[sdiy] slightly OT - earth hum

[Dave Kendall]

Thanks all.

The nord problem *was* something dumb and obvious - the Nord has 
unbalanced outputs, and I was using balanced leads.. Doh! (slap 
forehead)

Harry - so I guess it may be an advantage that the gear is only ground 
connected via audio lead grounds?

It's being used as a live keyboard + Mic mixer.

cheers,
Dave



On Mar 24, 2011, at 14:37, Harry Bissell wrote:

> BTW in my system I try to make the audio grounds (via shields) the ONLY
> connection by isolating all rack devices from the metal racks (and 
> each other),
> making sure that no MIDI cables have a ground connection (they should 
> not anyway...)
> and isolating all three-wire grounds from the mains. (I'm in the USA 
> btw.. 120VAC)
>
> If a rip-roaring circuit fault trashes my audio cables and selected 
> pieces of gear,
> so be it. At least when the system is working there is a substantially 
> lower noise floor.
> Isn't that what studio gear is supposed to deliver anyway ?
>
> 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
>