The AM Forum

As I am reconfiguring the speech amp in my Valiant - I was wondering if the higher quality (expensive) capacitors are desireable/needed in the audio section for coupling and/or bypassing.  Or if plain jane orange drops or ceramic disks are good enough.  While I'm asking, how about metal vs. carbon resistors?  Thanks.

Steve KK7UV

I will let others comment on the cap issue Steve.  Just don't use the metal resistors in RF circuits.  Inductance is a problem.

As for the caps, any poly type will work just fine.  Ceramic works too, but some say they don't have the "sound".  In this part, it all depends on what you want to do.

Don't bother with the "golden ears" high falutin' capacitors.  Use good quality, low leakage film types (Panasonic film caps are cheap and work well, orange drops if you wanna spend a bit more).  The controversy over supposed sound differences in coupling caps notwithstanding, the stock mudulator in the Valiant is never gonna be much below 5-10% distortion if you go for 100% peaks, so any so-called "sound difference" in coupling caps ain't gonna be heard.

As far as resistors, use whatchya got, but I always use 5%ers, they're better quality, more temp stable, and last much longer than 10 or 20%ers.

Generally, the problem area for bypass and coupling caps occurs in filter circuits where you are deliberately permitting a significant percentage of the applied audio voltage across them.  We should use quality caps for high pass, low pass and equalizing capacitors.  Where the capacitor reactance is very low compared to the load, it is not as important - although for the best possible sound, these caps should be high quality as well.

Aluminum, tantalum and ceramic are generally considered not so good.  Of course we have all used them, and they are reasonably OK.  Mileage may vary.