Hi all,

A long long time ago, I made an amplifier using two of these modules.
Since I made it in my yoof, I'm quite attached to it. Recently though,
my wife bashed her head on the underside of the shelf it was on. There
followed loads of crackling from the speakers accompanied by the
disturbing hum of power rails coupled directly to speakers. I sprang up
and flew across the room to switch the amp off (which wasn't easy since
I had to be careful to avoid my wife who was now rolling around on the
floor, clutching her head) but I was too late and the left channel was
toast.

I'm a bit mystified as to how the head-bashing could have caused any
damage but, aside from that, repairs are progressing and new bits are on
order; I only lost two of the output transistors, some resistors and a
couple of polystyrene caps. The only problem I'm expecting is how to set
up the quiescent current, since I can't find the original instructions
for the modules.

I know it's a bit of a long shot, but does anyone here happen to have a
set of instructions hanging around? I think it was quite a popular
module for quite a long time. The order code was HQ68Y.

Oh, and the wife's making a full recovery, by the way.

Cheers,

Colin.

Colin Stamp wrote:
Hi all,

A long long time ago, I made an amplifier using two of these modules.
Since I made it in my yoof, I'm quite attached to it. Recently though,
my wife bashed her head on the underside of the shelf it was on. There
followed loads of crackling from the speakers accompanied by the
disturbing hum of power rails coupled directly to speakers. I sprang up
and flew across the room to switch the amp off (which wasn't easy since
I had to be careful to avoid my wife who was now rolling around on the
floor, clutching her head) but I was too late and the left channel was
toast.

I'm a bit mystified as to how the head-bashing could have caused any
damage but, aside from that, repairs are progressing and new bits are on
order; I only lost two of the output transistors, some resistors and a
couple of polystyrene caps. The only problem I'm expecting is how to set
up the quiescent current, since I can't find the original instructions
for the modules.

how the **** did you lose polystyrenes?


I know it's a bit of a long shot, but does anyone here happen to have a
set of instructions hanging around? I think it was quite a popular
module for quite a long time. The order code was HQ68Y.


Don't have instructions, but there should be a trim pot pot somewhere.
Turn it so the current drawn (remove line fuse on the low voltage side
and meter across) is as low as you can get, the turn the pot up to give
5-10mA more than that.


Oh, and the wife's making a full recovery, by the way.

Cheers,

Colin.

On 28/09/10 23:32, The Natural Philosopher wrote:

how the **** did you lose polystyrenes?

They copped a bit too much heat from nearby resistors that were busy
converting themselves to smoke. Now they're a very funny shape.

Don't have instructions, but there should be a trim pot pot somewhere.
Turn it so the current drawn (remove line fuse on the low voltage side
and meter across) is as low as you can get, the turn the pot up to give
5-10mA more than that.

Thanks for that. Sounds like a good plan if I can't find the specific
magic numbers from Maplin.

Cheers,

Colin.

On Sep 28, 11:23*pm, Colin Stamp wrote:
Hi all,

A long long time ago, I made an amplifier using two of these modules.
Since I made it in my yoof, I'm quite attached to it. Recently though,
my wife bashed her head on the underside of the shelf it was on. There
followed loads of crackling from the speakers accompanied by the
disturbing hum of power rails coupled directly to speakers. I sprang up
and flew across the room to switch the amp off (which wasn't easy since
I had to be careful to avoid my wife who was now rolling around on the
floor, clutching her head) but I was too late and the left channel was
toast.

I'm a bit mystified as to how the head-bashing could have caused any
damage but, aside from that, repairs are progressing and new bits are on
order; I only lost two of the output transistors, some resistors and a
couple of polystyrene caps. The only problem I'm expecting is how to set
up the quiescent current, since I can't find the original instructions
for the modules.

I know it's a bit of a long shot, but does anyone here happen to have a
set of instructions hanging around? I think it was quite a popular
module for quite a long time. The order code was HQ68Y.

Oh, and the wife's making a full recovery, by the way.

Cheers,

Colin.

If one channels still ok and one toast, not hard to copy what the
other one's doing current-wise.


NT

On 28 Sep, 23:23, Colin Stamp wrote:
Hi all,

A long long time ago, I made an amplifier using two of these modules.
Since I made it in my yoof, I'm quite attached to it. Recently though,
my wife bashed her head on the underside of the shelf it was on. There
followed loads of crackling from the speakers accompanied by the
disturbing hum of power rails coupled directly to speakers. I sprang up
and flew across the room to switch the amp off (which wasn't easy since
I had to be careful to avoid my wife who was now rolling around on the
floor, clutching her head) but I was too late and the left channel was
toast.

I'm a bit mystified as to how the head-bashing could have caused any
damage but, aside from that, repairs are progressing and new bits are on
order; I only lost two of the output transistors, some resistors and a
couple of polystyrene caps. The only problem I'm expecting is how to set
up the quiescent current, since I can't find the original instructions
for the modules.

I know it's a bit of a long shot, but does anyone here happen to have a
set of instructions hanging around? I think it was quite a popular
module for quite a long time. The order code was HQ68Y.

Oh, and the wife's making a full recovery, by the way.


I hope she's going to stump up for a new amp!

--
Halmyre

In article ,
Colin Stamp writes:
On 28/09/10 23:32, The Natural Philosopher wrote:

how the **** did you lose polystyrenes?

They copped a bit too much heat from nearby resistors that were busy
converting themselves to smoke. Now they're a very funny shape.

Don't have instructions, but there should be a trim pot pot somewhere.
Turn it so the current drawn (remove line fuse on the low voltage side
and meter across) is as low as you can get, the turn the pot up to give
5-10mA more than that.

Thanks for that. Sounds like a good plan if I can't find the specific
magic numbers from Maplin.

It was normal to swap the fuse for a very low power sacrificial resistor
when setting the quiescent current, so that you can't draw too much
current to damage output stage, and if you try, the resistor alone goes
up in smoke.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

Hi Colin
I'm pretty sure I have a scan of the original construction article
if you still need it - assuming we're referring to the 50W MOSFET
module that was very much based on the Hitachi Mosfet data sheet. it
may take me a day or so to track it down...

Regards
J^n

Andrew Gabriel wrote:
In article ,
Colin Stamp writes:
On 28/09/10 23:32, The Natural Philosopher wrote:

how the **** did you lose polystyrenes?
They copped a bit too much heat from nearby resistors that were busy
converting themselves to smoke. Now they're a very funny shape.

Don't have instructions, but there should be a trim pot pot somewhere.
Turn it so the current drawn (remove line fuse on the low voltage side
and meter across) is as low as you can get, the turn the pot up to give
5-10mA more than that.
Thanks for that. Sounds like a good plan if I can't find the specific
magic numbers from Maplin.

It was normal to swap the fuse for a very low power sacrificial resistor
when setting the quiescent current, so that you can't draw too much
current to damage output stage, and if you try, the resistor alone goes
up in smoke.

Good plan.

jkn wrote:
Hi Colin
I'm pretty sure I have a scan of the original construction article
if you still need it - assuming we're referring to the 50W MOSFET
module that was very much based on the Hitachi Mosfet data sheet. it
may take me a day or so to track it down...

Regards
J^n
If its hitachi mosfets, they like a bit more current- 30-50mA increase
over minimum.

On 29/09/2010 08:47, jkn wrote:
Hi Colin
I'm pretty sure I have a scan of the original construction article
if you still need it - assuming we're referring to the 50W MOSFET
module that was very much based on the Hitachi Mosfet data sheet. it
may take me a day or so to track it down...

I've found a copy of the mag. Seems they reprinted the same project a
number of times it was so popular.

I found it in ...

Electronics - The Maplin Magazine
50W HiFi Power Amplifier
July 1993 issue 67

Scanning it right now ...

It's not a MOSFET amp.

--
Adrian C

On 29/09/2010 18:32, Adrian C wrote:

Electronics - The Maplin Magazine
50W HiFi Power Amplifier
July 1993 issue 67

Scanning it right now ...

It's not a MOSFET amp.


http://www.scribd.com/doc/38418078/50W-HiFi-Power-Amplifier-LW35Q-Maplin-Kit

--
Adrian C

On Sep 29, 7:02*pm, Adrian C wrote:
On 29/09/2010 18:32, Adrian C wrote:



Electronics - The Maplin Magazine
50W HiFi Power Amplifier
July 1993 issue 67

Scanning it right now ...

It's not a MOSFET amp.

http://www.scribd.com/doc/38418078/50W-HiFi-Power-Amplifier-LW35Q-Map...


Good work Adrian. I have that scan as well, but you beat me to it ...

J^n

On 29/09/10 19:02, Adrian C wrote:
On 29/09/2010 18:32, Adrian C wrote:

Electronics - The Maplin Magazine
50W HiFi Power Amplifier
July 1993 issue 67

Scanning it right now ...

It's not a MOSFET amp.


http://www.scribd.com/doc/38418078/50W-HiFi-Power-Amplifier-LW35Q-Maplin-Kit



That's perfect. Many thanks for sorting it out. It came just at the
right time too; I changed the output transistors this evening and tried
the set-up procedure. It lives once more! It's only on the bench at the
moment and I didn't have a speaker handy, but it works fine on a scope.
I'm well pleased. I might even forgive the wife )

Thanks again,

Colin.

Adrian C wrote:
On 29/09/2010 18:32, Adrian C wrote:

Electronics - The Maplin Magazine
50W HiFi Power Amplifier
July 1993 issue 67

Scanning it right now ...

It's not a MOSFET amp.


http://www.scribd.com/doc/38418078/50W-HiFi-Power-Amplifier-LW35Q-Maplin-Kit


well I am not surprised it blew up. Pretty amateurish design.

On 30/09/2010 01:40, The Natural Philosopher wrote:
Adrian C wrote:

It's not a MOSFET amp.

well I am not surprised it blew up. Pretty amateurish design.

FWIW I've found an old Maplin catalogue from 1985 with the original
project. (The days when the catalogue had projects and data sheets
printed inside that you could actually dream & build from!)

http://www.scribd.com/doc/38419958/50W-HiFi-Power-Amplifier-Maplin

First paragraph of that reads ...

"A superb quality 50W power amplifier. We threw away all our technical
specification handbooks and designed an amp that just sounded musically
perfect. When we'd finished we found that we'd got a pretty impressive
technical spec as well."

--
Adrian C

Adrian C wrote:
On 30/09/2010 01:40, The Natural Philosopher wrote:
Adrian C wrote:

It's not a MOSFET amp.

well I am not surprised it blew up. Pretty amateurish design.

FWIW I've found an old Maplin catalogue from 1985 with the original
project. (The days when the catalogue had projects and data sheets
printed inside that you could actually dream & build from!)

http://www.scribd.com/doc/38419958/50W-HiFi-Power-Amplifier-Maplin

First paragraph of that reads ...

"A superb quality 50W power amplifier. We threw away all our technical
specification handbooks and designed an amp that just sounded musically
perfect. When we'd finished we found that we'd got a pretty impressive
technical spec as well."

except temperature stability ;-)

The design is utterly conventional expect the temperature coefficient of
the output stages is highly positive, which is rather dangerous.

I can write bull**** like the above too.

I am a bit worried about it's hum rejection and switch on thump
characteristics as well.


Distortion and frequency response will be relatively good, for the day,
but when you do this for a living, that's just the start of the game.
There is no overload protection whatsoever apart from the fuse, no
thermal cutout, no SOAR protection, and I am not convinced that they
have got the hum as low as they should..nor arranged for the feedback to
start working before any serious power is delivered to the speakers, to
eliminate 'thump' on switch on.

"The Natural Philosopher" wrote in message
...
Adrian C wrote:
On 30/09/2010 01:40, The Natural Philosopher wrote:
Adrian C wrote:

It's not a MOSFET amp.

well I am not surprised it blew up. Pretty amateurish design.

FWIW I've found an old Maplin catalogue from 1985 with the original
project. (The days when the catalogue had projects and data sheets
printed inside that you could actually dream & build from!)

http://www.scribd.com/doc/38419958/50W-HiFi-Power-Amplifier-Maplin

First paragraph of that reads ...

"A superb quality 50W power amplifier. We threw away all our technical
specification handbooks and designed an amp that just sounded musically
perfect. When we'd finished we found that we'd got a pretty impressive
technical spec as well."

except temperature stability ;-)

That's why Q6 is thermally coupled to the output transistors.


The design is utterly conventional expect the temperature coefficient of
the output stages is highly positive, which is rather dangerous.

I can write bull**** like the above too.

I am a bit worried about it's hum rejection and switch on thump
characteristics as well.

It uses a split power supply, and so long the input 0Volts, thw output will
very quickly go to 0V. I would expect more a click than a loud "plop".



Distortion and frequency response will be relatively good, for the day,
but when you do this for a living, that's just the start of the game.
There is no overload protection whatsoever apart from the fuse, no thermal
cutout, no SOAR protection, and I am not convinced that they have got the
hum as low as they should..nor arranged for the feedback to start working
before any serious power is delivered to the speakers, to eliminate
'thump' on switch on.


It was the circuit in its day, as you say there's no output current
protection, but with two output transistors in parallel, each with a 12A
continuous rating it could cope with some mistreatment. Whether the fuse
would go first would be questionable!

Most complementary circuits would stick to npn's in the top half and pnp's
in the bottom, this circuit has an inversion in both.

However most designs had non-complementary npn output transistors, typically
with an inverter in the "top" half.

I recall building one (non-complementary style) and it was exceptionally
good with regards to hum. I could get very cheap 2N3055s!! I feel the
long-tailed pair in the input stage was inherently insensitive to power
supply variation, which is the section with all the voltage gain.

On 30/09/10 01:40, The Natural Philosopher wrote:

well I am not surprised it blew up. Pretty amateurish design.

It's better than anything I could have done and, to be fair, my pair did
last over 20 years before one of them blew up. Even then it took a good
whack to do it.

I'm wondering if it was a collector-heatsink short on one of the output
transistors that did it, due to a long-forgotten bodge when I built it.

The holes in the heatsink bracket were too small for the insulating
bushes and, rather than drill them out, I cut down the bushes to match
the transistor tab thickness. Looking back, it was a pretty stupid thing
to do as it didn't leave any margin for error. I reckon one of the
transistors shifted a bit upon cranium-to-shelf contact.

Cheers,

Colin.

On 30/09/10 12:37, Adrian C wrote:
On 30/09/2010 01:40, The Natural Philosopher wrote:
Adrian C wrote:

It's not a MOSFET amp.

well I am not surprised it blew up. Pretty amateurish design.

FWIW I've found an old Maplin catalogue from 1985 with the original
project. (The days when the catalogue had projects and data sheets
printed inside that you could actually dream & build from!)

http://www.scribd.com/doc/38419958/50W-HiFi-Power-Amplifier-Maplin

First paragraph of that reads ...

"A superb quality 50W power amplifier. We threw away all our technical
specification handbooks and designed an amp that just sounded musically
perfect. When we'd finished we found that we'd got a pretty impressive
technical spec as well."


Yep. I remember that quote from the catalogue well. It gave me a mental
picture of some bloke beavering away in a Maplin back-room:-

Randomly assemble some components.
Flick switch - puff of smoke. Bugger!
Randomly assemble some components.
Flick switch - puff of smoke. Bugger!
Randomly assemble some components.
Flick switch - puff of smoke. Bugger!
Randomly assemble some components.
Flick switch - horrible noise, but no smoke. I'm on to something!
Make random changes.
Flick switch - puff of smoke. Bugger!
..
..
..


Mind-you, I still bought two kits.

Cheers,

Colin.

On 30/09/10 14:11, The Natural Philosopher wrote:
Adrian C wrote:
On 30/09/2010 01:40, The Natural Philosopher wrote:
Adrian C wrote:

It's not a MOSFET amp.

well I am not surprised it blew up. Pretty amateurish design.

FWIW I've found an old Maplin catalogue from 1985 with the original
project. (The days when the catalogue had projects and data sheets
printed inside that you could actually dream & build from!)

http://www.scribd.com/doc/38419958/50W-HiFi-Power-Amplifier-Maplin

First paragraph of that reads ...

"A superb quality 50W power amplifier. We threw away all our technical
specification handbooks and designed an amp that just sounded
musically perfect. When we'd finished we found that we'd got a pretty
impressive technical spec as well."

except temperature stability ;-)

It seems stable enough. I've driven it pretty hard at times, including
80W RMS per channel continuous sinewave into 8R dummy loads for half an
hour or so when I first built it.


The design is utterly conventional expect the temperature coefficient of
the output stages is highly positive, which is rather dangerous.

I can write bull**** like the above too.

I am a bit worried about it's hum rejection and switch on thump
characteristics as well.


Distortion and frequency response will be relatively good, for the day,
but when you do this for a living, that's just the start of the game.
There is no overload protection whatsoever apart from the fuse, no
thermal cutout, no SOAR protection, and I am not convinced that they
have got the hum as low as they should..nor arranged for the feedback to
start working before any serious power is delivered to the speakers, to
eliminate 'thump' on switch on.

There's just a faint click at switch-on, and the power supply rejection
is fine. With the input shorted, I have to stick my head right into a
speaker to hear anything, then it's just some hiss as I recall - no hum.
Mind you, It's been a long while since I stuck my head in a speaker with
the input shorted.

Mine has even less protection since I've shorted out the output fuse in
the name of lowering the output impedance and I've up-rated the power
supplies. I like to sail close to the wind )

Cheers,

Colin.

On Thu, 30 Sep 2010 14:11:42 +0100, The Natural Philosopher wrote:
I am a bit worried about it's hum rejection and switch on thump
characteristics as well.

I think they sold a separate kit to provide some form of switch-on delay
for the speakers (and various other goodies, too).

I remember thinking about building one of those amps, but then I ended up
going for a pair of their 150W ones instead; I had an old 19" instrument
chassis that was just crying out to have a large amp built into it. It
was a reasonable beastie, but I think the only thing I have left from it
is the transformer...

Colin Stamp wrote:
On 30/09/10 14:11, The Natural Philosopher wrote:
Adrian C wrote:
On 30/09/2010 01:40, The Natural Philosopher wrote:
Adrian C wrote:

It's not a MOSFET amp.

well I am not surprised it blew up. Pretty amateurish design.

FWIW I've found an old Maplin catalogue from 1985 with the original
project. (The days when the catalogue had projects and data sheets
printed inside that you could actually dream & build from!)

http://www.scribd.com/doc/38419958/50W-HiFi-Power-Amplifier-Maplin

First paragraph of that reads ...

"A superb quality 50W power amplifier. We threw away all our technical
specification handbooks and designed an amp that just sounded
musically perfect. When we'd finished we found that we'd got a pretty
impressive technical spec as well."

except temperature stability ;-)

It seems stable enough. I've driven it pretty hard at times, including
80W RMS per channel continuous sinewave into 8R dummy loads for half an
hour or so when I first built it.


The design is utterly conventional expect the temperature coefficient of
the output stages is highly positive, which is rather dangerous.

I can write bull**** like the above too.

I am a bit worried about it's hum rejection and switch on thump
characteristics as well.


Distortion and frequency response will be relatively good, for the day,
but when you do this for a living, that's just the start of the game.
There is no overload protection whatsoever apart from the fuse, no
thermal cutout, no SOAR protection, and I am not convinced that they
have got the hum as low as they should..nor arranged for the feedback to
start working before any serious power is delivered to the speakers, to
eliminate 'thump' on switch on.

There's just a faint click at switch-on, and the power supply rejection
is fine. With the input shorted, I have to stick my head right into a
speaker to hear anything, then it's just some hiss as I recall - no hum.
Mind you, It's been a long while since I stuck my head in a speaker with
the input shorted.


The last ever 150W design I did had everything. Down to the point where
even in the hot African sun, it would deliver into any load we threw at
it, for as long as the loudspeaker cones lasted, was fully short, half
short, open circuit protected, and was on the ragged edge of heat before
the thermal cutout went.

It had no switch on effects at all, because there was no current
delivered to the outputs beyond a mA or so in order to stabilise the
feedback before any serious power was applied to the speakers.

It was about my tenth or eleventh design for high power professional
use. After that I ended up designing software instead.

I cant remember the specs, but short of MOSFETS it was as good as any
bipolar design on the market.

Mine has even less protection since I've shorted out the output fuse in
the name of lowering the output impedance and I've up-rated the power
supplies. I like to sail close to the wind )


Removing the fuse will not affect the output impedance whatsoever.

That is a function of the feedback in the amp, and is likely to be well
below the resistance of the RF stabilising choke and the loudspeaker
cables themselves.

Cheers,

Colin.

On 30/09/10 23:51, The Natural Philosopher wrote:

Removing the fuse will not affect the output impedance whatsoever.

That is a function of the feedback in the amp, and is likely to be well
below the resistance of the RF stabilising choke and the loudspeaker
cables themselves.

The fuse is outside the feedback loop on this design but of course
shorting it out was indeed fairly futile. My defence is that I was
young. It isn't the silliest thing about the amp anyway. I had to use a
blow-torch to solder the power supply and speaker cables.

Cheers,

Colin.

On 1/10/2010 11:51 a.m., The Natural Philosopher wrote:
The last ever 150W design I did had everything. Down to the point where even in
the hot African sun, it would deliver into any load we threw at it, for as long
as the loudspeaker cones lasted, was fully short, half short, open circuit
protected, and was on the ragged edge of heat before the thermal cutout went.

It had no switch on effects at all, because there was no current delivered to
the outputs beyond a mA or so in order to stabilise the feedback before any
serious power was applied to the speakers.

It was about my tenth or eleventh design for high power professional use. After
that I ended up designing software instead.

Many years ago I built a couple of amps. The first couple were Wireless World
designs (Bailey, I think), the last, which I'm still using, is supposedly a Quad
405 copy, the current-dumper design. Someone at the place I was working had
made some circuit boards for it. My days of caring much about hi-fi are long
gone, but I'd be curious to hear your comments on this amp, which once was
highly regarded. I got rid of the pre-amps (a very old WW design) a few years
ago, and stuck in op-amps with only a volume control. I've never missed the
tone controls or filters.

Gib Bogle wrote:
On 1/10/2010 11:51 a.m., The Natural Philosopher wrote:
The last ever 150W design I did had everything. Down to the point
where even in
the hot African sun, it would deliver into any load we threw at it,
for as long
as the loudspeaker cones lasted, was fully short, half short, open
circuit
protected, and was on the ragged edge of heat before the thermal
cutout went.

It had no switch on effects at all, because there was no current
delivered to
the outputs beyond a mA or so in order to stabilise the feedback
before any
serious power was applied to the speakers.

It was about my tenth or eleventh design for high power professional
use. After
that I ended up designing software instead.

Many years ago I built a couple of amps. The first couple were Wireless
World designs (Bailey, I think), the last, which I'm still using, is
supposedly a Quad 405 copy, the current-dumper design. Someone at the
place I was working had made some circuit boards for it. My days of
caring much about hi-fi are long gone, but I'd be curious to hear your
comments on this amp, which once was highly regarded. I got rid of the
pre-amps (a very old WW design) a few years ago, and stuck in op-amps
with only a volume control. I've never missed the tone controls or
filters.

The difference between the circuits in magazines, and the circuits you
put in production are simple.

A magazine circuit worked well for one man, once.

A production circuit has to work well for all spreads of semiconductors
under all customer conditions.

The very first circuit I ever built from a magazine failed when I left
in in the sun. It was fine when I put it back in the shade. I was IIRC
13. That's when I realised that I had better start understanding what I
was doing. Since the guys in the magazines patently didn't.

I probably built half of all the HiFi amps of the period. Pretty sure I
did a Linsley hood was it a Bailey. Did a class A as well. Worked for
Uncle Clive, then on into HiFi proper for a couple of years, then the
music business for disco and PA and guitar usage..waste of my time
really. Only one of the firms I worked for still exists. (Actually only
one of the firms I worked for in my entire career doing electronics
still exists in this country, and that's Marconi Elliot Avionics, which
lingers on as SELEX Sensors and Airborne Systems. The other one still
exists in S Africa)

It was post Uncle Clive when I realised finally that technicians could
put circuits together and fiddle with them till they worked without
really understanding why they did, or the implications of their design
choices, that I finally answered the question of how alleged experts who
wrote for magazines could produce stuff that didn't work properly.
Because they were of the 'fiddle till it works' brigade.

Now we all did that,. but some of us with more insight started from
better places that required less fiddling to get to better results.

The better results in power amps came really from better output devices.
Essentially the better those were the more feed back you could slap
round the whole thing, without going unstable, and the lower distortion
you could get, and the higher frequency the nasties in the crossover
region could be pushed.

And 99% of the circuits were in fact mild adaptations of the
application notes supplied by the semiconductor magazines. That's where
the better fiddlers started their fiddling from.

Ultimately I realised that all a PA is, is an arrangement of power
devices that is broadly symmetrical to drive a complex load. and simply
work back from there. Those devices themselves have to be driven, safely
and securely so that all devices are inside the SOAR, and then they need
phase splitting if its class B, and then some kind of reasonably low
noise input stage.

Then try and keep the whole arrangement stable into just about any
possible load, with enough feed back to get distortion down..early stuff
we could do 0.1%, pretty soon I was hitting 0.025%, and by the time I
finished it was pretty much off the scale in the noise. Even low level
crossover was getting to be almost unmeasurable, compared with the 1-2%
it had been on e.g. a Quad 303. Frequency responses likewise went up as
better devices came along.

Hitachi complementary FETS were the best devices I worked with..back
about 1980 or so.

Really, there wasn't anything left to do then. You could produce an
amplifier that was better than any valve amplifier, ruler flat and
totally distortion free, in a back shed. You couldn't sell it though,
without employing the sort of spin merchant that made Alistair Campbell
look like Honest John, Or putting valves in it.

I realised from my time building high distortion guitar amplification
that people actually like distortion. It's something they get used to
and it sounds 'right' to them. Likewise natural resonances and
colouration in Loudspeakers.

Put them in front of a flat amp and really good loudspeakers and they
feel something is missing: It is. All the distortion and colouration
they are used to. The sound becomes naked and sterile, because all they
now hear is what is actually on the CD..

Well, the CD was in by then, and the cassette tape had taken the big
money out of the music business, prejudice and religion ruled the HiFi
world, and I was still broke, and no one wanted a circuit designer
outside of Silicon Valley or Japan so I started playing with
microcomputers and turned my back on it all.

I was in fact pretty disillusioned. I'd given them 'the closest approach
to the original sound' made em rock solid, and idiot proof, and realised
that that wasn't actually what they wanted. They wanted style, bragging
rights, fashion statements, a brand..not what I could provide really. I
majored in proper engineering.

At least in the music business they were more honest. 'Just so it
sounds like a Marshall turned up to 11, I don't care what that means,
that's what I want'.

I got a Technics amp once. Looked at the circuit diagram and thought
'hey, That's the way *I* broke the patent on that clever AAB design I
stole..and they integrated the whole lot on a chip to get temperature
stability' It was a ripoff of my ripoff!!..

And I wouldn't mind betting that the output of any Peavey guitar Amp to
this day is exactly the way I designed it (but not for Peavey!). So some
of the work lives on I suppose.






















..

We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember Colin Stamp
saying something like:

A long long time ago, I made an amplifier using two of these modules.
Since I made it in my yoof, I'm quite attached to it. Recently though,
my wife bashed her head on the underside of the shelf it was on. There
followed loads of crackling from the speakers accompanied by the
disturbing hum of power rails coupled directly to speakers. I sprang up
and flew across the room to switch the amp off (which wasn't easy since
I had to be careful to avoid my wife who was now rolling around on the
floor, clutching her head) but I was too late and the left channel was
toast.

Glad to see you got your priorities right. A wife can be replaced.

The Natural Philosopher wrote:

The difference between the circuits in magazines, and the circuits you
put in production are simple.

A magazine circuit worked well for one man, once.

A production circuit has to work well for all spreads of semiconductors
under all customer conditions.

The very first circuit I ever built from a magazine failed when I left
in in the sun. It was fine when I put it back in the shade. I was IIRC
13. That's when I realised that I had better start understanding what I
was doing. Since the guys in the magazines patently didn't.

I probably built half of all the HiFi amps of the period. Pretty sure I
did a Linsley hood was it a Bailey. Did a class A as well. Worked for
Uncle Clive, then on into HiFi proper for a couple of years, then the
music business for disco and PA and guitar usage..waste of my time
really. Only one of the firms I worked for still exists. (Actually only
one of the firms I worked for in my entire career doing electronics
still exists in this country, and that's Marconi Elliot Avionics, which
lingers on as SELEX Sensors and Airborne Systems. The other one still
exists in S Africa)

It was post Uncle Clive when I realised finally that technicians could
put circuits together and fiddle with them till they worked without
really understanding why they did, or the implications of their design
choices, that I finally answered the question of how alleged experts who
wrote for magazines could produce stuff that didn't work properly.
Because they were of the 'fiddle till it works' brigade.

Now we all did that,. but some of us with more insight started from
better places that required less fiddling to get to better results.

The better results in power amps came really from better output devices.
Essentially the better those were the more feed back you could slap
round the whole thing, without going unstable, and the lower distortion
you could get, and the higher frequency the nasties in the crossover
region could be pushed.

And 99% of the circuits were in fact mild adaptations of the application
notes supplied by the semiconductor magazines. That's where the better
fiddlers started their fiddling from.

Ultimately I realised that all a PA is, is an arrangement of power
devices that is broadly symmetrical to drive a complex load. and simply
work back from there. Those devices themselves have to be driven, safely
and securely so that all devices are inside the SOAR, and then they need
phase splitting if its class B, and then some kind of reasonably low
noise input stage.

Then try and keep the whole arrangement stable into just about any
possible load, with enough feed back to get distortion down..early stuff
we could do 0.1%, pretty soon I was hitting 0.025%, and by the time I
finished it was pretty much off the scale in the noise. Even low level
crossover was getting to be almost unmeasurable, compared with the 1-2%
it had been on e.g. a Quad 303. Frequency responses likewise went up as
better devices came along.

Hitachi complementary FETS were the best devices I worked with..back
about 1980 or so.

Really, there wasn't anything left to do then. You could produce an
amplifier that was better than any valve amplifier, ruler flat and
totally distortion free, in a back shed. You couldn't sell it though,
without employing the sort of spin merchant that made Alistair Campbell
look like Honest John, Or putting valves in it.

I realised from my time building high distortion guitar amplification
that people actually like distortion. It's something they get used to
and it sounds 'right' to them. Likewise natural resonances and
colouration in Loudspeakers.

Put them in front of a flat amp and really good loudspeakers and they
feel something is missing: It is. All the distortion and colouration
they are used to. The sound becomes naked and sterile, because all they
now hear is what is actually on the CD..

Well, the CD was in by then, and the cassette tape had taken the big
money out of the music business, prejudice and religion ruled the HiFi
world, and I was still broke, and no one wanted a circuit designer
outside of Silicon Valley or Japan so I started playing with
microcomputers and turned my back on it all.

I was in fact pretty disillusioned. I'd given them 'the closest approach
to the original sound' made em rock solid, and idiot proof, and realised
that that wasn't actually what they wanted. They wanted style, bragging
rights, fashion statements, a brand..not what I could provide really. I
majored in proper engineering.

At least in the music business they were more honest. 'Just so it
sounds like a Marshall turned up to 11, I don't care what that means,
that's what I want'.

I got a Technics amp once. Looked at the circuit diagram and thought
'hey, That's the way *I* broke the patent on that clever AAB design I
stole..and they integrated the whole lot on a chip to get temperature
stability' It was a ripoff of my ripoff!!..

And I wouldn't mind betting that the output of any Peavey guitar Amp to
this day is exactly the way I designed it (but not for Peavey!). So some
of the work lives on I suppose.


That's a very interesting post and echoes a lot of my experience over
the years. Thanks for that.

I recently came across this (it's been around for ten years, but passed
me by):

http://en.wikipedia.org/wiki/Gainclone

Says it all really. HiFi as a concept is pretty dead for me. Almost
everything audio sounds 'good enough' these days (if used in an
appropriate context, natch).

Dave Osborne wrote:
The Natural Philosopher wrote:

The difference between the circuits in magazines, and the circuits you
put in production are simple.

A magazine circuit worked well for one man, once.

A production circuit has to work well for all spreads of
semiconductors under all customer conditions.

The very first circuit I ever built from a magazine failed when I left
in in the sun. It was fine when I put it back in the shade. I was IIRC
13. That's when I realised that I had better start understanding what
I was doing. Since the guys in the magazines patently didn't.

I probably built half of all the HiFi amps of the period. Pretty sure
I did a Linsley hood was it a Bailey. Did a class A as well. Worked
for Uncle Clive, then on into HiFi proper for a couple of years, then
the music business for disco and PA and guitar usage..waste of my time
really. Only one of the firms I worked for still exists. (Actually
only one of the firms I worked for in my entire career doing
electronics still exists in this country, and that's Marconi Elliot
Avionics, which lingers on as SELEX Sensors and Airborne Systems. The
other one still exists in S Africa)

It was post Uncle Clive when I realised finally that technicians could
put circuits together and fiddle with them till they worked without
really understanding why they did, or the implications of their design
choices, that I finally answered the question of how alleged experts
who wrote for magazines could produce stuff that didn't work properly.
Because they were of the 'fiddle till it works' brigade.

Now we all did that,. but some of us with more insight started from
better places that required less fiddling to get to better results.

The better results in power amps came really from better output
devices. Essentially the better those were the more feed back you
could slap round the whole thing, without going unstable, and the
lower distortion you could get, and the higher frequency the nasties
in the crossover region could be pushed.

And 99% of the circuits were in fact mild adaptations of the
application notes supplied by the semiconductor magazines. That's
where the better fiddlers started their fiddling from.

Ultimately I realised that all a PA is, is an arrangement of power
devices that is broadly symmetrical to drive a complex load. and
simply work back from there. Those devices themselves have to be
driven, safely and securely so that all devices are inside the SOAR,
and then they need phase splitting if its class B, and then some kind
of reasonably low noise input stage.

Then try and keep the whole arrangement stable into just about any
possible load, with enough feed back to get distortion down..early
stuff we could do 0.1%, pretty soon I was hitting 0.025%, and by the
time I finished it was pretty much off the scale in the noise. Even
low level crossover was getting to be almost unmeasurable, compared
with the 1-2% it had been on e.g. a Quad 303. Frequency responses
likewise went up as better devices came along.

Hitachi complementary FETS were the best devices I worked with..back
about 1980 or so.

Really, there wasn't anything left to do then. You could produce an
amplifier that was better than any valve amplifier, ruler flat and
totally distortion free, in a back shed. You couldn't sell it though,
without employing the sort of spin merchant that made Alistair
Campbell look like Honest John, Or putting valves in it.

I realised from my time building high distortion guitar amplification
that people actually like distortion. It's something they get used to
and it sounds 'right' to them. Likewise natural resonances and
colouration in Loudspeakers.

Put them in front of a flat amp and really good loudspeakers and they
feel something is missing: It is. All the distortion and colouration
they are used to. The sound becomes naked and sterile, because all
they now hear is what is actually on the CD..

Well, the CD was in by then, and the cassette tape had taken the big
money out of the music business, prejudice and religion ruled the HiFi
world, and I was still broke, and no one wanted a circuit designer
outside of Silicon Valley or Japan so I started playing with
microcomputers and turned my back on it all.

I was in fact pretty disillusioned. I'd given them 'the closest
approach to the original sound' made em rock solid, and idiot proof,
and realised that that wasn't actually what they wanted. They wanted
style, bragging rights, fashion statements, a brand..not what I could
provide really. I majored in proper engineering.

At least in the music business they were more honest. 'Just so it
sounds like a Marshall turned up to 11, I don't care what that means,
that's what I want'.

I got a Technics amp once. Looked at the circuit diagram and thought
'hey, That's the way *I* broke the patent on that clever AAB design I
stole..and they integrated the whole lot on a chip to get temperature
stability' It was a ripoff of my ripoff!!..

And I wouldn't mind betting that the output of any Peavey guitar Amp
to this day is exactly the way I designed it (but not for Peavey!). So
some of the work lives on I suppose.


That's a very interesting post and echoes a lot of my experience over
the years. Thanks for that.

I recently came across this (it's been around for ten years, but passed
me by):

http://en.wikipedia.org/wiki/Gainclone

Says it all really. HiFi as a concept is pretty dead for me. Almost
everything audio sounds 'good enough' these days (if used in an
appropriate context, natch).

well those chips are not that much good for top end applications really.

They are good enough for guitars though, and I used a few in my
time..hung some weird feedback round em to do high output impedance and
soft clipping a la vox AC 30..

But they are good enough to be called 'hifi' for sure.

And ten times better than most loudspeakers..:-)

On 2/10/2010 8:07 a.m., Dave Osborne wrote:

That's a very interesting post and echoes a lot of my experience over the years.
Thanks for that.

I recently came across this (it's been around for ten years, but passed me by):

http://en.wikipedia.org/wiki/Gainclone

Says it all really. HiFi as a concept is pretty dead for me. Almost everything
audio sounds 'good enough' these days (if used in an appropriate context, natch).

New to me. Thanks.

The 'HiFi' world has become one gigantic scam, or comedy, depending on your
level of cynicism. Gold-plated speaker cables costing more than my amplifier
cost to make, and having, of course, no audible effect. Take a glance at one of
the up-market hi-fi mags, the level of ridiculousness is beyond belief, surreal.

I remember many years ago reading an interview with a British designer-builder
of high quality cheap speakers. He wasn't doing very well selling his stuff,
which was very good value for money, until he raised his prices significantly.
This caused his sales to increase markedly, but he was so disgusted with this
evidence of what the market cared about that he quit.

Gib Bogle wrote:
On 2/10/2010 8:07 a.m., Dave Osborne wrote:

That's a very interesting post and echoes a lot of my experience over
the years.
Thanks for that.

I recently came across this (it's been around for ten years, but
passed me by):

http://en.wikipedia.org/wiki/Gainclone

Says it all really. HiFi as a concept is pretty dead for me. Almost
everything
audio sounds 'good enough' these days (if used in an appropriate
context, natch).

New to me. Thanks.

The 'HiFi' world has become one gigantic scam, or comedy, depending on
your level of cynicism. Gold-plated speaker cables costing more than my
amplifier cost to make, and having, of course, no audible effect. Take
a glance at one of the up-market hi-fi mags, the level of ridiculousness
is beyond belief, surreal.

I remember many years ago reading an interview with a British
designer-builder of high quality cheap speakers. He wasn't doing very
well selling his stuff, which was very good value for money, until he
raised his prices significantly. This caused his sales to increase
markedly, but he was so disgusted with this evidence of what the market
cared about that he quit.


I have to say, I was more or less in that camp.

I could have made money with the contacts in the music biz by making a
crappy overstyled valve guitar amp and selling them for a grand apiece.

Think Mesa boogie.


Oh they are actually £1500 new these days.

there must be all of 80 quids worth of parts in em.

But as Keith Richards said 'its less about who you sleep with, than
sleeping with yourself, for the rest of your life, so to speak'

On 1 Oct, 20:07, Dave Osborne wrote:


Says it all really. HiFi as a concept is pretty dead for me. Almost
everything audio sounds 'good enough' these days (if used in an
appropriate context, natch).

Speakers still matter. The rest is just past caring, and has been for
30-ish years,

Except MP3s, which do still sound a bit limited if you're from Bristol
and have a decent system to compare on.

On 02/10/2010 00:02, Gib Bogle wrote:

The 'HiFi' world has become one gigantic scam, or comedy, depending on
your level of cynicism.

Tragicomedy, surely? Hear that rumble? It's the sound of Gilbert
Briggs, Harry Leak and Peter Walker tuning in their graves...

--
Andy

On 2/10/2010 12:48 p.m., Andy Dingley wrote:
On 1 Oct, 20:07, Dave wrote:


Says it all really. HiFi as a concept is pretty dead for me. Almost
everything audio sounds 'good enough' these days (if used in an
appropriate context, natch).

Speakers still matter. The rest is just past caring, and has been for
30-ish years,

I agree completely. I'm using old Tannoy Monitor Golds that my dad bought in
the 70s (I think). Unfashionably big boxes, but I have a big room.

Gib Bogle wrote:
On 2/10/2010 12:48 p.m., Andy Dingley wrote:
On 1 Oct, 20:07, Dave wrote:


Says it all really. HiFi as a concept is pretty dead for me. Almost
everything audio sounds 'good enough' these days (if used in an
appropriate context, natch).

Speakers still matter. The rest is just past caring, and has been for
30-ish years,

I agree completely. I'm using old Tannoy Monitor Golds that my dad
bought in the 70s (I think). Unfashionably big boxes, but I have a big
room.

Pretty good, even today.

We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember Gib Bogle
saying something like:

Speakers still matter. The rest is just past caring, and has been for
30-ish years,

I agree completely. I'm using old Tannoy Monitor Golds that my dad bought in
the 70s (I think). Unfashionably big boxes, but I have a big room.

Ditto, but with Leak 3080s here.
http://listeninn.com/Website/Used-Sp.../Leak-3080.htm
They need resuspending now, but were utterly great in their day.
I will probably spring for a suspension kit, as they're worth it.

In article , Gib Bogle g.bogle@auckland
..no.spam.ac.nz scribeth thus
On 2/10/2010 12:48 p.m., Andy Dingley wrote:
On 1 Oct, 20:07, Dave wrote:


Says it all really. HiFi as a concept is pretty dead for me. Almost
everything audio sounds 'good enough' these days (if used in an
appropriate context, natch).

Speakers still matter. The rest is just past caring, and has been for
30-ish years,

I agree completely. I'm using old Tannoy Monitor Golds that my dad bought in
the 70s (I think). Unfashionably big boxes, but I have a big room.

Should you want of pass them on to a good home for a crate of beer
tokens drop me a mail)...
--
Tony Sayer

On 02/10/2010 18:39, tony sayer wrote:
In , Gib Bogleg.bogle@auckland
.no.spam.ac.nz scribeth thus
On 2/10/2010 12:48 p.m., Andy Dingley wrote:
On 1 Oct, 20:07, Dave wrote:


Says it all really. HiFi as a concept is pretty dead for me. Almost
everything audio sounds 'good enough' these days (if used in an
appropriate context, natch).

Speakers still matter. The rest is just past caring, and has been for
30-ish years,

I agree completely. I'm using old Tannoy Monitor Golds that my dad bought in
the 70s (I think). Unfashionably big boxes, but I have a big room.

Should you want of pass them on to a good home for a crate of beer
tokens drop me a mail)...

I'm considering offloading my old Active Linn Isobariks along with the
tri-amp stack of Naim 250 replicas I home-built. ( schematics and
layouts supplied! )

But I'd only be prepared to offload them to a loving home.

Do you reckon anyone would be interested in such audio relics?

--
Ron

In article , Ron Lowe
scribeth thus
On 02/10/2010 18:39, tony sayer wrote:
In , Gib Bogleg.bogle@auckland
.no.spam.ac.nz scribeth thus
On 2/10/2010 12:48 p.m., Andy Dingley wrote:
On 1 Oct, 20:07, Dave wrote:


Says it all really. HiFi as a concept is pretty dead for me. Almost
everything audio sounds 'good enough' these days (if used in an
appropriate context, natch).

Speakers still matter. The rest is just past caring, and has been for
30-ish years,

I agree completely. I'm using old Tannoy Monitor Golds that my dad bought in
the 70s (I think). Unfashionably big boxes, but I have a big room.

Should you want of pass them on to a good home for a crate of beer
tokens drop me a mail)...

I'm considering offloading my old Active Linn Isobariks along with the
tri-amp stack of Naim 250 replicas I home-built. ( schematics and
layouts supplied! )

But I'd only be prepared to offload them to a loving home.

Do you reckon anyone would be interested in such audio relics?


Yes just need to advertise in the right place!..

Ebay would be a good start..
--
Tony Sayer

On 3/10/2010 6:39 a.m., tony sayer wrote:
In , Gib Bogleg.bogle@auckland
.no.spam.ac.nz scribeth thus
On 2/10/2010 12:48 p.m., Andy Dingley wrote:
On 1 Oct, 20:07, Dave wrote:


Says it all really. HiFi as a concept is pretty dead for me. Almost
everything audio sounds 'good enough' these days (if used in an
appropriate context, natch).

Speakers still matter. The rest is just past caring, and has been for
30-ish years,

I agree completely. I'm using old Tannoy Monitor Golds that my dad bought in
the 70s (I think). Unfashionably big boxes, but I have a big room.

Should you want of pass them on to a good home for a crate of beer
tokens drop me a mail)...

yeah, right. Recently I noticed a slight imbalance between the two sides,
which turned out (luckily) to be caused by damage to one of the crossover units.
Some time, presumably long ago when the speakers were installed in my parents'
house, some sort of over-driving had made a resistor very hot, melting some of
the surrounding plastic casing and damaging a capacitor. It could have been
some misbehaviour from my dad's DIY amp, or from his DIY kids. All better now,
and my daughter will inherit them.

I also have a pair of Spendor BC1s that I'm not using but can't bear to part
with. It was a tossup, but I decided to use the Tannoys when they came available.

In article , Gib Bogle g.bogle@auckland
..no.spam.ac.nz scribeth thus
On 3/10/2010 6:39 a.m., tony sayer wrote:
In , Gib Bogleg.bogle@auckland
.no.spam.ac.nz scribeth thus
On 2/10/2010 12:48 p.m., Andy Dingley wrote:
On 1 Oct, 20:07, Dave wrote:


Says it all really. HiFi as a concept is pretty dead for me. Almost
everything audio sounds 'good enough' these days (if used in an
appropriate context, natch).

Speakers still matter. The rest is just past caring, and has been for
30-ish years,

I agree completely. I'm using old Tannoy Monitor Golds that my dad bought in
the 70s (I think). Unfashionably big boxes, but I have a big room.

Should you want of pass them on to a good home for a crate of beer
tokens drop me a mail)...

yeah, right.

OK, Wagon of beer tokens..

Recently I noticed a slight imbalance between the two sides,
which turned out (luckily) to be caused by damage to one of the crossover units.
Some time, presumably long ago when the speakers were installed in my parents'
house, some sort of over-driving had made a resistor very hot, melting some of
the surrounding plastic casing and damaging a capacitor. It could have been
some misbehaviour from my dad's DIY amp, or from his DIY kids. All better now,
and my daughter will inherit them.



I also have a pair of Spendor BC1s that I'm not using but can't bear to part
with.

Another very good English designed speaker)..

It was a tossup, but I decided to use the Tannoys when they came
available.

--
Tony Sayer