Trace Elliot Super Tramp 80w issues with preamp section

[frjaraur]

Hi everyone,
I am new here, thanks for admitting me. I reach out this forum while I was searching for a solution to my solid state amp problem. I own an old Trace Elliot SuperTramp 80W, the one with just one speaker and no valves in the preamp section. I was very happy with its clean and distortion sounds, very good even adding distortion pedals in front, but suddenly it started to sound very low. I think it had some problem before because before this I noticed it was very noisy even without anything plugged. It had a continuous hiss (more than usual or at least that I remember). So I decided to open it and verify if there was any dust or ground problem (it is an amp from 1996) but none seemed obvious. I closed it and started to play normal, but then suddenly it started to sound very very low. I tested bypassing the preamp plugging directly my guitar to the return plug and it works fine, hence it seems to be the preamp section. In fact the problem affects both channels (clean and dist/boost). I am not good at electronic, I just play guitar ;P, but a very good friend of mine can help me if you give me some tips. I have the electronics scheme and maybe the problem is at the beginning of the sound chain or right after before it is given to the poweramp section. Can you please help me finding the source of the problem or at least give me some tips on how can I find it, what can I test or verify?. I haven't seen any damaged component or at least I wasn't able to recognise any problem visually.

Many Thanks in Advance,
Javier R.

[g1]

First, put a patch cord between send and return, and try your guitar into the regular input again.

[frjaraur]

Hi,
Many thanks for your quick response!!!. I've already did that test and I had the same result, volume very very low. It doesn't seem related to the fx-loop plugs because it should be bypassed.

[g1]

As the sound came back and then went away again, it is likely an intermittent connection or bad solder joint.
Some chopsticking around the preamp area might help to isolate the problem area.

attached is a schematic that will hopefully be the correct version for your unit.
You cannot view this attachment.

[frjaraur]

Hi g1,
I am probably confusing you. The sound does not come and goes, it is very very low, specially compared with the volume I get if I plug directly my guitar in the fx-loop return.

Thanks for the schema, that's the one I am using to try to understand the circuits phases.

Many Thanks for your comments.

[g1]

Does your friend have a multi-meter and know how to safely work inside of amps with power on?
If so, I would start by verifying that the preamp is getting it's proper DC voltages from the power supply.
This can be done by measuring the DC volts at both sides of the following resistors:
R20,R45,R29,R72,R10,R5

[frjaraur]

Thank you very much, I will verify these resistors. Hopefully I can do it during the weekend and let you know the results

Many thanks for your help,
Javier R.

[frjaraur]

Hi,
I managed to measure voltage on each resistor ends. Here are the results (left to right and up to bottom following the schema):
- R5 - 28,84V and 29,3V
- R10 - 29,3V and 30,2V
- R72 - 30V and 24,8V
- R27 - 27,7V and 16V
- R29 - 30V and 28,4V
- R45 - 28V and 29V
- R20 - 29,2V and 34,6V

As far as I understand, all of them seem right because they are close to 30V and R20 is close also to 35V in the right side (+35V From TRAMP OUTPUT PCB).
I really though it will be easier :|

I attach the values in the schema and links to a couple of videos showing the problem as it is strange how the reverb sounds in this situation, although it maybe normal ...

Channel 2
Channel 1

Many thanks for your help

Best Regards,
Javier R.

[mandu]

Did you try to connect the preamp output to another amp?
Or from another audio source to the power amp input?

Regards.

[frjaraur]

Hi,
I already tested the poweramp inpput and it works fine. I think the issue is located in the preamp section, although I haven't tested the preamp output on to another amp. I don't have another amp with fx-loop, can I test it pluging directly into the input of another amp?.

[Tassieviking]

I would not recommend plugging the effect send into the input of another amp, however if you measure the voltage from the guitar itself and then turn the volume of the amp down until the send signal is the same or lower level as from the bare guitar it might be ok.
The output of a guitar is very low so you do not want any signal you put in to be much higher then that or you risk damaging the pre-amp of the other amp.

Make sure you turn the level of both channels right down if you are going to try this.

[frjaraur]

Hi all,
sorry for the delay answering. I did test sending the signal from the fx-loop to another source. I used my Blackstar ID Core 40H, which is a head, but I used my headphones when I connected the send output from Trace Elliot amp connected to the only one input in the Blackstar. Same results, very very low sound. As we previously commented and expected, the problem is in the preamp section. I don't know if is just the output from the preamp (which will probably affect the fx-loop send output) or just some component in the section. Can you please help me identifying the source of problem?.

Many Thanks in Advance,
Javier R.