[Boatanchors] Disc caps vs paper caps

[Glen Zook]

I don't have a "golden ear"!  However, I can often tell a slight difference between using a disc ceramic and other types of capacitors in audio coupling circuits.  Now my ability to hear high frequencies is better than most.  Back when a number of television remotes used ultrasonic tones for control, I could easily hear those tones.  That ability may have some effect in being able to tell a slight difference.

However, I definitely agree that most people cannot tell any difference and, for all practical purposes, replacing audio coupling capacitors with disc ceramics will have no apparent effect on the quality of the audio.  This is especially true of "communications" audio which is generally limited to the 300 Hz to 3000 Hz segment.

As for the snubbing capacitors:  Back when vibrators were in widespread use, every new vibrator came with replacement snubbing capacitors.  If the capacitors were not replaced, the warranty on the vibrator was void.  I believe that this was because failure of the snubbing capacitors played a significant role in the fact that the vibrator needed to be replaced.
 
Glen, K9STH


Website:  http://k9sth.com


________________________________
 From: J. Forster <jfor at quikus.com>
To: Glen Zook <gzook at yahoo.com> 
Cc: Mark Foltarz <foltarz at rocketmail.com>; "Boatanchors at mailman.qth.net" <boatanchors at mailman.qth.net> 
Sent: Thursday, September 27, 2012 9:58 AM
Subject: Re: [Boatanchors] Disc caps vs paper caps
 
> There have been cases where using disc ceramic capacitors as the coupling
> capacitors in audio circuits has resulted in problems.  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.  

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".  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.
>  
> 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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