[sdiy] 1-quadrant multiplier with 2164

Todd Sines sines_list at scale.la
Thu Jan 20 19:32:05 CET 2022


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

As you can see even a smaller clone can be quite costly.
https://reverb.com/item/3590031-analogue-systems-rs-240-bode-frequency-shifter
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

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
"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
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> 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] 
> 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> 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] 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> 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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