Reverb - odd behavior

[txstrat]

Hi all,

in one of my latest builds I realized that the reverd sounds good but has some odd side effect. If I listen closely I can make out a sort of delay (very quick like a tremolo effect turned way over speed).
As in all of my builds I'm using a one tube reverb (like Tubenit introduced) and the only difference is the reverb tank, which is not a 4AB3C1B but a 8AB3B1C (the difference should only be the size of the tank). In- and output impedances are almost the same.
I've never heard the effect of a dwell control pot. Will changing the dwell - using a pot or maybe a different grid to ground resistor - change this "sort of delay" effect?

Matt

[Tubenit]

Hi all,

in one of my latest builds I realized that the reverd sounds good but has some odd side effect. If I listen closely I can make out a sort of delay (very quick like a tremolo effect turned way over speed).
As in all of my builds I'm using a one tube reverb (like Tubenit introduced) and the only difference is the reverb tank, which is not a 4AB3C1B but a 8AB3B1C (the difference should only be the size of the tank). In- and output impedances are almost the same.
I've never heard the effect of a dwell control pot. Will changing the dwell - using a pot or maybe a different grid to ground resistor - change this "sort of delay" effect?

Matt

I have found the dwell pot to be very important to the reverb tone I have wanted. Typically with a 1M dwell pot, I have it set on 5-7.

On one build, I had limited room and ended up using a 680k dwell resistor and found it useable. I think the 1M dwell resistor creates sort of "ghost note" effect which may be what you're trying to describe?

You could also try a 5751.

Without seeing a schematic with the reverb circuit, it's difficult to offer other considerations.

With respect, Tubenit

[txstrat]

Hi Tubenit,

thanks for your quick answer.
My reverb circuit is exactly like in the schematic of the 5E3 with reverb (you posted it in a diferent thread). I'll try a smaller resistor and report back.

Matt

[txstrat]

Changed the grid to ground resistor with several values down to 330k. Only the amount of reverb changed a bit, but not the vibrating "noise".
I can hear it most clearly when I just strumm the strings and have the reverb on full open.
When the reverberated sound fades out the vibrating is clearly audible.

[Tubenit]

Changed the grid to ground resistor with several values down to 330k. Only the amount of reverb changed a bit, but not the vibrating "noise".
I can hear it most clearly when I just strumm the strings and have the reverb on full open.
When the reverberated sound fades out the vibrating is clearly audible.

Not sure what to advise you? You could try a different insertion point after the volume/tone stack prior to the next gain stage?

OR experiment with lower voltage on the reverb trannie? Or try different value cathode caps and resistors?

Hope you can get it resolved & if you do, please post the resolution

With respect, Tubenit

[txstrat]

OR experiment with lower voltage on the reverb trannie?

Hmm, voltages. Yeah, that seems to be the only thing I haven't checked against my other builds, which work great.
Don't get me wrong, this one works great as well, just this tiny amount of vibrating in the offswelling reverb could be less.
I'll check the voltages.

Thanks Tubenit

[Tubenit]

I forgot to ask, did you lower the .1 coupling cap after V1 to .01? Maybe too much bass signal is still going into the reverb?

You could also reduce the .001 dwell cap to maybe 500p or even 390p?

And is there adequate filtering for the reverb circuit. In other words, did you add another filter cap in the B+ rail to filter the reverb?

Sure hope you can get it to work well for you! Don't give up .............. just keep experimenting.

With respect, Tubenit

[txstrat]

It's not a 5E3 circuit. More like a Champ II. Just the reverb circuit is the same. (BTW a great little 15w amp for clubs - even with a straight drummer).
The coupling cap after V3 (which is right before the reverb and the PI) is indeed 0.022uF.
I might decrease it to 0.01uF.
The Dwell cap is 470pF already.
Filtering ought to be OK. 1x47uF and 4x22uF all over the B+
Gonna keep your informed.

Thanks again

[Tom Phillips]

Have you tried a different tank in the amp? Or put the 8AB3B1C in a different amp to determine if the odd side effect follows that specific tank?

[txstrat]

Imagine picture: slapping my forehead
Haven't tried it yet, although it obviously seems to be the first thing to do.
Gonna try that first thing tomorrow.

Thanks for your thoughts Tom

[txstrat]

Tried both ways and found it IS the tank.
I found this one has a good amount more gain than the other tanks I'm using.
The vibrating sound is only there if I strumm the higher strings. Not audible with the low E or A strings.
Seems like I have to live with it. But as I said, it's only there when you KNOW it is there.