The Sequential Pro-One is another mono synth with a DAC. I still think that the way it's done is clever. Thanks, Ole On 3/22/26 7:12 AM, Michael E Caloroso via Synth-diy wrote: > > Correct me if I'm wrong but old synths using DAC for CV were all > > polyphonic. > > If it was programmable using solid state memory, it had DAC with MUX/ > S&H. Not limited to just polyphonics. > > Oberheim OB-1 monophonic was programmable and used a DAC with MUX/S&H > for CV. Released in 1977. > > Moog Source was another one, released in 1980. > > MC > > On Thu, Mar 19, 2026 at 7:14 AM Roman Sowa via Synth-diy <synth- > diy@synth-diy.org <mailto:synth-diy@synth-diy.org>> wrote: > > Correct me if I'm wrong but old synths using DAC for CV were all > polyhonic. That means a lot of CV sources needed. So they used S&H and > muxed DAC. To have PWM with fast enough response to feed MUX and > S$H, it > would have to run at enormouse frequency, not suitable to affordable > technology back then. And putting separate counter as PWM generator for > every CV is much more expensive, and takes more space than DAC-MUX-S&H. > Back then if you wanted a timer, you got 8253 offering 3 timers in one > package, and I'm not even sure if it had PWM mode at all. > > Roman > > W dniu 2026-03-18 o 21:39, Mike Bryant pisze: > > Does anybody know why these old synths didn't use PWM/PDM > techniques ? > > > > LS-TTL or CMOS feeding a comparator into an analogue integrator > gave 12 > > bits performance at audio frequencies even in the 70s so CVs good > enough > > for tuning would have been easy. > > > ------------------------------------------------------------------------ > > *From:* Synth-diy <synth-diy-bounces@synth-diy.org <mailto:synth- > diy-bounces@synth-diy.org>> on behalf of brianw > > <brianw@audiobanshee.com <mailto:brianw@audiobanshee.com>> > > *Sent:* 18 March 2026 19:02 > > *To:* synth-diy@synth-diy.org <mailto:synth-diy@synth-diy.org> > <synth-diy@synth-diy.org <mailto:synth-diy@synth-diy.org>> > > *Subject:* Re: [sdiy] Linear response VCOs? > > The Prophet 5, Rev 1 and Rev 2, use a 7-bit DAC made from hand- > picked > > resistors. There is a note in the Service Manual that you should > *not* > > replace these resistors because of the challenge of matching a > new one > > to the network. 1 LSB is calibrated to 1/12 V (0.0833 V) for easy > use in > > 1V/8va scaling. CV ranges from 0 V to 10.583 V (127/12), but the > Prophet > > 5 only uses the lower 6 bits for pitch, limiting the range to > 5.333 V > > maximum and thus 5 octaves. All CV were 7-bit, but the pitch > combined > > coarse and fine with the scale of the DAC changed so that there > were 64 > > steps in the coarse range plus another 128 steps in the fine > range. This > > wasn't quite as accurate as a 13-bit DAC, but still quite > accurate for > > the time. > > > > The Prophet 5 Rev 3 simply used a 16-bit DAC, but maintained the > > firmware design with 7 bits per CV, so the pitch did not enjoy a > full > > 16-bit precision. The 13-bit pitch values still have 16-bit > accuracy, > > though, just not 65536 steps of precision. > > > > One thing to note, Mark, is that a 6-bit DAC has an LSB that's > 1.56% of > > the total range, so 1% resistors would be quite awful. Then > there's the > > fact that a 1% error in the MSB could throw the whole binary > scale off > > enough that the values are not monotonic (i.e. an increase in the > code > > could actually cause a decrease in voltage!). A 7-bit DAC has the > LSB at > > 0.78% so you definitely need better than 1% precision. These > > manufacturers were not making a custom resistor array so much as > > hand-selecting individual resistors that were matched well across > the > > whole group. > > > > Today, not only are 1% resistors more readily available than they > were > > in the seventies, but you can even get 0.1% tolerance resistors at a > > reasonable. Still, that doesn't even get you to a full 9-bit DAC. > This > > illustrates how impressive DAC chip technology is. One of the > fasted DAC > > chips I've designed with can run at a sample rate of 125 MHz > (yeah, MHz, > > not kHz) based on current switching rather than voltage, but it > stops at > > 14-bit precision because the smallest current is only 0.0061% of the > > largest, and it's difficult to be precise enough at such a large > scale > > factor. Larger DAC precision requires a different technique than > > binary-weighted digits. Fortunately, there are many ways to > implement a DAC. > > > > Brian > > > > > > On Mar 18, 2026, at 4:34 AM, Tom Wiltshire wrote: > >> Roland had form for this. SH-101 uses a simple DAC built from a > few resistors too. > >> > >> Like Roman said, it doesn't really make sense nowadays when DACs > are cheap, but it was worth it then. > >> > >> Tom > >> > >> On 18 Mar 2026, at 11:31, mark verbos wrote: > >>> Like a TR-909. > >>> But, surely it is cheaper to use 1% resistors rather than a > custom resistor array made. > >>> > >>> Mark > >>> > >>> On Mar 17, 2026, at 18:44, David Manley wrote: > >>>> It's interesting to see how PAiA's John Simonton solved some > these issues in the 1970's by having a custom laser trimmed resistor > network built for their 6-bit "Equally Tempered DAC" to be used with > linear VCOs. See the bottom of the schematic on page 18, the > resistor values are on the last page. > >>>> > >>>> https://paia.com/wp-content/uploads/2024/05/8780pgs.pdf > <https://paia.com/wp-content/uploads/2024/05/8780pgs.pdf> > > <https://paia.com/wp-content/uploads/2024/05/8780pgs.pdf > <https://paia.com/wp-content/uploads/2024/05/8780pgs.pdf>> > >>>> > >>>> As is typical for PAiA a very low cost solution: build your > own DAC with a few components. > >>>> > >>>> -Dave > > > > > > ________________________________________________________ > > This is the Synth-diy mailing list > > Submit email to: Synth-diy@synth-diy.org <mailto:Synth-diy@synth- > diy.org> > > View archive at: https://synth-diy.org/pipermail/synth-diy/ > <https://synth-diy.org/pipermail/synth-diy/> > > <https://synth-diy.org/pipermail/synth-diy/ <https://synth- > diy.org/pipermail/synth-diy/>> > > Check your settings at: https://synth-diy.org/mailman/listinfo/ > synth-diy <https://synth-diy.org/mailman/listinfo/synth-diy> > > <https://synth-diy.org/mailman/listinfo/synth-diy <https://synth- > diy.org/mailman/listinfo/synth-diy>> > > Selling or trading? Use marketplace@synth-diy.org > <mailto:marketplace@synth-diy.org> > > > > ________________________________________________________ > > This is the Synth-diy mailing list > > Submit email to: Synth-diy@synth-diy.org <mailto:Synth-diy@synth- > diy.org> > > View archive at: https://synth-diy.org/pipermail/synth-diy/ > <https://synth-diy.org/pipermail/synth-diy/> > > Check your settings at: https://synth-diy.org/mailman/listinfo/ > synth-diy <https://synth-diy.org/mailman/listinfo/synth-diy> > > Selling or trading? Use marketplace@synth-diy.org > <mailto:marketplace@synth-diy.org> > ________________________________________________________ > This is the Synth-diy mailing list > Submit email to: Synth-diy@synth-diy.org <mailto:Synth-diy@synth- > diy.org> > View archive at: https://synth-diy.org/pipermail/synth-diy/ > <https://synth-diy.org/pipermail/synth-diy/> > Check your settings at: https://synth-diy.org/mailman/listinfo/ > synth-diy <https://synth-diy.org/mailman/listinfo/synth-diy> > Selling or trading? Use marketplace@synth-diy.org > <mailto:marketplace@synth-diy.org> > > > ________________________________________________________ > This is the Synth-diy mailing list > Submit email to: Synth-diy@synth-diy.org > View archive at: https://synth-diy.org/pipermail/synth-diy/ > Check your settings at: https://synth-diy.org/mailman/listinfo/synth-diy > Selling or trading? Use marketplace@synth-diy.org
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Re: [sdiy] Linear response VCOs?
2026-03-22 by Olav Kvern