This is like looking for the Holy Grail but is there a site containing photos
of track patterns and component lays for any modular units? Kevin had some on his old synthfool site but alas their not on the new site.
thanks
I’ve still got those pics and probably more than I used to host.
Are you planning on building? 
Thanks for reply…I built a 3C replica from schematics about 10 years ago
and am modifying and trying to get it as near to the original spec as possible..I’m using 901B,s.
( Not done the sequencer or the Bode (yet).)
Thinking of reworking the track PCBs and layout if possible hence need any photos for ref:
Also finding that despite meticulous tuning of 901A and 901Bs I only get about two octaves in tune..is this normal for an early 3C ( hence query about 921 osc.)
thanks Kevin
Many Moog modules changed things over the years.
I’ve seen at least 3 901 revs, complete with different PCB layouts.
I’ve seen 5 902 vca that were all different.
A proper 901 should be good for about 4 octaves of tracking.
However the tracking is not completely linear.
There can be dips or peaks where the frequency isn’t quite spot on, even though the input voltage is correct.
This ends up in 901 tracking great for 4 to 6 octaves, but many of the individual notes within that range being slighty off.
Therefore, banks of 901Bs can be individually off, even though they share the same 901A.
I’ve found that if you’re trying to achieve good tracking over a wide range, you actually have to curve trace the UJT trannys and others they use.
They have to be matched.
Along with high quality resistors and caps, things improve over what Moog originally offered.
It’s highly unlikely you can match the exact values necessary for the range switching, even with tacking on additional “trim” capacitors.
You can get close, but rarely will you be able to obtain confident octaves changes and retain the same beat rate with other vcos.
So when selecting the main integrator caps, go for the best high and low range accuracies and fill in the octave caps in between by hand.
It’ll work out easier when scaling.
Either way, cap selection should be done with the VCO well warmed up and in a room at constant temperature.
If you do matching operations, especially with multiple VCOs over several days, they’re gonna be off when played in groups.
As for 921’s, they’re a completely different animal.
They have a temperature compensated current source and considerable opamp buffering betwen waveforming sections.
Range switching is accomplished via matched resistors, which are far easier to match accurately then capacitors usually.
Their waveforms are much more pure (especially the sine) and there’s DC offset and purity adjustments for most waveforms.
Finally, they offer additional modulation and sync inputs and provide hotter levels.
The frequency range is considerable increased too and with less amplitude roll off towards high freqs.
And while they don’t require the additional -10v reference voltage 901s do, 921s do draw considerable more current.
I can provide you with a picture of the PCB of a 921 Osc Driver if you want. I don’t know if that will help you any. Thats the only official module that I currently have.
Eric
I’d like to see it just to know what Modusonics construction looks like! 
Think of these what you will. Im curious to know professional opinions of the construction.
The only discernable difference to the untrained eye is that instead of a rocker switch as found on the vintage units, they used a toggle switch. Personally I think its a superior switch but I know nothing about componants.
Cool! Thaanks for the pictures, Erik!
Those components look awefully lonely on that circuit board! 
Interesting seeing the plexiglass 
supports!
It might have been nice if they had twisted and/or cable tied the wires going to the controls but not a big deal (maybe it sounds better that way? Less cross talk??? 
)
So it uses a card edge connector to power it up? Do you need a special rack to use the Modusonics modules or ???
I’m most interested in Kevin’s L. assessment!
I’m most interested in Kevin’s L. assessment!
As you like it..
Looks ok overall.
Apparently rocker switches were nowhere to be found, so a toggle was used.
Plexiglas is normally found towards the rear, but original Moogs have an aluminum brace towards the front.
Latest revs of 921s had gold plated edge card fingers also.
Grounds not hooked up on PW in jacks, but present on CV ins.
Basically it’s a 921A…
They didn’t have much on 'em and just about everything on Bucki’s looks correct.
Purists might have a problem with the toggle vs rocker, but I can’t see too many areas for gripes.
About the only thing I’d do different (other than seating some of my resistors better is use a a DPDT toggle and double-up the contacts.
That would increase reliability a bit.
Really, no gripes.
Especially because I didn’t have to pay for it!
Thanks Kevin!
What’s the story on the card edge connector? Do Moog modules require a special rack that have the mating connectors attached at the back (like an API 500 series mic pre type rack) or do the power cables just have the appropriate connector?
Yeah That October I opened the box that I had waited several months for and I unrapped the bubble wrap and saw the panel and I was like “WOOOOOOW” then I saw the pcb and I was like “I paid 400 bucks for this???”
Well yeah the design appears simple. It doesn’t have a sound, it just controls up to 3 slaved Oscillators. I imagine that it doesn’t take much to perform that task as opposed to what an Osc does.
Now Kevin, if you have some comparitive shots of this 921A board to compare what Mike Bucki did to the stuff that Bob may have wired up, that woudl be great…But I don’t want this thread to get too off topic.
Eric
Erik,
I still think you should break open a piggy bank and get either a Club Of The Knobs C921B or Mos-Lab 921-B. It just seems like a crime to be denied a VCO to go with your driver! Only 5 euros price difference between them. . . 205 or 200 . . .only about $255 US$ at the moment! You could always sell it down the road when you can afford the Modusonics ones . . . . 
It almost hurts to upload this to my Minimoog.net domain, but here…
I’m sure MC could tear this design apart.
Thanks Kevin. Looks like there are some ‘rough’ solder joints there! 
Do you have a picture of an RA Moog or Modusonics 921B VCO to compare to? Just curious.
Also, sort of off topic but, do you happen to know the name of, if not a part number, for that kind of 14 pin power connector that COTK uses? I want to pick up a few of them and everytime I seach for them I can’t find them! 
Sorry for all the questions , I need to send you a donation or something!
Thanks!
John L Rice
Kevin, John,
According to Mike, when I order my 921B’s I will have to send the 921A back so that he can “tune” them toghether. I think this is the reason why I couldn’t just go and get a 921b clone. But its a very very expensive asthetic addendum to my otherwise Moogerfooger system lolol.
When I send it back to order my 921B, should I ask him to put grounds on the PWM and expect him to do so at no cost? lol
Oh, The dotcom rack frames hold the Moog style modules and the blank panels are a lot cheaper.
Eric
Lets compare…921s from 1977 and they still work great…just tweak the tuning every couple of years…this also has no ground connected at the PW in jacks.
Beautiful!
Did those come from a 15?
When I send it back to order my 921B, should I ask him to put grounds on the PWM and expect him to do so at no cost? lol
No, it’s a very minor issue.
The reason I bring it up that certain manufacturers have claimed that Moog didn’t hook up their jack ground wires because they used lock washers instead.
Of course that assumes that Moog (and anyone else) used lock washers to just provide ground connections, which is completely ludicrous.
Lock washers keep things in place and in Moog’s case, provide some spacing so the jack barrels don’t protrude as far past the panel.
According to Mike, when I order my 921B’s I will have to send the 921A back so that he can “tune” them together. I think this is the reason why I couldn’t just go and get a 921b clone.
Yes, they do need to be tuned together, but who else makes an exact 921B clone anyways?
COTK? Moon Modular?
The 921 (full 921, not A/B pair) PCB I showed here isn’t even remotely close to a real 921. It has CEM3340 in it! (from 1982!)
I would imagine if COTK made a 921B, that would be the case also.
Maybe someone can correct me?
I’m not sure I’ve ever seen an exact 921B clone offered from any manufacturer.
A Moog clone with curtis chips…oh man thats like travesty lololol.
Its all about Van’s serial number tags on the back of the module!
So Kevin, I think I read on the SYnth.com FAQ that Moog often used the panel to go to the ground. Does this sound accurate?
Looking at that PCB of the 921B id say theres quite a bit more going on than in the drivers that makes them a bit more expensive.
So in your opinion, are the Modusonics really “Authentic Reprocuction”?
In your mind do you still consider this a Moog product? I have goten flack on the Synth.com users group because they say its not really Moog, tham im paying for the name only, yatta yatta yatta.
Eric