[Elecraft] [K3] Additional Gain Stage for FP Mic?

[Wright, Robert]

Hi Jim,

A good generic textbook explanation, but the feature of interest here is that using the "apostrophe" setting REDUCES the noise floor.  I am not changing the overall gain.

The overall gain of FP.H at a mic gain setting of 35 is about the same at using FP.L'  (note the apostrophe) at a mic gain setting of 15 or so.  But the second combination produces a significantly lower noise floor and so looks to be a more optimum setting of the various gain stages (better gain staging).  I have noted no problems with overhead or dynamic range.

73, Bob, N7ZO


-----Original Message-----
From: elecraft-bounces at mailman.qth.net [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Jim Brown
Sent: Thursday, September 27, 2012 10:14 AM
To: elecraft at mailman.qth.net
Subject: Re: [Elecraft] [K3] Additional Gain Stage for FP Mic?

On 9/27/2012 9:37 AM, Wright, Robert wrote:
> Of course, one wonders whether any of this can be heard over normal HF propagation noise.

ALL pro audio products that accept mic inputs have controls to set input gain over a nearly 60 dB range. There are several reasons. First, some microphone types are more sensitive than others -- that is, they produce more voltage for the same sound level.  Second, the voltage produced by a mic depends on the loudness of the sound source and how close the mic is to the source.

The high and low settings in the K3 are simply two values of input gain that are suitable for the range of mics used with ham gear, and for sound levels of a voice at 3 -12 inches from the mic.  This "high-low" 
setting combines with the Mic Gain (the front panel pot) to set the total gain of the system. When the setting is too high, the audio chain in the radio is amplifying room noise, and can sound really awful on the air.

The "additional gain stage" should NEVER be used if it is not needed.  A good rule of thumb is that it should be used ONLY if you can't turn the Mic Gain pot up enough to get good audio levels as described in the K3 manual.

73, Jim K9YC
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