New Super Reverb build rustling noise mystery

[waldner]

Recently finished a Super Reverb AB763 build.  Works great and sounds great with one tiny exception.  When turning up the reverb- even with the tank disconnected completely- I get that soft rustling noise, like quiet crackles and pops.  The noise goes away completely when the reverb is turned all the way down and gets progressively louder as it's turned up.  It's also completely unrelated to any other controls. 

It's not the end of the world and I've experienced this kind of sound with many amps over the years, but given that it's a clean new build, it's driving me crazy that I can't get rid of it. 


I've reflowed every solder joint anywhere near things related to reverb and beyond
I've tried 6 different tubes in V3 and V4. 
I've choppsticked the crap out of every possible wire and connection. 

I've searched the web for other solutions but all I can find is talk of bad plate resistors or cathode bypass caps or resistors, which would seem to apply to vintage amps with old worn and drifted parts.  Are these possible problems in a brand new build with new resistors and caps? 

Any ideas would be appreciated.  See a gut shot below. 

[Joel]

I'm also interested in discovering possible sources for this sort of noise.  I have this sort of noise in an old solid state Rotel hifi amp (Left channel) and I believe it's beginning in one of my guitar amps.  Usually goes away once the amps are warmed up for a while.  Probably a cap, but which and where... no idea.

[sluckey]

I've searched the web for other solutions but all I can find is talk of bad plate resistors or cathode bypass caps or resistors, which would seem to apply to vintage amps with old worn and drifted parts.  Are these possible problems in a brand new build with new resistors and caps? 

Yes, especially since you used so many carbon comp resistors. That reverb recovery circuit is dealing with the lowest signal in the entire amp and can be a bit fussy.

[waldner]

Yes, especially since you used so many carbon comp resistors. That reverb recovery circuit is dealing with the lowest signal in the entire amp and can be a bit fussy.

Ok, maybe I try changing the V4 plate, V4B grid leak and V4 cathode resistors to carbon film or metal film.  I already have a carbon film for the V4A grid leak with a .002 bypass cap on it.

[waldner]

As usual Sluckey was correct.  I changed out the two V4 100K carbon comp plate resistors for metal films and the noise is totally gone. 


Good to remember that even brand new carbon comp resistors can cause this kind of noise in a sensitive reverb circuit.  Thanks Steve!

[Joel]

Hmmm...  I don't use carbon comp in my builds so I must have a different problem in them.  The hifi might might.  It's a 70's era stereo.

[p2pAmps]

As usual Sluckey was correct.  I changed out the two V4 100K carbon comp plate resistors for metal films and the noise is totally gone. 


Good to remember that even brand new carbon comp resistors can cause this kind of noise in a sensitive reverb circuit.  Thanks Steve!

FWIW, I have been buying these (new to me) resistors from Digikey and really like the results a lot.
https://www.digikey.com/en/products/detail/vishay-beyschlag-draloric-bc-components/PR02000201003JA100/7350662

Because I normally buy a bulk of all the values I commonly use these come on a ribbon which I personally love.  On your next build give em a try and I think you will be impressed.

Note: I have learned the hard way that proper wire dress will alleviate all sorts of noise issues along with awesome grounding techniques.  I am always learning myself.

Cheers!
Mike

Below is an example of my wire dress and grounding in case your interested

[dude]

P2PAmps,

So basically looks like your signal buss is just a wire, tied with others, to keep stable to the ground at the input jack? No thicker buss bar, just ground wire?

[sluckey]

P2PAmps,

So basically looks like your signal buss is just a wire, tied with others, to keep stable to the ground at the input jack? No thicker buss bar, just ground wire?

Look at some other pics on his website and you can clearly see a #12 or #14 solid copper buss bar running behind the pots. Several ground connections are soldered to this buss bar. And buss bar is connected to chassis at his preamp ground point.

[p2pAmps]

P2PAmps,

So basically looks like your signal buss is just a wire, tied with others, to keep stable to the ground at the input jack? No thicker buss bar, just ground wire?

Yes, a #14 copper wire from some romex, twisted in a drill to straighten out out.  Attached to the chassis near the inputs.  Things I connect are pot grounds, bypass caps, reverb trans ground, or anything in the signally chain.  The PS side is the power tube grounds, center tap(s), bias cap, etc etc.  It works for me quite well.

~m

[dude]

P2PAmps,

So basically looks like your signal buss is just a wire, tied with others, to keep stable to the ground at the input jack? No thicker buss bar, just ground wire?

Yes, a #14 copper wire from some romex, twisted in a drill to straighten out out.  Attached to the chassis near the inputs.  Things I connect are pot grounds, bypass caps, reverb trans ground, or anything in the signally chain.  The PS side is the power tube grounds, center tap(s), bias cap, etc etc.  It works for me quite well.

~m

Ok, you do have a copper #14 ground wire from Romex wire. I do the same, does work well. One thing, is your buss soldered to the pots or just at one end at input? Of course the end close to PS is not connected to PS. I always attach the grounded end to the 1st preamp tube cathode turret then from turret to bolt next to input jack along with the input jack ground. The buss floats (not attached to pots) to other end on a turret that sits free. And pick up the signal grounds as you mentioned. Just wondering if you soldered buss to pots, probably doesn’t make much difference if soldered to pots anyway, resistance takes the easiest path.

[p2pAmps]

Ok, you do have a copper #14 ground wire from Romex wire. I do the same, does work well. One thing, is your buss soldered to the pots or just at one end at input?

The Buss in fact soldered to all the pot grounds as indicated by the schematic I am working on.

Of course the end close to PS is not connected to PS.

Correct.  The only place I connect the ground buss is near the inputs on the Normal channel is a Super Reverb example.

I always attach the grounded end to the 1st preamp tube cathode turret then from turret to bolt next to input jack along with the input jack ground. The buss floats (not attached to pots) to other end on a turret that sits free. And pick up the signal grounds as you mentioned. Just wondering if you soldered buss to pots, probably doesn’t make much difference if soldered to pots anyway, resistance takes the easiest path.


I do solder each pot to the buss which gives me a sturdy buss to hang signaling wires on.  One exception is I run the Tremolo signal wires on the chassis away from the reverb wiring on the buss.  For me it alleviates tremolo ticking and noise on the tremolo along with a .022uF cap on the roach.

Again, this is just my method that works for my builds and is certainly not the ONLY way to get the job done as many have proven.

~mike

[tdvt]

Not to get too much away from the OPs topic, but one more query for Mike..

Are you getting a lower-noise benefit from bundling the wire runs to the buss, or is it more to keep things tidy (or a little of both)?

I am using a very similar buss configuration but hadn't tried bundling/zipties


PS the amp in the recent Uncle Larry vid sounds very nice

[p2pAmps]

Are you getting a lower-noise benefit from bundling the wire runs to the buss, or is it more to keep things tidy (or a little of both)?

So yes both and also make future pot changes a breeze.

Do this on your next build that has both verb and trem.  Bundle all the signally wire like I do on the buss but don't zip tie them yet ok.  Now, fire the amp and listen close and mess with verb / trem wires.  You will hear noise most the time ok.  I am not as smart about the (whys) like some of our forum brothers but I can tell you in my experience the trem and verb wires don't seem to play well together.  I separate them by running trem wires below on the chassis and everything else on the buss.  I also pay attention not to get too close to the B+ wires coming from your filter caps which has also caused me some heartburn in the past.  I hope this is useful info

Cheers
~m