Eden "The Metro" Bass Amp intermittent problem

[N Cook]

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.
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 ?

 

[Lord Valve]

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

 

[N Cook]

--
--

Of course not. ;-)


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

 

[Elvis Kabong]

--
--

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

 

[[email protected]]

re solder all connections on pc board but we have seen
the speakers in these amps fail frequently.
check the pigtail leads on the speaker basket, damaged
leads from loud playing can cause what you describe,
intermittent output.
play the amp really loud to trigger the symptom, with a bass.
or tap on the pc board with a plastic handle to find evidence
of the bad solder connections.
eden sells the replacement basket which bolts to the
magnet. easy field replacements.
the valve is ECC83.

 

[N Cook]

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.

 

[Arfa Daily]

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

 

[N Cook]

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

My thoughts exactly, someone fumbles around the front panel with full load
going through amp and breaks the line to the speaker at this switch.

Anyone know what the function of the 12V, 10 W "festoon " bulb in the
variable crossover in the cab is, fuse? variable impedance element?. Working
order but just curious

 

[Elvis Kabong]

My thoughts exactly, someone fumbles around the front panel with full load
going through amp and breaks the line to the speaker at this switch.

Anyone know what the function of the 12V, 10 W "festoon " bulb in the
variable crossover in the cab is, fuse? variable impedance element?. Working
order but just curious

Tweeter fuse. However, half the time the tweeter coil blows and half the time the light
bulb fuse blows. One needs to stock both items.

 

[Stephen Cowell]

....

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.

That's probably your culprit... going below
the minimum impedance. What is it rated for,
what are you running it at? SS amps overheat
when run below their rated min imp.
__
Steve
..

 

[N Cook]

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.

 

[DGDevin]

Eden used to have such a good name, yet here are all these posts about goofy
design issues and recurring problems, I wonder if this dates from them being
borged by the dreaded big fat corporation?

 

[bk]

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.

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

 

[N Cook]

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.

 

[N Cook]

Found another nasty under the ps board but don't think it is the main
problem.
This pair of wires to the speaker switch had one of the wires squashed
between a large W/W ceramic cased dropper under the ps and the chassis.
Melted through but as it cuts the earth to the speaker presumably no problem
as such and wire not broken. But there is smoke blackening or something
grimy in that area but it could be a small electrolytic parallel to the fan
cooked as it is directly over the large droppers and leaked electrolyte but
all rather nasty. The aluminium of the chassis directly under this
particular dropper has a strange flecked grey corrosion or something that
probably more likely due to electrolyte rather than vapours off the charred
PVC insulation. I don't see why this insulation has charred rather than just
melted as the owner never switched this speaker switch, I assume somewhere
maybe ages ago it was open at some point

Anyone know the function of the big triac on the mains, crowbar operation to
blow the mains fuse if too much mains power drawn ?, I've not traced any
triac associated line back into the amp that could trigger it as more active
amp protection.

 

[N Cook]

Found another nasty under the ps board but don't think it is the main
problem.
This pair of wires to the speaker switch had one of the wires squashed
between a large W/W ceramic cased dropper under the ps and the chassis.
Melted through but as it cuts the earth to the speaker presumably no problem
as such and wire not broken. But there is smoke blackening or something
grimy in that area but it could be a small electrolytic parallel to the fan
cooked as it is directly over the large droppers and leaked electrolyte but
all rather nasty. The aluminium of the chassis directly under this
particular dropper has a strange flecked grey corrosion or something that
probably more likely due to electrolyte rather than vapours off the charred
PVC insulation. I don't see why this insulation has charred rather than just
melted as the owner never switched this speaker switch, I assume somewhere
maybe ages ago it was open at some point

Anyone know the function of the big triac on the mains, crowbar operation to
blow the mains fuse if too much mains power drawn ?, I've not traced any
triac associated line back into the amp that could trigger it as more active
amp protection.

The corrosion i've photoed here
http://home.graffiti.net/diverse:graffiti.net/ali2.jpg
The overexposed T area is the mains transformer and the groove marked "<"
was created by the squashed/trapped cable or exposed wire core probably
vibrating.
From "<" to T only about 10mm so just 5 mm or so free gap to run these 2
speaker wires between mains torroid and high temp wire-wound dropper with no
added high temperature sleeving.
The grey flecking is what I'm assuming is electrolyte corrosion effect
rather than burnt PVC product.
If this fan lytic over the fan supply dropper leaked to short in use then
dropper would generate more heat as well so compounding as well as shorting
out the fan to the main amp heatsink. The owner had used the speaker switch
in the past, during sound checks. What a tangled web we weave.

 

[N Cook]

Before hard-wiring, the 2 lines from amp to speaker outlet , I've just
realised there are 12 chances of a break in that route, to and return.
3 pairs of IDC and pin connections in each line.

 

[N Cook]

The thermal protection circuit is activating before the 60 degree centigrade
fan switch is cutting in, under high load.
The fan switch temperature , testing in isolation , is about right.
I'd rather change the switch to a 40 degree one rather than tracing the
drift in the thermal protection circuit.
Any advice? or even if there is a recognised cure in the thermal matching
circuit ,eg replacing/matching Vbe of the sense transistors.

 

[N Cook]

I've never had an LED causing failure of an amp.
Intermittently o/c losing the fan supply ok signal that goes through this
LED to the pa causing it to shut down . Also not passing current to the
power-up hold-off circuit so pa failing to come on, thinking the fan supply
was absent. Like the fan lytic, both perched right on top of two large
droppers on the ps board.