[sdiy] slightly OT - earth hum

[Harry Bissell]

Might you have a bad audio cable with a broken shield ?

then the MIDI connection establishes the ground, trouble gone...

H^) harry




----- Original Message -----
From: Dave Kendall <davekendall at ntlworld.com>
To: sdiy DIY <synth-diy at dropmix.xs4all.nl>
Sent: Thu, 24 Mar 2011 10:29:25 -0400 (EDT)
Subject: Re: [sdiy] slightly OT - earth hum

Hi. All machines are on the same mains circuit.
Both Nord and mixer are not grounded by their cases. Would the easiest 
way be to fit a 3-pin mains plug to the Nord (with earth connection) 
and the mixer if possible?

I guess the real question i, whereabouts in the nord and tapco to 
attach the ground points...... I suppose it would be easy enough to 
connect a mains earth to the audio GND, but interestingly, without the 
MIDI cable between K2661 and nord it hums, suggesting that the Nord's 
audio GND is maybe not connected to the chassis, but the metal barrel 
of the MIDI jack does connect?

I'm missing something obvious I'm sure..

cheers,
Dave
On Mar 24, 2011, at 14:14, Ben Lincoln wrote:

> Dave, you've probably already looked into this, but are all of your 
> devices on the same mains circuit? Nearly all of the ground noise 
> issues I've run across over the years were the result of connecting 
> things that were powered by different circuits.
>
> It sounds like that's not what's going on with the mixer itself, if it 
> hums with literally nothing else connected to it, but maybe it's 
> what's happening with the Nord + mixer combination? Is the mixer 
> physically grounded/earthed by some other means, e.g. it has a metal 
> case and is sitting on a metal cabinet that's sitting on a concrete 
> floor, or something like that?
>
> On 2011-03-24 07:02, Dave Kendall wrote:
>> Hi.
>>
>> I may have to modify a mixer or keyboard, so it's not that OT... I 
>> have a nasty hum/noise problem, and maybe someone here has hit this 
>> problem before....
>> A Tapco 6306 mixer is connected to a Yamaha O3/D. The tapco hums 
>> loudly (60Hz with harmonics) with no audio connections made. It stops 
>> humming when balanced audio jacks from a Kurzweil K2661 are connected 
>> to it.
>>
>>  The K2661 has a 3-pin mains input, the Tapco is a wallwart (9V AC)
>> As soon as a Nord electro (2-pin mains) is connected to the Tapco, 
>> There is a horrible digital noise from the Nord, modulating in a 
>> pattern at a few kHz or so I guess.
>> However when Midi out of the K2661 is connected to the nord's MIDI 
>> in, all the problems go away.
>>
>> Would it be worth Modding both the tapco and the nord to accept 3-pin 
>> mains somehow?
>>
>> Anyone done this sort of thing before? Any advice would be most 
>> welcome.
>>
>> Apologies if this is too off-topic....
>>
>> cheers,
>> Dave
>>
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-- 
Harry Bissell & Nora Abdullah 4eva