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impedance mismatched ?

Audio Aero Capitol Mark 2 running directly into amplifiers via balanced outputs has a output impedance of 100 ohms.
My VTL 750 REFERENCE amplifiers balanced input impedance is 137 ohms. Is this a impedance mismatch which could possibly cause a audible [20 feet away] hum to result when using 1 meter balanced Interconnects? when using the RCA outputs and RCA inputs with same components as above [same impedance specifications for RCA also] their is absolutely zero hum. And yes the XLR pin configuration has been confirmed as being correct on my balanced Interconnects for these components. was suggested could be a ground loop causing the hum but when plugged all 3 components into a power strip the hum still remains, even if floating all the grounds with cheater plugs.
mejames
mejames OP
986 posts
 
hello Herman I believe your correct I checked the information again the specifications actually says input impedance 137kw is this actually same as 137k ohms? Thanks
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ivanj
35 posts
 
What brand of cables are they? I've had a number of balanced cables that really weren't balanced and hummed like crazy. They were just coaxs with XLRs stuck on the ends.
mejames OP
986 posts
 
they are XLO SIGNATURE 2 they don't hum when used in my friends system. Interesting note when I connect from the balanced players outputs using a XLR to RCA adapter and a RCA terminated Interconnects to the amplifier their isn't any hum problem?
gs5556
1,209 posts
 
The XLR introduces one more ground plane, so now you have the grounds from two or more outlets (the amps) and the grounds in the XLR cables creating a grid with loops.

The RCA's ground the signal to chassis only while the XLR's bond to equipment, so the RCA's break the grid (even though they're more prone to picking up common mode noise, their main advantage is not creating a ground plane).

XLR's reject common mode noise and can create ground loops, especially if the equipment they're connected to are on dedicated circuits.
gregm
3,395 posts
 
Looks more & more like a system ground loop. OTOH the 100->137kOhm connection looks good on paper.
Excuse my stating the obvious but, why not stay with rca OR try plugging the cdp into another outlet, with & without floating the ground -- just to check. In a similar situation (but with barely perceptible hum), I plugged the cdp's into a different outlet and REDUCED the noise (but you've probably been there & done that...)
Note that I use a pre & short rca IC for the cdp... Cheers
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