[sdiy] Free SSM2044, SSM2056 chips for pickup and one question about single supply VCAs

[Mike Bryant]

As audio ADCs don't like too low frequencies as they see it more as a wandering DC baseline, one often rolls off the bass anyway then lifts it back up in the digital domain.  I know a few people don't like this technique but I don't think there's much actually information one can lose in a 20Hz base note.
________________________________
From: Synth-diy <synth-diy-bounces at synth-diy.org> on behalf of René Schmitz <synth at schmitzbits.de>
Sent: 06 March 2024 14:02
To: synth-diy at synth-diy.org <synth-diy at synth-diy.org>
Subject: Re: [sdiy] Free SSM2044, SSM2056 chips for pickup and one question about single supply VCAs

Am 06.03.2024 um 01:31 schrieb brianw:
> It's very common to use a single supply and handle all signals with a DC offset internal to the circuit. This just requires biasing the op-amps to "virtual ground" - which is half of the supply voltage (or somewhere around there).
>
> I glanced at page 35 of that schematic, and the output op-amps on the right of the schematic have a series capacitor. This series capacitor will remove the DC output and present an AC signal beyond that point. The waveforms are probably all biased with a center around 6V instead of 0V.
>
> The drawback of this approach - besides requiring a lot more capacitors on the inputs (if any) and outputs - is that the frequency response is not flat all the way down to 0 Hz. It's usually not even flat down to 20 Hz, which we can hear. However, since nearly all "affordable" electronics do this, we're not really complaining about the sound.

The speaker cabinet in these organs problably doesn't go to 20Hz either.

It is not difficult to dimension caps such that the bass loss is avoided.

But one shouldn't make them too big either, as this can lead to problems
in recovering from certain overdrive situations.


Best,

  René

--

synth at schmitzbits.de
http://schmitzbits.de

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