Nashville 400 Mod Fail

[Ed Hubbell]

Well, I had the parts to do the Peavy tone mod and the reverb mod on my Nashville 400. Took it all apart, lots of soldering, took maybe 3 hours. I'm not used to de-soldering parts from a one sided board, but things overall seemed to go really well. No leftover parts, didn't de-solder the wrong locations. Cleaned the pots with deoxit F5.

There was one strange thing I noticed - There's a cap on the drawing that sure looked like a resistor to me. I had already snipped all the parts to be removed by the time I noticed this, so I just jammed a cap in there as per the instructions. This may have been a mistake. Anyone have any idea whether C13 (in the board B dwg, near the high pot) is really supposed to be a cap? What I cut out looked like a resistor.

Plug the amp in, and can't get it to make much of a sound. Finally turn the volume up on both pre and post, and I can play through it, but it's really quiet. I think my phone is louder. So obviously I did something wrong. Maybe more than one thing.

Anyway, I've now got parts on order to replace the filter caps, because I'm going to end up opening it back up and diagnosing things, might as well replace those, as they looked pretty old (or at least the glue on them did).

I also removed the molex for the inputs and soldered those in so as to reduce failures at the connector. Seemed wrong to have an extra connector there. Obviously I was overly ambitious.

If anyone has any suggestions or sees something way wrong, let me know. I've got a friend who builds amps, so he may give me a hand diagnosing what's up with it. For now, I think I'll keep it powered down. And if I need an amp, I'll borrow one of his.

[Chance Duhon]

I would definitely get rid of the IC power caps. Also change the smaller value caps to polyester or mica. If you use ceramic it will be harsh on the highs and high mids. It’s indeed a cap on C13.

[Gordy Rex]

Morning. Ed. Check your email…

[Ed Hubbell]

Thanks, Chance, for the confirmation that C13 was a cap. My amp building friend was ribbing me for replacing a resistor with a cap.

This forum is a valuable resource - I found this post: viewtopic.php?t=369509

The important bit:

Having worked on around 500 plus Peavey steel amps I have seen the number one issue to be a high resistance on the contacts on the power amp in jack. A quick fix, plug a short 1/4” audio cable from the pre out to the power amp input.

It was working before, so I didn't think the jacks would be an issue. But I plugged a cable in from front to back, now the amp is at full volume. Sounds pretty good to me, but I'm no tone expert.

I tried using deoxit on the switched jacks, but cleaning them didn't improve things. I'm thinking that maybe I squashed a switch jack under the board/transformer/heat sink when I was working with it, and maybe bent the switch contact or something.

Next step is to take the amp back apart. I'm going to maybe swap in some CLIFF CL1298A switched jacks - These are supposed to be self cleaning. And I'll replace some of the larger capacitors while I'm in there, just to get things current. Maybe pull out the molex to the rear connectors as well - No need not to have them be directly soldered. Seems like a Sunday project.

[Ken Fox]

There are small value caps that look like resistors in the amp.
Check the ones you took out with a meter. You’ll find they are likely not resistors