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In Reply to: RE: What would happen if I upped the uf value of an audio path capacitor posted by airtime on January 04, 2016 at 15:47:29
Hello,
Standard electrolytics are not great for this application. Changing the cap to a bi-polar electrolytic will cut the distortion to about 25% as much. Search for articles by Cycil Bates if want to get gory details, believe it was articles 4 & 5 that address electrolytics. Believe they are still posted on Linear Audio magazine website.
As audio signals are AC, using a bi-polar helps. Also if size can be fit in a larger uf cap will give better low end response. 47uf is large enough that low end isn't being effected much with usual in and output impedances. (10k ohms and up)
Follow Ups:
My rule of thumb for rapid estimation of low frequency cut-off, without doing the math, is that a 1.0uF capacitor will give you an ~2Hz LF cut-off (-3db point) with a 100K parallel resistance. This is sufficiently low to prevent phase shift at 20Hz. Therefore, 10uF would be more than adequate for a 10K parallel resistance. That's why I wondered (see below) why this unit would need 47uF in a coupling topology.
And yet we usually find that the bigger the capacitor (keeping capacitor type unchanged) the better it sounds, until ultimately it is removed and sounds much better still (provided offsets are handled). So I'm not sure it is so much about phase shifts, maybe more about low frequency noise in the playback making it sound more realistic.
However, in coupling the output of a phono stage to a linestage, one must be aware of rumble caused by LP warps and off-centeredness of the spindle hole. The spurious ultra-low frequencies thus generated can wreak havoc on the amplifier and speaker, sucking up lots of power for nothing, at best. Some older circuits used a hi-pass filter set at about 10Hz or 20Hz, for that reason for phono. I'm sure you know this; just saying... The custom of using such a filter seems to have disappeared in commercial products, like the "mono" switch and other features that used to be common in full-function preamplifiers.
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