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 Forum index » DIY Hardware and Software
modular buzz
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synthesist



Joined: Feb 17, 2011
Posts: 79
Location: austria
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PostPosted: Fri Oct 12, 2012 12:48 am    Post subject: modular buzz
Subject description: is it because I use bananas?
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Just a normal patch:

VCO goes to VCF goes to VCA goes to Mixer

The banana cable that connects the VCF with the VCA starts to buzz when my hands get near to it and it gets annoying loud when I touch it. The same happens when I connect the VCF directly with the mixer.

But when I touch a frontplate at the same moment it stopps buzzing. (The frontpanels are grounded.)

Do you folks think it wouldnt happen with shielded patch cables? And is there anything I could do?
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prgdeltablues



Joined: Sep 25, 2006
Posts: 162
Location: UK
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PostPosted: Fri Oct 12, 2012 3:06 am    Post subject: Reply with quote  Mark this post and the followings unread

I'd check your grounding on all parts of those modules. It sounds like a grounding problem. At synth voltage levels, unless you've got a very harsh electro-magnetic environment, there shouldn't be any problem with unshielded external cables carrying the signal. Some VCF's do seems to introduce slight noise. Might also be worth checking your power supply is large enough.

Peter
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ashleym



Joined: Aug 20, 2009
Posts: 179
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PostPosted: Sat Oct 13, 2012 6:32 am    Post subject: Reply with quote  Mark this post and the followings unread

if the buzz goes when you touch a plate it is a grounding issue rather than something shielded cable would save you from- with bananas you have a similar set of earths just not ones running through the cable.

As ever it is a recheck and test. You might end up with an extra panel earth strap. I agree with everything prgdeltablues said too.

Have you got separate panel and circuit board earths? This can help with overall noise levels.

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synthesist



Joined: Feb 17, 2011
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Location: austria
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PostPosted: Mon Oct 15, 2012 7:35 am    Post subject: Reply with quote  Mark this post and the followings unread

thanx for the help,

I dont have seperate panel and circuit board earth.

I just use the ground signal of every single module and attache it with a potentiomer that is fixed on the frontpanel since they are aluminum. So the "ground" should be all over the panels.

I dont know what to check and recheck. Do you mean I should check the ground contact?
Well my VCF panel and the VCA panel are not grounded since they are not aluminum but acrylic Surprised might this be the bug?

What do you mean with "extra panel earth strap"?
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prgdeltablues



Joined: Sep 25, 2006
Posts: 162
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PostPosted: Mon Oct 15, 2012 8:12 am    Post subject: Reply with quote  Mark this post and the followings unread

You say the VCF and VCA panels are not grounded, being acrylic. But have you connected your ground to the casing of any pots in those modules? That might be a source of noise - depending on the environment, etc, your body carries a decent static charge - which may be transferring to the front panel and thus introducing noise into the ground, which is effectively unterminated right behind the panel. By touching a grounded panel with another hand, you are earthing yourself and discharging that static - hence the hums disappears.

It's difficult to check grounding electronically other than for basic continuity, but you can check all grounds physically. A bad solder joint could be the problem.

You could try sticking aluminium or copper foil to the back of your acrylic front panel, and grounding that.
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