Re: resolved: best way to handle switching in audio pre-amp

From: Winfield Hill (hill_a_at_t_rowland-dotties-harvard-dot.s-edu)
Date: 12/08/04 

Date: 8 Dec 2004 03:36:34 -0800

Mac wrote...
>
> In an earlier post, I asked how to handle switching of line level
> signals in an audio pre-amp.
>
> I received a lot of good suggestions, but ultimately I think I will go
> with the ADG452, a quad analog SPST switch from AD with Ron = 4 Ohms.
> The logic input is TTL compatible when the logic power supply is +5V,
> and the performance of the analog switch is specified under single and
> split supplies of various different voltages.

 I didn't see the thread, but what's the appeal of using such a low Ron
 switch? Have you examined its capacitance specs? The high capacitance
 of a low-Ron switch can give trouble for the driving opamp, introduce
 high-frequency noise into the audio signal path from the supply lines,
 and no doubt endanger the genetic pool for your grandchildren as well.

 I'd start with a high-Z opamp follower after the CMOS switch, reducing
 any effect from a changing Ron with signal voltage, then evaluate my
 Ron spec, and avoid overdoing it. More (or less) is not always better.

 For example, a 74hc4053 often looks appropriate after such an evaluation. 

-- 
 Thanks,
    - Win

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