Stand alone reverb - feedback

[theundeadelvis]

So I've spent some time playing my standalone reverb unit, and for the most part it sounds great. Problem is, it sends my amp in to horrible feedback at higher settings. If it's just the guitar, amp, and the reverb unit it doesn't always do it, but often will when everything is turned up close to 10. If I put a tube screamer between the reverb and amp, it's pretty much unusable, even at low volumes it's almost instant feedback. I checked my voltages and they all look good, and I've tried a number of tubes. I'm at a loss. 

[eleventeen]

Have you tried...isolating the reverb unit on a piece of foam rubber or maybe just throwing a cardboard box over it to see if the output of your speakers isn't somehow getting into it?

[from "The Amish Amplifier Repair Book, Hints and Tweaks", vol 01 ©1937]

[tubenit]

Have you thought about perhaps creating a passive effects loop between the earlier preamp stages and the phase invertor and then insert the outboard reverb unit there?  Not sure about your unit so I don't know if that's a possibility for you or not?

I am using my FX and reverb unit in a passive effects loop prior to the LTPI on my Tweed Overdrive and have no trouble with oscillation even with the OD really kicked in.

My guess is that you're getting oscillation using it prior to the preamp (if I am understanding you correctly)?

With resepct, Tubenit

[Willabe]

FWIW, I fixed a Bed Rock (IIRC) amp one time that was giving the music stores owner fits from feedback. The verb tank was mounted on the lower back panel of the combo amp, with no rubber "shock" absorber gromets. Put a set in from a new tank I had , fixed the problem, they loved me.  Every dog has his day.     

     Brad     

[theundeadelvis]

eleventeen - I have it sitting fairly far away from the amp, so I feel like it's probably not that, but I may move it farther away just to test.

tubenit - I actually built this for a friend, so unfortunately I can't. If it was for me, I would definitely be willing to try it.

Willabe - It's mounted using the shock absorbing grommets, but I may try to isolate it even more.

Thanks for all the suggestions guys!

[Willabe]

Ok, but are they screwed down too tight? Also are the grommets old, hard, no sponge left to them? If so they can't/won't do any good. Just enough tension to keep the tank in place, but not enough to kill the isolation physically. It can be a fine line between the two. Just a thought.

   Brad      

[tubeswell]

Could be the pan feeding back (in which case you could try sticking the pan in a bag or wrapping it in acoustic dampening material of some sort). When it happens, if you put your finger on the back of the pan - does it stop?

[theundeadelvis]

Willabe - they're new, and it's not too tight. The pan can definitely float a bit.

tubeswell - you've got me thinking. I may pull the tank to completely isolate it from chassis to see if this is the problem.

[Baguette]

when everything is turned up close to 10.

If I put a tube screamer between the reverb and amp, it's pretty much unusable, even at low volumes it's almost instant feedback.

A bit off topic maybe, but...
I usually hate the sound of a Reverb Unit cranked. It's "too much", and I'm pretty sure it was designed to be used "moderately". My reverb box (although mine is quite a bit different from the original design since I replaced the 2 12AT7 stages in series by 2 12AX7 stages in //) gives a huge reverb Dwell on 7, Mix and Tone on 3.

Also, it seems pretty unusual to put the reverb BEFORE the distortion. No wonder a cranked reverb unit feeding a Tube Screamer will produce "serious sonic chaos".

[theundeadelvis]

Baguette - I agree totally with you. I don't like that much reverb either. Since this is for someone else, i just like to make sure everything is functioning as it should, because if the knob goes to ten, they'll eventually try it on ten and I'll get the "I think it's broken" call. Good point about using the TS after the reverb though. It was just a matter or how my gear was setup, and that was the easiest way to plug it in at the time. I'll move it to the front and see what happens.

[mat]

One thing You could try is to turn the pan in other way, that fixed my stand alone reverb build sound problems.

cheers,

[PRR]

> using the TS after the reverb

HIGH gain between sensitive tank and loudspeaker, it's gonna squeal.

Keep the gain from tank recovery to speaker as-stock. Put your rock-crusher in front.

I hope that's all it is.

[theundeadelvis]

Putting the TS in front of the reverb definitely made a huge difference. Seems to be working great now. Not that it's a huge issue, but out of curiosity, why would it not work with my EL34 singled ended Beast Champ? If I run the reverb in front of it, it's nothing but screaming feedback?

[tubeswell]

I still say pan feedback. The finger damping test is simple and cheap (and accurate if that is the issue).

[Willabe]

> using the TS after the reverb

HIGH gain between sensitive tank and loudspeaker, it's gonna squeal.

Keep the gain from tank recovery to speaker as-stock. Put your rock-crusher in front.

I hope that's all it is.

Like PRR said, you flip floped the two, it fixed it. It seems the tank does'nt like it, besides why distort a "complex" reverberated signal? Even if it did'nt squeal it would probly sound odd. Are'nt most guys pedal boards set up with distotion or wah 1'st, then time based Fx like, phaser, flanger, chourse, 2'nd, and verb last? When verb is 1'st, any Fx after it is now trying to prosses all of the multi reflected signals that are bouncing around, ie. reverb. Not the easyest thing to do, even for modern Fx pedals.

        Brad


                 

[Willabe]

theundeadelvis,

I'm sorry. I took another look at your post, and I think I misunder stood you, my fault.     

Are you saying if you put just your verb unit in front of your EL34 champ, it squeals? No TS? Yeah, that should'nt happen.

Maybe tubeswell's right? Anyway, sorry for posting with my foot in my mouth.


        Brad