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Re: extension cables

Subject: Re: extension cables
From: "Robb Nichols" robb_nichols
Date: Fri Jan 22, 2010 5:42 pm ((PST))

John Lundsten wrote:
> and found a pretty smooth response curve that began
> | to roll off at about 1K and extended to about -20dB @20KHz. The
> | low-impedance source and balanced line didn't maintain a particularly
> | compelling response with such a long cable, but it was substantially
> | better and quite useable in our application.
> As i say I don't know what your UPA-1 is (or the out Z of the mic you used) 
> but that seems a pretty dam poor performance to me.
Yikes!  My little gizmo placed in the same sentence as "pretty dam poor 
performance" kind of stings a little.  Herein lies the problem of trying 
to interact with the group while having commercial interests.  I should 
have been either more or less vague, rather than mentioning a part 
number without detail.

As John mentions, the signal degradation is a function of cable 
capacitance and source impedance.  Input impedance of the preamp matters 
too.  Our preamp is driving a pretty unrealistic length of little 24 
gage cable in that test.  And while I admitted that it wasn't great 
response, my point was that the response curve that I did have was 
pretty smooth, so it could be compensated for to a large degree with EQ 
or post processing--probably not best practice for high-fidelity 
recording, but many applications are more about detection.

The UPA-1 is a little weather-resistant mono mic preamp (more detail at  It only draws about 10mA, and 
has screw terminals for power and output.  So with two resistors and two 
capacitors, it can be configured to work as a balanced line driver and 
powered by phantom power. Output impedance as wired is about 50 ohms.  
The mic is irrelevant in this test.

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