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Vintage threads from the first ten years

Reverb feedback?

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9/17/2000 10:17 PM
Brett	Reverb feedback? I have a Sano combo tube amp with a spring reverb. I get a nasty feedback from the reverb. I found that if its (open) back is against a wall I will not get the feedback. What would cause this? How can I fix it? I am woriied about running it with the back covered up because it is poorly ventilated and gets real warm with the back open. Thanks

9/19/2000 8:16 PM
Stefaan Van Slycken	Reverb springs have always been trouble... they pick up a lot of hum, and they do weird things like that feedback. I don't know whether this is caused by a poor quality spring (what brand is it?) or just bad shielding. You should probably try shielding it, or look if all the springs that hold it in place are intact...

9/19/2000 9:16 PM

Brett,

There are two methods I've seen used to minimize this problem:

1) 'Fender' method - open side of reverb tank is covered with cardboard or thin wood, and then is placed inside a Tolex bag and screwed to the inside of the amp cab. Works pretty well.

2) 'Weatherstripping' method (maybe I'm the only one who's used it) - put four soft rubber grommets in reverb tank mounting holes, then line remaining bottom flange area with thick, dense adhesive weatherstripping from Home Depot or similar place. Then use wood screws w/washers thru the grommets into the inside of the cabinet (don't tighten too tight). This method worked pretty well, too - it basically uses the amp cabinet to do the same job the cardboard/wood does on the other method, and has a bit more vibration isolation.

Ray Ivers
R.A.G.E. Electronics

9/19/2000 10:13 PM

i believe that there may be some magnetic pull on the pan or springs from the speaker magnet. it can happen with the stock speaker, but if you replaced it with a speaker with a stronger magnet that makes it even more likly the cause. i say this because i use EV12L speakers in combos, and i've found that problem happening a couple times after putting the EV in an amp that never did that before. what i did to solve it was try different mounting positions. i unscrewed the pan and let it sit outside of the amp to see if that helped. it did, so i tried putting it back in the amp and re-positioning it till i found a place where it didn't do it. you can try the sides or a different position on the bottom. sometimes only a few inches will be enough. try it, you got nothing to lose, and it cured the prob for me a couple times. tryin to mount it with foam or weatherstripping or something like that may be worth a try to, but it never helped me, and probably won't help if it IS the speaker magnet.

-dale

9/20/2000 2:50 AM

Sypathetic vibration caused by speaker vibrations can cause this, especially if the tank isn't isolated from direct contact with the cabinet.

1. A bad/microphonic driver or return tube can cause this. Make sure you're using quality tubes and not chinese junk. Also make sure you use what your tube chart calls for. Some amps don't handle using 12AX7's in place of 12AT7's (the higher gain 12AX7 overdrives some reverb circuits making them noisey).

2. If the tank isn't already in a fender style vinyl bag, get one from someplace like mojo.

3. Check your cables, if they're not the high quality shielded variety, get yourself a good set.

These fixes should quiet your reverb problems down.

9/20/2000 10:20 PM
Brett	Thanks guys. Its a well made amp with good tubes. I put in a 12at7, it had a 12ax7 when I got it, and that cured the feedback. The reverb intensity is noticably lower but I never turned it past half way so its not a problem.

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