In article , Dave Plowman (News)
wrote:
In article , Jim Lesurf
wrote:


What are you doing at the *inputs* of the balanced unit?

It is balanced and fed from a balanced source. That bit works just fine.
Plugging or unplugging that bit makes no difference.

OK.

It gives the impression that the unit floats so simply acts as an
electrostatic pickup. Then expects you to dodge the consequence by
letting this put common mode voltages on both its outputs. But I'd
need to sit down with it and a scope, etc. to diagnose properly.

I've never had this problem before.

I've just done the following experiment.

Focusrite 2i2 as the output device on my ARMiniX (RISC OS). Used this to
play out some test sinewave files. (96k 24bit stereo). The 2i2 has two jack
outputs on its rear. Said to work both TRS balanced and TS unbalanced.

Used a Behringher UCA202 on my linux laptop to grab the output using
'arecord' to get a no fuss result. The UCA series all use unbalanced
phonos as aimed at 'home computer' market.

Did tests two ways.

1) Used a TRS - 2 phonos stereo adaptor to connect the 'left' output if
the 2i2 to the UCA202. Thus being able to see the 'balanced' output from
the 'left' jack output as antiphased signals on the 'L' and 'R' inputs of
the UCA202.

2) Used a TS - phono mono adaptor. As above but now getting the 'hot' out
as signal and grounding the 'cold'.

Used a DVM to monitor the signal levels. Set the 2i2 output level to max.
Played some -3dBFS sinewave tones.

Test (1) gave the expected antiphased signals. Level 800mVrms per side in
antiphase.

Test (2) again showed an 800mV signal.

So far as I could see, both versions were fine. No sign of hum or buzz and
negligable distortion when I FFT'd the results. So seems quite happy either
way. Which I think is what the 2i2 manual implies.

So it looks like grounding an output doesn't have any deleterious affects.
Only did this for a total of a few mins, though.

May try this with a Behringer UMC202 sometime as well just out of
curiosity.

I guess we'd need to know more details of your amp and setup to diagnose
what you're getting.

Jim

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