AW: Synth voltages

[Haible Juergen]

	>Regarding synth power supply voltages: 
	>
	>Minimoogs use +/- 10 volts.  
	>Moog modulars use +12/-6 volts (usually) 
	>Serge, Doepfer, etc use +/- 12 volts (usually) 
	>Most others (japanese, etc) use +/-15 volts. 
	>
	>Any thoughts on supply voltages versus S/N, reliability,
heat/drift, sound quality? 
	>
	>I'd be interested hearing any thoughts on this. :) 

Early components often did not withstand 30V. Something like a single
+12V supply was a very common thing. Adding a negative "auxiliary"
voltage was very helpful for setting bias points, current sources for
differential pairs and the like. A negative voltage was very convenient,
but it didn't need to be large, and keeping it small let you use the low
voltage
components of the old days. The EMS with its +12V / -9V supply is
another
example for this.
Today we still use things like CA3086 arrays or CD40xx stuff, which 
can only withstand 15V. I have actually seen +/- 7.5V sub-supplies for
CMOS switches somewhere.
On the other hand, the larger the supply voltage, the larger the maximum
voltage
of an opamp output. Better SNR, better Headroom, more dynamics.
Though most opamps can drive +/-14V with a +/-15V supply, the
*guaranteed* swing 
is only +/-10V. So with a +/-10V supply, only +/-5V swing is guaranteed.
This
makes 50% dynamics at 67% supply voltage, and the ratio becomes even
worse
with lower supply voltages. This is not so important with discret or
ota-based
circuits like synths, but it is very important for filter banks,
vocoders etc.
(I have seen the Designer of the MAM vocoder carefully tweaking the
supply
voltages the get the maximum headroom at some given circumstances - it
is very much optimized.)

Btw, large synthesizers often do not simply use a dual power supply (not
speaking of the digital 5V here), but have several stabilized
sub-suplies.

JH.