[AMRadio] Re: audio pots


D. Chester k4kyv at charter.net
Thu Sep 6 19:49:02 EDT 2007


> I wonder if you have any thoughts about building a speech amplifier
> for a modulator, perhaps a linear pot for gain control might be better.
> This is because if you want to have a little more modulation percentage 
> you
> can turn up the gain slightly but if the gain control is logarithmic then 
> a
> small amount of control adjustment at the last 75% of the controls range 
> may
> be pretty touchy.  I think some time we don't always consider the results.
> And beware, that there are also pots that are reverse log where the 
> majority
> of the resistance in the first 25% of the control.
>
> John, WA5BXO

You have a point, regarding the audio drive to the modulator.  I would still 
use a logarithmic control for the mic level, but after the speech amp and 
any audio processing, a final level control might better be linear, so that 
the percentage of modulation would be directly proportional to degree of 
rotation.

I use step attenuators in my  rig.  Each channel in the mic preamp is at 2 
dB per step, but the final level control to the transmitter is 0.5 dB per 
step, which gives good precise control over the level to the transmitter, so 
that the negative peaks almost, but not quite, reach 100%.

Don k4kyv 



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