EH-16 second power supply strangeness

[Tim Ressel]

Grant,

I've never seen one of these, but what you are describing sounds like
insufficient power supply filter caps. To check this, place a scope on the DC
filter cap and check the AC ripple as you change the voltage. My guess is you
will see significant ripple below 130 VAC. If this is the case, the fix is to
increase the filter cap size. The rule of thumb I use is 2000 uF per ampere of
current. You stated that this unit has always had this problem. Perhaps the
factory stuffed the wrong caps in. Perhaps they made a change and screwed up. Or
maybe they just plain cheaped out with small caps.

Tim Ressel--Hardware DQ
Hewlett-Packard
Verifone Division
916-630-2541  
tim_r1 at verifone.com 

> ----------
> From: 	Grant Richter[SMTP:grichter at execpc.com]
> Sent: 	Wednesday, July 28, 1999 12:21 PM
> To: 	synth-diy at mailhost.bpa.nl
> Subject: 	OT: EH-16 second power supply strangeness
> 
> My Electro-Harmonix 16 second delay (which I use with the spacerock band)
> recently quit working. The symptoms were it put out white noise at low line
> voltage.
> 
> So I went through and replaced all the electrolytic capacitors.
> That fixed it mostly, but in the process, I put it on a Variac
> and tried different line voltage levels.
> 
> Low and behold, there was a slight 60Hz intermodulation tone,
> at any input voltage below about 130 VAC. I realized in retrospect
> that the thing had NEVER been clean, some 60 Hz always bled
> through.
> 
> Has anyone else got one out there that can confirm this?
> Perhaps the transformer has gone bad, but I have never
> heard of a transformer "fading", they usually just go dead.
> 
> Thanks
> 
> Grant
>