Something New from Doc Sketchy

From circuitbending to homebrew stompboxes & synths, keep the DIY spirit alive!

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Prunesquallor
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Re: Re:

Post by Prunesquallor » Thu Nov 19, 2020 5:09 am

onthebandwagon wrote:
Wed Nov 18, 2020 11:27 am
Dr. Sketch-n-Etch wrote:
Mon Oct 26, 2020 12:48 am
Today, 25 October 2020, is Jon Anderson's 76th birthday. Jon Anderson is one of my all-time musical heroes.

Happy Birthday, Jon Anderson!!! :band:

Image
Is that the same guy who was in Bill and Ted's Adventure?
Yes. Alex Winter sung on all the classic Yes albums. :lol:

Back to topic, that interpolating scanner sounds fun, Dave!
If at first you don't succeed read the instruction manual.

RIP Ziggy, the companion in my avatar.

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Re: Something New from Doc Sketchy

Post by Dr. Sketch-n-Etch » Fri Nov 20, 2020 4:22 am

He was in Bill and Steve and Chris and Rick's excellent adventure.

Here's a couple graphics of the interpolating scanner circuits. These just generate the control trapezoids for four channels -- they need to be plugged into a quad linear VCA to make a complete scanner. A unique feature of these is that the fading and the width of the trapezoids can both be put under voltage control. Width is adjustable from all four channels occupying the same voltage space across the entire sweep field to the four channels being quite narrow and well separated. The circuit is set up so that, no matter the Width setting, the four channels are always evenly distributed across the sweep field, such that Channel A just goes off when the Fader is fully down, and Channel D just goes off when the Fader is fully up, no matter the width or separation of the channels. When I build it, I'll demonstrate this feature, which I'm pretty proud of (some algebra was involved). I hope to be building this up this weekend.

Incidentally, these boards (which are only 2.1" x 3.5") are meant to plug into each other via those grey boxes. I made this very small to accommodate putting it behind a 6hp eurorack panel.
ScanBoard1.png
ScanBoard2.png
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Re: Something New from Doc Sketchy

Post by KSS » Sat Nov 21, 2020 3:05 am

:tu:
Impressive as always!

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Re: Something New from Doc Sketchy

Post by Dr. Sketch-n-Etch » Tue Dec 01, 2020 7:11 pm

So, here's the finished product: the eurorack-format Doc Sketchy Interpolating Scanner (which I called "SCAN" because that's all I could fit on this tiny-ass euro panel).
EuroScan1.jpeg
EuroScan2.jpeg
It's admittedly a tad deep, but the client said that was OK. And yes, I know, my knob is too big (a common complaint with me).

This was a very easy build -- made easier by the discovery that I can easily cut this thin aluminum sheet with the old paper guillotine that I use to cut PCB material, so eurorack panels are now a snap to make. However, it was a bit of a challenge to troubleshoot. First of all, I had to change my control circuit slightly because if the fader was only taken down to GND, there was significant channel bleed when the WIDTH setting is low (wide overlapping trapezoids). I had an unused opamp on the board, so I repurposed it as a buffer for a small negative voltage (-12mV) and sent that to the bottom of the fader. This gives perfect silence when the fader is all the way down. Other than that, my control circuit worked perfectly, but that was a fairly major kludge.

The other problem was more tricky -- the trapezoids were looking more like wimpy little half-sines, and the symmetry of the channels across the fader was all wonky when the WIDTH control was increased. I checked and re-checked the layout several times, and it was completely correct. I knew that the circuit design was OK because I had an old board with more or less the same circuit on it and it worked perfectly. I decreased some current limiting resistor values, to no avail. Finally, on a hunch, I changed the zener diodes in my simulation from 1N4733 (1W) 5.1V diodes to 1N5338 (5W) 5.1V diodes, and -- lo and behold -- the simulated trapezoids now looked like wimpy half-sines. So, I carefully desoldered all 8 of the zener diodes and replaced them with the 8 zener diodes from the old board (which I also had to desolder, obviously) and the circuit now works perfectly with those old zener diodes. I'm assuming that the bag of 1N4733s that I recently bought from Small Bear are actually mislabelled 1N5338s. In the future, I am going to buy 1N5729 (500mW) 5.1V diodes on the assumption that, if their power dissipation is too high, it will still be within the right ballpark.
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Re: Something New from Doc Sketchy

Post by devinw1 » Tue Dec 01, 2020 7:53 pm

As we say in the Euro world; "If you can't go wide, go deep!".

Or something along those lines. :D

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Re: Something New from Doc Sketchy

Post by Dr. Sketch-n-Etch » Wed Dec 02, 2020 3:54 am

devinw1 wrote:
Tue Dec 01, 2020 7:53 pm
As we say in the Euro world; "If you can't go wide, go deep!".

Or something along those lines. :D
Yes, that's more or less exactly the situation with homebrew eurorack. I don't do SMD work, so this is what I have to do. In any case, other than the crazy troubleshooting, this module was a pleasure to build. I even managed to create a pretty decent slot for the fader, just by indenting and then drilling lots of holes along a line, then ratting them out with a chisel, filing with a tiny little file, then using a strip of sandpaper to smooth the edges. It was surprisingly fast and easy to do, and a lot less hassle and pain than trying to use a milling bit.
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Re: Something New from Doc Sketchy

Post by adam » Wed Dec 02, 2020 5:21 am

seen those home made manual pick & place machines?, two drawer runners, a usb endoscope and a suction tool made from an aquarium pump, like this:

https://www.instructables.com/Manual-Pi ... omponents/

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Re: Something New from Doc Sketchy

Post by devinw1 » Wed Dec 02, 2020 11:22 am

Dr. Sketch-n-Etch wrote:
Wed Dec 02, 2020 3:54 am
devinw1 wrote:
Tue Dec 01, 2020 7:53 pm
As we say in the Euro world; "If you can't go wide, go deep!".

Or something along those lines. :D
Yes, that's more or less exactly the situation with homebrew eurorack. I don't do SMD work, so this is what I have to do. In any case, other than the crazy troubleshooting, this module was a pleasure to build. I even managed to create a pretty decent slot for the fader, just by indenting and then drilling lots of holes along a line, then ratting them out with a chisel, filing with a tiny little file, then using a strip of sandpaper to smooth the edges. It was surprisingly fast and easy to do, and a lot less hassle and pain than trying to use a milling bit.
Yeah, you did a good job fitting all that into a small HP panel for sure. I personally don't understand peple who want 2HP and tiny ass modules though, and minipots....ugh ...not a fan. IMO, just get a bigger case, go wider, and enjoy being able to actually get your fingers on the knobs :D. :guinness:

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Re: Something New from Doc Sketchy

Post by Rex Coil 7 » Wed Dec 02, 2020 11:48 am

... pretty much ~me~ anytime I'm reading this thread ....
Amazed boy - 01.jpg
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5U MODULAR NORMALIZING PROJECT (for your entertainment) viewtopic.php?t=78836&highlight=
.. as of Dec 8th 2020 on a break for a bit .. contact me via bamco60@hotmail.com if needed.
WELCOME TO 2021 .. THE BEATINGS WILL CONTINUE UNTIL MORALE IMPROVES.

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Re: Something New from Doc Sketchy

Post by Dr. Sketch-n-Etch » Wed Dec 02, 2020 12:24 pm

adam wrote:
Wed Dec 02, 2020 5:21 am
seen those home made manual pick & place machines?, two drawer runners, a usb endoscope and a suction tool made from an aquarium pump, like this:

https://www.instructables.com/Manual-Pi ... omponents/
That's brilliant, and way beyond my capabilities or interest.

It reminds me of the time that I bought an XY milling table for my drill press, with a crank which moved the table exactly 0.05" with each turn of the crank. I thought "Wow, all I have to do is get the board exactly square on the table, and then I can just "crank-crank-drill, crank-crank-drill" for each hole in my board" and yes, that's pretty much how it worked. After a few boards (only narrow ones, because I couldn't mount wider ones on the table very well) I realized that it was easier and faster to just stand there and manually move the board on a piece of plywood for drilling, as setting up the table on the drill press and lining up and mounting the board on the table took well more than half the time it took to drill, and the cranking and drilling was still prone to mistakes -- one has to be especially careful with the drilling because the temptation is to start cranking before the drill is completely removed from the last hole, which can lead to broken drill bits and ratty holes, so a very definite drilling rhythm must be adopted. Long story short, that XY table sits on a shelf, largely unused and unloved. The only time I really need it is when I'm milling slots in panels for faders, but now I realize that the "many holes close together" technique is better and works faster (and allows me to make a slot of any width I want, rather than 1/8", which is the only milling bit I own).
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Re: Something New from Doc Sketchy

Post by adam » Wed Dec 02, 2020 1:16 pm

we've had one on the todo list for years at my hackspace, I think someone even bought some of the parts, haven't mustered the enthusiasm to build it yet, there's 80 of us ;)

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Re: Something New from Doc Sketchy

Post by Dr. Sketch-n-Etch » Thu Dec 10, 2020 7:33 pm

Stop the world: I wanna get off.

So, I'm so busy with schoolwork right now and I've fallen far behind on my builds for people. I finally got a stuffed and tested Frequency Shifter on a 6" x 8" PCB out to a customer in Iceland today, and I think I'll be able to finish the second Serge-format Quad Function Generator within the next few days. Then I have a huge order for a wiggler in France which I haven't even started yet, and given how slow the mail is right now, he might be waiting until late January. So, if you want me to make something for you, please wait until after Christmas to ask me.

And, oh yeah: Happy F-ing Holidays!
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Re: Something New from Doc Sketchy

Post by Dr. Sketch-n-Etch » Thu Dec 17, 2020 2:06 am

I got the QFG in the mail today, so I'm pretty relieved about that. The testing and troubleshooting only took one evening, and a pretty short evening at that, which was a bit of a pleasant surprise. A couple of solder bridges, one inverted diode, and a few resistor value changes to dim some over-bright LEDs and un-straighten what are supposed to be exponential (and, therefore, curvy) attacks, and it was ready to ship.

I don't plan to build another one of those fuckin' things for quite a while.
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Re: Something New from Doc Sketchy

Post by Prunesquallor » Thu Dec 17, 2020 3:07 am

Dr. Sketch-n-Etch wrote:
Thu Dec 17, 2020 2:06 am
I don't plan to build another one of those fuckin' things for quite a while.
Sell it to us, Dave. :hihi:

For the record, they are a tad good. :party:
If at first you don't succeed read the instruction manual.

RIP Ziggy, the companion in my avatar.

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Re: Something New from Doc Sketchy

Post by Dr. Sketch-n-Etch » Thu Dec 17, 2020 7:43 pm

Prunesquallor wrote:
Thu Dec 17, 2020 3:07 am
Dr. Sketch-n-Etch wrote:
Thu Dec 17, 2020 2:06 am
I don't plan to build another one of those fuckin' things for quite a while.
Sell it to us, Dave. :hihi:

For the record, they are a tad good. :party:
I wanna sell a 5U one -- they are so pretty, and soooo much easier to build (plus I can build the whole thing rather than just the guts).
15_Finished_QPG.jpeg
And, I just realized today, I never replaced the handwired jacks and LEDs on my new Dr Octature build with PCB mounted ones, so I guess I have a small project for the next day or two, before I get started on my big French board order.
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Re: Something New from Doc Sketchy

Post by Prunesquallor » Sat Dec 19, 2020 4:22 am

Dr. Sketch-n-Etch wrote:
Thu Dec 17, 2020 7:43 pm
I wanna sell a 5U one -- they are so pretty, and soooo much easier to build (plus I can build the whole thing rather than just the guts).
Post in the 5U forum? There's current excitement over there about (official) Serge DUSG and SSG modules. I bet they'll be up for something Buchla-esque.
If at first you don't succeed read the instruction manual.

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Re: Something New from Doc Sketchy

Post by Schlumpfhut » Mon Dec 21, 2020 1:56 am

Dr. Sketch-n-Etch wrote:
Thu Dec 17, 2020 7:43 pm
I wanna sell a 5U one -- they are so pretty, and soooo much easier to build (plus I can build the whole thing rather than just the guts).
15_Finished_QPG.jpeg
I just have to get my hands on the money and need to look for customs regulation. Then i would very much like to get one of those (with a black front panel if possible)

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Re: Something New from Doc Sketchy

Post by Dr. Sketch-n-Etch » Sat Dec 26, 2020 1:55 pm

Merry Christmas everyone! (actually, it's Boxing Day, but whatevs)

So, a couple of days ago, I realized that there was a small design error in my 4- or 8-channel "noiseless scanner" design. It was a very minor error where I failed to buffer the voltage coming from a rectifying circuit properly, so that the "Fade" voltage was not doing exactly what I wanted it to do, although the "InvFade" voltage, its mirror-image companion, was. I realized that I had to add a buffer to the Fade voltage, but this would have added an opamp to the circuit, which would have added an IC to the board, and I didn't want to do that. Well, after a bit of pondering and a bit of simulating, I realized that I could combine two of the opamp functions in the control signal chain into a single opamp. This freed up an opamp that I could use as the buffer.

Lastnight I completed the new layout, and it turned out very nice. I can do it as a stack of two boards 2.1" x 4.6", or a single board 4" x 4.6". Here are the "Build" images for the split boards:
4ChanScanSplit.png
and for the single big board:
4ChanScanBig.png
If anybody wants either of these, bare or stuffed, please PM me. Prices will be very reasonable.
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Re: Something New from Doc Sketchy

Post by Dr. Sketch-n-Etch » Sun Dec 27, 2020 7:01 pm

I just finished stuffing the 4" x 4.6" version of the layout above. I am about to test it. Hope it works.
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Re: Something New from Doc Sketchy

Post by Dr. Sketch-n-Etch » Tue Dec 29, 2020 3:22 am

Tonight, I made the 1U-wide 5U panel for the 4-Channel scanner I stuffed yesterday. The slot for the fader turned out quite nice, and everything fit perfectly the first time. Also, the module worked perfectly the first time -- no layout errors, no solder bridges, no mistakes. That was a welcome change.

So, no more electronics for probably the next week while I write a chapter for a Biomining textbook that I have been procrastinating over, but the deadline is looming.
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Re: Something New from Doc Sketchy

Post by Dr. Sketch-n-Etch » Fri Jan 01, 2021 12:33 am

HAPPY NEW YEAR, MOFOS!!!!!!!

Here's hoping that 2021 is just a bit less of a clusterfuck than 2020 was (although my personal 2020 wasn't too bad at all, actually -- at least, once I got out of the hospital in March -- because I've felt totally fine for the last nine months, and I managed to get quite a lot of electronics done).
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Re: Something New from Doc Sketchy

Post by Dr. Sketch-n-Etch » Wed Jan 06, 2021 2:37 am

Tonight, after much searching around, I finally did something I've been wanting to do for quite a while, ever since I've been building frequency shifters. I figured out exactly how to arrive at the optimal design of a 90-degree phase displacement network, and I put the solution into an Excel spreadsheet, and then I wrote a FUNCTION subprogram in Visual Basic which gives the RC of each stage in the all-pass network as a simple function call:

PDN90RC(F1,F2,NN,N)

where F1 and F2 are the minimum and maximum frequencies in Hz (for example, 15 Hz and 15000 Hz), NN is the number of all-pass stages in each chain (for example, 6 in each chain of a 12-stage PDN), and N is the number of the stage. So, for example, for a 12-stage PDN with a frequency range of 15 to 15000 Hz, one can instantly generate the 12 RC values thus:

1 3.0100E-02
2 8.6072E-03
3 3.8927E-03
4 1.9037E-03
5 9.4806E-04
6 4.7422E-04
7 2.3740E-04
8 1.1875E-04
9 5.9136E-05
10 2.8920E-05
11 1.3080E-05
12 3.7402E-06

Here is the phase error vs log frequency (max error about 0.18 degrees for this 3-order-of-magnitude situation):
PDN12-3OOM.png
Want to do, say, 0.1 Hz to 10000 Hz with a 20-stage filter? Here ya go:

1 4.8508E+00
2 1.4140E+00
3 6.6102E-01
4 3.3672E-01
5 1.7527E-01
6 9.1758E-02
7 4.8115E-02
8 2.5241E-02
9 1.3243E-02
10 6.9482E-03
11 3.6456E-03
12 1.9128E-03
13 1.0035E-03
14 5.2645E-04
15 2.7606E-04
16 1.4452E-04
17 7.5226E-05
18 3.8320E-05
19 1.7914E-05
20 5.2219E-06

Here is the phase error vs log frequency (max error about 0.11 degrees for this 5-order-of-magnitude situation):
PDN20-5OOM.png
It took about 5 seconds to generate these results. Now I can design a PDN that goes well down into the LFO range but still covers the audio range -- I couldn't do that with QuadNet.
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Re: Something New from Doc Sketchy

Post by KSS » Wed Jan 06, 2021 3:17 am

Well done! :tu:

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Re: Something New from Doc Sketchy

Post by Moog$FooL$ » Wed Jan 06, 2021 4:22 am

yeah!! i guess this means you have time for my projects??
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Re: Something New from Doc Sketchy

Post by Thorsday » Wed Jan 06, 2021 10:10 am

What does that mean for Frequency Shifter owners of light year's past?

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