ghost noise/buzz with playing (V4)

[beedoola]

I've been noticing a slight little buzz with each note on my V4. I mentioned in another thread my rocker switches were a little dirty/stiff. I was getting some increased noise/note interference when using the Treble rocker on the "+" position. I thought cleaning might help but that didn't.

The issue is still there (regarding the Treble rocker) and I'm wondering if the issue with the rocker and the general buzzing are related. To clarify, when I take the Treble rocker off the + position, part of the issue is resolved, but the general buzzing on each note - mostly bass notes is there.

I thought it might be a amp vibration issue. I brought the V4 home and put it on my bench, running it into a small speaker for testing and even at low volumes, the issue still occurs.

I took a chop stick and tapped the preamp tubes and V2 seemed like it might be microphonic - it was making a little noise audible through the amp when I tapped it.

I replaced it with a fresh JJ 12AX7 I had. I tapped around again, also on the top of the PCB and around R19/V3, I'm getting some amplification of my tapping into the amp. Its not loud, but its occurring; I'm not sure if that is a bad thing.

With regard to the Treble rocker. Is the noise likely mechanical, i.e. the switch, or something on the control PCB?

All the preamp tubes have been replaced, minus the 6K11. which is either the original, or certainly old.

[Liquids]

Sounds like a hot signal. the rocker's + highs setting increases gain of high frequencies, which increases distortion of high frequencies if it's a hot signal...

Easier to hear on lower notes though, because they tend to drive the amp harder in terms of voltage/gain, than a higher note, but they have harmonics that are in the high frequency range boosted by the + as well...

Try changing the sensitivity switch's setting. I should say, the lower gain setting is what is 'stock' on the V4b which doesn't have any sensitivity selection. That switch actually changes the headroom of an early preamp tube stage (kinda). You can fiddle with the volume knob from there and see if you get the same issue.

It may not be that, but it's worth eliminating, even if that isn't the issue.

Also, some level--sometimes a high level--of vibrational noise/microphonics is normal. Most amps have a lot of signal gain going on. Tubes also kind of amplify 'mechanical/vibrational' noise. Try turning up your amp sometime and tapping on your power tubes with a chopstick (start lightly). You will be surprised. Likewise with each tube. Thought some tubes and some tube positions do it more than others...

If you can record the buzzing, it would help. Like a real speaker recording--you'll nail down and see if it's speaker audible or a buzzing you are hearing in the room. It's hard to differentiate at times, oddly. However, if you capture it through the speakers, we'll know more. It could be so many things - a speaker issue, something loose, a misbias...so many possibilities. Audio might help if the sensitivity trick isn't doing it.

[Hangman]

hmm, could be a lot of things.

Did you end up setting your bias a little higher than the roughly 19ma per tube you were initially experiencing?

if there is enough crossover distortion that can certainly become audible.

do you have a scope? can you feed the input a 1k sine wave, plug the amp into a dummy load and view the output on the scope?

[tdbassman]

My V4-B had that same sound (ghost note buzz). Replacing the flyback diodes stopped the "haunting" sound. I still remember the help Hangman gave me on it. Tom D.

[beedoola]

hmm, could be a lot of things.

Did you end up setting your bias a little higher than the roughly 19ma per tube you were initially experiencing?

if there is enough crossover distortion that can certainly become audible.

do you have a scope? can you feed the input a 1k sine wave, plug the amp into a dummy load and view the output on the scope?

No, I left the bias stock.

The problem ended up being the instrument cable! I thought initially it was an issue with my pedalboard so I took everything out of my chain except guitar and cable but it was that cable that was causing it!

I also used a little Deoixt Gold G5 on the rockers. I'm not 100% sure, but that may have fixed the issue with the Treble Control/Treble Rocker.

[tdbassman]

As Coach Lombardi said: "When all else fails, go back to the basics. Cables is one of them.

hmm, could be a lot of things.

Did you end up setting your bias a little higher than the roughly 19ma per tube you were initially experiencing?

if there is enough crossover distortion that can certainly become audible.

do you have a scope? can you feed the input a 1k sine wave, plug the amp into a dummy load and view the output on the scope?

No, I left the bias stock.

The problem ended up being the instrument cable! I thought initially it was an issue with my pedalboard so I took everything out of my chain except guitar and cable but it was that cable that was causing it!

I also used a little Deoixt Gold G5 on the rockers. I'm not 100% sure, but that may have fixed the issue with the Treble Control/Treble Rocker.