bk wrote in message
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On Mar 20, 12:23 pm, "N Cook" wrote:
Arfa Daily wrote in message
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"N Cook" wrote in message
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Elvis Kabong wrote in message
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"N Cook" wrote in message
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Lord Valve wrote in message
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N Cook wrote:
Cut out in use then came back.
Next time failed to give output but owner noticed clip light
in
pre-amp
functioned as normal
Now I have it, I cannot induce it to fail.
Of course not. ;-)
Anyone know of generic/specific Eden problems?
Likely suspects the discrete wire IDC connectors for power
and
signal
interconnects, unsupported wire-wounds on end, mains thermal
switch.
Anyone know the identity of the valve/tube ?
12AX7.
If it's got an effects loop (or pre-in pwr-out jacks)
check for dirty normalling contacts.
Lord Valve
Expert
Thanks for the info.
Do they remove the valve labelling ? no trace of anything on this
one.
Send/return switches are the first things I look at with this
sort of
problem along with speaker plug/lead
.
I wondered if there was any Eden specific problem areas. I've not
checked it
out but is that a thermal cutout in the mains feed , rather than
filter, to
monitor general chassis temperature, not the output N/O(cold) one
for
the
fan
Their power supply boards have been known to become intermittent
even
though
they are double-sided PCBs. You may really have to pound on the
filter
caps to get the
bad one or the bad connection to act up. Also look underneath the
supply
PCB for high
watt
ceramic resistors sitting on the chassis with heat sink compound on
the
chassis
while they are soldered to the board but a lead may be broken and
only
touching
where it's supposed to be soldered.
Sometimes the zeners and their current dropping resistors (more
ceramic
ones)
for the plus/minus low voltage supply become overheated and melt
solder
or
get
bounced out of whack resulting in a loose lead.
I would suggest to run a signal thru it directly into the scope
bypassing
the dummy load
while tapping and wiggling things around or get it heated up with a
load
and tap around.
Try it both ways, but do it the cool way first, right?
Checked the pots for loose cases?
Customer already ruled out his bass, instrument cable, speaker
cable
and
cab or
did you?
Retighten the tube socket terminals and clean them?
Detachable AC cord plugged in firmly by the customer? Have him/her
demonstrate without
saying anything first. Then again, you just may have to have the
customer
come in with
their entire rig and demonstrate the problem.
Whatever it is, good luck. I know the feeling.
Ed
Sonic Surgery
New Orleans
Earth
I did not like the front panel switch in line with the speaker line.
In standby instead of cutting/shorting the main amp input you switch
out
the
speaker. IDC interconnects on the speaker lines and power lines seem
a
bit
irregular to me but as cut out rather than distortion those power
lines
presumably ok.
As 2 main bass speakers plus 1 in the cab, as sound died unlikely a
problem
with a speaker but will check the wiring in there as well as the
other
likely suspects.
I haven't come across one of these, but I can't help thinking that a
front
panel switch in line with the speakers, hooked via *any* kind of 'pin'
connector, let alone IDC ones, has got to be one of the most
ludicrously
crazy pieces of design work I have ever heard of - especially in a
bass
combo with two drivers in it. Peak currents of many amps will be
(attempting
! ) to flow through this combination ...
Arfa
I think I'll bypass this front speaker switch and wiring.
Its only rated 3amp and thats for AC, could easily be the problem, let
alone
potentially "fatal" to the amp. The cab wiring and pair of 4 ohm
speakers in
series seem fine.
I may trace the circuit around and between preamp o/p and amp i/p and
change
that switch to a line level cut function.
--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list
onhttp://home.graffiti.net/diverse:graffiti.net/- Hide quoted text -
How could the switch be "fatal to the amp"?
Designed appropriately, it's there to disable the speakers
in the event that one elects to operate things
'silently' as in use of stereo phones or in certain
recording situations. It isn't a common failure mode.
Yes, an intermittent switch will shut down the speakers but
as far as the power amp finals are concerned,
"fatal" is impossible as no current would flow when
imposing an open at the load connections.
Here's a tip: Instead of poking around blindly, give Eden
a call. They'll not only send *any* schematic you
desire, they'll also be the most helpful resource out there...
since they spawned the thing.
The output employs thermal protection via use
of an agc circuit which also operates the cooling fan.
Have you cranked the thing up against some dummys
in order to test for thermal related shut down? You should.
Any chance that the owner/operator is using too low of a load
impedance?
IIRC, the agc circuit can shut the power amp completely off. Barring
any
"connection-based" problem (previously mentioned),
a guess would be that something in the agc circuit is failing
or theres a problem with the impedance at the load.
Contact Eden.
bk
Here's a simple experiment unless you have a heart problem.
Find a small 12V relay , connect to a 12V dc source, hold the relay contacts
between thumb and index finger and disconnect the wire to the 12V supply.
This simply demonstrates the power of back emf and V=L* dI/dT, speaker
inductance about 1mH and peak current through a speaker of maybe 20 to 50
amps.
If those few hundred volts (at least) speaker induced back emf exceed the
breakdown voltage of whatever partial contact gap, not the final gap, soon
(microseconds) after the switch break/ poor IDC contact/poor pcb header pin
contact then goodbye pa.
It would not take much fumbling in poor light, drunkeness, confussion or
whatever to flip that switch in full use , its not recessed and in the back
of the cab. The owner does not use the switch so I will block off the
relevant outlet with a nylon bolt pushed in the 1/4 inch socket as a
reminder to him, not to use. The other 2 paralleled outlets are not
switched, but I may hardwire/solder back to the pa.
--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/