[sdiy] 1-quadrant multiplier with 2164

Todd Sines sines_list at scale.la
Thu Jan 20 20:36:46 CET 2022 

Ah ha!  Found it, can’t say you made it easy to track down
https://www.modwiggler.com/forum/viewtopic.php?f=16&t=246966

Would happily buy one of the Lazertran panel modules from you.

I am also building the 185 and 2 285s so you can see I like to get freaky.


Todd

> On Jan 20, 2022, at 2:27 51PM, David G Dixon <dixon at mail.ubc.ca> wrote:
> 
> There are now 87 Freak Shifts out in the wild all over the world, and everyone seems to be impressed with their performance.  Plus, the price is a measly US $300, which is a fraction of what other Bode frequency shifters cost.  (Bear in mind that I build each one by hand, and each one takes me about 5 hours, so they are not mass produced.)
>  
> Hence, not to put too fine a point on it, but I would say that the Freak Shift is the analogue design to beat.
> 
> From: Todd Sines [mailto:sines_list at scale.la] 
> Sent: Thursday, January 20, 2022 10:32 AM
> To: synth-diy
> Cc: David G Dixon; cheater cheater
> Subject: Re: [sdiy] 1-quadrant multiplier with 2164
> 
> [CAUTION: Non-UBC Email]
> I’m not very dialed in with the math, but I would say that Harald’s analogue design is the one to beat, and Don’s was more of a quasi-kludged modular building block that had mixed results. The math was right but the sound was a bit different, from what I can tell. 
> 
> The 185 is basically a dual mixer that combines 2 phase shifters and a ring modulator that are hard wired as a hopped up ring modulator. 
> Daniel (LA67) himself mentions that the Bode / Haible design is an “easier, flexible, and more modern" route to go.
> https://modwiggler.com/forum/viewtopic.php?t=211951 <https://modwiggler.com/forum/viewtopic.php?t=211951>
> 
> As you can see even a smaller clone can be quite costly.
> https://reverb.com/item/3590031-analogue-systems-rs-240-bode-frequency-shifter <https://reverb.com/item/3590031-analogue-systems-rs-240-bode-frequency-shifter>
> http://www.cluboftheknobs.com/pro_c1630.html <http://www.cluboftheknobs.com/pro_c1630.html> [970€]
> 
> The 285 rev 2, all analogue, does all of the above but puts all of the above components accessible on the panel to utilize the sections on their own.
> https://modwiggler.com/forum/viewtopic.php?t=194345 <https://modwiggler.com/forum/viewtopic.php?t=194345>
> 
> The 285 rev 1 design, based on a Spin FV1 DSP IC is “reasonable” according to Dave Brown
> https://modularsynthesis.com/roman/buchla285_fv1/buchla285_fv1.htm <https://modularsynthesis.com/roman/buchla285_fv1/buchla285_fv1.htm>
> "While not as good as the original all-analog frequency shifter, the performance is reasonable and the sound qualities are quite nice."
> 
> Haible’s design is still available, somehow, for sale at Random Source.
> https://randomsource.net/haible/vintage <https://randomsource.net/haible/vintage>
> http://jhaible.com/legacy/frequency_shifter_fs1a/fs1a <http://jhaible.com/legacy/frequency_shifter_fs1a/fs1a>
> 
> 
> 
> Todd
> 
>> On Jan 20, 2022, at 1:02 29PM, David G Dixon via Synth-diy <synth-diy at synth-diy.org <mailto:synth-diy at synth-diy.org>> wrote:
>> 
>> I suppose that anything is possible, cheater.  However, not really with a
>> Bode frequency shifter, which is what the Freak Shift is.
>> 
>> In case y'all didn't know, the Bode frequency shifter is really just a
>> trigonometric engine.  It realizes the so-called angle sum and difference
>> identities, and this gives the frequency shifting.  It will shift the
>> frequencies accurately over whatever frequency range that the Dome filters
>> give accurate 90-degree phase shift, and will give inaccurate shifting
>> outside of that range.
>> 
>> 
>> 
>> -----Original Message-----
>> From: cheater cheater [mailto:cheater00social at gmail.com <mailto:cheater00social at gmail.com>] 
>> Sent: Thursday, January 20, 2022 7:25 AM
>> To: David G Dixon
>> Cc: Neil Johnson; synth-diy
>> Subject: Re: [sdiy] 1-quadrant multiplier with 2164
>> 
>> [CAUTION: Non-UBC Email]
>> 
>> I wonder if it's possible to build a frequency shifter that shifts higher
>> harmonics more than lower harmonics.
>> 
>> On Wed, Jan 19, 2022 at 6:48 PM David G Dixon <dixon at mail.ubc.ca <mailto:dixon at mail.ubc.ca>> wrote:
>>> 
>>> I must confess that I've lost the thread of this argument just a little
>> bit.
>>> However, what I like about my approach (which I have used many times 
>>> in many different contexts) is that, in order to build a nice linear 
>>> VCA from 2164, you really need to have a clean 5V source anyway.  I 
>>> keep a pile of LM336Z5 for just this purpose, and use two opamps to 
>>> buffer and invert this to get low-output-impedance +5V and -5V 
>>> references on all my multipliers.  If one uses precisely matched 
>>> resistors on the inverter, then one can get those references within a 
>>> mV of each other -- the actual voltage doesn't matter (and it is 
>>> usually around 4.90V), but as long as they are equal and opposite, 
>>> then they can be used for precise multiplication.  This is one of the keys
>> to the precision of my Freak Shift frequency shifter circuit.
>>> 
>>> I don't really understand how adding a stable DC value to a signal 
>>> increases the noise of that signal.  I must confess that I also don't 
>>> care at all about it.  My method is the simplest.  You don't have to 
>>> pre-condition the incoming signals at all.  The CV signal is 
>>> unchanged, and the DC reference levels are simply summed to the incoming
>> signal.
>>> 
>>> If you want to change the actual levels, you can simply change the 
>>> resistor values.  I do this all the time.  One of the keys to my 
>>> one-VCA four-quadrant-multiplier circuit (of which there are two in 
>>> the Freak Shift, made from a single 2164 chip) is to lift and diminish 
>>> the CV such that the zero point of the multiplier is at +5V and full 
>>> +/- unity-gain multiplication occurs between +2.5V and +7.5V.  This 
>>> gives lots of headroom
>>> -- it essentially makes it impossible for the CV in the multiplier to 
>>> hit zero at the 2164 control pin (because the incoming CV signal will 
>>> never be anywhere near 20Vpp), which would give a dead zone on the 
>>> multiplication.  I achieve this simply by bringing the CV in through 
>>> 200k while using 100k on the reference voltages.  Of course, the 
>>> signal is now cut in half as well, so I simply double the feedback 
>>> resistor on the I-V converter.  As long as all of these 100k and 200k 
>>> resistors are within 0.1% of each other (and the 100k and 200k 
>>> resistors don't need to be in a precise ratio -- they only need to be 
>>> precise within their own values), and all incoming signals are AC 
>>> coupled through big back-to-back electrolytics, then the four-quadrant
>> multiplication is very tight, which is important for frequency shifting.
>>> 
>>> 
>>> 
>>> -----Original Message-----
>>> From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org <mailto:synth-diy-bounces at synth-diy.org>] On Behalf Of 
>>> cheater cheater via Synth-diy
>>> Sent: Wednesday, January 19, 2022 4:23 AM
>>> To: Neil Johnson
>>> Cc: SDIY List
>>> Subject: Re: [sdiy] 1-quadrant multiplier with 2164
>>> 
>>> [CAUTION: Non-UBC Email]
>>> 
>>> I wonder if it matters that Dave's version will create theoretically 
>>> more distortion on the positive swing of whatever vs the negative 
>>> swing, whereas my version will apply distortion (non-linearity) more 
>>> or less symmetrically... do the numbers show that it matters at all? I 
>>> bet it would matter with some, let's say, crappy devices.
>>> 
>>> On Tue, Jan 18, 2022 at 1:57 PM Neil Johnson via Synth-diy 
>>> <synth-diy at synth-diy.org <mailto:synth-diy at synth-diy.org>> wrote:
>>>> 
>>>>> This is certainly true but note also the importance of zero when
>>> multiplying. The zero signal stays zero no matter what you multiply 
>>> by. In Rutger's case that zero is in fact -5V, so the origin of Neil's 
>>> graph should be at -5V signal and zero control voltage. That is why 
>>> the level-shifting solution is so effective and it is also why I 
>>> believe Rutger is correct to call this a one quadrant multiplier.
>>>> 
>>>> Yes, this is just a bit of algebraic juggling.
>>>> 
>>>> If we take Dave's approach:
>>>> - convert the bipolar +/- 5V input to a unipolar 0 to -10V input
>>>> - add a -5V offset to the output _after_ the VCA (so no bearing on 
>>>> the quadrantiness of the VCA itself)
>>>> 
>>>> With a unipolar CV and a unipolar signal ... a 1-quadrant VCA.
>>>> And don't forget that as-drawn the linearised VCA is inverting.
>>>> 
>>>> Cheers,
>>>> Neil
>>>> 
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>> 
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