Super Reverb Volume Controls won't Silence the Guitar

[AtomicMassUnit]

Hi All, I'm working on a silverface super reverb, and noticed that the volume controls don't silence the guitar. In fact, even turning all the knobs all the way down doesn't. There's a dirty, quiet guitar sound present at all times if I play. Any ideas? Grounding out the grids of the first preamp stage silences it... All grounds seem to be good, 0 or 1 ohms...

[pdf64]

What is the resistance between the 2nd stage grid (=vol control wiper) and ground with it turned down?
Are the cathode bypass caps good?
Have you tried different tubes (V1 and 2)?
Pete

[soundguruman]

Hi All, I'm working on a silverface super reverb, and noticed that the volume controls don't silence the guitar. In fact, even turning all the knobs all the way down doesn't. There's a dirty, quiet guitar sound present at all times if I play. Any ideas? Grounding out the grids of the first preamp stage silences it... All grounds seem to be good, 0 or 1 ohms...

First, understand that there is nothing wrong. This is the way the amp was made.
Because of the type of pots, the wiring, and the location of the ground to the chassis, there is no 0 ohms to ground on the volume controls. It's the grounding. Also I suspect some of the parts bleed into each other on the circuit board, probably the larger ceramic disk caps that were used in these particular year amps....

Certain years of Super were made this way, and it causes audio to bleed thru even when the controls are turned to zero. The audio is distorted when the volume is down, that's normal also.

You will also notice that amps made this way have a "better" sound, and are more aggressive sounding than other Fender amps of the era.
For Blues, it grinds better, has a better high end bite, and also more Hiss, the bass controls work better..etc...than other Fenders of that era.

I would not try to "fix" it. but rather accept that it is made that way. Also, because of the unique tone, certain guitar player may like it better than other year Super...

I have worked on 2 of these type Super in the last 3-4 months. I think they sound better than other ones. They definitely have some kick and distortion that other Fenders don't have. They seem to want to grow up and be Marshalls instead of Fenders...

[g1]

Once long ago I asked the same question and was told "this is why Fender knobs only go down to 1, not zero". Not sure if that is the real reason but it works for me and helps me remember that it's pretty common with vintage Fender stuff.
It always helps to keep real world conditions in mind, what need is there for an amps volume to go to zero?
Also, 1 meg pots may not always go down to a perfect zero ohms, and are often bypassed by a bright cap.

[AtomicMassUnit]

Thanks all! That makes perfect sense.

[Leo_Gnardo]

I addressed this problem for a studio @ 20 years ago. First, many volume controls don't go all the way to zero when turned all the way down. Old controls often read 50 to 200 ohms. New ones, 10 to 20 - better but still not perfect. Measure some new volume pots, and pick the ones that go closest to zero, and substitute them for the ones in your amp.

There's also signal leakage within dual-triode preamp tubes. Here's what I did to "fix" that. Instead of using one triode as the first preamp stage, and the other as post-volume control gain, I swapped wiring around so that V1 tube handled both channels' first stage pre, and V2 both post-volume control gain. It wasn't perfect but it did reduce the problm to acceptable levels.

[Chuck H]

I don't have a ton of experience with these amps but I've seen this problem before. As mentioned, it was leakage within the tube itself. Replacing the tube for the offending channel fixed the problem. Other contributing factors could include old, high esr power supply filters, dirty pots, leaky coupling caps and oxidized ground connections (especially mechanical, not soldered connections) Not a huge problem since the amp isn't likely to be played on zero very much.

[JoeM]

My SR does the same thing with certain tubes. Try a different tube in V1 or V2 as mentioned above.

[soundguruman]

My SR does the same thing with certain tubes. Try a different tube in V1 or V2 as mentioned above.

I tried a new set of JJ and a new set of Groove, and it still did it...changed them all, and swapped them out one at a time with other good tubes. and this was in more than 1 super reverb. I tried recapping, all caps... and no change...needed recapping anyhow. I will admit using certain tubes, it will probably do it "less..." that is a distinct observation...the problem "almost" goes away... But I still believe, that it is just the way the amp was made to start with. I think that trying to "fix" it.... it's not really broken....just the result of the components used and the style of building at the time. You can approach it from the standpoint that it needs fixing to work a certain way...the way all the other Fenders do... Or accept that it's different, and sounds different, and is built a bit different too, in the grounding locations especially, and others... But I think I like it better the way it "is." seems to sound better. More sizzle, I like sizzle, even though it also has Hiss. More grind, I like the grind, it sounds "old."

[JoeM]

With good tubes and the volume at "1" (these Fenders dont go to zero), my SR is dead quiet, not just 'less'.