[sdiy] Temperature Compensated Exponential Converter Using SSM2164

[Richard Wentk]

On 6 Sep 2009, at 22:52, David G. Dixon wrote:

> Neil, I guess I haven't done enough synth diy up to this point to  
> have any
> problems with my PSU.  It seems to be rock solid at the point I  
> trimmed it
> to on day one.  Granted, I'm not loading it very hard, but then  
> again, I
> don't plan to.

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

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.

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.

> In most cases, using the rails as voltage sources for things like  
> schmitt
> trigger references, dc level shifter references, etc, is no big deal.
> However, as you say, given the inexpensive nature of decent voltage
> references (of which I perceive the REF02 to be the "Lexus", if not  
> the
> "Maserati", based on its price), then perhaps we should be  
> sprinkling these
> things around our circuits much more liberally.

It's a better idea to use a single Vref, probably parked on the PSU  
providing a reference rail with reasonable buffering and decoupling.

Using lots of different but equivalent Vrefs is a bit of a waste.

Richard