Layout for a micro-synth?

[Mark Hammer]

As noted in another thread, I have an EHX Guitar Micro-Synth on the repair bench.  I have pretty well all the schematics I need for it, but there are ONE HELLUVA LOTTA CHIPS ON THE BOARD and none of them are identified by any legending.  I could really use a component layout map or drawing of some kind so I could probe in the relevant places.

For now, it doesn't trigger or produce any sound other than the straight guitar signal.  The filter "works" but doesn't sweep.  Resonance works and both Start and Stop Freq controls will change the filter setting.

It's the first issue, or close to it, using the 5554 dual regulator, with no power-on indicator LED.  Has a pale green PCB.  If you could direct me to a legended pic or layout drawing, that would be terrific.

Thanks

[Scruffie]

I think there was an issue of Poly on your site that had some mods for that version which might have had some indicators.

[cjlectronics]

I've repaired a few micro synths over the years and I had to sketch a layout to make any progress.  As you can see, I had to redline my sketch. Hopefully it's enough to get you in the ballpark.  I also have the Functional check list and debugging list. If you need'm lemme know

The last one I repaired had a bad dual regulator IC.  I had to wire in a 78xx and 79xx regulators to get the power supply running. It worked great after that.  Good luck with the repair. 

[Mark Hammer]

I think there was an issue of Poly on your site that had some mods for that version which might have had some indicators.

It was Craig Anderton's mods in DEVICE, which I must have recalled and dug up about the same time you did.  And yes, they appear to refer to the same pedal issue as the one I'm working on.  I think I will do some of the suggested mods, given that the drawings correspond to what I see.

I've popped off a note to EHX's tech support.  Will they have a parts layout diagram that is 40+ years old?  Maybe, and maybe not.  CJ's drawing may be of use.  So thanks for that, buddy.

The trouble with the pedal is that the only chip that is distinctive is the dual regulator, and it's fine.  That leaves umpteen 4558s and 3094s, with little to distinguish their function unless I do a near-complete reverse engineering of the board.  I'm just trying to get the thing off my bench so I can get to my own projects.

[FUZZZZzzzz]

something maybe completely off topic:

In 1977, when I returned to New York in between trips, Mathews expressed an interest in developing the 6 Channel Pickup system to drive a guitar synthesizer, but it proved to be  too inconvenient.  Mathews  opted to develop an all analog  "stomp box synthesizer" and teamed me with his chief engineer David C0ckrell,  a former electronics expert for the British Navy.   Working with C0ckrell, we devised a  method to modify and shape an analog guitar signal to make it generate "other worldly" guitar sounds. Within a month,  we had a working prototype that featured a combination of a unique touch sensitive fuzz, a sweeping graphic equalizer, upper and lower octave generator, and an envelope follower with variable attack/decay settings.  It was dubbed "The Micro Synthesizer", the first stomp box synthesizer  for guitar.    Guitarist Jimmy Page used a  Micro Synthesizer on Led Zeppelin's recording of "No Quarter".

Maybe try to contact this guy directly.

https://captain6string.blogspot.com/

[pinkjimiphoton]

maybe Ronnie Neelie got one for ya Mark?
i'd contact him but am presently on sebatical from the book of farce
for refusing to submit to their draconian and pc views on freedom for all...

that said, i can't think of anything on no quarter that resembles anything possible with a microsynth.

clone theory? all over it. but micro synth?

mebbe just me

last microsynth i messed with was abandoned with me as unrepairable and not working.

turned out on the underside of the pedal were a couple trimmers that were accessible thru a couple holes, i guess so you could set the volume of the effect etc.

someone had twisted 'em off. so no output.  i turned 'em back up and had a blast with it til it sold

[Mark Hammer]

something maybe completely off topic:

In 1977, when I returned to New York in between trips, Mathews expressed an interest in developing the 6 Channel Pickup system to drive a guitar synthesizer, but it proved to be  too inconvenient.  Mathews  opted to develop an all analog  "stomp box synthesizer" and teamed me with his chief engineer David C0ckrell,  a former electronics expert for the British Navy.   Working with C0ckrell, we devised a  method to modify and shape an analog guitar signal to make it generate "other worldly" guitar sounds. Within a month,  we had a working prototype that featured a combination of a unique touch sensitive fuzz, a sweeping graphic equalizer, upper and lower octave generator, and an envelope follower with variable attack/decay settings.  It was dubbed "The Micro Synthesizer", the first stomp box synthesizer  for guitar.    Guitarist Jimmy Page used a  Micro Synthesizer on Led Zeppelin's recording of "No Quarter".

Maybe try to contact this guy directly.

https://captain6string.blogspot.com/

Thanks so much for that.  It actually connects a number of dots I always wondered about.  I had wondered why the Snarling Dogs overdrive pedals were so similar to the Hot Tubes, and now I know why.

He may well be someone who might also know something about the Guild Tri-Oct, that I have been trying to find out more about.  Sent a connection request on Linkedin.  Perhaps that can provide some follow-up.

[StephenGiles]

        0.9 MB    Microsynth layout1.jpg                                                                                                               


Is this any help Mark?

[ElectricDruid]

Maybe try to contact this guy directly.

https://captain6string.blogspot.com/

Very interesting. That's certainly a lesson in how *not* to enter the pedal business.

T.

[Mark Hammer]

        0.9 MB    Microsynth layout1.jpg                                                                                                               


Is this any help Mark?

That could be the ticket, Mr. G.  Many thanks.

[StephenGiles]

I drew that out around 1980-81, luckily it was still in my EH papers file, and luckier still my 14 years old scanner worked!!

[Mark Hammer]

Old scanners still working is not the miracle.  Having drivers for something that "ancient" IS.  I'm looking at a couple of scanners at the moment that probably aren't any older than that, and maybe not even that old, that won't run on anything past XP or 98.

[StephenGiles]

Old scanners still working is not the miracle.  Having drivers for something that "ancient" IS.  I'm looking at a couple of scanners at the moment that probably aren't any older than that, and maybe not even that old, that won't run on anything past XP or 98.

Mine is a Lexmark 1100, the printing function packed up several years ago, but the scanner albeit very slow still works quite well. The OCR is very good.

[StephenGiles]

From memory Mark, the output amps for were CA3094s, which is bad news if they need replacing, although again from memory if the 3094 output is from pin 1, a 3080 should work but would need a little re-routing of pcb tracks so probably not a good idea.

Are all connections to the sliders good? I remember the wires in the model I had were not at all flexible and could easily break a solder joint.

[Mark Hammer]

I still have a handful of 3094s left, though more 3080s.  Hopefully it will be an errant 4558.

[DiscoVlad]

These are the boards from my '90s reissue Micro Synth, which uses the 4558 + 2N6110 (or 2SB826 in this case) power supply rather than the 5554. The large chip is the 4013, but everything else is clearly labelled. Maybe it's helpful?

[Mark Hammer]

Appreciate the offer, but it's substantially different than the early-issue boards.  Thanks for the thought, though.  I think Stephen's hand-drawn layout will provide 85% of the identifying info needed.

[Mark Hammer]

Getting a little closer.  Replaced two 4558 chips and got the sub-octave.  But no distortion or octave-up yet, and no sweep.

Bit by bit.

[Mark Hammer]

Replaced three dual op-amps so far and I have triggered sweep.  All that's missing is the distortion and octave-up voice.  Yes!

[StephenGiles]

Great stuff Mark, I wonder what caused the 4558s to fail??