Ground Loop - P12 USB

The Dave Smith Instruments Prophet-12 Analogue Synthesizer

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Ambient Architect
Posts: 53
Joined: Tue May 26, 2015 1:39 pm

Ground Loop - P12 USB

Post by Ambient Architect » Sun Jan 17, 2016 12:01 pm

Hi Folks,

Odd one here.

I spent the majority of yesterday rewiring the studio due to an obvious ground loop on my vintage synth rack (a collection of old synths!), switching sockets quickly remedied this! However, something I have noticed on a couple of occasions is a rather large hum from the P12 through my UAD apollo when the USB cable is plugged in.

When this initially happened, my first port of call was to swap out the USB cable, which apparently fixed it. However yesterday it came back again and I can only compare it to something like a diesel generator, or jet engines ramping up when it happens! Pulling the USB cable fixes it but of course not ideal. I've booted up this morning and it's absolutely fine so what on earth (no pun intended) could be causing this anomaly? I'm slightly concerned as my beloved P12 is approaching the end of its 12 month warranty.

Thanks!

yewtreemagic
Posts: 35
Joined: Thu Mar 19, 2015 5:34 pm

Re: Ground Loop - P12 USB

Post by yewtreemagic » Mon Jan 18, 2016 9:34 pm

Hi,

It can be tricky when you've got a USB cable connecting a grounded synth like the P12 and a grounded interface like your UAD Apollo, since as soon as you plug in that USB cable you're creating a ground loop. I wrote some time ago about such problems, so having a read here may help clarify:

www.soundonsound.com/sos/dec08/articles/qa1208_2.htm

As I say there, it's tricky to resolve, although some people have managed to connect their USB cable via a specialist isolator. The simplest solution would be if you could use a MIDI connection instead of that USB one- this always works, since MIDI uses an opto-isolator, so there's no direct connection between the gear.


Martin

Ambient Architect
Posts: 53
Joined: Tue May 26, 2015 1:39 pm

Re: Ground Loop - P12 USB

Post by Ambient Architect » Wed Jan 20, 2016 10:58 am

Hi Martin,

Many thanks for the very helpful reply.

It has been fine all weekend but did it again just now. Long story short, I double checked everything was tight in my 7 port Belkin hub and it went away upon moving it so perhaps a loose connection somewhere! My king Korg was also doing this so I can rule out the P12 as that has also stopped humming!

I have probably read your article at some point in the past as I used to get SOS around that time period, shall have to sift through my mags!

Cheers.

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