Schematic for Realistic/Radio Shack Electronic Reverb??

[C Bradley]

I think the title says it all. Any one know where the schematic is?? It's model #32-1110B

Chris B

[Tim Escobedo]

I have a schem for the radio shack reverb. Not sure if it's the same model number, but it's the same as my ancient RS reverb box from more than 15 years ago. Anyone willing to host it?

[Mark Hammer]

Is this the one in the black case that is battery operated, or the one in the metallic case with a line supply, "expander" control and separate mic preamp?  I have a scanned schematic for the latter, but not the former.  There is no indication of the model number on it.

[drew]

tim- email it to me- spam@toothpastefordinner.com

I'll put it up.

[C Bradley]

Mine is the small battery powered one. Four slider controls: Mic Volume, Delay, Depth, and Repeat, IIRC. I've just got the board with me here, the case is still at my parents house. The box that it came in says Electronic Reverb on it, and it's made by Realistic, sold by Radio Shack. It's probably about 15 years old. I bought it new from Radio Shack for $30.

Tim, could you please e-mail me that schematic you've got? My e-mail is:

teleman28056@yahoo.com

I'll also post it on my schematics page.

Thanks!

Chris B

[C Bradley]

What I'm trying to do is to adapt this reverb unit to use with guitar, but I'm getting some distortion. I'm using the Mic inputs, and I've changed the gain of the first stage to range from 2.5 to 12.5, which seems reasonable. My guitars range from a stock Mexican telecaster to a Epiphone with a SD Invader in the bridge.

I'm not exactly sure how a delay/reverb works, could someone give me a crash course in analog delay/reverb?

Chris B

[drew]

http://www.toothpastefordinner.com/realistic-reverb-schematic.gif

[Mark Hammer]

Thanks for posting.  I'm looking everywhere for a bias voltage feeding the input of the MN3207, but I'm not seeing it anywhere.  Anyone else see it, bearing in mind it can be introduced well before the BBD as long as there are no DC blocking caps en route.

[C Bradley]

Thanks Tim! That's exactly the one I was looking for.  

Chris B

[brett]

I'd really appreciate it if someone would explain how this reverb unit works.  I've heard it said that true reverb requires multiple echos with different time delays.  Now I don't know much about this circuit, but there seems to be a single clock chip and a delay chip and a few filtering stages.  So does this circuit produce true reverb, or is it a filtered, regenerated echo?  This stuff is clear as mud to me.

Also, would this circuit work ok using a PT2399?  I kinda like the simplicity of the PT2399.  Internal clock, easy control of delay and repeats, etc....

[C Bradley]

Alright! I got this thing workin' like I wanted. R5 and R3 traded places, VR1 was reduced to 10k and R53 was replaced by a 15k to increase the output level. Yee-haw! Now I've just gotta put it in a bullet-proof enclosure, buy the pots and jacks I need, and get the power supply working right.

It really does some cool metallic sounds. Sounds like you're playing inside a big empty water tank! The delay control is really useful, because I can do some flanging by turning the knob while I'm playing.  :twisted:  This is one sick effect!

The board is about 4.5" x 4", plus I've gotta have room for knobs, jacks, and a battery. How big of a box do you guys think I'll need?

Thanks!

Chris B

[C Bradley]

So does this circuit produce true reverb, or is it a filtered, regenerated echo?

I'd say it's more of a filtered, regenerated echo. It looks to me like the four emitter followers are there to create a propagation delay, IC1-A and IC4-B are input/output buffers w/ a little gain, IC4-A looks like a controlled gain feedback circuit, IC3 is a clock for IC4, which if I'm not mistaken creates and controls the majority of delay. How'd I do Mr. Hammer?

Chris B

[Mark Hammer]

Not bad, except for a few details.  Each of the emitter-follower stages you refer to is actually a 2-pole lowpass filter.  So, the BBD is followed by 8 poles of lowpass filtering.  That's pretty steep, although two of the filter sections are tuned differently.  Given that the BBD would have to be clocked pretty low to generate any appreciable delay (and I wouldn't expect more than 100msec out of a 1024-stager like the MN3207), that makes the filters all the more necessary since the clock signal would likely be in the audio range.

But yeah, it is a regenerative echo.  Interesting sounds can be gotten by making C18 in the feedback loop much smaller to shave off bass on each repeat (try 0.1uf), and/or by making C15 larger to shave off more treble on each repeat (try .0047 to .0068).  I have a much longer post elsewhere here on one of the delay-related threads about why this does what it does.

[puretube]

Thanks for posting.  I'm looking everywhere for a bias voltage feeding the input of the MN3207, but I'm not seeing it anywhere.  Anyone else see it, bearing in mind it can be introduced well before the BBD as long as there are no DC blocking caps en route.

From Collector Q1 ("line in") there`s a voltage divider R12/R14, which leads
DC (Ub/2) to pin2 of IC1B, from that one`s output through R18 to BBD`s input....




//www.puretube.com

[Mark Hammer]

Perhaps, but doesn't  C11 also serve as a DC blocker?

BTW, the connections to the IC1-b inputs are obviously erroneously drawn.  From the appearance, there is actually no physical input to IC1-b, which obviously would result in very little delay sound.  :wink:

[puretube]

yes, at least 2 dots are not drawn at the input of that opamp.
So I assume the situation is meant to look similar as dotted at IC1 A:
R12/R14 (as well as R5/6/13) connected to pin3(IC1 B`s non-inv. input), while C11 is hooked to pin2 (inv. input), ie.: DC-gain=1, AC-gain about 2.8 with a little high-roll-off (C10).
(Btw.: dunno the pin-out of AN6552).

[C Bradley]

Mine's got 4558's in it, if that helps. I'm assuming that the AN6552 is the same pinout. It makes sense from a manufacturing view point. That, and Radio Shack's website has a list of components and shows the 4558 as a substitute part.

Chris B