ASM-1 and power supply problems...

[jorgen.bergfors at idg.se]

Don't use switching regulators in an analog synth! They might cause problems 
like the one described and besides, they're just too un-vintage. Also the 
fairly moderate current requirements don't justify them. Use one with a 723 and 
a large bypass transistor instead. The 723 precision voltage regulator is the 
perfect choice for this kind of application. I use the PSU from the Formant, 
which is excellent. You can get the Formant schematics from Anders Sponton's 
site. http://www.tellus.vallentuna.se/gymninfo/personal/anders/andersus.html

/Jorgen




MIME:aschrock at cs.brandeis.edu on 98-04-23 16.14.57
To: oncken at umr.edu @ SMTP 
cc: synth-diy at mailhost.bpa.nl @ SMTP  (bcc: Jorgen Bergfors/IDGSE)
Subject: Re: ASM-1 and power supply problems...

On Thu, 23 Apr 1998 oncken at umr.edu wrote:
> 
>    Now for the questions... I have a +-15 volt power supply for the ASM-1 
> It was purchased at a surplus electronics store for $20.  It worked fine 
> at first, but after it was installed in the case it started SCREAMING at 
> me.  It makes this annoying high pitched whine whenever its plugged in.  
> It not only comes through on the audio out of the synth, but you can hear 
> it comming from the power supply itself.  The power supply seems to 
> power the synth just fine, but the whine changes very slightly in pitch 
> in response to the LFO... 
>    
>    Anybody have ideas about whats causing this?  Have I done something 
> terribly wrong?  Is it a common problem with power supplies?  Most 
> importantly, can you tell me how to fix it?  

I had horrible problems with noise and LFO bleedthrough until I switched
power supplies. I was using one which was arguably too cheap... after
switching I haven't had any further problems. I switched to a MAP platinum
power supply, since I didn't have the time to design one myself. 

Andrew