Question re line level balanced input

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I want to use my existing dynamic mic and line level audio rack processing equipment (noise gate, limiter, downward expander, EQ) with my Flex 6600 [Yes, I am aware that the rig has most of these functions inside, but my equipment is there, and is fun].   To avoid hum and ground loops, I want to keep cabling fully balanced up to the back panel.    I notice that my new Flex 6600 has a 1/4 inch balanced input.

Question 1:   The hardware reference manual, on page 22, section 7.5, talks about the balanced 1/4 inch audio input.  It contradicts itself saying "it can be used as a mic level or line level input",
but then next in section 7.5.1 on the same page says "currently supports MIC level audio only".

[OK, I have XLR to TRS attenuators, so I can deal with that just fine, no worries.]
But, does the above contradiction in the manual imply that the hardware circuitry has switching,
that in the future can accept and attenuate live level, once firmware catches up?  Or is it simply
a mistake in the documentation, and only ever going to be a MIC level balanced input?
If that is the case, no worries, but you would want to fix the second sentence in section 7.5.

Question 2:     The AUX input on the 15-pin "D" connector does have a line level input (consumer line level -10 dB), but from the pin-out in the manual, this looks like un-balanced?  In other words, I only see line in and ground, not Line in +, line in -, and ground.   So if I wanted to use
balanced line level input on the 15-pin AUX connector, and keep it balanced, I would need my own adapter cable with a 600:600 ohm audio transformer close to the back panel to keep my longer cable truly balanced.  Is this correct?


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Neal Pollack, N6YFM

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Posted 1 year ago

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Steve K9ZW, Elmer

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I think you have this correct.

I'm running Balanced to the 1/4" TRS with a simple patch cable (sans attenuator) with good success.

Though I have lots of outboard equipment, I've trimmed it to running the Shure SM5B through a small Behringer EQ/Amp to the radio.


Steve K9ZW 

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Steve, just curious.  Are you doing your EQing and any other processing in the Behringer or in the Flex?  I am using a dbx 286s channel strip here (just the mic preamp section, a Sennheiser e835 dynamic mic, and the EQing in my Flex 6600M.  Seems to work AOK.  I have a Behringer DEQ 2496 Ultra Curve Pro left over from my former ESSB days I may press into service just for kicks.
73, Bob
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Steve K9ZW, Elmer

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I’ve migrated to all in the software. The external runs straight.

That way I can get basically the same audio in my station output when remote as well as in the shack with consistent profiles.


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Neal Pollack, N6YFM

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While Flex has not yet replied to the question above about the documentation,
for those who want to make an XLR to 1/4 inch TRS adapter, for the MIC input
on back of the Flex 6600, the following may be useful;

Adapter Wiring:

Attenuate Line Level audio gear to Flex 6600 MIC level balanced 1/4 inch TRS input:

All about the different audio line level voltage (Consumer vs. Pro):


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Duane N9DG

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I find this to be the gold standard quick-ish reference for all things analog audio interfacing: