Fuzzy signal to speaker on Peavey Nashville 400

[mortald]

Hello,

Wondering if anyone here has experience with '80's era Peavey amps? Here's my issue.

1) Particularly on low notes, I got a fuzzy, flappy sound.

2) I replaced the speaker basket with a new one.

3) Now it's just fuzzy (no more flap).

4) I tested the new basket out of the cab, in case it was a mounting issue. Still fuzzy.

5) The pre-amp-out signal, though a little noisy with RFI hum, does not fuzz.

6) Using the power-amp-in from the line-out of another head known to be good, also fuzzes.

7) I opened up the amp and didn't notice any leaky caps or burn marks.

8) The power cable was missing a ground lug, so I replaced the power cable.

9) The unit still turns on, but the fuzz remains.

10) Fuses were replaced with the correct values just in case.

11) If the volume is on, the 'mid' pot every now and then when turned releases an explosive "pop." It happened twice, but the cone seems to be ok.

12) The pots were cleaned. Scratchy sound is now repaired, but intermittent pop can still occur with "mid" pot.

I do not have the right equipment to test the filter caps or power supply. I only have a multi-meter. As a starting point, should I just drain the caps and replace them before sending it to a shop? I bought the amp for $260, plus $100 for the basket, and was quoted around $100-$220 for the repair. I can't afford to have $580 invested in a $260-$350 amp, so I'm trying to do it myself (if possible).

Also, I'm thinking I should just replace the "mid" pot since de-oxit isn't completely working.

PLEASE HELP!!!

[pdf64]

It's worth trying it with a different speaker, just to totally rule that out.

[Bob M.]

NV400 amp repair...

Hi mortald,

pdf64 gives you good advice: Use another known-good speaker (4 ohm) and another known-good amp with the NV 400 speaker to see if the fuzzy sound appears to be associated with the amp or the speaker.

Peavey amps and Nashville 400 amps in particular have problems with the molex connectors used all thru the amp. These must be re-tensioned and cleaned well. I cannot guarantee this is the source of your trouble but this and other maintenance issues like cleaning pots, tightening grounds, re-seating ICs, and visual inspecting the components and also the solders (on the other side of the circuitboard) is the usual regimen. Many techs who frequently work on these amps recommend that the speaker output wire be hardwired to the circuitboard, as opposed to connecting to the speaker with the stock molex connector. You have to very carefully clean the mid and shift EQ pots (that might even warrant removal from the circuitboard). That big popping noise that the mids make when dirty can really hurt your hearing as well as the speaker so be careful. If these pots resist cleaning, Peavey is very good with replacement parts. They are priced reasonably and ship very quickly: Highly recommended. They also provide a reasonably priced repair service, if your care to ship just the chassis to Meridian, MS. If you're determined to do it yourself, get a NV400 schematic and parts layout, Peavey part number 81501040. They provide/sell these inexpensively.

The vast majority of issues occur in the power supply/power amp with solid state equipment. As your tests have seemed to isolate this to the power amp, you probably have a bad transistor or IC in the power amp somewhere. But first you should measure the critical power supply voltages: +/- 52 volts on the large (4700uf) filter caps, and the +/- 15 volt supply across the nearby 22uf caps. Depending where you are in the country, I can recommend some techs who are very familiar with this amp and it's failure mechanisms.

Good luck,

Bob M.

[Tom Phillips]

...should I just drain the caps and replace them before sending it to a shop? ...

In addition to the above good advice it is MHO is that if you don't have a specific indication that a certain part is bad it's not a good idea to just start replacing parts. Especially if you don't have the experience and confidence that you can keep going until you find all the problems. If you end up sending it to a shop you end up paying for basic charges anyway and it's really difficult to prevent them from doing things over again. You already paid $100 for a new basket that it appears you did not need. Now you have a spare and some additional experience.

... I'm thinking I should just replace the "mid" pot since de-oxit isn't completely working.

That's a good idea if you want the learning experience. But, if you end up sending the amp to Peavey, it may be overall less expensive to let them do it.

Regards,
Tom

[Enzo]

We have been discussing this one on the PV forum too.

His foam rubber vent plug in the center of his magnet had disintigrated and gotten inside, where it turned to goo in the voice coil gap.

He tried a new basket, but had not managed to clean ALL the old goo from the gap. SO the new basket sounded funny too. A thorough cleaning solved the problem. No more black goo in the gap.

[Tom Phillips]

Interesting. Thanks for reporting the status Enzo.
It's always nice to hear what the final resolution was.

[mortald]

update on amp issues

Thanks everyone for the input.

Here's a link to the other forum. Sorry but I sort of forgot about this posting after getting an initial response from the PV site. So I apologize for the delay.

• View topic - Fuzzy signal to speaker on Peavey Nashville 400

What's really odd about the mid pot, is that deoxit, seems to work for a little while, then a few days later it's scratchy again. I'm going to replace the pot myself, and see if that resolves all remaining problems, now that the speaker fuzz has been resolved.

I'm doing this myself more for the savings than the experience. Got a quote here in Los Angeles, that was a minimum of $100 just to look at the thing. So far, it's only cost me $5 for a new power cable with a ground lug, along with some q-tips, masking tape and rubbing alcohol I had lying around to clean the goo.

I think the new speaker basket was defective, so I returned it. Never got it to sound clean, but the old speaker is now clear and is sounding pretty nice.

[Enzo]

OK, what I said over there:

The pot may have some loose debris inside that moves around but gets back in the way.

The little bifurcation at the tip of the wiper may have some fibers stuck in it.

And if it just won't clean up, then replace it.