Reverb Hum

[BobD]

I have a homebrew Deluxe Reverb that hums when I turn up the Reverb knob.

Right now I have all of the preamp tubes and the 12AT7 reverb driver tube out and the reverb tank disconnected and it still hums. If I remove the recovery tube the hum stops.

The fact that the reverb knob effects the hum means the source is BEFORE the knob. The fact that the tank is disconnected means it's AFTER the reverb return jack.

This only leaves a few components to pick up hum and I've shielded the wire connecting the reverb pot to plate. The wire connecting the grid to the reverb return jack seems very sensitive - I can hear it buzz in the speakers when I get close with the probe and I hear it thump in the speaker if I tap it with the probe. This wire is only about 2" long. Should I shield it ?

Any suggestions as to where the hum could be coming from ?

[Don Symes]

You've got the right section - and it's a really sensitive gain stage. Some questions:

1) do you have the 220k grid-to-gnd grid resistor in place, with good connections at both ends?

2) that triode's Rk/Ck ground connection - is it to the same point to which the reverb pot gets grounded (and the 220k Rg already mentioned)? Is it a good, solid connection?

Hope this helps!

[Enzo]

When you say the tank is disconnected, did you unplug the cable from the pan itself, or did you pull it at the chassis end? The cable should could be faulty.

Are the return jacks grounded to chassis? Try isolating them from chassis and grounding the shield contact to the cathode resistor ground of the return amp.

Is the body of the reverb control grounded? Check for continuity from the rear cover of the pot to chassis.

That wire might be sensitive, and it wouldn't hurt to shield it, but I don't think that is your trouble.

When you built the thing, did you keep all heater wires away from that wire? Any wire carrying AC current will radiate into nearby signal wires. Try pushing wires in the neighborhood from side to side and see if any of the wires affect the reverb noise. SOmetimes moving a quater inch is all it takes.

[BobD]

Reverb Hum

The 220k grid-to-ground is in place. It's attached to the reverb return jack and grounded on the little tab which connects to the chassis.

The Rc/Ck is not grounded to the same point as the 220k grid-to-ground. I used a "galactic ground" system as KOC likes to call it - with the only exception being the 220k grid-to-ground and reverb send/return jacks. I've succefully used this grounding scheme on 5 amps now (without reverb) so I have a pretty fair idea as to what I'm doing... I disconnected the 220k grid-to-ground and ran a jumper to the neg side of the stages Rc/Ck with no improvement.

I disconnected the tank at the chassis end so the cable is out of the equation.

The return jacks are grounded to the chassis. Now that I think about it, I ran a jumper from the 220k grid-to-ground but I left the jacks grounded. I'll isolate them tonight.

The body of the reberb pot should not be grounded to chassis, I'll check tonight.

I tried the "chopstick" method with no results. The heater wires are pushed tight against the chassis.

Maybe I just have to live with some hum ?

[Enzo]

The body of the pot SHOULD be grounded so it acts like a shield. if it is not grounded, then the pot cover acts like an antenna.

Grounding everything to the chassis might work in some amps, but like anything else, when it doesn't, the fact that it did elsewhere is irrelevant. Currents flowing through the chassis from A to B will combine with other currents, such as your reverb signal, when they share a path through teh chassis. And when they do, you get ground hum. Don't know that that is the issue here, but it is common enough.

[Josh_B]

I have this EXACT same problem, and have tried all of the same fixes - to no avail. Did anyone have a solution?

[Bruce / Mission Amps]

Isn't it amazing that a real Deluxe Reverb does not have this reverb hum problem but 99% of home builders refuse to wire the pots, power supply and ground their clone reverb amps it like Fender did because some self appointed Net Guru thinks their super whiz-bang woof woof ground system is superior.... !?

[Amp Kat]

Isn't it amazing that a real Deluxe Reverb does not have this reverb hum problem but 99% of home builders refuse to wire the pots, power supply and ground their clone reverb amps it like Fender did because some self appointed Net Guru thinks their super whiz-bang woof woof ground system is superior.... !?

Gee I love that terminology and it's so true !

[Josh_B]

Hi Bruce,
I agree with you 100%. I inherited this Vibroverb chassis, pots, transformers, etc and it didn't have a brass plate. Otherwise, I'd have used it!
My Mission 5E3x2 got me really hooked on building. I've learned a lot in the last year or so. Thank you for the help!

[Josh_B]

I ripped out the copper-wire-on-the-back-of-the-pots grounding scheme and installed the brass plate..... FIXED!!! Quiet as a church mouse!

+1 to Bruce Collins (again)

Bruce - can I still buy a 5F11 chassis from you?

[Bruce / Mission Amps]

I ripped out the copper-wire-on-the-back-of-the-pots grounding scheme and installed the brass plate..... FIXED!!! Quiet as a church mouse!

+1 to Bruce Collins (again)

Bruce - can I still buy a 5F11 chassis from you?

Yeah, just email me at soulkicker@missionamps.com

[gonziak]

Hello! This is Martin from Poland, a great topic. I have the same problem with my moded fender deluxe reverb reissue in which I have changed everything. Today I have installed the brass plate and noticed much improvement with the reverb hum. Now I've got ground loop hum. Would you tell me how to ground the input shields, cathodes and all the rest, which were connected to bus pots wire? How should it be grounded with the brass plate?
Thanks for any advice.

[Josh_B]

Hi Martin,
You just solder the preamp section and cathode grounds directly to the brass plate. It will take a lot of heat, so do the soldering with the plate out of the amp, and use a high-wattage iron. Keep the wires as short as possible.

Good luck!

Here is a good example - you can see bare wires going from the cathode components to the plate.

[gonziak]

Thank you. Yeah, much better now. I still have the hum but much, much less. Should it disappear completely? I solder the shields, cathodes, and preamps ground to the different points of brass plate (to the nearest points ) is this ok, or should I find the common point?

[Josh_B]

It sounds like you did just great. Try isolating the reverb send and return jacks from the chassis ground and running their grounds to the brass plate also. That may help.

Have you tried using a chopstick to move wires around to fine tune your lead dress and layout? That is an art form all its own.