[Boatanchors] Fw: Re: Disc caps vs paper caps

[Kees & Sandy]

Yes, ceramic capacitors are "microphonic" to differing degrees, but you can use them for RF or Audio bypass to ground with no ill effect. The best ones for Audio coupling between stages and output (in my opinion) are Teflon, if you can afford them, followed by Poly caps. There are probably others.

73 Kees K5BCQ

---------- Original Message ----------
From: "J. Forster" <jfor at quikus.com>
To: "Glen Zook" <gzook at yahoo.com>
Cc: "Boatanchors at mailman.qth.net" <boatanchors at mailman.qth.net>, Mark Foltarz <foltarz at rocketmail.com>
Subject: Re: [Boatanchors] Disc caps vs paper caps
Date: Thu, 27 Sep 2012 07:58:42 -0700 (PDT)

> There have been cases where using disc ceramic capacitors as the coupling
> capacitors in audio circuits has resulted in problems. &#65533;This is usually
> due to the fact that, under certain circumstances and with certain
> capacitors, the capacitors can act as a transducer and the audio can
> actually be heard from the capacitor!

True. This is the piezoelectric effect I mentioned a couple oif days ago.
Because they are reversible electro-mechanical transducers, they equally
can avt as crude microphones, vicking up vibration auch as hum.

> Many people can tell a slight difference between the use of disc ceramic
> capacitors and the new "poly" types of capacitors when used as coupling
> capacitors in audio stages. &#65533;

Somehow, this is very suspect to me. Hum level, perhaps.

> However, for practical communications use,
> that difference is so slight as not to make any real difference in how
> the signal "sounds". &#65533;For high fidelity audio applications, that
> difference may, or may not, be noticed.

IMO, only noticable with the "golden ear" crowd.

> For bypass use, at both r.f. and audio frequencies, use of a disc ceramic
> capacitor works fine with the advantage of the disc ceramic capacitors
> being that they are usually much less expensive than the other types of
> capacitors.
> &#65533;
> Glen, K9STH

As to use as vibrator snubbing capacitors, they are PROBABLY OK. I am not
100% certain. Some years ago, I set out to formally analyze a vibrator
circuit. It is by no means anywhere near as simple as it looks. I suspect
most of the design and application information has been gained by "cut and
try".

Generally, you want the capacitor to be big enough such that the capacitor
will store an equal amount of energy as the inductor without overvoltaging
the contacts.

Best,

-John

=================

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