Those of you verbing out rocket variants...

[eddie25]

Do you guys notice a difference in sound in higher gain situations, when you unplug the tank? Even with the verb knob at zero.

I have an amp that has an extremely annoying fizzy sound riding on top of the gain, that goes away when I unplug the tank. I have tried nearly everything and I'm thinking I either have a ghost or that maybe it's design related and has just become more apparent in this amp for some reason. I haven't noticed it in previous builds of the same amp before.

[M Fowler]

No I can't say that I have noticed that but then I again only during early voltage documentation have I ever had the reverb pan disconnected.

Maybe that fizzy sound is there when the reverb is plugged in as well but masked by the reverb somewhat.

[Cliff Schecht]

If you unplug the reverb and leave the jack floating, the stage for this could be oscillating. Maybe try shorting the recovery input stage to ground with a custom RCA jack.

[Firestorm]

It sounds like the dreaded insect parasitic. The reverb send side will have a big signal on it and could cause that if it's coupling to something. I'd check there first. See that the cable shielding is intact and try chopsticking all the leads on the send side: transformer leads, jack leads, etc. The return side has a much smaller signal, but check that too if you can find the problem on the send side of the circuit.

[Ian444]

With the tank plugged in, do you get the fizz sound with the reverb pot turned all the way down?

With the tank plugged in, do you get the fizz sound with the reverb driver tube pulled out and reverb pot turned up?

If the answer to both is no, maybe the reverb driver tube is oscillating, a 1K grid stopper on that tube might fix it. Just a stab in the dark...

[eddie25]

The sound is ONLY there when the tank is plugged in, that probably wasn't that clear from my original post.

The verb pot does not affect the sound, but pulling the driver tube does, akin to disconnecting the tank.

Must be a parasitic for sure. I've tried many different tubes. Usually I have an a-ha moment when I post an issue here, so hopefully I can figure it out today. I'm gonna try a grid stopper and shielding the grid to the driver tube which I'm surprised I didn't try yet, good ideas. I've tried all forms of wire swapping and layout possibilities that I could. Thanks again.

I'm also now wondering if I've tried anything besides a 12ax7 in the driver spot...

[FUCHSAUDIO]

Play with the drive signal level into that tube. Sometimes hitting the driver tube too hard causes that spitty shit to happen. You could also add a resistor in series with the input grid (to add rolloff), pad the input signal with a voltage divider or pot, increase the value of the cap from plate to cathode, and also add a resistor (use a pot to find a good value) in series with the cathode cap to ground to reduce gain of the driver tube incrementally. Lots of ways to skin that oscillating cat...

[eddie25]

Well shit! That was it. I was on too much of a roll and needed something humbling like that to come up. How I didn't catch it right away, I don't know.

It's ended up as two paralleled 33K grid stoppers on the driver tube, for about 16.5K. After that I ended up lowering the value of the 220K going to the reverb pot from the verb return triode, which affected the verb in a good way. I'm also using a smaller pot value than usual for the verb, so it's got a pretty nice range now. And best of all I was finally able to tweak for tone without this damn fizz.

I should mention that I'm basing this all of the 'normster' version of the verb.

Thanks fellas, hopefully if someone has a similar problem in the future they'll run across this thread.

[FUCHSAUDIO]

That's why we're here....

[angelodp]

Glad you sorted it out. Can you post a gut shot please. What value did you go down to on the 220k you mentioned. To what effect.

A

[Ian444]

There seems to be 2 slightly different schematics, one has a 220K resistor feeding a 100K reverb pot, the other has a 100K resistor feeding a 250K pot. The first uses a 12AX7 reverb driver with bypassed 820 ohm cathode resistor, the second uses a 12AT7 driver with 2k2 bypassed cathode resistor.

The 2 schems are here
https://tubeamparchive.com/viewtopic.ph ... 532#149532

[M Fowler]

I use the 220k feeding the 100k reverb pot like Normster has shown in his layouts.

Mark

[eddie25]

There seems to be 2 slightly different schematics, one has a 220K resistor feeding a 100K reverb pot, the other has a 100K resistor feeding a 250K pot. The first uses a 12AX7 reverb driver with bypassed 820 ohm cathode resistor, the second uses a 12AT7 driver with 2k2 bypassed cathode resistor.

The 2 schems are here
https://tubeamparchive.com/viewtopic.ph ... 532#149532

This could have been my problem as well. Mine is actually similar to the layout for the EL34 amp layout in that link, but I'm using a 12ax7. Balls. I had used a 250K pot previously in some amps, but I like the swing of the 100K in this one.

Anyhow I used a 150K across the 220K to the pot and it seemed to give me a tad more verb, super subtle though. Sounds great now.