The next day, a
packet of
transistors will arrive in a box a foot square, conveyed by UPS, who
don't
usually get to me until late afternoon.


Why do you think they charge the price they do ?

The use of 'satellite warehouses' is well established. Someone must have
done the sums. You can bet UPS don't get their standard fee for such
an operation.


Graham


Farnell don't charge me shipping, and to be honest, I've never felt that
their prices are excessive, given the stockholding that they have, and the
normal efficiency of their service.

Arfa



Likewise. I can phone my order for 1 transistor at 6pm if I need to, and it
is here, free delivery, next day. That's what I need to be able to do.

Certain things, like cable and connectors, are cheaper elsewhere, but for
everyday components I order from them exclusively and pay monthly.
Parts are usually the smallest part of the bill anyway, and the customer
pays for them, so ultimately I am not bothered about trying to save them a
few pence if it takes more time and hassle (and possible labour charge) to
do so. Neither, I suspect, are they.




Gareth.


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