Moog Music Forum

Last calibration to be done in my system 55 (before sending the ... temperamental modules to the K... ing L for a careful check) is the one reported in the object.
Honestly, I am not a tech, neither am I totally analphabetic (low level english, but sufficient), but I believe that who wrote the manual had smoked something bad that night : "Apply fixed output SAWTOOTH to another VCO control input. V-trig clamping by patching from AUX OUTPUT SAWTOOTH."
I guess to get a periodic modulation of the VCO at a fair frequency.
"Turn clamping point to 98% - ON THE PANEL THERE IS NOT 98% , the range goes until 90%) and adjust F for lowest possible clamping point". How? oscilloscope? By ear?
Any interpretation is welcome

This isn't as hard or critical as it appears.

First, use your ear. A scope might help, but you won't need it.

Set the front panel clamping knob to any high value.
A 90% panel marking IS about 98% of the pot's travel.
The idea is just that you want some additional travel of that pot later to allow zeroing in on a clamping input.

You'll hear a subtle pitch warble and you're to adjust the trimmer to the maximum effect with that panel pot not quite fully up.
Afterward, the front panel control should be able to find that "sweet spot" again.

Btw, the clamping input isn't something used that often, but can be interesting when used with the 960 sequencer.
For example, try clocking the sequencer from that 921 and taking individual seq stage triggers into the clamping input.

Rocket science.

I understand all of this analog stuff. Got it. Took me a while. But the 921a/b system baffles me.

Can one of you guys explain to me what the 'a' does and why it is required if you are "playing via sequencer or keyboard"; Also, what if you want to play two different sequences to one OSC each; is that possible or do you need two 'a' modules also?

And what is clamping, and why does it output some derivative of voltage (1.3 something) instead of 0..5; Terry once explained to me how you can double up and triple up the voltage and it almost made sense at the time (he speaks quickly : ).

Is there a guide that outlines the diff between the way that modern OSCs are structured and how the 921 series works?

I just talked myself off of the MOS-LAB ledge yet again (and am instead buying a few single space OSCs of different types). But ultimately, I think I'm destined to own a set of 1x'a', 3x'b' and the switching module. I just have to have it. I hit Seb with a question or two now and then but feel bad because he's busy with real work : )

Thanks.

EMwhite wrote:Can one of you guys explain to me what the 'a' does and why it is required if you are "playing via sequencer or keyboard"

The important function of the 921A module is to provide linear to exponential conversion. Without it the 921B will not track to the v/oct standard of the keyboard and sequencer. If two or more 921Bs ganged to a 921A are set at different pitch intervals, the 921Bs will maintain their intervals. The "frequency" control on the 921A controls any 921B ganged to it. If you want independent intervals or polyphonic control, you need more than one set of 921A/B.

Also, what if you want to play two different sequences to one OSC each; is that possible or do you need two 'a' modules also?

You need (n) 921A modules to play (n) sequences