Re: Recommended capacitors for AF circuits

RoyalHeart, Thomas, wrote...

I'm playing around with a circuit, but I am getting a lot of squeal
I believe to from my choice of polarized electrolytic caps (220n
and 470n) where polarized caps are not indicated (application circuit
in the LM1036 data ***). (Seemed like they would work, given that
most have one end grounded.)

The electrolytics are the only ones I have at the moment, and before
I buy a different type, I would like some recommendations on the
type(s) to get.

Most of the large (47uF, 10uF) capacitors shown on the LM1036 app
circuit are electrolytics, used for bypass, etc., where they have
little AC voltage across them and therefore don't disturb circuit
performance. This includes the output capacitor if you choose a
large enough value. According to the data***, you may want to
increase the value of the 10uF caps to reduce any low-frequency
effects on the bass control, you could use three 47uF for the IC.

Some of the smaller ones shown may be electrolytic types, if you
wish (and can find them). These are the 0.22uF caps, which just
bypass the DC control voltages. They may also be smaller ceramic
types, say 0.1 or even 0.01uF, because they're simply present to
insure no signal couples into these lines from your wiring to the
panel, etc. One of the beauties of the LM1036 is the way it lets
you implement front-panel analog gain and tone control, without
routing any actual signals to the panel.

But be careful of Ct and Cb. These are the critical capacitors
used for treble and bass tone-control. They have significant AC
voltages at the tone-control frequencies, so if you use types
with high dielectric absorption, etc., such as ceramic caps, they
can introduce serious distortion into your audio signal. Follow
Martin Griffin's suggestion and read Walt Jung's classic capacitor
articles, http://waltjung.org/Classic_Articles.html DigiKey has
high-quality polypropylene film capacitors that should work well.


--
Thanks,
- Win
.