Pefftronics SB-101 Rand-O-Matic dissection.

[digi2t]

Yes folks... it's here. I think this one stands right up there with the Ludwig Phase II, and I believe collectively, as with the Ludwig, we can break it.

Here is what I have so far. My eyes are going buggy, and I would appreciate someone stepping up to the plate to do the schematic. I'll be more than happy to do the back tracing, verification, and answer all pertinent questions. I'm hoping the as the schematic develops our house brainiacs will be able to decipher the unknown IC's.

The component and trace picture are high resolution, so download them, and blow them up on your computer.

Control reference;


Trace side (note that the image is reversed, so I could use it to copy the components onto it);


Components;


Note that the two TL064's are upside down vis-à-vis the square pad indication of the board. There must have been an error in the original board layout. Follow my indications in picture.

Top side traces;


Ironically, I found that one of the 10K trimmers (above IC12) was actually broken. It controlled the amount of maximum feedback. For some reason, it had been pried off the board somewhat, enough to break the wiper lead. It explained why I found the feedback control rather weak. I removed it, and replaced it with a new multi-turn, and I have now adjusted it to where max feedback will take the input signal into runaway oscillation, which is kind of cool.

I'm going to go over it some more to ensure that there are no errors, missing connections, etc. The tantalum caps around IC1 are a bit of a crap shoot. Other than the polarity markings, there is no values on them. Measuring them in place with my capacitance meter, I get readings of 82nF to 88nF. They are slightly smaller than a 1uF cap that is on the board, so I'm making an educated guess here. I'm not really keen on removing one just to measure. IC1 looks like a dual opamp for mixing the dry and wet signals.

Anybody wish to join my asylum?  

[jrfox92]

That's interesting, I just happened to wonder if there were any schematics being made after looking at Greg Edwards' rig.

[digi2t]

Updated picture, with some overlays, and IC's list. UKToecutter is working on the schematic.



IC11 is still a hold out.

[~arph]

Strange thing that IC11.

The bottom 4x4 pins connect to the outputs of the flipflops. and the top section mainly connects to fixed voltages, except pin 4 which connects to an inverting input of IC6. and pin 1 which seems unconnected. so maybe some binary to voltage (DAC) converter?

[R.G.]

I looked at it. Best guess is that it's an R-2R resistor network, used as noted as part of a D-A converter. The logic setup seems to support that kind of setup.

There are some unusual telecom ICs that 11 might be, but finding one like that is going to be difficult.

If the design does what I think it does, it took a whole lot of parts and work to do what is today one uC.

[~arph]

This one seems to fit the bill.. MC1408


https://www.physics.rutgers.edu/ugrad/327/MC1408-8_3.pdf

[digi2t]

I am, as I often am here, awestruck.

And humbled.

Did I mention awestruck? 

Greatly appreciated fellas. At least now I have a complete list of parts to order for the breadboard.

[R.G.]

A bit of kibitzing.

If the circuit is what I think it is, quite a bit of it could be replaced by one 8-pin or one 14-pin PIC to do the random generation, possibly the triangle/etc. stuff as well, including the D-A chip.

if you can finish drawing up an even crude schematic, which pin of which IC goes to which pin of the other, that might be easy to see.

[~arph]

That would not surprise me either

[digi2t]

UKToecutter is working on a schematic right now. Once I have it back traced to the original, I'll post it.

Would be cool to see what "New School" tricks can be used to re-create this.  It's quite an odd bird, but I get a real kick out of it. Lots of weirdness.

We could maybe do two different PCB's, "Old School", and "New School". 

[UKToecutter]

I've done my bit.

Over to you for back trace Dino.

[jrfox92]

I've prepared myself to spend more money than I should to build this if you get a working schematic made. 

[digi2t]

I've prepared myself to spend more money than I should to build this if you get a working schematic made. 

Please replace the underlined word in the above statement with "when".

I've already ordered all the IC's.

I've done my bit.

Over to you for back trace Dino.

On it.

[digi2t]

Alrighty then...

I've traced, traced, and double traced, and this is what I have to date (click on images to get larger images from Photobucket);



And, the schematic that Andy has developed from it (ignore the rotary switch LED's, that's a possible add-on);



I have this monster on the breadboard right now. Sweeping the mix pot, full dry side is loud and clear, full wet side is at a lower volume output, but no delay, modulation, or random at all. I have signal up to the 571, and after the 571 to the 7569, but nothing coming out of the 7569. Right now I'm wondering if I've missed something in the trace, or if the 7569's that I bought are duds.

Major head scratching going on here. Bum chip? Bum breadboard? Bum trace? Grrrrrrrrr.... Anyone see something I'm not getting here?

[UKToecutter]

Teaser........

Prototype boards arrived....





Fiddly as the component density is quite high.
I have send a couple of boards to digi2t.
I expect he'll probably have one tested before my regulators and chips arrive.

[mph]

Great !!!
it looks very nice. I really love your pcb's 

Does that mean the problem encoutered by Dino is solved?
what was the culprit?

[UKToecutter]

Pretty much.
His breadboard was playing silly buggers and with all that wire it was pretty noisy.
I guess that's why I just got a short prototype run so that we can 'prove' it.

I should have ordered all my chips before I went on holiday but the boards arrived early so I was caught out.

[glops]

Pretty much.
His breadboard was playing silly buggers and with all that wire it was pretty noisy.
I guess that's why I just got a short prototype run so that we can 'prove' it.

I should have ordered all my chips before I went on holiday but the boards arrived early so I was caught out.

Very Beautiful, as always!

[digi2t]

OK, I've been messing with this on and off for a couple of weeks now, and something is just not cooperating. 

First of all, there was a trace error on the original schematic, so here is the new one. You can click on it, download it, and zoom in.



It's based on this corrected trace;



On the clean side of the mix knob, it's fine, but the wet side is total schisse. Very distorted, with pulsing distorted repeats in the longer delay settings. I've audio probed up to the NE571, and everything sounds OK up to it, but it goes south from there. Andy's sounds about the same. I probed the input of the 7569 on the original, and I have a clean signal going in, with a delayed signal coming out. On the proto board, the signal going in is distorted all to hell.

Anyway, I'm going to keep poking around at this, but if anybody spots something that I should be checking, please hollar. I'm also wondering if this might be a biasing problem with the 570/1, or a board layout problem. I'm going to have to back track here, and compare the two, point by point. I feel another big fat learning curve comin' on....

[Hugomess]

oh man, the pics are gone. does anyone have the schematic saved?