Korg PME series Waveshaper

[Rodgre]

Does anyone have the low-down or even a schematic for the old Korg PME multi-effect series Wave Shaper pedal?

It seems like it's some sort of fuzz, but maybe more fun? I'd love to find one, but they're ridiculously overpriced, so I thought maybe someone had the skinny on what was going on in this box.

Roger

[Mark Hammer]

I have one, oddly enough. though I haven't fired it up in years.  There are a whole lotta chips in there, including some LM13600's if memory serves, and a bunch of SIP op-amps.  When you consider that the whole PME series transferred switching and power management *outside* the little modules, what's left in the box makes it a surprisingly dense circuit for a distortion.  I've never attempted to reverse engineer it.

Wouldn't surprise me a bit if it was similar to the Bobby Beausoleil square-wave shaper that showed up in POLYPHONY and which Tim Escobedo simplified and adapted on his site.  I imagine the LM13600's are part of support circuitry intended to keep it sputter-free.  because it's been so long since I've used it, I can't remember whether the wave-shapping capabilities varied with note frequency or not.  If it did, that would most certainly identify the circuit as a variation of a simple attack/decay shaper of a squared waveform.  Who knows, maybe, if it's THAT dense a circuit, it extracts the pitch and adapts the duty cycle so that the waveshape control is similarly effective for lower and higher notes.  If deep in the bowels of this thing were a pitch detector, that would make me a very happy man.

[Rodgre]

Here I am again. Wondering if anyone has had a peek under the hood in the last 15 years. There aren't any great videos or even descriptions of what it does online. The mystery intrigues me but I wonder if you don't hear about it much because it just doesn't sound that good.

Any info?

Thank you

Roger

[Mark Hammer]

I did fire it up recently.  It sounds decent.  Not where-has-this-been-all-my-life but decent, and the sort of thing one would find specific uses for rather than leave on like an overdrive.  The control that"shapes" the waveform provides some usable variation, though I think the midrange control actually does more.  The Sustain control setting is crucial.  That would suggest some sort of threshold-based triggering.

If it didn't have so many wires flying all over the place, I might take a crack at decoding it.  But it would require some time.

[Scruffie]

If you can get some better photos of both sides, I'd be willing to take a crack at it.

I saw in the manual it states it's monophonic so one would assume there is triggering.

Are all the SIP just dual op amps are or is there anything fun?

[garcho]

Wow, I gotta say, seeing something Korg built that looks like that makes me feel a lot better about my own builds 
What's all that weird stuff under the trim pot?

[Rodgre]

Wow. What a rats nest!

It seems like it might be a lot of complicated circuitry to do something kind of one-trick-pony-ish. In my dreams, it's wavefolder and a PWM circuit to make cool synth sounds, but in reality, it's probably just an extreme square wave fuzz that lets you skew the square wave a little? I think I'm just so curious because there is so little info online about it. I've still yet to hear a good demo of what it actually sounds like.

Roger

[garcho]

Like Mark said, if you haven't already, check out Escobedo's "circuit snippets" for simplified square-y synth-y sounding distortions, there are a few he's put out there. I think what makes these cool is not the actual distortion-izing, but what you do with all those harmonics after you square it up.

[Mark Hammer]

1) The shiny stuff seen near the trimmer is just solder flux that leaked through the holes.  There's actually quite a bit of it all over the board.  It only looks like it is centred around the trimmer because of the lighting and angle of the photo.

2) All SIPs are 4558.  All 8-pin DIPs are TL072.  So, ten op-amps and two OTAs, in total.  The smaller transistors are all K2785 and the one TO-92 style transistor by the headers is labelled K81.  There are other numbers on the transistors as well, but I'm naively assuming they are all some 2SK-type.

3) I can probably whip up some time to take a bunch of more surgically-precise photos that might permit the more industrious to attempt a reverse engineer.  You'll need to give me some time, though, since I'd have to assure that all vertically-mounted resistors and cap values are visible or at least documented.

4) Having one doesn't, by itself, make me look forward to a schematic.  However, if there are interesting mods that could be identified, THAT makes me more interested in learning more about the inner secrets, as I would imagine it does for others here.

5) While it does appear to use some sort of triggering, I seem to recall it can handle chords without going berserk like your average analog octave-down unit.  Yet one more mystery to solve.

[Scruffie]

4) Having one doesn't, by itself, make me look forward to a schematic.  However, if there are interesting mods that could be identified, THAT makes me more interested in learning more about the inner secrets, as I would imagine it does for others here.

While a basic clone would be nice to have, that's what I was most interested in, even if there isn't simple mods, it might contain interesting building blocks that could be expanded on.

5) While it does appear to use some sort of triggering, I seem to recall it can handle chords without going berserk like your average analog octave-down unit.  Yet one more mystery to solve.

Trigger might be the wrong word as there's no digital business going on, threshold dependent might be more applicable. But I did see a demo and yes it definitely didn't seem to solely rely on monophonic playing but I assume if you want to actually get a saw wave rather than just distortion, that's the cost.

I would assume half the 13700 is in a compressor duty, especially with the 'sustain' control name, hopefully the other half is doing something interesting.

Some photos would be great when you can get to it.