[sdiy] OBXa LFO questions

[ColinMuirDorward]

Thanks Chris for this explanation!
I became curious about the original after acquiring a UBXa, which seems to
have an LFO/voice, but under normal circumstances they are all doing
exactly the same thing, pretending to be just one (or two, for dual layer)
LFO. It seems Behri followed the original model, but left the door open for
a more "modern" approach.
Regards,
Colin

On Sat, Nov 16, 2024 at 8:55 PM Chris McDowell <declareupdate at gmail.com>
wrote:

> This page.
> [image: PastedGraphic-1.png]
>
>
> And it's this section of the circuit:
> [image: PastedGraphic-2.png]
>
> Half of U150 + U157 make up a little VCO (our LFO. 1 of 2, this is the
> upper LFO).
> The other half of U150 + U149 + U148 make up a sample and hold.
> That middle 4053 section selects between noise and the LFO triangle
> output, the 4053 further right selects between that result and the LFO
> square output. That final 4053 selects between all this (the upper LFO) or
> the lower LFO, which I assume is for when you aren't splitting the keyboard
> and all voices are on the same preset, thus using the same LFO.
>
> Chris McDowell
>
> On Nov 16, 2024, at 9:59 PM, ColinMuirDorward <colindorward at gmail.com>
> wrote:
>
> Thank Chris, can you point to which page has the LFO?
> Regards,
> Colin
>
>
> https://thecreativeinitiativeswarehouse.cargo.site/
> https://www.instagram.com/colinmuirdorward/
> <https://www.instagram.com/colinmuirdorward/>
> https://www.instagram.com/thefollower__________________/
>
>
> On Sat, Nov 16, 2024 at 8:27 PM Chris McDowell <declareupdate at gmail.com>
> wrote:
>
>> In the schematic I see two analog LFOs and no LFOs on the voice card. So,
>> not digital, and not per-voice.
>>
>> It is a "single" global LFO, but there are two so that the upper and
>> lower programs each have their own.
>>
>> Cheers,
>> Chris
>>
>> On Nov 16, 2024, at 7:34 PM, ColinMuirDorward via Synth-diy <
>> synth-diy at synth-diy.org> wrote:
>>
>> 
>>
>> Hi, wondering if anyone can chime in about the OBXa architecture.
>> I'm wondering about the LFO, and how it is generated. Digitally?
>> Also wondering if there is just a single/global LFO, or if it's provided
>> per voice.
>> I tried asking the interwebs... but there is just so much noise out there.
>> I also tried looking at schematics, but that was a bit beyond me.
>> Kind regards,
>> Colin
>>
>> --
>> https://thecreativeinitiativeswarehouse.cargo.site/
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>> <https://www.instagram.com/colinmuirdorward/>
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>>
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-- 
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https://www.instagram.com/colinmuirdorward/
<https://www.instagram.com/colinmuirdorward/>
https://www.instagram.com/thefollower__________________/
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