[sdiy] Prophet 5 weirdness.

[Dave Magnuson]

I would certainly investigate the power first.    I had some interesting noises / zaps from older gear (in particular) when they were powered from two different circuits.   

 

First, unplug both racks and confirm voltage / neutral / ground on your two receptacles

 

Next, I’d measure voltage from hot-to-hot, neutral-to-neutral and ground-to-ground on the two receptacles.   Be aware you could have a 240V differential, so set your meter accordingly.

 

Next,  disconnect the audio cable, power up both racks.   Measure voltage chassis-to-chassis between both racks, then audio ground-to-audio ground on both racks

 

After that, run all that gear from one outlet and see if plays nicely

 

That should help diagnose where the problem actually lies

 

Dave Magnuson

 

From: Synth-diy [mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of Jim Blair
Sent: Monday, March 14, 2016 4:03 PM
To: synth-diy at dropmix.xs4all.nl
Subject: [sdiy] Prophet 5 weirdness.

 

Hi all. Thanks in advance for your help!

 

I have a Prophet 5 rev 3.3, which someone in the distant past converted into a brain-only format. So, no keyboard. Midi only. It's now happily residing in the lower row of a modular. It works great, and sounds amazing. The PSU has been recapped, and new regulators installed. All is well.

 

Almost.

 

Get this. When I plug the audio out into a guitar amp or a pedal, the synth works great. But when I plug it into my API preamp, or Sansamp rack unit, the synth loses it's mind. All the front panel lights start flickering, and the output is all loud and nasty noises.

 

I think that the Sansamp and API are both plugged into a different AC house-circuit than the P5, but I'm not sure of this yet. More investigation is required. I run other synths, both modern and vintage, into the Sansamp and API all day long, and have never experienced a problem. 

 

Thoughts?

 

 

Jim

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