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Re: Interference or bad amp?

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Jordan Wolf
Re: Interference or bad amp?
on Sep 6, 2011 at 12:18:46 am


Upon looking at images of your audio interface, I don't see any balanced outputs. I see XLR inputs on the front and RCA outputs on the back. What do you mean when you say in your original post, "iMac FW out to Presonus Inspire to speakers via balanced XLR"?

Are you using an RCA-XLR cable? If so, it is not a balanced connection. However, as long as the cable run is under 15', you should be okay using RCAs either way. This leads me to think the issue maye be elsewhere, since you already tried going RCA into the speakers directly.

Okay, first I'll offer some advice(not to be snarky, just informative): when troubleshooting, it is important to try devices that are both similar and dissimilar to the DUT (Device Under Test). It is also important to only change one variable at a time.

So far, you have discovered that your computer (connected to the AC power from the wall) causes hum/buzz. You have also discovered that devices NOT connected to AC power exhibit a hum-/buz-free response.

If you haven't already, run your audio interface via firewire and not using the AC adapter (if you are even using that). If this has already been done and the problem remains, try running an extension cord from another outlet and plugging your devices into that.

You ideally want all deviced that are going to be interconnected on the same circuit so that the voltage potential to ground between each device is kept low (that "potential" or voltage is what you hear as 60Hz and the odd-order harmonics thereof).

As another idea, if you have access to a bus-powered audio interface with balanced outputs, try that to see if it will help - my guess will be that it helps somewhat, but not entirely, if it's a power issue.

Please keep us up-to-date on your findings.


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