Peavey Bass Amp Distorted

[Gnash]

I have an old Peavey TKO 80 bass amp. When you play through it, it sounds all garbled even at low volumes. I tried swapping the speaker and this made no difference. The amp has a pre-amp output and if I run this into my mixer, the resulting sound is fine which leads me to believe that the problem is with the amp/speaker portion rather than the pre-amp part of the equipment.

I seem to remember that this same thing happened to the amp several years back but then it just got better. Now it's been like this for a while. It's a great little amp and I'd like to get it working again. Any suggestions?????

[randomair]

I would direct your sites towards the caps or bad connections in the power amp. I have had similar problems with these amps before , I seem to recall bad connections in the power amp section but that is just a guess from experience. Im sure Enzo or any number of the helpful knowledgeable folks on this forum will get this pegged for you. Hope this helps. Good luck!

[Enzo]

Get the schematics from Peavey. Then set you meter tp DC volts and meausre the +/- supplies to the power amp. They should be about the same. Now flip the meter to AC volts and read the same +/- supplies. I would expect very little AC,maybe a volt, and each should be about the same as the other. If one rail has a lot more AC than the other, then you likely have a bad filter cap.

[amptech]

I had one of these in the our workshop last week and it was in a bad way such as eq sliders all bent side ways and no sound and chassis fixings missing !
After replacement of pre and post gain pot's and reflow solder work to the board
I then feed a singal in and tested line o/p of the amp to our test amp with good singal there.
Next thing was I fed a patch lead from line o/p to power amp in and all was ok there,but removing this patch lead there was no singal to be heard on the o/p.
After singal scoping each op-amp stage and checking that supply rails correct at +-15 and +-42 dc I then replaced the power amp i/p socket & all returned to normal.
Try feeding a singal direct to power amp in and see if you hear it at the speaker end.

[Enzo]

He has output to the speakers, it is distorted though. Your amp sounds more like a bad cutout contact on the power amp in jack. Patch preamp out to power amp in with a cord and see if the sound returns.

[amptech]

Do you have a scope/sine generator to check singal at the out put?

carry out some cold checks with in the o/p stage such as resistor values that have gone high or open, also this amp is fixed bias no pot adjustment needed.

Don't for get to check the base,collector,emitter, voltages on the out put to-3 transistors and because there mounted on that thin brackit don't keep the unit running to long as the o/p will heat up quick.

Because it's a pane to remove the main board carry out a volt check on the driver transistors, there mounted on the small heatsinks on top of the board.