3 Dec
2009
3 Dec
'09
7:13 p.m.
On Thu, 3 Dec 2009 23:52:03 +0100
fons(a)kokkinizita.net wrote:
On Thu, Dec 03, 2009 at 10:29:54PM +0000, Folderol
wrote:
I use the old fashioned method of wiring resistors directly on
standard glass loaded wafer switches. Initial tests suggest the
bandwidth well exceeds 20kHz - as opposed to less than 1kHz for many
quite expensive commercial units.
As promised, PDF attached.
Mmmm. Just 1 picofarad of stray capacitance on the switch
and wiring, in parallel with 9M, will create a filter with
its 3 dB frequency in the audio band. And 1 pf is really
nothing, expect more. This will lead to gross errors at anything but the
lowest frequencies.
Is there any reason why an audio level meter should
have such a high input impedance ?
No reason at all, except that being a cheapskate I was able to
convince the boss that a good true RMS meter would be useful in the
workshop :)
A 10M input is more-or-less mandatory in this case, but anyone else
should feel free to make the ladder impedance whatever they like.
--
Will J Godfrey
http://www.musically.me.uk
Say you have a poem and I have a tune.
Exchange them and we can both have a poem, a tune, and a song.