Rub-a-Dub Reverb Deluxe in feedback

[JackSkellington]

Hello guys!
My first post here.
I play guitar and I learnt to build pedals, but I'm just moderated expert.

I built a Rub-a-Dub Reverb Deluxe on veroboard. I'm testing it and it seems to sound good. I tried the "only wet signal mod" taking off the 22k resistor, and also this works well.

I have just a problem. I can't set the dual pot over the half.
1776 board has a 100k Linear dual pot, but the layout I found has a 250k dual pot, it should allow longer decay. But if I set the decay pot over the half, after a while I got a sort of feedback effect, like with some high gain distortion, but clean, then it gets dirtier and pretty louder. The only way to kill it is turn the decay pot to min.
I power it with battery.

Is the dual pot too much big the problem?

Thank you!

[m-Kresol]

my guess would be that the dual pot is some kind of internal feedback (the BTDR reverb bricks is essentially pt2399 delays set to short delay times). so if you go too high, it will start to self oscillate as any delay would. just a educated guess though, I could be wrong

[JackSkellington]

Thanks for reply.
If you wrong I wrong, too. Indeed I think the same thing.
I assume if I replace the 250k dual pot with a 100k I could solve the problem or at least I could set the pot in a more useble range.

I can settle with this bigger pot right now. But I would be sure if I replace it I can get better result.

(I wanted try the self oscillatin trick with a Rebote delay 2.5 soon).

[m-Kresol]

you could try adding a 150k resistor in parallel to lugs 1 to 3 of the pot and see if that tames it. this would result in approximately 100k maximum

[gtr2]

I don't know of the vero layout but the actual build document for the PCB lists 100kB.  More than that will create oscillation with some BTDR-3H's.

Josh

[JackSkellington]

I take the vero layout on tagboard. Verified.
Probably it is exactly like you said gtr2, about the oscillation.

And thanks m-Kresol for your suggestion.
Do I just solder a resistor between lug 1 and 3? It is a dual pot, so I assume I should do the same thing on both the part. It is so?

[m-Kresol]

yeah, you have to do it with both parts of the dual pot.
you can also try using alligator clips, if you have some, to test it first. Adding the resistor in parallel won't give you a linear response (as is needed by the build doc) but rather a logarithmic one, so it might be hard to dial in the decay.

[JackSkellington]

I'm gonna make some tests and let you know.
And if I can use this 250k dual pot for another project (but I hardly think so) I could replace it with a 100k.

Thanks again!

[gtr2]

I take the vero layout on tagboard. Verified.
Probably it is exactly like you said gtr2, about the oscillation.

Not probably...that is the problem

[JackSkellington]

Hi guys!
Dual pot 250k for Decay replaced with a dual pot 100k.
Now the pedal works much better. I tested just for a while, but seems I just can get oscillating with decay at max, and it comes out very very slowly. Of course that it is an extreme setting, the pedal is good even with Mix and Decay pot at 12 o'clock.
Added a switch for "only wet" mode.

Pictures are coming.

Thanks at all!

[JackSkellington]

Pictures!
1. Work in progress: How I did it.
2. Work completed.

Nice very usable reverb in light or heavy setting. Enough silent, not how the reverb built-in on my Amp, FFFFFFFF! .

With high gain distortion the reverb give me an unexpected effect. I have a sort of presence/treble boost.