How to silence reverb tank feedback?

[Chuck H]

Ok, I built this outboard dedicated reverb amp that's good for about fifteen watts. It's a combo with the amp, speaker and tank all in the same cabinet. The input is adjustable for host amps from five to 100 watts. Using my 20 watt amp I get very saturated tones from the reverb amp at about half volume, so I'm thinking that close to dimed would be right for a 100 watter. The trouble is that with the volume knob above 8.5 the tank and speaker start having a conversation. I've tried extra padding with some luck and now I'm thinking about trying a pad of that memory foam stuff used for mattress pads or possibly even spring mounting the tank. I'm hoping for insight from anyone who has dealt with this.

Thanks

Chuck

[Enzo]

Feedback is accoustic. Keep the sound energy out of the reverb pan.

DO NOT screw the pan down tight. That just guarantees the cab vibrations shaking the pan. Those spongy grommets are for damping vibration. The scrws should be tight enough in the wood so they don;t fall out. The pan itself should be free to wiggle.

Put the pan in a reverb bag.

Cut a piece of carboard the size of the pan's outer mounting plange. Tape it over the open side of the pan with a couople strips of masking tape. NOW put it in the bag.

Yes. you could even wrap a thin layer of foam rubber or small hole bubble wrap around the pan before going in the bag too.

Look at the top surface of the pan - big flat metal panel. Get some of that peel and stick rubber weatherstripping. it is like 3/4" wide maybe and 3/8" thick perhaps. Roll off a stripe of that the length of the pan and stick it right down the centerline. This will damp off any resonances in that flat panel. Car makers do this inside large body panels on cars to reduce "sheet metal" noises.

Rotate the pan 180 degrees. FLip the pan upside down. vertical on the sidewall. No, I don;t care that the pan was made to face some particular direction. ANy help?

Try a different pan.

[Kazooman]

In the good old days (a.k.a. "before reverb bags") the tanks were mounted with springs. Perhaps some amps are still made this way. The four corners of the tank are attached to mounting posts with fairly light gauge springs. This helps isolate the tank, but if you hit the amp hard enough to get the reverb's inner springs bouncing around you get a lot of noise. I agree with Enzo that adding some stick-on foam basically all over the place can help dampen out sympathetic vibrations. Actually, there can be some thin foam inside the tank to keep the springs from hitting the walls. Just don't let it contact the springs during normal use.

A while back I built a clone of my '60's Fender Reverb. Here is a picture that shows how the tank is mounted. The mounting posts are just some long bolts with holes drilled through them to accept the springs. The tank I purchased called for mounting with the open face down. The original has the open face facing the front of the cabinet with a lever device to clamp it in place for transport, so I had to modify my layout of the components.



Try some foam, try some cardboard, try a bag, try some springs, and try different mounting orientations. You should be able to isolate the tank pretty well.

[dai h.]

is this feedback through space or vibration? (For vibration,) I remembered there was such a thing as a "reverb tank bag" (apparently correctly) :

Reverb tank bag? - Telecaster Guitar Forum

page with pictures and application of extra cushioning:

GA15RVT Update Photos

dunno if that will help but that is what I remembered.

edit: oops, already beat to a better answer (again)

[Enzo]

Vibration can come through the cab walls, through the air, any way you can think of. You have to kill each path.

Yes, the pan in the current re-issue Fender Tube Reverb is mounted hanging from four large corner springs like that.

[Chuck H]

All good answers. And I tried everything but spring mounting. I even wrapped the whole pan in three layers of bubble plastic with continued issued.

I did isolate the problem to the cabinet resonance, as opposed to the speaker. Logically it has to be both speaker AND cabinet, but it's predominantly the cabinet. Even sitting on a layer of carpet pad the pan and cabinet would slowly start to hum, getting louder and louder. Interestingly it's at a low enough frequency that it reverberates very little. Placing the pan on a different plane on one of the back panels does resonate at a frequency that reverberates though. It's a clear finish pine cab and is very acoustic, appearantly. Anyway...

I managed to solve this one short of spring mounting by cutting two narrow strips from the carpet pad and placing the pan on those instead of the full mat of carpet pad. Less surface area = less vibration transfer... I suppose. So... It's pan in bag (with cardboard as usual) sitting atop a narrow strip of carpet pad at either short end.

Thanks

Chuck

P.S. Hope my experience helps someone else. Cause that's over two hours of reverb pan mounting that I'm never getting back.

[dai h.]

cool. Sounds like you got it worked out Chuck. FWIW (though I guess you don't need anything different now) there is this material Sorbothane (invented in UK IIRC, and featured long ago in That's Incredible? that comes in sheets and "feet" (for enclosures or whatever) and this stuff is really effective versus shock. Bought a couple of small squares long ago and it came in different thicknesses and levels of (pliability? softness/hardness). 'Course if you can come up with a cheaper low tech solution (as you seem to have done) that is fine of course too. I think Neil Young(?) suspends his Fender Reverb Units from the ceiling w/a rope to counter problematic vibration effects.

[Chuck H]

I think Neil Young(?) suspends his Fender Reverb Units from the ceiling w/a rope to counter problematic vibration effects.

That wouldn't surprise me a bit. I read somewhere that Neil has motorized pots on his 5E3 to control them with a foot pedal! Hard to believe though. I considered trying it but figured the noise on the preamp from the pot motors would be problematic. I can't believe that even shielded motors wouldn't make a lot of noise in that area of the amp.

So, yup. All done sounding great and perfoming well. I did make some minor circuit refinements too. I'm calling this one a win. Can't wait to deliver it to my customer. He's gonna need a Kleenex to wipe away a joyful tear

Chuck

[jimboyogi]

I think Neil Young(?) suspends his Fender Reverb Units from the ceiling w/a rope to counter problematic vibration effects.

I've read that Dick Dale does this as well.

[Kazooman]

Good that you have minimized the problem. A "bag on springs" experiment would be interesting if there was enough room in the cabinet to pull it off.

I guess the ultimate solution is to use separate amp and reverb units as opposed to an amp with a built in tank.

[dai h.]

I've read that Dick Dale does this as well.

ahh, could be my error!

okay, I remember reading this in GP:

The first thing the signal always sees is the input of a Fender reverb unit. The reverb pan is not in the unit; its usually underneath the stage. This one happens to be more susceptible to vibration than other pans, but it has the tone he likes. he can tell when I try to substitute another reverb pan. Its really important to have the old style, funny shaped 6V6. Of course, that first 12AX7 is extremely important, and the reverb is rarely off.

Neil Young's Amps

so I gather both NY and DD take measures to counter vibration effects.

[Chuck H]

I've heard that Jerry Garcia was a bit nutty too about taking measures to make funky old gear work for his live show.

I have heard a few old tanks that were SUPER sensitive. Bordering on unusable. In these cases the springs were sympathetic to higher frequencies and would feed back almost like microphones. I never tried to save one (because I didn't think to hang it I guess) but IIRC, other than the squealing, they did sound better than the average reverb pans.

Chuck