<html><head><meta http-equiv="Content-Type" content="text/html; charset=us-ascii"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">Aah!! Thanks Jonatan! <div class=""><br class=""></div><div class="">Yes, that would make a lot of sense. If the modulation is done to the master clock VCO, then the dividers only have to worry about producing note frequencies, and that's a lot less demanding.</div><div class=""><br class=""></div><div class="">I'll do some more research and see how close the notes get.</div><div class=""><br class=""></div><div class="">Thanks again - that's what I was missing. I was focussing too much on the DCO page and not looking at the master clock generation.</div><div class=""><br class=""><div class="">
<div>Tom</div><br class="Apple-interchange-newline">
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<div><br class=""><blockquote type="cite" class=""><div class="">On 12 Jun 2024, at 19:48, Jonatan Liljedahl <<a href="mailto:lijon@kymatica.com" class="">lijon@kymatica.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="auto" class="">IIRC the counters are actually driven by a high frequency VCO, which allows smooth pitch modulation (by pitchbend wheel etc).<br clear="all" class=""><br clear="all" class=""><div class=""><div dir="ltr" class="gmail_signature" data-smartmail="gmail_signature">/Jonatan<br class=""><a href="http://kymatica.com/" target="_blank" class="">http://kymatica.com</a></div></div></div><div class=""><br class=""></div><div class=""><br class=""><div class="gmail_quote"><div dir="ltr" class="gmail_attr">ons 12 juni 2024 kl. 15:20 skrev Tom Wiltshire <<a href="mailto:tom@electricdruid.net" class="">tom@electricdruid.net</a>>:<br class=""></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;padding-left:1ex;border-left-color:rgb(204,204,204)">Update: Sorry, I was wrong - LFO pitch modulation is *not* possible on the Bit 1. I looks like they introduced that on the Bit 01 and 99 and the DCO design is identical, so the problem remains.<br class="">
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<br class="">
> On 12 Jun 2024, at 14:03, Tom Wiltshire <<a href="mailto:tom@electricdruid.net" target="_blank" class="">tom@electricdruid.net</a>> wrote:<br class="">
> <br class="">
> Hi All,<br class="">
> <br class="">
> I've been having a look at the Crumar Bit 1 DCO schematics. It's quite an interesting design. The Bit99/Bit01 synths are an update of this.<br class="">
> <br class="">
> <a href="https://archive.org/details/synthmanual-crumar-bit-1-schematics-late-revision" rel="noreferrer" target="_blank" class="">https://archive.org/details/synthmanual-crumar-bit-1-schematics-late-revision</a> <br class="">
> <br class="">
> The gist of it is that there's 8253 counters generating a clock at 16 x the note frequency. This clock then drives a 4520 4-bit counter. The clock itself and the four counter outputs are added together with weighted resistors to make a staircase approximation to a ramp wave. Since the highest square wave is at 16 x the note frequency, the first missing harmonic is the 32nd at -30dB, so it's not too bad as a quick approximation to a ramp. The ramp is fed to a comparator to generate a PWM output in the usual way, and there's a single-transistor fullwave rectifier to create a "triangle" waveform too. It's supposed to be another Mario Maggi design, and it does seem to have his quirky fingerprints.<br class="">
> <br class="">
> However, there's one thing I don't understand. The 8253 counters are clocked at 2MHz. The output is 16 x the note frequency, so a highish C (MIDI Note 84) needs a frequency of 16.744 KHz. For that frequency, the counter is using a division value of 119, but the previous note 83 uses 127, so there are only 8 frequencies per semitone - clearly audible. From there on up, the situation gets even worse.<br class="">
> <br class="">
> Basically, I can't see how there's enough frequency resolution, especially for any sort of modulation (and LFO pitch modulation is possible).<br class="">
> <br class="">
> Any ideas what's going on?<br class="">
> <br class="">
> Thanks,<br class="">
> Tom<br class="">
> <br class="">
> ==================<br class="">
> Electric Druid<br class="">
> Synth & Stompbox DIY<br class="">
> ==================<br class="">
> <br class="">
> <br class="">
> <br class="">
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