old Radio Shack stereo reverb/analog delay # 42-2108

Schemo:

http://natwlad.free.fr/images/realistic%20stereo%20reverb%20schem.jpg


For some reason I cant for the life of me figure out how to make it so there is just the delay and no dry signal on the outputs. Anyone have some thoughts? I just cant figure it out.

Thanks!

Realistic Stereo Reverb # 42-2108

ok, what if i take out c110, and c109? im going to try it.

Remove R113 R114

> what if i take out c110, and c109?

Or that, sure, same difference.

PRR said:

Remove R113 R114

> what if i take out c110, and c109?

Or that, sure, same difference.

Click to expand...

Great, thanks for the reply. Glad I wasn't off track. Hopefully today I get some time to try it. I Love the sound of these old BBD delays.

Tried it, works great now. Thanks!

Much more usable on sends now.

I also switched out the trimmer that trims out the clocking signal with a higher quality 20 turn trimmer, now the clocking signal is quieter and I also added a 120pf cap in series with the 270pf "S" cap for a longer delay time.

Much more usable device now!

Does anyone have the schematic for this one the stereo version 42-2108?

Yes.

mjrippe said:

Yes.

Click to expand...

SUPER!!! 

I would like to add a pot for feedback control (on the stereo version 42-2108, shouldn't matter).
But I can't figure out what to replace!

Some resistor near the BBD chip, i presume?

RM said:

I would like to add a pot for feedback control (on the stereo version 42-2108, shouldn't matter).
But I can't figure out what to replace!

Some resistor near the BBD chip, i presume?

Click to expand...

I think I changed R213. Nope, wrong...

I did replace R229 and R230 with a pot.

Why both?
I am not sure what R230 does, but I placed a jumper on R229 and voila, it self-oscillated like crazy.
So I am thinking if I could just replace R229 with a 5k potentiometer + suitable resistor (maybe 3-4k)?

Ideally,  I want:
Full resistance = no feedback at all, zero resistance = self-oscillation. Where in-between would be something like the standard 6,8k value.

I'm not great at electronics, but so far my mods have worked out good!

If you look at the closest pot under r229, vr102, the resistor pair r229 and r230 is doing the same thing, vr102 is working as a voltage divider and r229 and r230 is doing the same thing.

Tip....  Google "potentiometer and voltage divider", and learn something new... 

RM said:

Why both?
I am not sure what R230 does, but I placed a jumper on R229 and voila, it self-oscillated like crazy.
So I am thinking if I could just replace R229 with a 5k potentiometer + suitable resistor (maybe 3-4k)?

Ideally,  I want:
Full resistance = no feedback at all, zero resistance = self-oscillation. Where in-between would be something like the standard 6,8k value.

I'm not great at electronics, but so far my mods have worked out good!

Click to expand...

So I assume just replacing r229 would be ok then?

No not really...

But you could have a try and se if you get the feedback signal quiet enough for your use (depends on the size of the pot), for example when when you just want one echo/slap. The function of the voltage divider is to ground the input to the feedback circuit when you want no feedback, if you keep the r230 in the circuit you cant ground the input signal to the feedback circuit, and therefore not get what you want = zero feedback.

RM said:

So I assume just replacing r229 would be ok then?

Click to expand...

> feedback control

When I did mod my RS reverb/delay for feedback, I just copied the most common way to implement a feedback pot, and I did so by looking at other analog delay schematics. Both Ibanez AD9 and Boss DM2 have taped into the signal, and regulated it back to the input of the BBD circuit, at the same point as where the echo level pot is. I did the same and it works fine on mine...