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Old 26th February 2012, 10:58 AM   #101
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Glad to hear you worked it out Dean I hadn't seen this and was just about to post you this link as I thought it might help. F5 power amplifier

Since you have sorted the problem it's probably irrelevant but it might help someone else who reads this thread

Tony.
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Old 3rd March 2012, 02:04 AM   #102
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Hey Tony.

Thanks for that last link, I could not make exact sense of it though. Is there something I should be trying with my setup?

As i mentioned, the hum doesn't come from the amp or the miniDSP when either is used with other devices, only when they are connected together.

Could this be an impedance matching issue?

Does anybody have any suggestions of what I might try next?

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Old 3rd March 2012, 02:17 AM   #103
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Hi Dean, is the problem with the MiniDsp present when only one channel is connected to it? If not (but it is there when more than one channel is connected) then the problem may be similar to the problem that dvb-projekt had.

I'm not versed enough in impedance matching problems to know whether that may be an issue. Does the minidsp run off a powersupply that has a safety earth connection or is it a wall-wart type supply? If it has safety earth, you *may* need an earthloop breaker.

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Old 3rd March 2012, 02:44 AM   #104
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The issue is constant under all conditions. So when i run 1 channel from the dsp to the amp with the matching channel shorted on the amp I still get the hum.

The dsp runs from a wall-wart style 12v1a supply with no safety earth. I have tried many different supplies including a regulated bench top supply and still have the same issue. I have been able to lessen the amount of noise using different supplies and a miniDC but the buzz is still clearly audible in all cases.

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Old 5th March 2012, 02:25 PM   #105
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I have been reading the thread you suggested Tony and have had a chance to try some different star earthing config's. Still have the buzz but learning more.

One thing I know for sure is that with only 1 channel connected to a single trafo I have no hum, when I connect the second channel (psu+amp) I get the hum back. I am still trying some more star earth options and will report back.

From the thread i found ESP's site and copied the diagram attached.

Will the values stated for the 'Ground Loop Breaker' be appropriate for my setup?

I have 3 x 400vA Taroidal's running 2 x Audiosector LM4780 PSU/AMP kits each.

Cheers
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Old 5th March 2012, 08:13 PM   #106
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Hi Dean, I don't think that the earth loop breaker is going to help (unless one of the other components you are connecxting to is also earthed to safety earth. The loop occurs through the interconnects and out through the mains wiring.

The bridge should be fine, 400V 35A is much more than the mains can deliver, and it is mains level faults you are concerned about with safety earth. I found that I had to go to an 18 ohm resistor instead of 10 ohms to get a reasonable amount of attenuation (my earth loop was between my PC and my Amp.

A quick question, If you only use one channel of each amp connected to separate transformers do you still get the hum? ie turn on say two of the traffo's but only use one channel of each amp connected to that traffo.

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Old 6th March 2012, 01:55 AM   #107
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Hey Tony.

Good question and that's the point shedding the most light at the moment. If I disconnect the second psu/amp combo from the transformer the buzzing stops. But when I add the second channel to the trafo, the noise is back.

Just working on a drawing of current wiring and will post asap for clarity.

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Old 6th March 2012, 02:46 AM   #108
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Here's the drawing of the current wiring. As you can see I have followed others advice and redone 'some' of the star earthing.

Can anybody suggest others things that need changing?

Also note that the 2 PSU's on each transformer are wired in parallel.

Its when I disconnect one of these psu/amp combo's that the buzzing stops.

Is it OK to wire two of these PSU's in parallel?
Have I somehow created an earth loop by doing this?

PS. Cant hurt to install the 'Loop Breaker' to avoid any issues with other 'earthed equipment' I might use later so I may go ahead with that anyway.
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Last edited by thunk303; 6th March 2012 at 02:52 AM. Reason: Clarity
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Old 6th March 2012, 07:47 AM   #109
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Any input?
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Old 6th March 2012, 07:58 AM   #110
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Quote:
Originally Posted by thunk303 View Post
... But when I add the second channel to the trafo, the noise is back.
Is that with the inputs grounded, floating or the DSP connected?
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