Something New from Doc Sketchy

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indigoid
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Re: Something New from Doc Sketchy

Post by indigoid » Wed Jan 06, 2021 10:41 pm

for your next trick, make it generate an optimised (fewest different parts) BOM using only E12 values :sb:
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Re: Something New from Doc Sketchy

Post by Dr. Sketch-n-Etch » Thu Jan 07, 2021 11:18 pm

Thorsday wrote:
Wed Jan 06, 2021 10:10 am
What does that mean for Frequency Shifter owners of light year's past?
Nothing. I used a thing on the internet called QuadNet to design the optimal PDN for my previous design, and my new code gives exactly the same values.

The issue was that a) QuadNet is a pain, and b) it wouldn't allow me to design down into the LFO range.
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Re: Something New from Doc Sketchy

Post by Dr. Sketch-n-Etch » Thu Jan 07, 2021 11:20 pm

indigoid wrote:
Wed Jan 06, 2021 10:41 pm
for your next trick, make it generate an optimised (fewest different parts) BOM using only E12 values :sb:
Actually, all kidding aside, I'm doing exactly that, but with E96 values. It won't be an "optimized" BOM, though -- I'll have to specify the C values I want to use, and then it will automatically generate the 1% resistor pairs to achieve the RC values. I know how to do it -- I just haven't done it yet.
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Re: Something New from Doc Sketchy

Post by Dr. Sketch-n-Etch » Mon Jan 11, 2021 11:55 pm

UPDATE: I wrote the little code for the resistors, and now I can use the PDN90RC function to calculate all the RC time constants for the phase displacement network, set the capacitor values, and then use my new E96RES function to find the nearest lower value of resistance from the E96 series. By subtracting that result from the original value and using the function again on the difference, I can find the value of the second resistor to put in series with the first to give RC within about 0.02% of the desired value.

For example, one of the RC values is 0.06308266 s. So, if I choose a 1uF capacitor, the resistor I need is 63083 ohms. So, I use the function once:

E96RES(63083) = 61900

Then I use the function again with the difference:

E96RES(63083 - 61900) = 1180

So, the two resistors in series are 61900 + 1180 = 63080, which is within 3 ohms of the target of 63083 for a relative error of -0.004%. Using this method to generate the resistor pairs for every stage, and then calculating the new RC time constants gives a phase angle plot which is indistinguishable from the original one.

Pretty sweet, eh?
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Re: Something New from Doc Sketchy

Post by KSS » Tue Jan 12, 2021 5:47 am

Very sweet! :tu:

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Re: Something New from Doc Sketchy

Post by Dr. Sketch-n-Etch » Mon Jan 18, 2021 5:29 pm

UPDATE: I just finished laying out the 4-channel morphing scanner design with auto-scaled CV range on a single PCB which is 4" x 6.4". It's pretty elegant. I'm making one for somebody already. If anybody else wants one, please let me know.
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Re: Something New from Doc Sketchy

Post by Dr. Sketch-n-Etch » Fri Jan 29, 2021 4:15 am

Hey Team,

Tonight I finished my very first "Frequency Shifter Lite" -- this is a Bode frequency shifter with no oscillator, but with a second, slightly beefier Dome filter which generates signals in quadrature from 0.1 Hz to 10000 Hz, so that anything from a VCO to a slow LFO can be used to drive the shifter. Here's a picture and the layout graphic:
FSLite.jpg
FSLite Build Pic.png
So, the PCB is divided into three rows of circuitry. The top row, with 6 TL072, is the 12-stage Dome filter for the audio signal, which generates signals in quadrature between 15 and 15000 Hz. The bottom row, with 9 TL072, is the 18-stage Dome filter for the modulating signal, which generates signals in quadrature between 0.1 and 10000 Hz. The middle row is the two four-quadrant multipliers and the summing and differencing amplifiers for doing the frequency shifting.

So far I've tested the two Dome filters and they work perfectly. All the caps have been hand selected to be within 0.1% of their desired values. I haven't actually tried frequency shifting or phasing yet -- got lazy -- but will test tomorrow. This is the first of two identical units I'm building for a fellow wiggler.

This PCB is 6" tall and 5.3" wide. However, it could very easily be built as a stack of three PCBs 2" wide (there are very few interconnections between the three sections), which could be built behind a 1-Moog-unit panel, or, turned sideways, behind a 1-MOTM-unit panel. The controls are very simple, since there is no on-board VCO.

If anybody wants one of these beasts, send me a PM. I'll be making a video possibly tomorrow.
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Re: Something New from Doc Sketchy

Post by KSS » Fri Jan 29, 2021 4:22 pm

That's incredible! :tu:
Looking forward to the video!

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Re: Something New from Doc Sketchy

Post by devinw1 » Fri Jan 29, 2021 4:33 pm

Really cool!

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Re: Something New from Doc Sketchy

Post by devinw1 » Fri Jan 29, 2021 4:42 pm

On those dome filters, does one just simply cascade 8 (or 12) of a basic single pole all-pass like fig 1 here:

https://www.analog.com/media/en/trainin ... MT-202.pdf

Or is there more to it?

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Re: Something New from Doc Sketchy

Post by Dr. Sketch-n-Etch » Sat Jan 30, 2021 3:44 pm

devinw1 wrote:
Fri Jan 29, 2021 4:42 pm
On those dome filters, does one just simply cascade 8 (or 12) of a basic single pole all-pass like fig 1 here:

https://www.analog.com/media/en/trainin ... MT-202.pdf

Or is there more to it?
The 12-stage is two parallel chains of 6 basic first-order all-pass sections, and the 18-stage is two parallel chains of 9. They are the same configuration as shown in Figure 1 of MT-202. The trick is to tune them to get the minimum phase error, and that is hard, but I figured it out. Each of the 12 (or 18) stages must have a very specific time constant, and I achieve that with hand-selected capacitors and 1% resistors. Since each stage uses two resistors in series to get to a very specific value, I had to order almost 60 distinct values of 1% resistors to make these two Dome filters. I ordered 25 of each value so I can make many of these units. I've arranged them in individual baggies in the order in which they go into the PCB, so I have these "Dome filter kits" all set up so that the next build will be very quick. I also sorted my film capacitors (102, 103, 104 and 105) into 0.1% bins and put those into separate baggies. When I want to build, for example, the 18-stage filter, I need 4 each of 102, 103 and 104, and 6 of 105. I will then look at my baggies and decide if I have enough values within two adjacent mantissas. For example, for this build, I took all the caps out of the "995" and "996" baggies, so I used 0.995 and 0.996 nF, 9.95 and 9.96 nF, 99.5 and 99.6 nF, and 995 and 996 nF caps. After I take them out of their baggies, I remeasure them all to confirm that they fall within that 0.1% tolerance. It's a bit tedious, but it guarantees excellent phase response.
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Re: Something New from Doc Sketchy

Post by Dr Gris » Sat Jan 30, 2021 5:13 pm

Dammit. Still lusting for the full monty version of the Frequency Shifter. Well, still no gigs due to Covid so not much $ to spend.
Besides, my car needs repairs, aaarrgghh
But I shouldn't complain, many people have a much worse situation.
Looking forward to more demos. Keep up the good work.

Best
//M

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Re: Something New from Doc Sketchy

Post by devinw1 » Sat Jan 30, 2021 5:38 pm

Thanks for that explanation Doc! Yeah, I can see how you need to get everything quite tightly toleranced on something like that being the end result is trying to even shift phase over the entire (rather wide) frequency band. It's especially hard with the caps because even nice film caps you are pretty much looking at being able to buy them at 2% on a good day, usually more like 5% tolerance!

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Re: Something New from Doc Sketchy

Post by AlanP » Sat Jan 30, 2021 5:41 pm

Oh wow. I've always wanted to build a frequency shifter, but they have an intimidating BOM behind them!

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Re: Something New from Doc Sketchy

Post by Dr. Sketch-n-Etch » Sat Jan 30, 2021 8:53 pm

devinw1 wrote:
Sat Jan 30, 2021 5:38 pm
Thanks for that explanation Doc! Yeah, I can see how you need to get everything quite tightly toleranced on something like that being the end result is trying to even shift phase over the entire (rather wide) frequency band. It's especially hard with the caps because even nice film caps you are pretty much looking at being able to buy them at 2% on a good day, usually more like 5% tolerance!
I like the Topmay TMCF07 Box film caps that Small Bear sells -- they are good, and the price is right:
http://smallbear-electronics.mybigcomme ... 001-f-1-f/
They seem to mostly fall within a +/- 2% tolerance range. For instance, for the 10 nF caps, at least 80% of them will fall within 9.80 and 10.20 nF. I buy 100 of them at a time, and separate them into 0.1% bins when they arrive. Even if they are further out of tolerance, I can still use them if they are all similarly out. If all of the caps are, say, 970 or 1030, it doesn't matter, as long as they are all the same.
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Re: Something New from Doc Sketchy

Post by Prunesquallor » Sun Jan 31, 2021 5:07 am

Could this be shoehorned into 4U?
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Re: Something New from Doc Sketchy

Post by Th°ne » Sun Jan 31, 2021 6:51 am

Prunesquallor wrote:
Sun Jan 31, 2021 5:07 am
Could this be shoehorned into 4U?
Yes, 6" height fits in 4U

Beautiful Doc !

Cheers !

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Re: Something New from Doc Sketchy

Post by Dr. Sketch-n-Etch » Tue Feb 02, 2021 7:58 pm

OK, Bitches, I decided to put the Frequency Shifter Lite behind a panel. I built this board for somebody else (Th°ne, actually), and it is destined for a 4U build, but I couldn't resist. Also, I need to thoroughly test this beast, and that's always nicer to do with a panel.

I also had to come up with a snappy name that fits between the mounting screw holes, so I came up with "Freak Shift" -- not bad.

Presuming this all works, I'll make a brief video (number 4 in my ongoing series on YouTube), and then build a second one just like it. Then, perhaps, I'll build my own PCB for this panel, but I'll probably split this PCB into three parts 2" wide and stack them up, to make a less deep module. This module is about 7" deep, and that's pushing it even for my case.

You may also notice, if you compare the PCB picture here with the last one, that I added a TL072 and some circuitry onto the middle row of ICs. This was to provide a buffer amp for the Wet/Dry pot. I forgot to put this on the original layout, and so I had to kludge it on. I do these kludges in such a way that, from the top, you can't even tell it wasn't part of the original layout. Of course, it is now part of the layout, so the second board I make will not need this kludge.
FSLitePanel.jpeg
FSLiteGuts.jpeg
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Re: Something New from Doc Sketchy

Post by Dr. Sketch-n-Etch » Tue Feb 02, 2021 9:52 pm

OK, so I just tested the unit. However, before I did that, I realized that I stupidly kludged on an inverting amplifier, when all I needed was a non-inverting buffer, so I removed the two unnecessary resistors and rearranged the rest into a simple buffer.

Anyway, let me just say that I think I've out-done myself. This thing is super cool! It's cooler than the full-service frequency shifter. There are a couple features that make this unit unique.

One is the SOURCE switch, which allows you to switch between the output of the 18-stage Dome filter processing the MOD input, or the separate SIN and COS inputs. This is for if you already have a quadrature oscillator you would like to just plug into this unit. However, what I've discovered is that you can put anything into those inputs and get some pretty interesting results.

The other new thing is the WET/DRY control. This sends the IN and AUX mixture to one side of the pot, and the OUT MIX from the SUM/DIFF control to the other side of the pot, and crossfades between them. This allows for lots of subtle blending of the input signal into the output. However, when nothing is plugged into the AUX input, it is normalled to the OUT MIX, so the WET/DRY control then takes on a different flavor.

Also, the AUX input normally provides feedback of the output, which is necessary for phasing duties. However, what I've discovered is that using it even when the MOD input is at audio frequencies really gives a sort of phased flavor to the output. Turning this up on my other unit during frequency shifting made things sound pretty harsh, but here it sounds much more interesting. I'm not sure why.

I'll make some sort of video later tonight, after I clean up my workshop a little bit.
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Re: Something New from Doc Sketchy

Post by kdjupdal » Wed Feb 03, 2021 5:51 am

Very interesting.
I've got a few questions:
- is it a thru-zero freqency shifter? I think some FS are and some are not, and maybe it doesn't matter much anyway, but would be interesting to know.
- for normal shifting, what do you recommend as a modulator? Does the sine wave need to be as clean as possible?
- If you only patch in a modulator (and no input) will you get the 0° and 90° phase version out?

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Re: Something New from Doc Sketchy

Post by indigoid » Wed Feb 03, 2021 6:29 am

How well do the extremes of the frequency range compare in real world vs. your calculations?

6x4" would fit behind a 32hp Eurorack panel... hmmmmmmm
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Re: Something New from Doc Sketchy

Post by vtl5c3 » Wed Feb 03, 2021 11:05 am

FS Lite is very intriguing! I'd be very interested to hear a snippet where human speech is used for both inputs.

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Re: Something New from Doc Sketchy

Post by Dr. Sketch-n-Etch » Wed Feb 03, 2021 5:53 pm

kdjupdal wrote:
Wed Feb 03, 2021 5:51 am
Very interesting.
I've got a few questions:
- is it a thru-zero freqency shifter? I think some FS are and some are not, and maybe it doesn't matter much anyway, but would be interesting to know.
- for normal shifting, what do you recommend as a modulator? Does the sine wave need to be as clean as possible?
- If you only patch in a modulator (and no input) will you get the 0° and 90° phase version out?
There is no such thing as a "through-zero frequency shifter." There are frequency shifters that have through-zero FM VCOs as the modulator (including my "full-service" frequency shifter described in previous posts and in three videos on YouTube). In the case of the FREAK SHIFT you can plug an external TZFM VCO into the MOD input and now you have a TZFM frequency shifter.

Another way that a frequency shifter kinda goes from negative to positive is by scanning from SUM to DiFFERENCE. These are just two ways of processing the multiplier outputs to get upshifting or downshifting (single sideband generation either of the sum of the two frequencies or the difference of the two frequencies). I have a SUM/DIFF control that crossfades between the two. In the middle, you have both up and down shifting, or both sidebands, which is basically another way of saying that you have a four-quadrant multiplier.

Yes, for normal shifting, sine waves are the preferred modulator signals. This is because they only have one frequency, so they only generate single sidebands. This is true for any FM or AM work, of which frequency shifting is just a specific flavor.

If you only patch the modulator, you hear nothing, because only the IN (and AUX) signals flow through the audio path. The output of the Dome filter (from the MOD input), or the SIN and COS inputs, only control the 2164 at the heart of the dual multiplier. In other words, all they do is modulate. However, the outputs of both Dome filters can still be tapped and sent wherever you want. After all, it's just the PCB I'm selling (at this point) -- if you want to put on pins for extracting the outputs of the Dome filters, then that is your prerogative.
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Re: Something New from Doc Sketchy

Post by Dr. Sketch-n-Etch » Wed Feb 03, 2021 5:55 pm

vtl5c3 wrote:
Wed Feb 03, 2021 11:05 am
FS Lite is very intriguing! I'd be very interested to hear a snippet where human speech is used for both inputs.
I will definitely do this when I make my next video, which should be tonight. (I got lazy yesterday, and just ended up bingeing Season 2 of Angel with the Chud (my younger daughter).
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Re: Something New from Doc Sketchy

Post by KSS » Wed Feb 03, 2021 8:42 pm

Dr. Sketch-n-Etch wrote:
Wed Feb 03, 2021 5:53 pm
it's just the PCB I'm selling
Cost of an FSLite PCB?

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