I’,m getting really cheesed off with drift on my 901b osc’s , the fault of the 901a exponential converter (and amp). Without sampling its virtualy impossible to play/record chamber music etc as tuning is always a major issue.
Has anyone tried any other alternative to the 901a to control the 901b’s?
If at all possible I really want to keep the 901bs on the system. I tried
using a Kenton set to Hz output direct to the 901bs but no joy.
Has anyone tried the Mini’s exp. converter on the 901b’s?
That should read …EXPONENTIAL !
A 901a is a complex way to arrive at a simple solution.
There’s all sorts of matched pairs and they’re all temperature sensitive.
(take your finger and touch a transistor and the pitch will change.)
If nothing else, you’ll probably find that if you seal off the component side of 901a from air flows and drafts AND if it’s calibrated well, it’ll hold it’s tuning better over time.
Arp and Emu understood this concept better than Moog by using sealed modules.
For an example, take the back off an older Minimoog and blow on the vcos.
Arp Odys too.
Blow air around these VCOs and you’ll hear the pitch sail.
Same thing on your 901a.
There’s transistors all over the board and front to rear air flow.
Plug up the jacks and seal it off and it will behave somewhat better.
The 921a was simpler.
Why not make a board with you need from present-day components?
Present-day PCB programs allow you to make 22 pin edge card pins.
I don’t think it would be too hard to find a talented tech to make a better expo converter and driver that adheres to Moog’s specs.
Thanks Kevin
Great (synth)minds think alike !!! thats what I have been musing on this past month to re- work the 901a but not being to up on electronic theory
Ive got a hard task but sure I will get there.
The 901bs just sound SO good compared to other stuff..for the chamber music I’m doing they are pefection, I hear REAL cellos and REAL brass etc in them etc etc (only better)