Peavey Classic 30 Reverb Howl

[Mark Black]

I come begging again...

Most of the time these amps present me with a pretty straightforward and easily cured set of problems, but this one is really challenging me.

So what we have is a Peavey Classic 30, black "tweed" covered, serial #10831049. The reverb will take off and start howling at any setting over about 6 on the reverb control. The offending resonant frequency is close to 100Hz. The tank is a long Accutronics (too long?) marked 4EB2C1B, making it a type-4, 600 ohm input, 2250 ohm output, medium decay, output-grounded, no-lock, "horizontal open side down" mount. Drive & recovery are both via op-amp circuitry in this amp as many of you probably know.

First thing: can anybody tell me if this is the correct tank for this amp? It sure is a tight fit in that cab...

Assuming "yes" to that question has anyone encountered and successfully cured this problem on one of these amps, and if so how?

Pulling the tank out and holding it away from the amp certainly cures it as one might expect (hardly a long-term solution). The drive & recovery circuitry seems to be functioning correctly as per the schematic, and I have done the usual solder retouch at all the common spots.

Things I have tried:

1. Added cardboard under tank inside of bag (there was none present as found).
2. Tried inserting a piece of foam under and/or over the tank.
3. Mounted the tank loosely, tightly, screws through tank grommets (as found), and screws through bag only.
4. Experimented with various caps in series with the tank output in an effort to reduce low frequency response (this really didn't work very well).
5. After determining which spring in the tank seemed to be the offender (touching it damped the oscillation) I even removed a bit of its length in an effort to change the resonant frequency.

Help Mr. Wizard(s)!!

Thanks guys -
Mark

[Thorny]

If i had one in the shop, I would tell you which model it is - but I don't. You can always call peavey to find out and even get suggestions. Those guys at peavey really have EXCELLENT customer service from my experience. You might have the wrong tank, also just for giggles - swap the input and output RCA jacks on the tank and see what happens (I have had occasionally odd things happen when they are reversed). If it does not work switch them back.

I don't recall if that one has tube driven reverb - but if so, check the tubes to see if they are correct and are not microphonic.

I have also had overactive tanks before - ones that the springs are too loose. I changed out the tank in those circumstances.

Good luck and report back.

[Mark Black]

Hi Thorny and thanks for the reply -

Yes - Peavey is one of the best when it comes to customer support I agree. I was just hoping to circumvent the holiday weekend wait.

This is indeed a solid-state drive & recovery circuit so no easy tube fix.

Did the swap on the input/output jacks too (forgot to list in my previous post) - no joy...

Interesting your observation about overactive tanks and having replaced with good results. At this point I actually hope this IS the wrong tank, but maybe it actually is simply an aberration from production norms and a new (same part number) tank would be the fix. I've got to think that with the springs, transducers, sheet metal, and other bits that make up a reverb tank there are all kinds of possibilities for altered frequency response.

[Enzo]

4EB is right tank. None of the other stuff matters that much. if you got the jack grounding wrong, it just wouldn't work right at all.

Some pans are just sensitive. Moving where it sits in the bottom there can help. I know there is not a lot of room. it does need to float so no screwing down tight. try flipping the bag over so it is upside down.

Sometimes you just need a new pan. get it from AES www.tubesand more.com) PV is usually reasonable on parts, but they charge too much for reverbs.

The problem is acoustic energy getting onto the long springs. WE already isolated them from direct sound, though a layer of bubble wrap might help. But the innards are suspended by four short springs. Stuff a little crumb of loose foam up into each spring to damp it. If it doesn't help, poke the foam back out.

[Mark Black]

Hi Enzo and thanks for the reply on this Christmas Eve day.

That foam in the suspension springs is another thing I tried but forgot to mention in my first post. Also the placement which seemed to alter but not cure the problem.

I hadn't thought about bubble wrap - we've got a bunch of the smaller size at my day work - maybe I'll try that. Also hadn't thought of trying the tank upside-down. Guess I've been thinking a little bit INside the box...

Thanks also for the verification on the tank number and for the pointer on replacement cost.

Another thing that comes to mind (and might be a handy thing to have around) is this stuff: http://www.partsexpress.com/pe/showd...number=268-015
Which might work if wrapped around the tank or placed under it in the cab.

If I find something that works I will certainly post it, as this seems to be a common thread on the web.

Thanks again - Mark