[sdiy] Arp odyssey VCO...

[rob]

Hi Jean-Pierre,
I agree, old designs can be refreshed. The later Odyssey VCO is a
slightly more stable/accurate design than the V1, and is the design I am
currently replicating with a commercially available PCB. The V2 uses a
CA3046 to provide "similar" NPN transistors; this can be upgraded with
more accurate NPN transistor arrays. The V1 uses NPN/PNP matched
transistors which is a bit harder to achieve, although modern
transistors are closer in tolerance than 30 years ago. 

The main upgrade I am implementing is a more accurate power supply to
the VCO core. The originals depend on the 15V synthesizer power supply
providing a stable voltage and this clearly can be improved upon using
local PCB mounted voltage references. However that's still leaves the HF
tracking, how accurate is your VCO at C6 - C8? 

VCO designs from the 1970's are still very usable, but power supply
stability and modern components can really help. I have recently
replicated an E-mu Systems VCO from 1972 and it easily competes with
modern designs. It has a high quality voltage reference for the VCO core
and the frequency pots, and HF tracking via a trimmer (as per the E-mu
Systems Audity) rather than selecting a resistor...  

Regards
Rob
www.emulatorarchive.com



I was looking at the ARP Odyssey VCO schematics
today and was thinking of its simplicity and yet
its wide linearity.. easily 6-8 octaves.
I tested it on my version I (Odyssey 2800).
http://www.physicsenterprises.andrews.edu/diy_archive/manuals/arp/odysse
y/od
y_30.gif
Should it still be considered even with today's
comparator/fet IC's. Just replacing the few needed
parts with new chips and good caps could be a real
good choice for a modular VCO...?
Just my opinion.

Jean-Pierre Destrochers