From: Richard Atkinson (rga24_at_cantab.net)
Date: 2008-09-24 01:06:55
I put up some information about the mod online: http://rga24.blogspot.com/2008/09/vic-20-audio-modification.html On Aug 6 2008, Richard Atkinson wrote: >Hello, > > I was listening to some VIC-20 demos and it occurred to me that the VIC > sound output always sounds rather muffled, as if a treble tone control > had been turned down. So I had a look at the schematics of the new and > old VICs, and found that both have a 1.6kHz low pass filter (single stage > RC network, 6dB/octave) in the audio output stage. On the old VIC > (324001) it is R16 (1K) and C20 (100nF) and on the new VIC (251027) it is > R8 (also 1K) and C10 (also 100nF). > > So I tried replacing C10 on a new VIC with a 10nF capacitor, to bring the > cutoff frequency of the filter up to 16kHz, and the result was > substantially brighter sound. The effect is most noticeable on demos such > as pwp's Robotic Liberation, where the new waveforms (viznut waveforms) > have a lot of high frequency content. > > What's also interesting as an aside is that on the new VIC (the cost > reduced model) there is an external audio input from pin 2 of the > cartridge port, connected via another 1K resistor R40, which is not > present on the old VIC. > >Richard > > > > Message was sent through the cbm-hackers mailing list > -- Richard Atkinson MA (Cantab) MEng Director, Atkinsoft Ltd 33 Brimley Road, Cambridge CB4 2DQ. Office 01223 353449 Mobile 07951349449 Company No. 06411520 VAT No. 922271741 Message was sent through the cbm-hackers mailing list
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