Something New from Doc Sketchy

[Dr. Sketch-n-Etch]

Frequency shifter? You have my attention! Is it a riff off existing designs, or something you've cooked up yourself?

Mathematically, it's a Bode frequency shifter (I tried building a Weaver shifter once and failed miserably). However, all of the circuit components are of my own design. The TZFM VCO is a dual-core simplified Rubicon set up so that the two cores are always 90 degrees out of phase, the multipliers are linearized 2164 circuits of my own design, and the 90-degree phase displacement network is my own design based on the free software QuadNet (for a 12-filter unit creating 90 degree phase displacement between 15 and 15,000 Hz). There are no trimmers in the PDN or the multipliers, only on the VCO (one for 1V/octave tuning and four for sine and cosine wave shaping). The secret to trimmer-less multipliers is to a) hand-select the gain resistors, and b) to AC couple all the inputs.

I've got the entire circuit on five PCBs 2.1" x 5.7", including the Panel PCB. There will be 8 pots, 8 jacks, and 3 switches on the panel. I just finished laying out the Panel PCB about five minutes ago and will be building the panel tonight. I'm gonna start with the panel this time, just for shits and giggles.

[Moog$FooL$]

hey.... did you pcb mounting jack yet??
also, you may wanna do a separate & all new post once this is ready for a video..... after all, it sounds really interesting & others that don't come to this thread may wanna check it.

[Dr. Sketch-n-Etch]

Tonight I made all the boards for the frequency shifter project and installed all the jumpers. I also completely stuffed the Panel board with all the pots, switches, and pin headers. I also made the panel, and it turned out great, but I made two tiny mistakes. In my haste, when I was moving things around to get the various pots on the correct sides of the panel, I neglected to move the tiny little endpoint labels for two of the pots with their pot titles, so they don't make any sense. I'm tempted to just scratch them off, but that would break the plastic seal of the Lazertran, so I'll just live with it. I never look at that crap anyway -- I don't know why I used endpoint labels, because I usually don't. I prefer a more minimalist panel with just plain titles above the pot and nothing else -- no lines or other markings. I should've stuck with my usual plan. Oh well, I've already fixed the FPD file, so next time I won't make that mistake. I'll probably finish this module tomorrow, if my wife lets me work on it (she may have other designs on my weekend time).

[Dr. Sketch-n-Etch]

hey.... did you pcb mounting jack yet??

They haven't shown up on the Small Bear site yet, so I can't order them yet.

also, you may wanna do a separate & all new post once this is ready for a video..... after all, it sounds really interesting & others that don't come to this thread may wanna check it.

Hmm, that's a pretty good idea. Let's see whether it sucks or not first, though.

[Dr. Sketch-n-Etch]

The Sketchy Labs Frequency Shifter is finished:

FreqShiftFront.jpeg

FreqShiftBack.jpeg

This is a Bode frequency shifter. This thing is effectively an analog engine for carrying out a sum-of-products trigonometric identity. It consists of four main parts: a quadrature VCO for generating sine and cosine carrier waves, a 90-degree phase displacement network for converting any audio signal into its component sine and cosine equivalents, a dual four-quadrant multiplier for multiplying the sines and cosines of the carrier wave and audio signal together, and an output amplifier for generating the sum and difference of the two multiplier outputs. Doing all this manifests a trigonometric identity, as shown in the following diagram, and this identity guarantees that the frequency of the audio signal is shifted by the frequency of the carrier wave, either up or down:

BodeFS.png

Also, mixing the output back in with the audio signal gives a very nice phaser effect when the VCO is run in LFO mode.

So, the panel turned out perfectly. This is actually the second panel I made -- the first one had some textual errors -- I tried to fix them by scratching off the offending text and filling the holes with clear nail polish, but then I made the fatal mistake of rebaking the panel to get rid of some roughness, and the nail polish burned and turned black, and actually ruined the aluminum underneath. I ended up throwing the whole thing away and starting over.

Also, this is the first module that I've built in a while that worked perfectly the very first time -- no design mistakes, no layout errors, no solder bridges. This entire build took me about two days. I've become a bit of a module-building fiend.

As you can see from the rear-view picture, this build consists of five PCBs. They are all 2.1" wide and 5.7" long -- I was able to get the four circuit boards from a single 6" x 8" blank. The outer two boards are the Rubiquad circuit (a simplified TZFM dual-core Rubicon VCO set up to generate quadrature waveforms such as sine and cosine) split onto two boards, the third board is the dual four-quadrant multiplier and the input and output amplifiers, and the fourth board is the 90-degree phase displacement network. The board attached to the panel is the panel board, which has all the pots and switches, and also has an analog multiplexer for processing the four different waveforms of the Rubiquad VCO. This is actually kinda cool -- the two VCO WAVE switches actually represent two digital bits driving a DG409 dual four-channel multiplexer. When the switches are both down (0 0), one gets sine and cosine, when the left switch is up and the right is down (1 0) one gets triangle and cotriangle, in the opposite situation (0 1) one gets zigzag and cozigzag (or zig and zag), and when both switches are up (1 1) one gets square and cosquare (in this context, the prefix "co-" just means that that wave is 90 degrees out of phase with the other). The zigzag wave is something I added to this build and it gives very pleasing results, especially in phaser mode.

Before I tried testing the whole module (which is scary), I tested all the individual parts.

-- The VCO worked perfectly but I still have to finish adjusting the sine shaper and tune it for 1V/octave (I'll do that tomorrow).

-- The dual multipliers give what look like perfect four-quadrant multiplication (as they should, since I hand-selected all the gain resistors to within 0.1%). The dual quadrature multiplication is very cool, especially with the zigzag waveform. I'll make sure to include that in tomorrow's video.

-- The 90-degree PDN is especially awesome. I tested it by feeding it a sine wave from my Rubicon and scanning the frequency from 15Hz to 15kHz by playing octaves and turning the octave selector switch, and measuring the two outputs on my oscilloscope in XY mode. If the PDN is working well, one should get a circular Lissajous figure across the entire frequency range. I got a perfect circle and it didn't budge at all as I changed the octaves -- it was only very slightly deformed at the highest frequency of 15kHz. I compared this with my previous PDN, and I think that maybe this one is just a little bit better than that one. I hand-selected the 12 film capacitors (four each of 102, 103 and 104) to get virtually perfect values. The resistors are 1% tolerance, just randomly pulled from the bags (I have a little kit of resistor values just for this PDN design -- 22 very specific values which, when combined with the three cap values, give 12 allpass filters with very precise corner frequencies -- I can build 10 of these before I have to order more resistors).

Stay tuned for a video demonstration of this beast, which I will try to achieve tomorrow afternoon.

[KSS]

Been excited to DIY this one ever since you posted this earlier photo. Well done! Have you decided on PCB set price yet?

[tobb]

The Sketchy Labs Frequency Shifter is finished:
FreqShiftFront.jpeg

Wow again!

[synkrotron]

Looking forward to the video

[devinw1]

Badass!

[Dr. Sketch-n-Etch]

I started to make the video tonight, but found that I couldn't hold my phone and play the guitar at the same time. I ended up just playing my guitar through the frequency shifter for about 15 minutes, then my wife complained that it was too late for me to be making so much noise, so the video will have to wait until tomorrow. I'll try to get someone to manipulate the phone (camera) for me while I play and twiddle knobs.

[synkrotron]

I'll try to get someone to manipulate the phone (camera) for me while I play and twiddle knobs.

You wife, perhaps

[Dr. Sketch-n-Etch]

Here's the first of a two-part video on the frequency shifter. I'll be making the second video later this evening, after I buy a thing to mount my cellphone on a tripod.

[Dr. Sketch-n-Etch]

Here's Part 2. It's unique...

[Revok]

It sounds great. The wave shapes are awesome in phaser mode! Put me down for a pcb set if you end up making more.

[Schlumpfhut]

As soon as i have paid off my student's debts i WILL get some of these great modules (with black faceplates hopefully)
Can't wait for the day to come

Keep up the good work and let's see what you come up with next. The List continues to grow.....

[KSS]

Very nice.

[Leverkusen]

Wow, it sounds and looks very nice - I would love to build one.

I wonder how TZFM would affect the sound frequency shifting? Also does the internal oscillator appear on the output when you feed in a static DC signal?

[Prunesquallor]

Great mad scientist stuff, Doc!

[devinw1]

Damn, that's awesome. I feel like guitar guys would go for this big time if you did it as a stomp box.

[KSS]

[Dr. Sketch-n-Etch]

Wow, it sounds and looks very nice - I would love to build one.

I wonder how TZFM would affect the sound frequency shifting? Also does the internal oscillator appear on the output when you feed in a static DC signal?

I'm afraid not, because I have bloody great big decoupling caps on all the signals going into the multipliers (8 47uF electrolytics in back-to-back pairs to make them into bipolar 23.5uF caps), so no DC is getting through the device at all. It would be easy to bring the waveforms out to the panel, but I chose not to do it on this unit. It would simply require adding two jacks to the panel -- these could easily be squeezed into the rows of jacks at the bottom to make them rows of 5. There is plenty of space. I could layout a special panel for this type of build in about 10 seconds... in fact, I just did it:

2U FS VCO FPD.png

I'd also have to add two pins to the Panel PCB, which would take 5 seconds. You should know, however, that this VCO doesn't track terribly well because it has no high-frequency compensation network. You get about 4 or 5 good octaves out of it, and it starts to go a little flat above about 1 kHz. This is not intended to be a musical VCO, but it could be a useful quadrature LFO. I should have thought of that before I made that panel. Oh well, I guess I'll have to build another unit (darn, it's not like I don't love building this shit).

And I've now changed the layout (it took more than 5 seconds).

[Prunesquallor]

You'll probably scoff, but 4-5 octaves ain't bad for experimental shits and giggles. (Bear in mind I have Buchla 258s in my set-up.) The quadrature LFO sounds fun as well.

But the all-important question we're all asking, of course, is could it be Serge-ified?

[Dr. Sketch-n-Etch]

You'll probably scoff, but 4-5 octaves ain't bad for experimental shits and giggles. (Bear in mind I have Buchla 258s in my set-up.) The quadrature LFO sounds fun as well.

But the all-important question we're all asking, of course, is could it be Serge-ified?

Of course, but our friend Loudest Warning will have to design the panel.

[oldenjon]

Very cool! Been looking forward to this and would love to have one. Are you preferring to build modules for people over selling PCBs these days? Either way is fine with me, especially since you've been catering to the 4U crowd, but I've been curious about that. And if you're going to modify the panel design to bring out the waveforms, might as well modify the PCB design to add high frequency compensation right? Kidding / Not kidding

[Dr. Sketch-n-Etch]

Very cool! Been looking forward to this and would love to have one. Are you preferring to build modules for people over selling PCBs these days? Either way is fine with me, especially since you've been catering to the 4U crowd, but I've been curious about that. And if you're going to modify the panel design to bring out the waveforms, might as well modify the PCB design to add high frequency compensation right? Kidding / Not kidding

No, I have no plans to add high-frequency compensation. If you want a really high-tracking VCO, I'll happily build you a Dixie.

Concerning the Frequency Shifter, I'm happy to etch you some boards. As it stands now, there are four circuit boards, all 2.1" x 5.7", but they can easily be compressed to two boards 4" wide. For a 4U application, the boards could be 4" wide and up to 6" long, but there are quite a few interconnections between the two. Maybe you can tell me what you would prefer. I can make the boards anytime. The board set will cost $50 US plus shipping. There should also be a panel board, but without a 4U panel design, I don't know what that would look like. If you want to send me a 4U panel design, then I'll happily lay out a panel board and figure out how to connect it to the other boards. Just make sure that all the panel components conform to a 0.05" grid.