[sdiy] Sonic qualities of parts..

[JH.]

Sounds like a capacitive divider, built from a X7R and a "good" capacitor, 
might make a nice distortion device!

JH.


----- Original Message ----- 
From: "Neil Johnson" <neil.johnson97 at ntlworld.com>
To: "George Hearn" <georgehearn at btinternet.com>
Cc: <synth-diy at dropmix.xs4all.nl>
Sent: Wednesday, September 17, 2008 8:28 AM
Subject: Re: [sdiy] Sonic qualities of parts..


> George,
>
>> My tuppence.. Ceramic caps CAN be bad but can also be very good, it 
>> depends
>> entirely on the type and the value required.
> [snipped]
>
> Good advice.
>
> I would add a further caution to X7R/Y5V in that the capacitance  varies 
> quite considerably with DC bias, to the extent that you could  end up with 
> 10-20% of the original value.  This effect is a right  pain when selecting 
> decoupling capacitors, as you can be caught out  ending up with 
> insufficient decoupling capacitance.
>
> For example, check out this AVX datasheet:
>
> http://www.avx.com/docs/catalogs/cy5v.pdf
>
> The second figure "Capacitance change vs. DC bias voltage" shows why  they 
> give these capacitors such a wide tolerance.  For example, if  you choose 
> a 100nF 6.3V capacitor for decoupling a 5V rail, in  practice you'll get 
> closer to 10nF decoupling.
>
> Now imagine what this effect would have in the signal path - the 
> capacitance would continuously vary with signal amplitude.  Here's  some 
> interesting reading:
>
> http://www.electronicsweekly.com/Articles/2007/10/02/42307/choose- 
> capacitor-types-to-optimize-pc-sound-quality.htm
>
> To counter the bad news, they are incredibly cheap compared to other 
> ceramic dielectrics.  And I've even heard of applications that make  use 
> of this effect as voltage-controlled capacitors in RF  applications. 
> Unfortunately for us you only get about 10:1 range  (about 3 octaves).
>
> Cheers
> Neil
> --
> http://www.njohnson.co.uk
>
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