[sdiy] Patchable polyphonic synth with FM or AM transmission idea

Wed Dec 26 20:29:53 CET 2018

Sorry about my earlier recommendations; didn’t realize you wanted all analog.

As far as switches go, I really like the Intersil (now Renesas) BiCMOS 16x8 crosspoint switch IC. Low ron and very very low crosstalk. I used it when designing the Music Man ‘Game Changer’ guitars for pickup switching, but, it maxes out at 15V.
https://www.renesas.com/us/en/products/audio-video/video-switching/unbuffered-crosspoint-switches/device/CD22M3494.html

Rock & Roll,
Oren Levy

> On Dec 26, 2018, at 09:09, cheater00 cheater00 <cheater00 at gmail.com> wrote:
> 
> analog switch ICs are terrible, let's just skip them. You're not
> making an analog switch ic based system anywhere near close a medium
> sized modular, it's insanity and prone to shitloads of interference.
> same with mod busses. the switch ICs are very proprietary. I haven't
> found a digital multiplexer IC that was good, has anyone got any good
> suggestions?
> 
>> On Wed, Dec 26, 2018 at 5:16 PM Tom Wiltshire <tom at electricdruid.net> wrote:
>> 
>> Why not make a number of “analog virtual patch cables” with analog switch ICs? Each cable has a switch at both ends, one selects between X sources, and the other selects between Y destinations. This is conceptually very similar to a genuine modular with hardware cables, but the control signals can be fanned out to however many voices you have.
>> 
>> Alternatively, you could have a “mod buss” type system, where each module output could be sent to a particular destination buss, and each module input could be switch to tap signal from a given buss. Again, control signals for the switches in such a set-up can be fanned out to however many voices are required.
>> 
>> For any polyphonic system (except the early oberheims?), the control panel is separated from the voice generation, so you can think about the interface separately from the audio-producing part of the circuit.
>> 
>> Tom
>> 
>> ==================
>>       Electric Druid
>> Synth & Stompbox DIY
>> ==================
>> 
>>> On 25 Dec 2018, at 22:40, cheater00 cheater00 <cheater00 at gmail.com> wrote:
>>> 
>>> I want to make this work for an all-analog synthesizer, but rather
>>> than use crosspoint switches I want to use patch cables which makes
>>> things much less annoyingly complex and expensive. The thing is, where
>>> on a monosynth you have a single patch cable, on a patchable polysynth
>>> you have n patch cables, one for each voice. So I am currently trying
>>> to work out how to do this using a single patch cable, and frequency
>>> domain multiplexing came to mind. I'm 100% certain an FPGA cannot do
>>> FDM, since almost all of this is analog, so I'm looking at dedicated
>>> radio transmitter chips. At $4 per chip, it's not so bad. The question
>>> is how to make the chips talk to a single medium without fighting each
>>> other.
>>> 
>>>> On Tue, Dec 25, 2018 at 11:24 PM Ben Bradley <ben.pi.bradley at gmail.com> wrote:
>>>> 
>>>> What you're describing sounds all-digital.
>>>> 
>>>> It seems to me a crosspoint switch would be the thing to have on each
>>>> (analog) voice, and have them controlled by the usual microcontroller
>>>> for a polyphonic analog-signal-path synthesizer. Of course, this is a
>>>> woefully incomplete description.
>>>> 
>>>>> On Tue, Dec 25, 2018 at 4:58 PM oren levy <orenlevysticky at gmail.com> wrote:
>>>>> 
>>>>> You can use the FPGA to combine all the data you are trying to transmit into a single stream that you can transmit over a single cable.
>>>>> MADI interfaces are expensive as a unit. There are various ways to implement MADI at a board level with microcontrollers and FPGAs.
>>>>> Other options would be to make your own protocol. Using a TRRS cable should be able to provide enough bandwidth at more manageable speeds that won’t require you to think about transmission line theory.
>>>>> 
>>>>> 
>>>>> Rock & Roll,
>>>>> Oren Levy
>>>>> 
>>>>>> On Dec 25, 2018, at 11:13, cheater00 cheater00 <cheater00 at gmail.com> wrote:
>>>>>> 
>>>>>> The objective is to be able to create a way for a single patch cord to
>>>>>> carry 16 voices. I'm not sure how an FPGA in itself will help me, have
>>>>>> you got any ideas?
>>>>>> 
>>>>>> MADI interfaces are prohibitively expensive.
>>>>>> 
>>>>>>> On Tue, Dec 25, 2018 at 9:19 PM oren levy <orenlevysticky at gmail.com> wrote:
>>>>>>> 
>>>>>>> I think you’d be better off using FPGAs so you can mux the signals however you want along with data. Either a bunch of small ones or one big one per module.
>>>>>>> If you just want to share audio and don’t want to mess around with FPGAs, you can probably use a protocol like MADI. Not sure if MADI has a DC coupling requirement but if not, CV could also be passed.
>>>>>>> You’d probably want a very stable clock to sync all the modules to and optimize clock phase delays so everything can mux/demux in sync.
>>>>>>> 
>>>>>>> Rock & Roll,
>>>>>>> Oren Levy
>>>>>>> 
>>>>>>>> On Dec 25, 2018, at 10:01, Mike Beauchamp <list at mikebeauchamp.com> wrote:
>>>>>>>> 
>>>>>>>> 
>>>>>>>>> transmission. In a 16 voice system, at about 5 output functions per
>>>>>>>>> module, and 12 modules, you can easily use up ~1000 of those, which
>>>>>>>>> drops the price to $4. I was wondering what everyone thinks about this
>>>>>>>>> sort of scheme.
>>>>>>>> 
>>>>>>>> So there's $4000 worth of just one IC in a single complete polysynth?
>>>>>>>> 
>>>>>>>> 
>>>>>>>> 
>>>>>>>> _______________________________________________
>>>>>>>> Synth-diy mailing list
>>>>>>>> Synth-diy at synth-diy.org
>>>>>>>> http://synth-diy.org/mailman/listinfo/synth-diy
>>>>>>> 
>>>>>>> _______________________________________________
>>>>>>> Synth-diy mailing list
>>>>>>> Synth-diy at synth-diy.org
>>>>>>> http://synth-diy.org/mailman/listinfo/synth-diy
>>>>> 
>>>>> _______________________________________________
>>>>> Synth-diy mailing list
>>>>> Synth-diy at synth-diy.org
>>>>> http://synth-diy.org/mailman/listinfo/synth-diy
>>>> 
>>>> _______________________________________________
>>>> Synth-diy mailing list
>>>> Synth-diy at synth-diy.org
>>>> http://synth-diy.org/mailman/listinfo/synth-diy
>>> 
>>> _______________________________________________
>>> Synth-diy mailing list
>>> Synth-diy at synth-diy.org
>>> http://synth-diy.org/mailman/listinfo/synth-diy
> 
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at synth-diy.org
> http://synth-diy.org/mailman/listinfo/synth-diy
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://synth-diy.org/pipermail/synth-diy/attachments/20181226/410fe341/attachment.htm>