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?
so. first up, I've entered the power supply section into eagle.
But it seems overly complicated
(https://dl.dropboxusercontent.com/u/19219628/Msynthpower%20supply.gif)
Could I just omit all of this and use a charge pump for -9v???
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 (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...
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 :)
I'd like to know how this turns out. Loved my microsynth in theory, but couldn't find much practical use for it.
Quote from: Scruffie on June 06, 2014, 02:16:03 PM
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...
cross posted w/ DIYSB
sanity check for my schem please?
should this work?
(https://dl.dropboxusercontent.com/u/19219628/squarewave%20jr%20schem.png)
;D ;D ;D
(https://dl.dropboxusercontent.com/u/19219628/squarewave%20jr%20PCB.png)
8) 8) 8)
I'm in for a board or two, once you have verified it, if you have a spare..... I would mind grabbing one. ;D
Digging the additional -9V pad, would be usefull to add a ThirdNut germ booster in there.
Quote from: GrindCustoms on June 07, 2014, 05:26:52 AM
I'm in for a board or two, once you have verified it, if you have a spare..... I would mind grabbing one. ;D
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
Great!
Quote from: the3secondrule on June 07, 2014, 03:20:04 AM
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?
Quote from: kothoma on June 07, 2014, 06:03:23 AM
Quote from: the3secondrule on June 07, 2014, 03:20:04 AM
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.
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 (http://files.effectsdatabase.com/docs/schematics/eh_microsynth.pdf)
any ideas, as I am most definitely winging it ;D
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.
Quote from: the3secondrule on June 08, 2014, 12:00:24 AM
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.
Just use a LM13600, it'll drop in, save those CA3094 for repairs (they're very rare) and save you about $8 or something.
It's exactly the same part internally for the most part, you only need a CA3094 if you need access to the darlington buffer and for some special functions.
Quote from: Scruffie on June 08, 2014, 12:05:37 AM
Just use a LM13600, it'll drop in, save those CA3094 for repairs (they're very rare) and save you about $8 or something.
It's exactly the same part internally for the most part, you only need a CA3094 if you need access to the darlington buffer and for some special functions.
Noted, and schem updated.
If I understand rightly (which I probably don't) Pin 1 (amp Bias) correlates to pin 5 on the 3094, and controls the gain.
I'm not sure what to do with this information though :)
Pin 1 or 5 depending on chip controls the transconductance.
I think (don't hold me to this at all) that pin 5 is being used to basically gate the square wave off depending on your playing dynamics.
I'm not sure how the OTA is doing its thing. But I'd say you'll at least need to include the parts marked FULL WAVE RECTIFIER, PEAK FOLLOWER, and SQUARE WAVE MODULATOR, as you did. But maybe more from that corner of page one?
The lowpass filter tries to make the input signal more sine-wavy. And that is doubled in frequency.
This octave-up signal goes into the peak follower. That looks like creating two peaks per original wave cycle.
But what does the square wave modulator opamp+transistor do? Bias offset?
It looks like that signal makes the OTA reduce gain at the upper and lower peaks of the input signal and so distorting/waveshaping the input signal into something square-wavy?
Why is (originally) more of the envelope follower supplied into the square wave modulator opamp+transistor?
yeah,
I've updated my schem above to include the full wave recto, peak follower and square wave modulator.
Theres some discussion on DIYSB, suggesting that the peak follower / square wave modulator are imposing the dynamics of the original signal on the square wave? http://www.diystompboxes.com/smfforum/index.php?topic=107049.0 (http://www.diystompboxes.com/smfforum/index.php?topic=107049.0)
This is all above my pay grade, I just want to built a crazy fuzz ;)
I see your initial design followed 2) of Keppy's post. That would imply that all waveshaping/distortion is done with opamp A6A. But the gain of A6A seems too low for this.
In 3) Keppy indeed claims that the OTA just (or mainly) reestablishes the original envelope.
He's certainly right that the original dynamics is restored. But I still have the feeling that also essential distortion is introduced here. But maybe I'm wrong.
yup - consensus seems to be that the OTA is responsible for the squarewaving of the signal, and i'm not gonna argue ;)
at the end of the day, I like the fuzz tone enough to want to replicate it as closely as I can, even if I don't necessarily understand the workings...
I think your current design with the A5B/A6B/Q1 path into the OTA could do the trick.
Looking a bit more at the rest of page one I still can't make up my mind if this is needed for the square.
Maybe this has some noise gate function?
Quote from: kothoma on June 08, 2014, 08:59:11 AM
I think your current design with the A5B/A6B/Q1 path into the OTA could do the trick.
Looking a bit more at the rest of page one I still can't make up my mind if this is needed for the square.
Maybe this has some noise gate function?
As I mentioned above it looked like it's there to gate off the square wave.
Having pulled up the factory schematic for the reissue, the OTA is named 'Sustain Modulator' so yes I think it is a gate probably to stop the square from going out of control or glitching too much.
However while it may not strictly be needed I imagine it does impart some qualities on the sound.
Quote from: Scruffie on June 08, 2014, 12:06:50 PM
As I mentioned above it looked like it's there to gate off the square wave.
Right, that escaped my attention... Nice to see my guesswork supported.
Quote
However while it may not strictly be needed I imagine it does impart some qualities on the sound.
Yes, hard to tell from the drawing. At least it doesn't look like a gate used to chop up the signal into a square wave.
Also, any suggestions for fun stuff i can do with the unused half of the 13600?
Yep. Add the slow attack VCA of page two ;)
OK, then you'll need all stuff from page 1 (only no A7B), but you can use the OTA as mixer stage and save one opamp of your current design.
Actually, if I can use the OTA as a mixer, then I'll probably use the final OPamp for a tone stack. I assume the squarewave will need some filtering, since it would otherwise pass through the filter section of the microsynth
Kothoma -got any examples of how I'd use the OTA as a mixer?
Now you make me think, but wouldn't you just feed in the different signals via additional C29/R86s similar to a regular opamp?
Hmmm. I think I'm going to try and build this as per the schem I have now. If I'm only using one half of of the OTA, I might as well go with a 3080 instead? Still in production, and cheaper than a 3094. Aside from the different pinout, is a 3080 a direct sub for half a 13600?
No it lacks the output buffer darlington, you need to add that in.
Yes. But it tends to be noisier.
You could do this and compare:
http://2.bp.blogspot.com/-P7jqffl_ejk/UHVUB0pXl-I/AAAAAAAAC-k/p2HwRW-52S0/s1600/LM13700+Daughterboard.png
13700 and 13600 basically the same.
Sent from my GT-I9100 using Tapatalk 2
Quote from: Scruffie on June 09, 2014, 11:39:03 AM
No it lacks the output buffer darlington, you need to add that in.
Ah ok. Would I need to do anything with the unused half of the 13600? I saw a thread reccomending connecting unused opamp to ground to stabilise them. Would I need to do something similar?
Hmm, as far as I remember, you don't need to do anything special but you can ground the current input... but you might want to do a bit of research as i'm not certain.
just working on a layout for this one, and I had a bit of an idea...
I assume the squarewave signal will need some sort of filtering / tone control. i was thinking about having a couple of pads for send / return after the OTA. would most likely leave them jumpered, but it would mean I could send the square wave to a graphic EQ for some tone shaping. Any thoughts on whether this would be best going before or after the level pot for the squarewave signal?
Love seeing the progression of this!
i think this is good to go:
(https://dl.dropboxusercontent.com/u/19219628/Screenshot%202014-06-15%2018.54.58.png)
Ordered. Once this is verified I'll have a couple of spares if anyone's interested ;)
Quote from: the3secondrule on June 16, 2014, 10:20:46 PM
Ordered. Once this is verified I'll have a couple of spares if anyone's interested ;)
I'm still in! :D
If you successfully figured this one out, I'll be in for one too! I have a microsynth, but only use it for the squarewave and octave features. It's the Siamese Dream sound in a box :).
Me too!
Sweet. Depending on interest, I might look at getting a small run of boards done (assuming the proto's work)
Rej, you'll be pleased to know my next board will be the AD9. Will start on the schem tonight...
Quote from: the3secondrule on June 17, 2014, 04:35:25 AM
assuming the proto's work
Good luck for this!
I'm really curious how it'll sound.
Yep, also interested.
plus 1
In case anyone was wondering where this was at, I received a message on Facebook today, from a kind gentleman in Tokyo who had received my boards from OSHpark 8)
I'm glad I labelled the boards "tinnitus industries", and I'm glad he took to effort to look me up on Facebook. Boards are now en-route to New Zealand so hopefully I'll be building the prototype shortly ...
Sorry, Jeremy, but I've got to laugh at that :)
Quote from: alanp on July 15, 2014, 09:55:12 AM
Sorry, Jeremy, but I've got to laugh at that :)
I had a good chuckle myself ;)
I'm eager to see this working!!
I see this paired with a Kraken as a MicroSynth killer.
Very cool layout, I would love one also.
Cody
All in good time 8)
Need to build it first
Boards arrived. Will hopefully build and verify tonight y'all 8)
Quote from: the3secondrule on July 22, 2014, 05:24:59 AM
Boards arrived. Will hopefully build and verify tonight y'all 8)
Very cool news. Hope it all works out.
Cody
Found another bug in my layout - easy fix though.
Just need to pick up a couple more resistor values, then I can fire it up.
Fingers crossed 8)
We're all pulling for you! If this works as expected, I think everyone is gonna want to build one...wait, how many extra boards do you have? :o
Haha, only two spares, but I've got rev2 ready to send to fab if this works 8)
WE HAVE FUZZ!
Sounds pretty good/nasty too, if I do say so myself.
The octave up is a little glitchy, but the fuzz is massive and woolly - unsure if it needs any filtering, I may still try sending the square wave signal to an EQ pedal to play around with it
Plenty of interest so I'm offering up the boards for $11us ea if anyone is keen. Includes postage anywhere in the world.
couple of caveats - these are proto's, so there's a couple of fixes needed -
a couple of jumpers, and a pad that need to be isolated from ground.
Also, it requires +/-9v, so i'm running it off a roadrage.
first in first served
WOOHOO
Congrats, sounds like you have it working just right. I was jamming with my Microsynth and the octave up is kind of glitchy anyway, that's what makes it such a great pedal. You get a little bit different sound with every pick attack. I'll be down for the Rev2 board when those are ready. Great work!
Quote from: lars on July 23, 2014, 03:25:41 AM
Congrats, sounds like you have it working just right. I was jamming with my Microsynth and the octave up is kind of glitchy anyway, that's what makes it such a great pedal. You get a little bit different sound with every pick attack. I'll be down for the Rev2 board when those are ready. Great work!
Yeah, that's how I remembered my microsynth working, but since it's long been sold, I didn't have anything to compare my pedal against. you can dial out a bit of the gating with the squelch trimmer, it's also fairly interactive with the gain control. (I made this an external control, mostly because I didn't have any 10K trimmers).
Is the octave up fairly thin sounding compared with the guitar signal on the original?
The squarewave fuzz sounds massive on it's own, and positively monolithic with the guitar and octave blended in.
Pretty happy with how this turned out!
Congrats, I'm happy you got this to work. So you'd say you stripped it down just right?
yeah, I'm very happy with how it turned out.
I thought it might've needed some filtering on the output, but the squarewave sound good to me.
The octave up maybe does need some of the highs shaved of the top.
Question for those who know more about OTA's than me - should I utilise the onboard buffer, for the output of the squarewave signal? I can't see why not, but I didn't on my proto...
I didn't notice the octave up sounding thin on my original, I would say it just adds more midrange to the overall sound, kind of hollow-sounding. The octave up notes actually seem to sound louder than the base note. The tracking certainly isn't perfect; sometimes you can hit the same note and not get the same octave up behavior. It depends a lot on your pick attack.
One board claimed, still got one spare. if anyone's keen, PM me ;)
Quote from: lars on July 23, 2014, 11:58:11 PM
I didn't notice the octave up sounding thin on my original, I would say it just adds more midrange to the overall sound, kind of hollow-sounding. The octave up notes actually seem to sound louder than the base note. The tracking certainly isn't perfect; sometimes you can hit the same note and not get the same octave up behavior. It depends a lot on your pick attack.
I ran pretty fast and loose with some of my component values, just so I could finish my build rather jam heading out to buy parts, so that could account for some differences. It's a very fuzzy octave up
I'm going to compare the octave up in the lowrider, I think they share a similar topology. I'll see if there are any differences.
Hallo, im sorry im resurrecting an old post, but this one seemed to be a succesful one. I m a bassist looking fot that synth tone too, would it be possible to upload final schematic again? I imagine there are no pcbs Left. Thanks a lot,
Sergio