[sdiy] Using AS3320 as a CEM3320 replacement in vintage polysynths

[Steve Lenham]

On 28/01/2021 18:46, Tom Wiltshire wrote:
> 
> Does anyone have any experience to offer having tried this? Are the old 
> and new chips close enough to be direct replacements? Or maybe with a 
> bit of trimming?

Not the most demanding of applications (or in fact a polysynth), but I 
used an AS3320 to replace one of the two CEM3320s in a Linn LM-1.

I found that the Alfa device needed quite a turn of the trimmer to 
deliver the same (fixed) cutoff frequency as the original. Whether this 
is characteristic of the reproduction or just device-to-device variation 
I can't say based on a single sample, but I was close to running out of 
adjustment range. That might be an issue in some designs.

On the plus side, having tried both new and old devices in the same 
socket, I can say that the Alfa part was noticeably quieter than the 
original CEM.

I would definitely replace ICs across the board if working on a poly. 
Far better to have a slight discrepancy between your synth and other 
synths that you don't own and will never hear than a discrepancy between 
voices of the same synth!

One day I intend to do exactly this with my battered Jen Synx 508. Like 
a very very poor man's OBX, the Synx was upgradeable from 5 to 8 voice 
cards, with each one using a 3310, 3320 and 3360. I picked up some empty 
voice cards a while back and mean to fill both them and the original 
five with Alfa ICs.

Cheers,

Steve L.
Benden Sound Technology