So how did i spend the last months? Well with the RMIF OPUS!

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synthiaks

Well-known member
Joined
Oct 8, 2013
Messages
278
Location
Berlin
Hello everybody!

I thought that i should post some info about a repair project that has taken up A LOT of my spare time lately. I know this isn't the place where much synths gets discussed but what the h*ll, this is where i lurk the most so why not.

I giver you the RMIF OPUS!
 

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This guy looks like something made in the 70s but as far as i could tell my unit was produced after 1989. some of the caps inside had 89 printed on them...

Its a polyphonic analog synth made in the Soviet union (Or just after they were no more). Mine didn't work at all the Power LED did light up but no sound at all. Well lets open it up then...
 

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WTF...

So some of you might have suspected this when i said "Polyphonic analog synth" but this is  based on octave dividers and a main oscillator. Lets take a closer look at that mess!
 

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so now some of you maybe understand my sudden interest in Octave divider ICs from the former Soviet union. This thing is like Organ technology but made in the late 80s. It has a classic state variable filter, a ring modulator(!??) and a nice chorus.

 
Im going to post a Little more in detail what I did to this unit. And also provide some audio. Just lost some time this week!

:)
 
Haha, I knew someone would comment on that.  :)

You haven't heard the Opus yet though! This synth is RAW!
 
I suspect this unit was made somewhere 89-90 (crazy...) I was hoping for the SAJ to (As i have 4 of them), but the Dividers in the soviet synths should be some clones of the MM5824N, however I'm not quite sure of that.

I had 4 of the Dividers broken, but eventually found some similar Soviet IC that would fit with some modification. 

Here is my long "Me/Myself" conversation about it:

https://groupdiy.com/index.php?topic=73443.0

The Main Oscillator was also not working so it all started out with NOTHING. No sound anywhere... I eventually found the Broken OP amp, I just put an 741 in there and it seem to work fine. All in all the thing has like 25 PCBs and i must have found about 15 broken OP-amps in there.

The thing looked like it had been spending 10 years in a cold/Wet basement here in Berlin. 25% of all the transistors were showing Oxidation on some of the legs and had no Contact. By the way, those Soviet KT315 transistors look so cool.

I recaped all the cards. And only that was like 2 days of desoldering.

After a closer look at the schematics i realised that the Ringmod card was the same as the 3 other "Tremolo" cards but with a smaller Capacitor so i just made the Tremolos "High speed" switchable, voila... 4 Ringmods!

The Sub bass part was not going through the Filter or the Chorus so i made that selectable.

the filter was always (!!?) running through the Chorus, i found that a bit stupid so i also have a switch for the filter parallel to the Chorus at the output amp.

The only mod i unsure of is a change of resistor in the Resonance feedback path in the State variable filter. Im not sure if it is possible to get more resonance that way or if i'm only changing the filter Response.  (ooh... The Math..)

I haven't fine tuned it all yet but the thing sound so "Good"! Not like a Pro5 or Memory Moog good.. But like Weird/Good.

Lastly, i would not recommend anybody to take on this synth for a client as a "Repair Job" its just to crazy. But as a Project to Learn and get into Soviet IC/Schematics/Alphabet and general Fault checking skills... This is the bomb!

Sound will come

S
 

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Cool!
Is it more like an organ (i.e. Farfisa) than a polysynth (i.e. Juno)?
How many keys can sound at once? 
 
These orange bustards are a local meme among (post-)Soviet engineers. The factory/lab where it was developed is nearby my studio, a friend of mine works there, makes guts for satellites.
 
dmp said:
Cool!
Is it more like an organ (i.e. Farfisa) than a polysynth (i.e. Juno)?
How many key s can sound at once?

Yeah, its Organ tech but with synth parts. Some of the Crumars (compact) did use the same technology but with the SAJ chip.

All keys Kan sound at the same time The master Oscillator feed the 12 octave divider chips with 12 high Frequency  notes that get divided down. So 12 cards with  5 octaves on each.

The cool thing with it is that normally these poly/organ/synths are quite boring and limited but this one has slightly more possibilities which makes it interesting. You can squeeze quite a bit of different sounds from it. With my few basic mods even more.

@dbelousov:

I have read about them quite a bit. They seem prone to fail, look cool though. I even ordered some just for fun.

S
 
It was a "default" transistor for every Soviet engineer for decades. It and its PNP brother КТ361 were literally in everything,  and even SMD versions are available now. There are more photos http://www.155la3.ru/kt315_361.htm
 
synthiaks said:
I suspect this unit was made somewhere 89-90 (crazy...) I was hoping for the SAJ to (As i have 4 of them), but the Dividers in the soviet synths should be some clones of the MM5824N, however I'm not quite sure of that.

I had 4 of the Dividers broken, but eventually found some similar Soviet IC that would fit with some modification. 

Here is my long "Me/Myself" conversation about it:

https://groupdiy.com/index.php?topic=73443.0

The Main Oscillator was also not working so it all started out with NOTHING. No sound anywhere... I eventually found the Broken OP amp, I just put an 741 in there and it seem to work fine. All in all the thing has like 25 PCBs and i must have found about 15 broken OP-amps in there.

The thing looked like it had been spending 10 years in a cold/Wet basement here in Berlin. 25% of all the transistors were showing Oxidation on some of the legs and had no Contact. By the way, those Soviet KT315 transistors look so cool.

I recaped all the cards. And only that was like 2 days of desoldering.

After a closer look at the schematics i realised that the Ringmod card was the same as the 3 other "Tremolo" cards but with a smaller Capacitor so i just made the Tremolos "High speed" switchable, voila... 4 Ringmods!

The Sub bass part was not going through the Filter or the Chorus so i made that selectable.

the filter was always (!!?) running through the Chorus, i found that a bit stupid so i also have a switch for the filter parallel to the Chorus at the output amp.

The only mod i unsure of is a change of resistor in the Resonance feedback path in the State variable filter. Im not sure if it is possible to get more resonance that way or if i'm only changing the filter Response.  (ooh... The Math..)

I haven't fine tuned it all yet but the thing sound so "Good"! Not like a Pro5 or Memory Moog good.. But like Weird/Good.

Lastly, i would not recommend anybody to take on this synth for a client as a "Repair Job" its just to crazy. But as a Project to Learn and get into Soviet IC/Schematics/Alphabet and general Fault checking skills... This is the bomb!

Sound will come

S

synthiaks = Герой Социалистического Труда  ;D

 

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rock soderstrom said:
synthiaks = Герой Социалистического Труда  ;D

Awwww.... Stop it!! ( turning embarrassed red )

here are some sounds, and NO i don't play keyboard well

https://drive.google.com/open?id=1so5eOUEann_4iMXL1vHYAwQsoGDy5bJR

S
 
So I PM'd OP re: Soviet divide down synths, as I have a TOM 1501 with issues most likely related to the divide down circuits. (I'm not that skilled at repair, and will likely have the guy working on my Quadra take a look at it.) It's very similar in sound to the Crumar Orchestrator/Multiman, which is a sound I do favor.

Except the main divider chips are the same but apparently very oddball with 16 pins instead of 14. I'm currently trying to source replacements. The war in Ukraine has made that more difficult. No one in Belarus or Kazakhstan as responded yet, and I'm having to use Google Translate!

As an aside, there's a guy in England who makes plug in replacements for a bunch of 14 pin octave dividers and top octave generators. FlatKeys Home

I can start another thread once I get deeper into this thing.
 
Hey and thanks Dir your Story
I’m curious to make some mods to my Opus to’ and could need some help finding my way through this synth as i’m not able to reed Russian ;-/.. would be grate to have som help to find where are the write cards .. also I would be happy to know what kind of CV voltage is controlling the ring mod etc. Would you give me some information on the spot where you leading the Bass to filter mod!?’ Would be so good to get some more Orientation ..;-))! Let me know
Regards from hamburg
 

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