Doc Sketchy's new analog FREQUENCY SHIFTER!

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Dr. Sketch-n-Etch
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Re: Doc Sketchy's new analog FREQUENCY SHIFTER!

Post by Dr. Sketch-n-Etch » Sat Jun 05, 2021 4:02 pm

rediris -- Yes.

transferpoint -- No.
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Re: Doc Sketchy's new analog FREQUENCY SHIFTER!

Post by Dr. Sketch-n-Etch » Sat Jun 05, 2021 4:29 pm

Bernie Hutchins wrote:
Wed Jun 02, 2021 8:50 pm
Dr. Sketch-n-Etch » Wed Jun 02, 2021 2:10 am said in part:
“…….it turns out that the key to accurate single-sideband generation in the Bode frequency shifter is AC-coupling of the quadrature signals going into the multipliers -- they don't talk about that in Electronotes -- I had to discover that little gem myself. …….”

Any mention of a need of removing the DC components is OBVIOUS (high school trig), clear to most everyone here, and I suspect we did cover this if one looked carefully. This removal of DC from the quadrature signals can be done by trimming (best) or by AC coupling (which is, after all, HP filtering and subject to the resulting magnitude and transient responses).

I suspect that achieving the best sideband separation is more a matter of addressing differential phase error (which I believe we reported) and/or well-trimmed sum/difference circuitry.

What analysis (like “classical sensitivity”):
http://electronotes.netfirms.com/EN195.pdf
(see pp 4-10) led to your purported discovery?

-Bernie
First of all, Bernie, nothing is OBVIOUS until you try it, as least not to me. I built a prototype and was disappointed with the clarity of the sidebands, even when all of the resistors were hand picked for accuracy. Then I noticed that there was a bit of DC on my Dome filter output, so I did some thinking about that and realized that it would be the main source of inaccuracy in the multipliers, which I confirmed with simulation (I simulate everything). So, I slapped back-to-back 47uF electrolytics on the multiplier inputs, and that cleaned everything up. Also, I confirmed that the caps were large enough to pass signals well down in the LFO range without attenuation.

Also, the accuracy of the sum/difference circuitry is about the least critical thing. That was the one part of the Freak Shift circuit where I didn't have to take any special precautions -- no trimmers or hand-selecting of resistors, just 1% resistors straight outta the bag are good enough. I built one with trimmers there, but it made absolutely no difference.

There are only two trimpots on the entire module and they are there to ensure exact cancellation of the input signals in the signal inverter which is the trick to making a pair of balanced modulators from a single 2164 chip. The actual multipliers require no trimpots at all. All I have to do is to ensure that my +5V and -5V sources are exactly equal and opposite (which requires two hand-picked identical resistors on the inverter) and that all of the gain-fixing resistors in the multiplier circuit (of which there are eight) are also hand-picked identical. I just measure a bunch of 100k resistors and put them in separate baggies at 0.1% intervals. All I have to do is to take all ten important 100k resistors for any given build from the same bag, and the multipliers are guaranteed to work perfectly and generate very clean sidebands. This is easier than it sounds, since 80% of my latest batch of 100k resistors seem to be either 99.5k or 99.6k.

I should also mention that building 50 of these Freak Shift modules would have been absolutely impossible had I not figured out how to solve the general Dome filter problem, which I learned from Orchard's 1950 paper, by way of Douglas's 1961 thesis. Now that I have a Visual Basic code not only for solving the RC constants using an Excel command, but also for finding the best pairs of resistor values from the 1% E96 series, I can very quickly find the best combinations of resistors for the capacitors I have on hand. In other words, I can do in seconds what it would have taken hours to do before, presuming that I could have even found a good solution for an 18-stage Dome filter with accurate phase displacement over five orders of magnitude of frequency.
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Re: Doc Sketchy's new analog FREQUENCY SHIFTER!

Post by foliephonics » Sun Jun 06, 2021 4:13 am

Thank you Doc, great job !

:tu: :yay: :hail:

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Re: Doc Sketchy's new analog FREQUENCY SHIFTER!

Post by geremyf » Sun Jun 06, 2021 8:54 am

Hi, Apologies I have read through the thread but I'm wondering what the final depth ended up being? 3"?

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Re: Doc Sketchy's new analog FREQUENCY SHIFTER!

Post by Bernie Hutchins » Sun Jun 06, 2021 8:05 pm

David - Thanks

Since the issue here is associated with DC coming out of the dome filters, we are forced to suppose that the dome filters are defective (very unlikely), or that there is (are) DC components at the dome outputs courtesy of whatever non-dedicated signal sources you are using as inputs.

Such DC components do not affect the (double sideband – e.g., balanced) multiplier sidebands, but manifest as “leaked” components at the ORIGINAL (unshifted) frequencies.

At the multiplier outputs any failure to balance the summer gains (and/or compensate for mismatched multiplier gains) results in incomplete cancellation of the UNINTENDED SIDEBAND (harder to notice).

Originally, problems were few since FS’s usually had ONE dome filter driven by a microphone amp (AC coupled) and a dedicated quadrature oscillator.

-Bernie

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Re: Doc Sketchy's new analog FREQUENCY SHIFTER!

Post by Dr. Sketch-n-Etch » Mon Jun 07, 2021 1:52 pm

Bernie, the Freak Shift has both dedicated SUM and DIFFERENCE outputs as well as a blended output OUT which is the buffered output of a crossfading pot connected to both. I generally only use OUT myself, but I don't hear any of the wrong sideband at the pot extremes. Of course, if the attenuation was less than -40 dB or so it would still be very faint and hardly noticeable.

In any case, this is intended to be a musical tool, and not a laboratory instrument for generating perfect single sidebands, but I have still been pretty darn careful while also trying to eliminate construction and calibration complexity. The trick with so many of these things is to find the right balance between accuracy and cost-effectiveness. Most analog frequency shifters cost from $800 to $2200 if you can find them at all -- Freak Shift is $300, and I believe that it is the best one of the bunch.

Also, my first version of this frequency shifter had a dedicated quadrature oscillator (a dual-core Rubicon VCO with one core permanently synced to the other in such a way that it generated the quadrature triangle). It works great, but the Freak Shift is simply much cooler and more versatile because of the quadrature source Dome filter, and the fact that anything can be used as an external SIN and COS source with the flick of a switch (even things that are not in quadrature).
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Re: Doc Sketchy's new analog FREQUENCY SHIFTER!

Post by Dr. Sketch-n-Etch » Wed Jun 09, 2021 2:57 am

UPDATE: I finished unit 23 today. This is the first one that didn't work right away. The 18-stage Dome filter worked in the audio range, but in the LFO range the Lissajous figure went oval and eventually turned into a diagonal line. I couldn't see any solder bridges or anything. So, I set it aside, had dinner, watched a couple episodes of Sweet Tooth on Netflix with my wife, then finally had another look. I measured all of the RC resistors, and they were all OK. Then I started measuring the caps. One of them didn't register any capacitance. Then I saw it: a cold solder joint -- one lead from the capacitor was not really touching the solder all around it. I confirmed this when I was actually able to pull the cap lead out of the hole. Anyway, long story short, I soldered it in properly and now that unit works perfectly.

That may be only the second cold solder joint I've made in 13 years of DIY electronics.

Panels come Friday, and then a whole bunch of wigglers are gonna get Freak Shifts.
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Re: Doc Sketchy's new analog FREQUENCY SHIFTER!

Post by zengomi » Wed Jun 09, 2021 5:23 am

That account was surprisingly inspiring, Doc. As a non-DIYer having but a single self-built module (R•S Triple+ Waveshaper) under my belt, I'm more interested now in having another go, albeit with a simpler module than Freak Shift.

Looked up "Sweet Tooth". Will check it out. Thanks for that, too.

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Re: Doc Sketchy's new analog FREQUENCY SHIFTER!

Post by pekbro » Wed Jun 09, 2021 5:33 am

Dr. Sketch-n-Etch wrote:
Wed Jun 09, 2021 2:57 am


Panels come Friday, and then a whole bunch of wigglers are gonna get Freak Shifts.
Awesome!

Also "Sweet Tooth" is a cool show imo. I had to stop after a couple episodes to keep from watching them
too fast. :lol:

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Re: Doc Sketchy's new analog FREQUENCY SHIFTER!

Post by Dr. Sketch-n-Etch » Wed Jun 09, 2021 2:49 pm

UPDATE: All the Freak Shift invoices have now been sent. If you were expecting one but didn't get it, then please send me a PM.

Update 2: Tonight we will finish Sweet Tooth (it's only 8 episodes)... kinda dreading it, cuz we're running out of things to watch. There are, however, apparently some fresh episodes of Unforgotten with the incomparable Nicola Walker and Sanjeev Bhaskar that we haven't seen, so looking forward to those. I'm really in the mood for a good British crime drama.
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Re: Doc Sketchy's new analog FREQUENCY SHIFTER!

Post by Dr. Sketch-n-Etch » Fri Jun 11, 2021 1:43 am

Here's the very first completed eurorack Freak Shift, with a laser-engraved black anodized aluminum panel:
BlackFreakShiftFront.jpeg
BlackFreakShiftSide.jpeg
I finally worked up the courage to drill the holes in the panel, and it went pretty easily with a step drill. This one goes out to Adam in Maryland tomorrow. I have one more panel to drill and that one will go out to Casey in Minnesota. My artist buddy is back from vacation, so tomorrow I'm going to engrave maybe 10 more panels, so I'll be able to send out all the black-panel orders. Also tomorrow, the regular panels are supposed to come from Cincinnati, so this weekend I'll be testing and packing Freak Shifts. As of today, I have 24 units completed, and I've tested all the Dome filters, but I still need to test the actual multipliers and output amps, and adjust the two trimmers on every unit. I figured I'd do that once the panels were on.

If anybody has any knob colour preferences, please let me know via PM. I have every colour of knob, but I don't have an infinite number. I will have to mix and match, but I'll try to colour-coordinate.

I might just make a short video with this unit before I send it off.
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Re: Doc Sketchy's new analog FREQUENCY SHIFTER!

Post by pekbro » Fri Jun 11, 2021 2:01 am

Awesome! Dang that black panel looks cool, oh well... Maybe you should consider setting up a donation link, I would donate
$10 towards getting you a small drill press. A usable 10 " press is going to be under $200 US. -just sayin.

-Cheers

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Re: Doc Sketchy's new analog FREQUENCY SHIFTER!

Post by Dr. Sketch-n-Etch » Fri Jun 11, 2021 2:36 am

I have a drill press, pekbro! How do you think I drill all those PCBs? I spend at least an hour every single day standing in front of a drill press. I was just scared to scratch the black panels. Also, I ordered a hand punch from Eastwood for punching the holes, but it hasn't arrived (and I don't even think they've shipped it -- their customer service has not impressed me). Punching will be a lot easier and faster than drilling, but I don't know when the hand punch will come, but at least now I know I can drill the holes cleanly.
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Re: Doc Sketchy's new analog FREQUENCY SHIFTER!

Post by pekbro » Fri Jun 11, 2021 2:59 am

Dr. Sketch-n-Etch wrote:
Fri Jun 11, 2021 2:36 am
I have a drill press, pekbro! How do you think I drill all those PCBs? I spend at least an hour every single day standing in front of a drill press. I was just scared to scratch the black panels. Also, I ordered a hand punch from Eastwood for punching the holes, but it hasn't arrived (and I don't even think they've shipped it -- their customer service has not impressed me). Punching will be a lot easier and faster than drilling, but I don't know when the hand punch will come, but at least now I know I can drill the holes cleanly.
Ahh ok, it sounded to me like you were trying to do it by hand drill. I was pretty impressed with those holes thinking you had done it
by hand. I know guys who can actually do it by hand with mad drilling skills acquired from many years of machining. lol

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Re: Doc Sketchy's new analog FREQUENCY SHIFTER!

Post by Dr. Sketch-n-Etch » Fri Jun 11, 2021 1:35 pm

The Freak Shift PCB set involves roughly 1000 holes in 5 different sizes. There is no way that anyone is going to do that with a hand drill. I can drill about one hole every two seconds when I'm really on a roll, and it takes just about exactly one hour to drill one board set for the Freak Shift. If I had to do it by hand, it would be completely impractical (it's not terribly practical as it is).
Last edited by Dr. Sketch-n-Etch on Fri Jun 11, 2021 1:41 pm, edited 1 time in total.
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Re: Doc Sketchy's new analog FREQUENCY SHIFTER!

Post by Dr. Sketch-n-Etch » Fri Jun 11, 2021 1:41 pm

UPDATE: The metal hand punch tool I ordered from Eastwood is back-ordered and would not be available until August, so I cancelled that order and ordered one from KMS in Canada (the same place I bought my drill press) that is in stock. I had to call Eastwood on the phone to learn of the back-order situation.

I require a slightly beefier hand punch than the one that is available everywhere, because the dies for that one only go up to 7/32" and I need to punch 3/8" holes.

I can drill the holes in the black panels, but it is a very time-consuming and nerve-wracking pain in the ass. Hence, I am going to drill the second panel I have made, but wait for the hand punch to arrive for the rest of them. As I said, this second hand punch is supposedly "in stock online" and I'm picking it up at the store, so I'm hoping it comes next week. Hence, two black Freak Shifts will go out in the mail, probably on Monday.
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Re: Doc Sketchy's new analog FREQUENCY SHIFTER!

Post by pekbro » Fri Jun 11, 2021 2:30 pm

hmm well that sounds pretty rough. Maybe one of those DIY CNC machines. I know the guys at Delta Sound Labs have one and were making very nice aluminum cases with it, I have 1 of those cases and love it. 1/4 " Aircraft Aluminum. Dunno if they use it for their modules, or if its DIY. Probably, the guys an engineer. Anyway, then you just have to load the thing. Of course thats not going to help you, but maybe worth looking into. I would have thought the manufacturer would drill the holes in the pcb for you from the CAD files.
Of course, I don't have any idea. It just seems like a big hassle for you. *shrug

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Re: Doc Sketchy's new analog FREQUENCY SHIFTER!

Post by BenB » Fri Jun 11, 2021 2:51 pm

Exciting, looking great Doc

What type are the knobs please? So as to look up the different colours available

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Re: Doc Sketchy's new analog FREQUENCY SHIFTER!

Post by BlinkyLights » Fri Jun 11, 2021 3:00 pm

thicc

I like it.

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Re: Doc Sketchy's new analog FREQUENCY SHIFTER!

Post by Dr. Sketch-n-Etch » Fri Jun 11, 2021 8:52 pm

The panels came today. Here's the "His" and "Hers" modules side by side. The Metalphoto panels look spectacular, I think.
FreakShiftHis&Hers.jpeg
Next week I mail a bunch of modules out.

You may have noticed the subtle difference between the output jacks on the two panels. We had to move the words out of the rounded square because the laser engraver rendered the negative words too faintly.
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Re: Doc Sketchy's new analog FREQUENCY SHIFTER!

Post by Moog$FooL$ » Sat Jun 12, 2021 3:50 am

wow!! both are kinda nice..... hopefully worth the wait for those who are waiting.

put me down for a black one in Frac (of course). :razz:
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Re: Doc Sketchy's new analog FREQUENCY SHIFTER!

Post by Dr. Sketch-n-Etch » Sun Jun 13, 2021 1:32 pm

25 units built so far. I'm building about 5 a week now, so I'll have the rest finished in just over a month.
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Re: Doc Sketchy's new analog FREQUENCY SHIFTER!

Post by synthpriest » Mon Jun 14, 2021 6:11 am

So great this project moved that far, the panels both look so beautiful. :guinness:

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Re: Doc Sketchy's new analog FREQUENCY SHIFTER!

Post by Dr. Sketch-n-Etch » Mon Jun 14, 2021 2:36 pm

Here's the first 25 units, all empanelled. You'll notice there are only two blacks and 23 naturals. This is because I still have to get the rest of the black panels from my buddy Ian. I dropped the blanks off to him last week, but he couldn't do then right then. Hopefully I'll get the rest this week.

I still have to do the final testing (multipliers and output amps -- the Dome filters have all been tested and all work perfectly) and adjust the trimmers (super easy -- just put my scope on a couple of pins with an input signal but no modulation signal, and adjust until the multiplier output disappears). Also, I still have to put the knobs on 22 of them. I'll do that as I test each one. I'll be testing today and should start mailing tomorrow.

Finally, a huge shout-out to Danjel van Tijn (owner and proprietor of Intellijel) for loaning me a knurled knob tightening tool -- those eurorack jacks are impossible to empanel without it.
First25FreakShifts.jpeg
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Re: Doc Sketchy's new analog FREQUENCY SHIFTER!

Post by drowld » Mon Jun 14, 2021 2:47 pm

Look amazing. I need this in my life
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