Fix a preamp?

[OOD]

I've got a Peavey TNT 130 and I'm pretty sure the preamp is messed up in it. I can play through the pre amp but it's all distorted and very quiet.

Is it possible to fix the preamp?

 

[Passinwind]

For a qualified tech, quite likely. I assume you've verified that the power amp section is working correctly, eh?

 

[B-string]

It's possible to fix the preamp, the power amp and even the speaker, any of which could be the problem with what you described.

 

[fdeck]

Here are my thoughts on the matter. First of all, this work requires at least the ability to work on line powered gear safely, so the default answer is to take it to a tech. With that said, I'd check out the system as follows:

1. Verify that your cables are good! Don't do what I did, and disassemble an amp in order to find out that I had a bad cable.

2. Verify that the power amp and speaker are good. Power amp repair can be daunting for a beginner because the global feedback loop makes it counter intuitive.

3. The "laying on of hands" is simply to go in and re-seat every internal connector that you can find. This is where you have to be familiar with working on line powered gear safely. but you basically unplug and re-plug every connector.

4. If you are certain the problem is in the preamp, then I'd suggest a rule that I follow: Almost all electronic problems are actually mechanical in nature. That's because strictly electronic components are typically more reliable than things like pots, jacks, switches, connectors, etc. If I reach this point on an amp, then I'm looking very closely at the printed circuit board (nowadays I use an inspection microscope due to my age) for cracked solder joints, such as around the input jack. I might also prophylactically spray pot cleaner into the pots.

5. If you get to this point without success, then it's schematic time, tracing the signal through the circuit and figuring out where it doesn't make sense.

 

[beans-on-toast]

Anything can be fixed. Doing it in a cost effective way has to be considered. It could be a quick fix, it could take more bench time than you are willing to pay for.

It could be oxidation on the jacks in the signal pathway. Here is a simple test. Try inserting an instrument cable from the pre-out to the power amp in jacks. See what happens.

 

[OOD]

For a qualified tech, quite likely. I assume you've verified that the power amp section is working correctly, eh?

Yeah it seems to work fine when I plug into just the power amp. Not as loud that way of course, but I used some pedals to make up the lost gain.

Here are my thoughts on the matter. First of all, this work requires at least the ability to work on line powered gear safely, so the default answer is to take it to a tech.

Thanks for the check list. I think I'll take it to a tech for most of these.

Anything can be fixed. Doing it in a cost effective way has to be considered. It could be a quick fix, it could take more bench time than you are willing to pay for.

It could be oxidation on the jacks in the signal pathway. Here is a simple test. Try inserting an instrument cable from the pre-out to the power amp in jacks. See what happens.

I'll give it a try.