Trace Elliot Super Tramp Twin- Low Volume

[ChewyNasalPrize]

Hey guys- I got this TE Twin- all solid state that has a volume issue.

Sound comes out but it is very weak- not distorted or crackly or anything... just very "far away" and quiet sounding.

I also have a TE 1x12 combo that works great. I ran a patch from the effects loop send of the good amp to the return of the bad amp and the volume becomes normal (LOUD) on the bad amp but it is a dry signal that responds to the good amp's eq (but no reverb comes through- either the good or bad amp's). I can control the volume of both amps independently of each other.

I tried reversing the patch- send from the bad amp to the return of the good amp. While sound comes through- it is weak just like in the bad amp.

Any ideas on where to start looking for the problem?

Thanks.

Chews.

[ChewyNasalPrize]

Update:

I pulled the chassis and a visual inspection doesn't turn up anything suspicious- nothing burnt, broke, loose, etc. Only one fuse in the back of the amp and it is fine.

[g1]

schematic attached
Is the problem the same for both channels?  Do all the controls seem to be doing something?

[ChewyNasalPrize]

Yes- all controls appear to be functioning properly- just everything is very low volume.

[g1]

  Then if both channels are the same, it must be something common to both channels.
That leaves the power supply to the preamp, or the circuitry between C32 and the preamp out jack.
  What are your DC voltages on either side of R20 ?

[ChewyNasalPrize]

Not sure I'm doing it right but R20 reads 0.3 mV on both sides.

It does look a bit discolored to but maybe that's normal.

Edited to say: the "discoloration" was just a shadow.

[ChewyNasalPrize]

Should the amp be plugged in and turned on? I didn't have it plugged in when I tested the voltages.

[g1]

  Yes it needs to be on. 
But before you even do that, measure it's resistance, meter set to ohms, one probe to each side of resistor.  It should measure 220ohms or less.  If it measures much more resistance than 220ohms it is bad.

[ChewyNasalPrize]

Ok, I measured the resistance and both sides are registering right at 211 ohms.

I measured DC voltage again with the amp on and it reads 30 volts on one end and about 33 on the other.

[g1]

  The approx. 30V on both sides of that resistor is good. 
I outlined earlier how both channels are separate until C32 where they join.  As the problem occurs in both channels, it is then likely the fault is after C32.  You said the fault also showed up at the FX send jack, so it should be between C32 and FX send.  If it's a bad connection, it should respond to physical input like tapping the circuit board with an insulated item such as a plastic pen body or chopstick.
  If it's an actual bad component, the most likely suspects in that area are TR12 and C33.

[ChewyNasalPrize]

I hooked up the fx out from the twin to the fx in of another amp and still there is signal but very weak. I poked around on the board and put pressure on the fx out jack but nothing. No popping, crackling or volume fluctuations.

Can I test C33 and TR12 without removing them?

[J M Fahey]

Ok, now you need to signal trace elliot  it   :lmao:

meaning you inject 100mV 1KHz at the "guitar input" and follow it along the preamp, until you find where it fades.

No need for a super duper *audio* or "lab" multimeter, because this is not a precision measurement anyway, but having one which reaches down to 200mVAC scale is necessary (around 30/35 U$)  , the ubiquitous U$10 ones with just 2 AC scales, 200VAC and 700VAC don't cut it, for obvious reasons.

[ChewyNasalPrize]

 :lmao: That's funny!

So how exactly do I inject 100mV 1KHz at the "guitar input" ??

I have an iPod I usually run into amp for testing for sound. Will that work?

I also have a pretty good digital multimeter.

[J M Fahey]

Perfect.

Download all 5 tones for future use (100/250/440/1k/10k Hz) from:
http://www.mediacollege.com/audio/tone/download/

Typical MP3 players supply 100/200mV through the headphone out

With the proper 1/8"stereo to 1/4"mono cable you inject 100mV at the input (measure them with your multimeter, that's why a 200mVAC (or at worst 2VAC) scale is needed, you'll see nothing on a 200VAC scale)

Then measure VAC at some selected points in the circuit and look for inconsistencies.

For example we usually expect to find 10X to 20X higher level at a gain stage output, meaning if you feed it 100mV you expect a couple Volts out ... if not the stage is probably bad.

Or, say, you send 1 VAC to an effects loop, you expect same 1VAC at the other end.
If not, suspect a very dirty/corroded contact and so on.

Or a typical Fender/Marshall tone control has around 10X attenuation (that's why they are passive controls) so if you feed it, say, 1 VAC you expect some 100/200mV at the other end (depending on settings) ... finding 10mV is obviously wrong.

And so on.

The good troubleshooting is:
first measure basic DC voltages, then inject audio and search for abnormal AC ones.
When you find an error, then recheck all around that stage and only then think what might be bad and replace it.

The BAD troubleshooting is just to start replacing parts and hoping to hit the jackpot.

Just a free sample: with 100mV 440 or 1k Hz at the input, expect some 500mV at Tr1 drain, best measured after C5 , so as to get just audio and not the DC present on TR1 drain ... although a "good" multimeter should have no trouble with that.

The $10 multimeters will gladly tell you you have some 25 or 30 VAC there  , without even injecting anything  :loco ... with a straight face and not even blushing  :trouble

[ChewyNasalPrize]

Thanks J M! This will be handy for future reference!

I actually sold it a few days ago in "as-is" condition to someone who wanted the speakers mainly (Celestion Vintage 30's). Didn't make sense to me to keep fooling with it given what he offered.

I should have posted this at the time but I forgot.

Thanks to everyone for your help on this one. 

Chews.