EHX microsynth squarewave fuzz (or suggest another squarewave fuzz)

[the3secondrule]

Hey guys,

I remember my old EHX microsynth being one of those pedals that was super awesome fun, but not hugely practical - except for the squarewave - man, I must have used that for everything in one of my old bands.

So I was thinking I'd try and whip up a schematic for the squarewave only - or maybe clean/squarewave/octave up. assuming I could get such a thing happening, would there be any interest in getting some boards made?

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Or, can anyone suggest a similarly gnarly sounding squarewave fuzz I could build?

[the3secondrule]

so. first up, I've entered the power supply section into eagle.
But it seems overly complicated


Could I just omit all of this and use a charge pump for -9v???

[the3secondrule]

Next question ... hopefully someone who knows will have a look at this

I'm working from the schematic here: http://www.harpamps.com/schematics/bsynth1.pdf
I'm way out of my depth here, but it seems like the sections around smoothing filter/peak follower/trigger and stop/start detector could be omitted? not sure...

[Scruffie]

Someone posed this very question on DIYSB recently - http://www.diystompboxes.com/smfforum/index.php?topic=107049.0

Read the second post, make clear what you want and can take it from there

[thesameage]

I'd like to know how this turns out. Loved my microsynth in theory, but couldn't find much practical use for it.

[the3secondrule]

Someone posed this very question on DIYSB recently - http://www.diystompboxes.com/smfforum/index.php?topic=107049.0

Read the second post, make clear what you want and can take it from there

Wow! Thanks Scruffie. I didn't even think to see if anyone else had tried this.
Wonder how it worked out...

I have everything up to the Octave up entered into eagle. will need to tack a mixer/output on the end i'm guessing, to mix the octave/square/guitar signals. maybe a passive tone control as well...

[the3secondrule]

cross posted w/ DIYSB

sanity check for my schem please?

should this work?

[the3secondrule]

 

[GrindCustoms]

I'm in for a board or two, once you have verified it, if you have a spare..... I would mind grabbing one.

Digging the additional -9V pad, would be usefull to add a ThirdNut germ booster in there.

[the3secondrule]

I'm in for a board or two, once you have verified it, if you have a spare..... I would mind grabbing one.

Digging the additional -9V pad, would be usefull to add a ThirdNut germ booster in there.

All good ... i'll keep this thread updated with any progress. I'll be adding the octave up circuit once the squarewave is verified as working too

[GrindCustoms]

Great!

[kothoma]

should this work?

This looks just like amp-lowpass-amp-mix to me. I would have guessed the magic square wave shaping happens in the OTA you left off. But what do I know?

[Scruffie]

should this work?

This looks just like amp-lowpass-amp-mix to me. I would have guessed the magic square wave shaping happens in the OTA you left off. But what do I know?

I would be inclined to agree seeing as it is just a 3rd order sallen key driven by a non-inverting gain stage in to an inverting gain stage as you say, i'm guessing that low pass filtering is partially used to stop the OTA from going in to too nasty a distortion.

[the3secondrule]

So, if i was to omit the peak follower and squarewave modulator, but add the OTA in, can I just disconnect pin 5 of the OTA, or will it need to see some current to function properly (OTA's are a bit of a mystery to me still).

referencing the schem here, FYI: http://files.effectsdatabase.com/docs/schematics/eh_microsynth.pdf

any ideas, as I am most definitely winging it 

[the3secondrule]

Schem updated. used a 3080 as I don't have a part for 3094 in eagle. I intend to build it with a 3094 though, as they are still available from smallbear.