Shed some light on the Moog 921-A Oscillator Driver

[eXode]

Hi,

Is there someone on this forum that could describe how the Moog 921-A Oscillator Driver works? I see that there's only one control for pulsewidth control in each group of 3 oscillators (Moog 921-B). Does this mean that you can't have different pulsewidth settings on 921-B oscillators in the same driver group? Also I'd like further descriptions on how the Driver works.

Thanks in advance!

[EricK]

The driver is a control module for the 921B's. I believe that you can have up to 5 chained together.

Basically all that I can answer is that the 921B's can operate independantly in LFO mode, but in order to track @ 1 volt per octave they have to be controlled by the driver.

THe driver module contains the pitch control inputs, and the rectangular wave control inputs. The outputs are hardwired to the connector pins on the back of the module (rectangular width control being on pin 6 on the 921b).

See moogarchives.com for details. Click on instruments and modules and 921a and b and see the technical specs.

Some other members here can give you even more information.

I have a 921a with no power supply and no associated 921b (yet).


Eric

[eXode]

Thanks for the reply!

I looked into moogarchive and found the answers I was looking for. It is as I suspected that the driver functions as a 'master' to all the oscillators in it's group. It means that the pulsewidth is indeed set on all connected oscillators simultaneously in that particular group. In other words you would need 3 of each (921-A & 921-B) to have 3 oscillators that can have individual pulsewidth settings. It's a shame that the oscillator nor the driver don't have a switch on the front to select between driver width setting or default standard square. If you are building a larger system I guess it would be OK because you might have 9 oscillators or more but for a entry system of just 3 oscillators and one driver it feels like it leaves you slightly crippled.

For reference of what I'm talking about. I was looking at the MOS-LAB SYSTEM 16 A (Click MODULES, scroll down the list and click on SYSTEMS).

[EricK]

Wouldn't the 921 VCO solve your problem then?
3 oscs = 6 spaces

[Just Me]

Or S.Com Q-106 Oscillators. They stand alone and don't need a 'driver' to control them.
http://www.synthesizers.com/q106.html

[eXode]

Wouldn't the 921 VCO solve your problem then?
3 oscs = 6 spaces

Do you mean the COTK 921 VCO? Yes It would indeed solve that problem.

Or S.Com Q-106 Oscillators. They stand alone and don't need a 'driver' to control them.
http://www.synthesizers.com/q106.html

Yes I've been thinking of that as well. I know that you can ask COTK to do their modules with .com powering so you can mix and match as well, if you need to.

It's just that for an european the MOS-LAB 16A seems to be quite an attractive package.

But that's another matter entirely, go for MOS-LAB or go for DotCom and mix with COTK stuff.

[EricK]

Those 921's will work too. I like the system 16 and I like the way those MOS lab and COTK systems work, and I like the idea of dotcoms.

Theres one thing though that I think is really important though, and that is the Original spec Fixed Filter banks. Having an eq using pots is one thing (like the dotcom) but a member brought up that it's the torridial coils that really adds to that "Modular" sound.

So Im going with modusonics on modules like that, expensive as they may be and Im banking on Mike coming back to the grid and operating under normal circumstances again.

EDIT: IM NO LONGER GOING TO DO OR TO ENCOURAGE ANYONE TO DO BUSINESS WITH MIKE BUCKI OR MODUSONICS DUE TO HIS FAILURE TO RECTUFY NUMEROUS INSTANCES WHERE CUSTOMERS HAVE FAILED TO RECEIVE THEIR MONEY/GEAR BACK FROM HIM.


Eric

[MC]

The 921A includes the all important linear to exponential conversion circuit. It converts the linear V/oct to exponential current that "drives" the oscillator to produce frequencies on an exponential scale.

The reason the driver was separate back then was tuning drift. The design of linear to expo converters hadn't yet matured and that's where much of the tuning drift was. It was a lot easier to get three VCOs to track from a shared driver. Back then if three VCOs had independent linear to expo converters, there wasn't a chance in hell they would track.

Without the 921A driver, you'd have to drive the 921B VCO with a v/hz controller. Which is the hard way to do it.

[oakpal]

This has probably been addressed somewhere in the forum, but I can't find the answer.
I have a Moog 1C with 921 series oscillators. I want to add additional 921B oscillators to
this system. Which of the clone brands will work with the original Moog 921A? I understand
there may be power supply issues, but I am concerned about the control voltage and pulse width
links between the modules.

Thanks

Peter Lutz