Micromoog tuning

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atkbg
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Micromoog tuning

Post by atkbg » Fri Sep 15, 2006 3:59 pm

Does anyone here have experience correcting a micromoog drift?
The issue is when a key is released, the pitch drifts down.
The power supply has been rebuilt and is putting out a steady +/-15v.

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Maschinengeist
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Post by Maschinengeist » Sun Sep 17, 2006 6:26 am

I can get you the service manual (in PDF) for $5.00. Everything's there for the micromoog.

Email me for details
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Post by atkbg » Wed Sep 20, 2006 2:19 pm

I believe I've traced the issue down to c212 which is .27uf,50v @ 20%. This cap is charged with the voltage from the keyboard. While the key is depressed, the cap is continuously loaded. When the key is released, the voltage should be held until drained by the utility buffer. The schem states the cap is polycarb, which, to my knowledge, are no longer available.

Does anyone know of the best replacement? Aluminum electrolytics and mylar are available from mouser in this value.

If this doesn't stablize, than I'm going to have to check throught the utility buffer.

Any input is greatly appreciated.

Thanks.

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Post by shagghie » Mon Nov 27, 2006 8:51 am

atkbg wrote:I believe I've traced the issue down to c212 which is .27uf,50v @ 20%. This cap is charged with the voltage from the keyboard. While the key is depressed, the cap is continuously loaded. When the key is released, the voltage should be held until drained by the utility buffer. The schem states the cap is polycarb, which, to my knowledge, are no longer available.

Does anyone know of the best replacement? Aluminum electrolytics and mylar are available from mouser in this value.

If this doesn't stablize, than I'm going to have to check throught the utility buffer.

Any input is greatly appreciated.

Thanks.
Did you ever trace this down and fix it? if so, please post what cap you went with and what the results were... ta!

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Post by Maschinengeist » Wed Nov 29, 2006 7:28 am

In 2000, the polycarnonate has been withdrawn from manufacturing.

Find below what's recommended as replacement of the polycarbonate capacitor
www.charcroft.com wrote:The most common suggested alternatives to polycarbonate (PC) are polypropylene (PP) and polyphenylene sulphide (PPS) although polyester (PET) may be suitable for capacitance tolerances of 5% and above. Polyphenylene sulphide provides performance characteristics which are closest to polycarbonate film but it is also subject to the risks associated with using sole-sourced raw materials. Designers therefore may wish to consider polypropylene film which has a lower dissipation factor across the entire temperature range. For higher tolerance applications, polyester film, which matches the capacitance stability of polycarbonate over time but not over changes in temperature, may be suitable.
If you still want a polycabonate capacitor, you can find it if you know where to look. Warning: since their rarity, they sell at not exactly clearance prices.
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atkbg
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Post by atkbg » Wed Nov 29, 2006 4:04 pm

The issue ended up being trimmers. After recapping the power supply, testing voltages around the sum and osc itself that all came out OK, I just replaced the trimmers.
I still need to replace the filter scale trimmer. I have a few on order.

As far as the poly cap, I left it in place. The downward pitch is only a few cents per second if the key is released and I haven't found it to be *that* much of an issue. I'm also not sure that it is the cap. It could be fet. However, changing the cap with a slightly higher/lower value only changes the amount/speed of the glide, so an exact match is not necessary. So, I may swap out the cap in the near future.

I LOVE this keyboard! Its so much fun! Shaggie, did you get the one with the plywood bottom the other day? I see you have the sinch-jones plug on order. I'm really interested in hearing what you come up with on that.

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Post by shagghie » Wed Nov 29, 2006 6:48 pm

atkbg wrote:
I LOVE this keyboard! Its so much fun! Shaggie, did you get the one with the plywood bottom the other day? I see you have the sinch-jones plug on order. I'm really interested in hearing what you come up with on that.
LOL, I don't remember one with plywood bottom....help me out a bit.
I was looking at this one, to add to the one I stumbled on at GC over T-day weekend:

http://cgi.ebay.com/Vintage-1976-MicroM ... dZViewItem

But that one looked a little iffy, so I passed. If it was $300 I would have snatched it up, but otherwise, too much risk.

Yes, I did order the plug...and my understanding is that it is used for when you want a constant trigger so as to be able to run audio through the filters, yeah?

I'm still trying to source a midi-to-cv solution that allows me to scale down to .95v/octave.

Here's a question, is there any reason I couldn't take one of those SYNHOUSE.com midi conversion kits made for the micromoog, and just build my own little box just for it with 1/4" jacks and a PSU? This way I can leave the micromoog unmolested, but still have a decent midi-to-cv converter box that is pre-scaled to .95v/octave. Anyone here done this before?

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Post by atkbg » Wed Nov 29, 2006 11:14 pm

The micro I was referring to was too much at $350 and if it had plywood, than *someone* had been in there making god knows what mess.

Not sure on the Synhouse box, but it sounds like it should work.

I'm actually looking to make a 1v/oct controller (bass pedals). It has a fine adjustment to bring it to .95v. I've found the schematic for one on Ken Stones site:
http://www.cgs.synth.net/modules/cgs10_pedal.html
and I've already got the pedals. I'm going source out the parts and see how much its going to take.

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Post by shagghie » Wed Nov 29, 2006 11:34 pm

atkbg wrote:The micro I was referring to was too much at $350 and if it had plywood, than *someone* had been in there making god knows what mess.

Not sure on the Synhouse box, but it sounds like it should work.

I'm actually looking to make a 1v/oct controller (bass pedals). It has a fine adjustment to bring it to .95v. I've found the schematic for one on Ken Stones site:
http://www.cgs.synth.net/modules/cgs10_pedal.html
and I've already got the pedals. I'm going source out the parts and see how much its going to take.

Wow, how cool will that be? The Micro would make a fine bass synth that route, IMO. The question i have is how/if you will control filter cuttoff via CV with that setup?

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