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Re: Ls5 and external phantom power

Subject: Re: Ls5 and external phantom power
From: madl74
Date: Tue Jun 10, 2014 4:33 pm ((PDT))
> Off-topic: Just listened to the "spider in the bag" piezo preamp clip
> too. Sounds very clean and I'm intrigued about the JFETless nature of
> it. I've tried several circuits with "low noise" opamps and all were
> much noisier than JFETs. (My learning curve is vertical too, but it
> tends to get stuck at a lower latitude!) 


Noise is never off-topic. The idea of "noise impedance" is often 
misunderstood. I can't find a simple explanation of "noise impedance" except 
that it gives the lowest overall noise if the mic impedance is matched to 
the input stage noise impedance. This is a different parameter to input 

Low noise preamps are not easy to design, hence the cost can be substantial. 
It depends on the type of on-chip amplifier used and the feedback circuit. 

Mic transformers are out of fashion, but they are another way of matching a 
low impedance into a higher noise impedance input.
calls it the "optimum source impedance" and if anyone can put this paper 
into plain English, I'd be grateful. :-) 

Dave Brinicombe 

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