Something New from Doc Sketchy

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Dr. Sketch-n-Etch
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Re: Something New from Doc Sketchy

Post by Dr. Sketch-n-Etch » Mon Jun 15, 2020 3:36 pm

Why, thank you very much, Rex Coil 7!!

Lastnight, while playing with the FS once again, I realized that I might have left the output amplifier section just a tiny bit under-designed. You see, I assumed that just selecting the various input and gain resistors to all be exactly the same (in this case, 30.06k) would be enough to get sufficient summing and differencing of the multiplier outputs (XY). However, what I didn't take into account is that those outputs might be ever so slightly different in terms of their overall magnitudes. For example, if one XY has a peak amplitude of, say, 5.05V and the other is, say, 4.91V, then simply summing and differencing them precisely is not going to eliminate the unwanted sidebands. There needs to be a trimmer on each of the output amplifiers to balance the two XY signals so that the unwanted sidebands are exactly cancelled in each case. I know from listening to the FS outputs that this is not happening currently, so these trimmers must be added. I have changed the layout to accommodate them, and will kludge them onto the existing Multiplier/OutputAmp board tonight to make sure that my scheme works.
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Re: Something New from Doc Sketchy

Post by Dr. Sketch-n-Etch » Tue Jun 16, 2020 1:48 am

Tonight I kludged in two trimmers to balance the multiplier outputs going into the output amplifiers (summing and differencing). I think it was worth it. The SUM output in particular got a lot cleaner as a result of trimming. The DIFF output didn't improve all the much, but it wasn't too bad to start with. I think it was pretty close to optimum without the trimmer.

The trimming is easy to do -- I just put an audio sinewave from the Rubicon into the INPUT input, and an LFO sinewave into the EXP FM input, set the frequency to a medium high setting and had it going slowly up and down. Then I listened to each output and turned the trimmers until all trace of the other output disappeared (or reached minimum audibility). Then I played the sinewave on the keyboard, and it sounded pretty clean through both outputs.

No analog shifter is ever going to be perfect, but I think this one is pretty darn good. I think I'm done now. $450 US gets you one.

EDIT: I have also decided to add the option for trimmers (all trimmers are optional on the Multiplier/Output-Amp board) on the multipliers. Only one trimmer per multiplier is required, to balance the audio signal either going into the inverter and on into the multiplier, or bypassing around the multiplier. Ideally, these would be exactly equal, but a trimmer at the junction point (probably 1k for 30.1k resistors) can guarantee proper balancing. The result will be the ability to trim out any undesired sidebands. I'm not sure how easy it will be to trim these -- it may require a spectrum analyzer (which I have as part of the PicoScope software).
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Re: Something New from Doc Sketchy

Post by Dr. Sketch-n-Etch » Thu Jun 18, 2020 3:33 am

Tonight I made a new Multiplier board with the two sets of trimmers -- one on the multipliers (to eliminate control bleed-through) and one on the output amps (to get clean separation of the SUM and DIFF output signals). It worked very well.

I hooked up my Picoscope and looked at the spectrum of the multipliers, and was able to trim out the control frequency spike to about -40dB on the logarithmic plot. On the linear plot, I only saw that two spikes of the positive and negative sidebands -- the control spike was essentially zero (and it was inaudible). So, I'm really happy about those trimmers. I'm not entirely sure they were strictly necessary, but it's nice to be able to manually trim out all but the sidebands.

For the output trimmers, I just listened to the output and set the trimmers where the influence of the other output was minimum (which is the same as yesterday when I just had a kludged board). When I looked at the output spectrum on the Picoscope, I saw a big spike for the one isolated sideband from each output, and the rest of the spectrum was nicely attenuated.

So, I believe that this frequency shifter is quite precise, and that I'm completely done with design and layout. All I need to do now is get a few orders, so I can make some more!
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Re: Something New from Doc Sketchy

Post by Rex Coil 7 » Thu Jun 18, 2020 3:37 am

:coffee-machine: :popcorn:
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5U PROJECT - (skip pages 4 through 6, boring junk) ... https://www.muffwiggler.com/forum/viewt ... highlight=

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Re: Something New from Doc Sketchy

Post by indigoid » Thu Jun 18, 2020 10:18 am

I just saw this post on Twitter... it seems you're not alone in using Excel as a CAD tool:

Zap him again! ZAP THE SONOFABITCH AGAIN!

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Re: Something New from Doc Sketchy

Post by Dr. Sketch-n-Etch » Thu Jun 18, 2020 2:04 pm

indigoid wrote:
Thu Jun 18, 2020 10:18 am
I just saw this post on Twitter... it seems you're not alone in using Excel as a CAD tool:

I note that she did this in 2002, which was before the best version of Excel came out (with Office 2003).

It should be noted that the stuff I do with Excel 2003 is way harder and more frustrating to do with later Excel programs. They really screwed up the whole Office suite with later updates, as far as I'm concerned (and 2003 was the first essentially bug-free Office suite). People laugh at me, but I'll never stop using Office 2003 (or Windows XP Professional -- the only WIndows operating system worth a damn).
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Re: Something New from Doc Sketchy

Post by BugBrand » Fri Jun 19, 2020 7:04 am

Lots of interesting stuff throughout - & love the lisajous figures!

The QuadNet software is a great find - thanks!

I need to read through more about your DC offset details as that's an area I've slightly struggled with before - or found small errors creeping in at least. I'd tried a similar multiplier to what I think you're using (in other non-FS tests) and found bleed to be an issue (though note now you're matching the resistors carefully..). So I'm using AD633s for now & have trimmers on the test boards to implement shortly.

Oh, one little suggestion -- you're using back-to-back electros to make bipolars - I've really liked the Nichicon range BP electros - smart green towers!
eg: from Mouser here's an example one...

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Re: Something New from Doc Sketchy

Post by Dr. Sketch-n-Etch » Fri Jun 19, 2020 12:02 pm

Thanks, Bugbrand! I laid out for back-to-backs because I knew I'd be able to get them locally. I could just as easily use bipolars and short the second cap pads.

For this shifter, I'm finding these simplified multipliers to be perfectly adequate. We're not sending men to the moon -- we're just making freaky sounds!
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Re: Something New from Doc Sketchy

Post by Dr. Sketch-n-Etch » Sat Jun 20, 2020 3:16 am

OK, Wigglers, I changed my mind. I will be offering a 4U board set for the Frequency Shifter. However, it's going to be fairly expensive -- $100 US. It will involve four 4" x 6" (estimated length) boards -- a Panel board, a Translator board, and two Circuit boards. The whole stack will be fairly thin -- only about 3 cm -- I'm just finalizing the layouts this weekend. I didn't think I was going to be able to eliminate wiring, but now it would appear that it is possible, which is why I changed my mind.
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Re: Something New from Doc Sketchy

Post by Revok » Sat Jun 20, 2020 11:12 am

:sb: awesome!

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Re: Something New from Doc Sketchy

Post by Dr. Sketch-n-Etch » Tue Jun 23, 2020 11:23 pm

Well, I finally sold one (a 5U unit)!
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Re: Something New from Doc Sketchy

Post by Paradigm X » Wed Jun 24, 2020 9:21 am

you should put a post in for sale/5u format forums, its a bit buried in here. :)

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Re: Something New from Doc Sketchy

Post by loki » Wed Jun 24, 2020 12:45 pm

I want a 4U board set. One question, I have a 100 pieces of the SSI2164 and no SSM2164s. How awkward will it be for me to use them. I'm assuming you are still using SSM2164s.

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Re: Something New from Doc Sketchy

Post by Dr. Sketch-n-Etch » Wed Jun 24, 2020 3:15 pm

loki wrote:
Wed Jun 24, 2020 12:45 pm
I want a 4U board set. One question, I have a 100 pieces of the SSI2164 and no SSM2164s. How awkward will it be for me to use them. I'm assuming you are still using SSM2164s.
I use Coolaudio V2164D. SSM2164 has long been obsolete.

Are your SSI2164 chips through-hole? I was under the impression that they were only doing SMD. My layouts are through-hole, so if you've got SMD chips, you're going to have to create adapters.

In any case, they're pin compatible. However, the SSI chips use different values for the stability network. I use 499R-560pF, but the SSI datasheet recommends 200R-1200pF, although it says that the 499R-560pF combination "also works well for R_in greater than 20k" which all of mine are, so yeah. Probably anything between 200R and 500R, and 560pF to 1200 pF, will work. The RC value of the former is 280ns, and the latter is 240ns, so any combination of R and C that gets you a time constant between 240ns and 280ns will work just fine (say, for example, 240R and 1nF). I bought 1000 499R resistors and a massive bag of 560pF ceramic caps from Digi-Key for all my 2164 needs (which are substantial, as you can imagine).

It's too bad they didn't build the stability networks into the chip. Now that would have been an improvement!
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Re: Something New from Doc Sketchy

Post by Dr. Sketch-n-Etch » Wed Jun 24, 2020 3:36 pm

Paradigm X wrote:
Wed Jun 24, 2020 9:21 am
you should put a post in for sale/5u format forums, its a bit buried in here. :)
You are right. Also, my good friend Moog$Fool$ has suggested that I create a Sketchy Labs Facebook page to sell my wares. I will be doing that in the near future (although the prospect of doing it appeals to me about as much as getting a root canal -- I'm not sure why).

Also, the Small Bear order finally arrived with all of my PCB-mounted jacks, so I can finally truly finish all my recent 5U builds. :yay:
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Re: Something New from Doc Sketchy

Post by Dr. Sketch-n-Etch » Fri Jun 26, 2020 12:42 pm

So, lastnight I made a couple of Jack PCBs -- one for my build, and one for the build I'm doing for a fellow Wiggler. I wired mine up to the existing build, and I couldn't be happier with how it turned out:
FinalWiring.jpeg
I arranged the PCB so that the pins are in the same order as they are on the Connector PCBs, so that makes wiring a mindless task more focused on aesthetics than accuracy. The green wire is GND, and the other colours were just selected to be different on either side. Maybe for my next one I'll do rainbows.
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Re: Something New from Doc Sketchy

Post by Moog$FooL$ » Fri Jun 26, 2020 7:27 pm

nice..... i like that one. u are really getting your shit together. finally.
how long did it take??
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Re: Something New from Doc Sketchy

Post by Dr. Sketch-n-Etch » Sat Jun 27, 2020 2:20 pm

Moog$FooL$ wrote:
Fri Jun 26, 2020 7:27 pm
nice..... i like that one. u are really getting your shit together. finally.
how long did it take??
About 12 years.
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Re: Something New from Doc Sketchy

Post by maltemark » Sat Jun 27, 2020 2:49 pm

3U jealously looking at freq shift
Feel free to use my old samplepacks: https://freesound.org/people/altemark/
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Re: Something New from Doc Sketchy

Post by Prunesquallor » Sat Jun 27, 2020 2:53 pm

Dr. Sketch-n-Etch wrote:
Sat Jun 27, 2020 2:20 pm
Moog$FooL$ wrote:
Fri Jun 26, 2020 7:27 pm
nice..... i like that one. u are really getting your shit together. finally.
how long did it take??
About 12 years.
:lol: :lol: :lol:
If at first you don't succeed read the instruction manual.

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Re: Something New from Doc Sketchy

Post by Moog$FooL$ » Sat Jun 27, 2020 6:47 pm

maltemark wrote:
Sat Jun 27, 2020 2:49 pm
3U jealously looking at freq shift
do some 5u....... presto!! no more jealousy. :hyper: :tu:
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that fat cat had to go..... wasn't even mine.

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Re: Something New from Doc Sketchy

Post by KSS » Sat Jun 27, 2020 8:49 pm

maltemark wrote:
Sat Jun 27, 2020 2:49 pm
3U jealously looking at freq shift
Why be jealous? Horizontally it's only 30HP. Maybe 32. Wouldn't need to change anything but panel graphics and jack board.

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Re: Something New from Doc Sketchy

Post by Dr. Sketch-n-Etch » Sun Jun 28, 2020 1:49 pm

This would have been a euro module, but Intellijel took a pass on it. They figured it wouldn't sell enough units to justify the expense of getting it built, since it is a fairly elaborate analog circuit that basically does one thing (that can also be done digitally for much less expense, evidently). If I'd have had this design back in, say, 2015, they might have gone for it, but I was a few years too late.
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Re: Something New from Doc Sketchy

Post by Dr. Sketch-n-Etch » Tue Jun 30, 2020 2:05 pm

Today my small discovery was that EVERY zener diode must be tested.

I finished a 5U Frequency Shifter for Paradigm X, and upon testing I noticed that the two VCO cores were producing waveforms with significantly different voltage levels. I thought something was seriously wrong, and did a massive search for solder bridges, replaced quite a few chips, etc, etc, and nothing helped. Then I checked the levels coming out of the core comparators and they were both more or less exactly 20Vpp, as designed. That means that the problem had to be with the zener diodes.

Each core requires a single zener diode within a zener bridge to set the voltage level of the waveforms. I use 3.9V zeners for this (1N4370) since there are two diodes in each direction in the bridge and they each add about 0.5V (in fact, the diodes I bought in bulk from Digi-Key are extremely consistent, and measure 0.533V to 0.537V -- assuming an average of 0.535V, that means that the zener should be 3.93V to give 10Vpp waveforms). I replaced the one zener that was low, and it got worse. So, I thought, I'll replace them with 1N4371s (of which I had 3) which are 4.3V -- I measured them as well, and they measured around 3.0 to 3.1V -- more than a volt low! So, then I thought, what if I measured some 1N4372s (4.7V) -- the first three diodes I pulled out of the bag measured 3.9V, 4.4V, and 3.9V, so I installed the two low ones and VOILA the damn thing works perfectly.

So, going forward, my new policy is to measure every zener diode and put them in bin bags to the nearest 0.1V, regardless of their denomination. Then I will have a collection of precision zeners that I can pull out and use as needed. What a bore!
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Re: Something New from Doc Sketchy

Post by Dr. Sketch-n-Etch » Tue Jun 30, 2020 2:07 pm

How do you test a zener diode? Here's how I do it: 15V to 3.3k to zener (stripe end) and zener (bare end) to GND. Measure the voltage across the zener. I did it on a breadboard for convenience, or you could just use alligator clips. If you install the zener backwards, it will measure about 0.6V (like a regular Si diode), so you'll know you've done it wrong.
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