Power Supplies?

[Martin Czech]

> >What are well-regarded power supplies for synth modules?  I currently use 
> >a homebrew +-15v supply built up from some 7815 and 7915s and I'd like to 
> >start using something better.  This could make the whole system more 
> >stable maybe.  

Yes, that's a very important question. Could some of the experienced engineers
give a statement here, please ?

My $0.01 :

>Walt Jung has a nice linear supply published in an article in EDN
>Magazine.  
>They can be found at http://www.ednmag.com
>You have to "register" to gain access to the archived articles.
>The article is written by Walt Jung and is in the 01.02.97 issue.

I'll try to dig that up. Rush into the library.

Well, there are 78xx and 79xx from different suppliers on the market, I
think.  They may have very different characteristics if they come from
different fabs.  I checked a 7815 by heating it up (short it, very
hot), the voltage change was about 1% (after removing the short of
course). This is no good  reference voltage.  

>Mind you, the power supply is not normally the weakest link in analogue
>synths. The expo convertors are usually the main source of worry.

Ok for some opamps, but the reference voltage for the expo converter should
be very stable. I worry about that.

I can't say anything about noise, I noticed none (audio !), but maybe
people complain about 1/f noise (i.e. short time drift).

>My long term plan is to use a supply like the one featured in the Digisound 
>system; +/-15V using 723 regulators, precision trimmers, series pass 
>transistors for plenty of current and output protection against excessive 

Some audio projects like preamps  etc. choose 723 indeed.

>......I think a better way might be to put separate regulators on each
>board/module.
>they are cheap enough, and it gives valuable isolation from clock/gate
>transients.
>A large psu, no matter how designed, is IMHO an achilles heel. 

I think this is a good idea, and I'll give a seperate regulator to
EVERY module, or even functional unit. This is cheap today and I can
provide a RC filter network before every single regulator, with a
medium size electrolyt, and a ceramic disk for faster transients.
Maybe also zener diodes and varactors to prevent damage by line
glitches (lightning). Very noisy circuits could get also a series L, to
filter out short transients (in and out).  A distributed set of 10 1.0
Amp regulators drawing 1 Amp alltogether will certainly live much
longer then a central single regulator. No bypass transistors are
needed in most cases.  Also, the heat will distribute via the metal
module housings, so it will be not noticeable.  And another good idea
is to keep  switching currents from relays, leds, everything that's
nonlinear etc. away from audio supply, both vdd and ground. So this
means also having serveral grounds (clean and dirty).  They should only
meet in the central ground point (some ic have already separate ground
pins, be carefull, don't let the voltage across different grounds get
too large in this case, latchup!)


Just my $0.01$