[sdiy] Elektor Formant Re: Test / Sequencer / Arduino

Thu Mar 26 17:50:50 CET 2015

Ok, the 5V supply is only used by the VCOs, indeed, and only for this schmitt trigger, a bit odd design indeed. No idea why a 7413 is used there. 

In those days I never thought about it really, I just built it. And it works alright.

It would be fun to know more about the design process of the Formant back then. Who knows we can find mr. Chapman? 

Rick

> On 26 Mar 2015, at 15:48, Harald <sdiy at haraldswerk.de> wrote:
> 
> Hallo Rick,
> 
> the main point for using the REF02 was to get rid of the 5V power rail at all. Second was for decoupling. The benefits in case of temp stability are marginal as you said.
> 
> I kept the 7413 Schmitt Trigger because i want to stay close to the original.
> 
> There might be some reasons for coupling the generated signals or hearing something at the output when it should be quiet. Let's discuss this point in another thread or offline.
> 
> I made two boards. You can find the waveshaper at my site.
> 
> The VCO's are tracking that well, that i decided to reactivate my old scanner keyboard plans for going polyphon. You can see some pics on my blog.
> 
> Rebuild of the 24dB filter (with 13700) is on its way. May be going for 36dB. And a ladder filter as well.
> 
> Harald
> 
> www.haraldswerk.de
> 
>> Am 26.03.2015 um 11:40 schrieb Rick Jansen:
>> Hallo Harald,
>> 
>> More good werk on the Formant!
>> 
>> And yes indeed, changes in the 5V indeed influence pitch. However, the
>> specs of the uA723 voltage regulator used to obtain the 5V are that
>> there is a typ. 0.003% change in the output voltage per degree C, the
>> REF02 spec is 20 ppm (for the C variety), which translates to 0.002%
>> change per C, if I calculated correctly? If I calculated that right
>> there may not be a big gain in using a REF02? The uA723 is not a bad part.
>> 
>> My Formant DOES have some coupling of the generated signals: you can
>> sometimes hear a soft whine in the output signal even when it should be
>> silent. It could well be that this is via a power line somewhere!
>> C4/680n on the 5V line is pretty far from the V++ pin of the
>> schmitt-trigger, I may try adding another one to see if I can get rid of
>> that whine.
>> 
>> Another drift factor could be that the threshold of the 7413 or the
>> LS7413 varies with temperature... Yes, it does. Both Umin and Umax vary
>> with temperature. Hmm. Perhaps it would be better to use a good opamp
>> comparator in a new design.
>> 
>> I like the sync addition!
>> 
>> And a nice looking board it is too. The original VCO board is far too
>> big, it would have been nice if it was 2 separate eurocards in the first
>> place. But I guess they preferred a board where people could make no
>> mistakes.
>> 
>> Thanks, I will read your site more later.
>> 
>> rick
>> 
>> 
>> 
>>> On 26/03/2015 10:24, Harald wrote:
>>> Hallo Rick,
>>> 
>>> for your resting uA726 this might be of interest:
>>> http://www.haraldswerk.de/NGF/NGF_VCO_CORE_ONE/VCO_CORE_ONE.html
>>> I have rebuild the Formant VCO with some modern parts keeping the
>>> overall architecture original.
>>> 
>>> Harald
>>> 
>>>> Am 25.03.2015 um 14:50 schrieb Rick Jansen:
>>>> hi Carsten,
>>>> 
>>>> Great work! Its clearly visible you put a lot of work and effort into
>>>> your Formant. How did you make the white front panels by the way?
>>>> 
>>>> I've always wondered who C. Chapman is. In some web pages he's referred
>>>> to as "Cyril Chapman", as "Colin Chapman" in others. I seem to remember
>>>> someone from Elektor mentioned the name is a writers name, but he could
>>>> not recall the authors true name. Or perhaps it was C. Chapman himself
>>>> who told me :-)
>>>> 
>>>> The Formant is from 1977, some parts now *really* are hard to get, 38
>>>> years later... The uA726 is scarce, older Moog mini's and Memory Moogs
>>>> use them too, and they are sought after as repair parts. The CA3084 PNP
>>>> array may be hard to find, and the CA3080 OTA's are getting rare too.
>>>> 
>>>> All in all, building a Formant is a project only undertaken by the
>>>> brave. Or was it the foolish?
>>>> 
>>>> As for the sequencer: I'm going to try if it is feasible to finish it by
>>>> replacing the oldfashioned digital circuits by an Arduino Uno (14
>>>> digital I/O pins). Perhaps even an Arduino Mega, which has even more
>>>> digital I/O pins (54!).
>>>> 
>>>> Best, and thanks for the links!
>>>> 
>>>> rick
>>>> 
>>>> 
>>>>> On 25/03/2015 12:18, Carsten Toensmann wrote:
>>>>> Hi Rick,
>>>>> 
>>>>> when I started my own Formant project (MSS2000) I read your pages of
>>>>> course
>>>>> to get an impression of what it could mean to start such a huge
>>>>> project. And
>>>>> yes - it was a LOT of work, but it was worth it. I never built a
>>>>> sequencer
>>>>> for it though but a MIDI interface.
>>>>> 
>>>>> Nowadays it seems to me that the Formant disappeared from the DIY
>>>>> scene more
>>>>> or less, which is a pity in my opinion, so I hope you will manage to
>>>>> reanimate your system and continue your project.
>>>>> 
>>>>> I finished my Formant project in May 2008 after a building time of 6
>>>>> years.
>>>>> The system has been part of several music productions and I like it.
>>>>> See
>>>>> details on http://www.analog-monster.de/tagebuch_en.html
>>>>> 
>>>>> Regards
>>>>> 
>>>>> Carsten
>>>>> 
>>>>> -----Ursprüngliche Nachricht-----
>>>>> Von: synth-diy-bounces at dropmix.xs4all.nl
>>>>> [mailto:synth-diy-bounces at dropmix.xs4all.nl] Im Auftrag von Rick Jansen
>>>>> Gesendet: Mittwoch, 25. März 2015 11:38
>>>>> An: Synth-Diy
>>>>> Betreff: [sdiy] Test / Sequencer / Arduino
>>>>> 
>>>>> Hi,
>>>>> 
>>>>> This is both a test message and a new-old project revival note. I was
>>>>> notified traffic on synth-diy may have halted, but as far as I can see
>>>>> everything still works.
>>>>> 
>>>>> For the Formant I was, years ago, designing and building a sequencer,
>>>>> as we
>>>>> all do one time in our life. This one is inspired by the Synthanorma
>>>>> Sequenzer, as used by Kraftwerk and Tangerine Dream, in that it does
>>>>> not
>>>>> have potmeters but uses 12-position rotary switches.
>>>>> 
>>>>> Mine has 3 rotary switches per step: 1. note duration 2. octave, 3.
>>>>> pitch. A
>>>>> switch, a trigger output and a LED (to impress the ladies) are also
>>>>> included.
>>>>> 
>>>>> I was in the process of doing a circuit built with the regular HC
>>>>> digital
>>>>> ic's, like timers, counters, multiplexers etc etc, and a DA-converter.
>>>>> 
>>>>> Basically the circuit already work[ed][s], but you know how it is when
>>>>> duty
>>>>> and jobs and relatinships take their time: such projects get shelved.
>>>>> 
>>>>> For years I've seen projects in magazines like Elektor, using small
>>>>> digital
>>>>> controllers like Arduino. Usually I skipped those, as that is not the
>>>>> kind
>>>>> of electronics I personally like a lot. But I realise now how cheap and
>>>>> versatile they have become. They're almost a uA741. Perhaps even more
>>>>> Arduino's are sold than uA741's these days. And, with analog in/out,
>>>>> and
>>>>> digital in/out pins. Impressive.
>>>>> 
>>>>> I even saw that is is quite easy to sync an Arduino program with the
>>>>> MIDI
>>>>> clock!
>>>>> 
>>>>> Here is the current status:
>>>>> 
>>>>>    <http://dropmix.xs4all.nl/rick/Emusic/Sequencer/>
>>>>> 
>>>>> Now I need to bring back to life the Formant, which has been sitting
>>>>> there,
>>>>> unused for about 10 years. Hope the elco's are all still keeping their
>>>>> liquids!
>>>>> 
>>>>> Best,
>>>>> 
>>>>> rick
>>>>> 
>>>>> 
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