[sdiy] Temperature Compensated Exponential Converter Using SSM2164

[Antti Huovilainen]

On Tue, 8 Sep 2009, Richard Wentk wrote:

> A lot of classic synth circuits worked just fine with rail refs.

A lot of classic synth circuits were also horribly out of tune on gigs.

> Yes, they're theoretically crappy. But some of that analogue sound comes 
> from unpredictable random variations. If you start putting 
> atomic-precision Vrefs throughout a circuit you'll lose some of that 
> character.

Do you? Have you made A/B comparisons with otherwise equivalent circuits? 
Are the PSU variations truly random and not strongly correlated with VCO 
resets and LFO cycles?... (rhetoric question)

> There's also the cost/complexity issue. If your PSU is designed 
> properly, rails should be stable enough. It's cheaper to design a PSU 
> with reasonable quality than it is to start sprinkling Vrefs throughout 
> every circuit.

I doubt this. References are dirt cheap (you only need stability and 
lowish tempco, not absolute accuracy). "Stable PSU" is an oxymoron at 
microsecond switching speeds (rails have finite impedance).

Finally and IMO most importantly: using local references is much easier to 
get right than making sure 100% of your PSU wiring is optimized to 
minimize interference.

Antti

"No boom today. Boom tomorrow. There's always a boom tomorrow"
   -- Lt. Cmdr. Ivanova