Other Amps

Anyone know how to quieten a reverb?

1

It's been a while since I had an amp with a spring reverb, so I'm still getting used the the reverb in my DRRI. I have managed to improve it a little (to my ears) - I have swapped out the two-spring tank for a 3-spring Accutronics of the same size I just happened to have and it sounds a lot better. I also swapped out the stock generic 12AT7 reverb driver for a NOS GE 12AY7 and it made a big difference - much smoother.

But at anything above about 2 on the reverb level there is a buzz/hum sound related to the reverb I can't get rid of. Even if I turn the channel volume to zero it's still there. It only goes away with reducing the reverb level or switching off the reverb with the footswitch. It's annoying because now that I have some cool reverb I'd like to use it.

I tried better RCA cables and they made no difference. Any ideas?

Thanks!

2

Have you tried a 5751 in the Reverb Return?

There might be something helpful in the Moyer Mods that I used on my CVR a dozen years ago to improve this same aspect. All sorts of noise reduction clues...I'm sure some relate to the Deluxe. I use a NOS 12AT7WA in the Driver slot...same low noise.

It's likely a grounding issue...there might be a better spot to place the internal chassis ground lead...

https://www.google.com/sear...

What happens when you don't use the footswitch?

3

"I have swapped out the two-spring tank for a 3-spring Accutronics of the same size I just happened to have and it sounds a lot better." Are you talking physical size or do the input/output impedences match?Did it make the noise with the original tank?Does sound like a grounding issue,if you are using the wrong tank,different tanks can have a different ground arrangement on the input or output connections.Could have a ground loop.

4

Be sure that the Reverb output jack on the tank is not on the side nearest the power transformer.

5

Agree with stokes. Return everything to original. Any hum? If not then it’s the tank or the tube. Even a “NOS” GE tube can hum. The “4AB3...” tanks used on most Fenders are grounded on both send and return. Check tank orientation like Winnie says. If it sounded fine before then it should be easy to find the culprit.

6

I'm pretty sure it did hum with the stock tank but that easy enough to check. Thanks! I'll letcha know how it goes.

7

It won't cure any hum problems, but if you find yourself never turning up past 2 or 3 on the reverb knob, I suggest dropping the 3M3 dry mixing resistor to 1M or so. It'll give you more useable range on the pot.

Also maybe look into some of the treble-taming caps from the Silverface amps. They'll darken the 'verb a bit and make it more useful for non-surf things.

8

What Winnie Thomas said! I couldn’t figure it out in my bandmaster reverb for years. Then I turned the tank around and voila!

9

Thoughts outside the box here, my 2 cents....Not sure if you are aware that the Gretsch Executive amp was made by Victoria with mostly Fender parts from a DRRI, including the reverb. Also I understand that the circuity is very similar. Anyway, about 3-4 years ago Paul Pigat posted a thread under Gretsch Amps, called Executive Mods noting an issue with his reverb and term. I have the same amp but never noticed a problem until I used it with the pedal switch. Hissing all over the place, Same as you described. There were several fixes in the response, but since I know nothing about electronics, I had an amp tech fix it for me.

Being more experienced than me, you may find something there that you have not thought of. I would include the like but no clue how to do it.

BTW There is another thread called Executive Hum.

Good luck with the issue.

10

Take it to a good tech! You're just making it worse. Use a regular 2-spring MOD tank. Accutronix went out of business years ago & a Korean company bought the name. parallel 12AT7's are used because they are high current, low impedance dual triodes. A high impedance , low current tube like a 12AY7 can't drive a spring properly, and also won't match the impedance of the reverb transformer which has a 26,000 ohm primary to match the 12AT7. Springs are like little 8 ohm speakers...they need high current tubes with a matching output transformer. Tubes like 12AX7, 12AY7, & 5751 provide high voltage gain, but very little current. Also, none of this will fix a hum.

11

I have now put a known to be good 12AT7 in the driver position - no difference. Two different 12AT7s in fact. I've tried with the original tank, in both directions - no difference. In fact I even tried with no tank connected - no difference! The hum/buzz increases as I turn the reverb knob up. Unplugged the footswitch - no difference. Pulled all the preamp tubes except the PI - no difference. Tried a few different tubes in the PI postition - no difference.

Putting the amp back to stock makes no difference. Maybe I'm just not used to how much noise a tube reverb makes? It's pretty loud! The stock tank is just as noisy but sounds a bit crap compared to the 3-spring tank. The 3-spring tank actually sounds good. Yes it is a Korean Accutronics but it would appear that it's not the cause of the hum.

12

I built a PR for a guy a while back. After a week he brought it back, said it hummed badly. Plugged it in at my house and it was silent. Turns out he lived in a mobile home, ungrounded outlets, fluorescent lights and next to a power pole. Worse case scenario for EMF.

Before opening up the amp have you tried playing it in different rooms of your house or a different house? Reverb circuits are big antennae that will pick up stray EMF and amplify it. Just ruling out one more variable.

13

Take it to a tech...youre just chasing your tail. FWIW, looking at the back, the fifth tube from the left is the Reverb return. If turning the Reverb knob does anything with that tube removed, you need to have a word with your drug dealer because the Reverb knob was no longer connected to anything. Also, the spring won't work in both directions, the Reverb knob SHOULD make hum if there's no tank plugged in or the cable is removed, and the 12AT7 has nothing to do with hum. If you have any JJ tubes in there, replace them and then take the amp to a good tech.

14

JimmyR, I have a tube amp (Fender 75 Lead) and the reverb is very quiet, no hum, no crackling, it's very quiet even if I turn up the reverb knob. I'm a tech and IMO, Billy Zoom's insistence that you take the amp to a good technician is sound advice. The trouble you are describing is not normal noise, or something that you can fix by swapping tubes and reverb pans around. There is probably something wrong with an internal component ie capacitors, resistors, that need to be identified by proper troubleshooting by a technician.

15

Billy's right, of course! That said, if it is in fact a buzz rather than a low-pitched hum, it's almost certainly a ground issue, probably where the ground attaches to the metal strip that runs along the front of the amp below the control knobs.

Bad tubes? Maybe... It's always good to try different tubes, but use the correct type! You can substitute a lower gain for the take-up side (5751, AU7, or AY7, and nothing else), but only an AT7/6021/ECC81 will function properly as a driver. It's probably not just a tube, though; that would cause a weak signal, hissing, roaring or tearing sounds, a truly deafeningly loud low hum, or intermittent pops. There's also a slim chance that one of the tube sockets is loose or dirty, but you can usually tell just by wiggling 'em.

Here's what else it could be: Bad cables or dirty connectors. There's usually a good chance that that's all it is, but you tried that already.

Bad footswitch (less likely than you'd think)

Poor lead dress

Noisy grid resistors (more likely in an older amp with carbon comp resistors, and more likely to cause hiss than hum or buzz)

Unbalanced PI tube (unlikely - this usually affects dry signal)

Ceramic cap leaking DC

A tank that needs shielding, whether from a nearby transformer or a too-close speaker magnet, although the latter is more likely to cause feedback by messing with the springs

'Dirty" wall power, nearby devices with variable resistors, computers, fluorescent lights, etc.

So you see, trouble-shooting this problem can be difficult, since there are so many potential causes. I've dealt with almost every one of them, and that's with only two DRs (one original BF and one RI). I'd try tube subs and new cables at home (and you have) but stop there if I were you. It's very dangerous to mess around with an amp that has over 400 volts of power if you don't know what you're doing.

(I started this post before the one above it, btw)

16

One more thing: reverb noise will NOT increase as you turn the amp up. What's unacceptable at bedroom volume will be negligible when it's louder. There will almost always be a little bit of noise when it's over about six (I play a lot of surf). It should be inaudible below that unless your head's right in the speaker. A really good tech can get it to the level of a small lizard breathing when it's on 10.

17

Here's somethingI have come across in my travels.I have had hum issues in my basement. We have terazzo flooring with a grid of aluminium separating sections. If I have a pedal or a cable too close to one of these I get a hum in the amp .I rectified this by lining the bottom of my Fender Reverb footswitch with aluminium foil tape as well as the wooden base that acts as an insulator for the reverb tank.Presto! No more hum.I had a friend complain about the same type of issue playing certain stages in his travels,which I suspect may have been wiring under the stage. He would move the reverb pedal artound the stage a bit to find the quietest area and tape it down there. I do the same mod to every fender footswitch that crosses my path .Can't hurt to try it.

18

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