[BUILD] Fritz Euro Teezer VCO

[synthcube]

We are very pleased to announce availability of the Ian Fritz Euro Teezer Thru-Zero VCO.

The aluminum euro panel design by clarke68 is 18hp- and is very complementary to the euro Threeler VCF design: they look great together!

This is a two-pcb set with all panel components soldered to the panel pcb. (The dual gang tuning pot does require a bit of flying wire assembly. )
The PCB set has been tested and modified a bit from earlier Teezer versions, optimized for 12V.
All analog, all thru-hole.

Please feel free to use the thread for build examples, questions, mods etc-- the updated Ian Fritz build guide is available as a free download from the webstore , along with the synthCube kit BOM that shows our choices for certain options like the matched transistor pair, et al

special gratitude to ian fritz for collaborating with us, and to our beta testers clarke, mike, pete, raph and quincas!

euro teezer vco

[paterursus]

This is excellent - so happy to see this in Euro! I'm a huge fan of Ian's designs. Can you provide more information on the dual-gang tuning pot (R12)? I didn't see any information on that in the BOM. Is it a 10-turn, and do you have a recommended part number? Also, about the turn-counting dial - do you have a suggested part number for that? What is a recommended outside diameter?
Thanks, and thanks for bringing this product to the DIY community!

[synthcube]

Here's the BOM we are using for first run kits including the multiturn pot and Bourns multi-turn dial P/Ns... these are not inexpensive by comparison with 'average' eurorack controls but we felt that part of what makes Ian's Teezer design unique is that fine tuning initial frequency- so we kept it!

A few other design points--
a) the panel pcb uses alpha 16mm right angle pots and LJE black barrel 3.5mm stereo jacks (like euro klee sequencer) for height consistency
b) ian chose to use a lot of 1/8w metal film thru-hole resistors to save layout space-- they have smaller bodies than their 1/4w counterparts...so evaluate the pcb before deciding on which resistors you want to use.. since the larger body 1/4w resistors will not fit the pad spacing the same as the 1/8w type
c) you have multiple choices for the matched transistor pair-- well documented in ian's build guide
d) full schematics, notes, and PCB stuffing/layout drawings are also in ian's build guide...

[paterursus]

Thanks for clearing that up. This is super exciting!

[paterursus]

Having some trouble checking out on the SynthCube site. Sent you guys an email about it through the contact form.

[synthcube]

yes, we're sorting some checkout issues resulting from recent changes to credit card compliance requirements... thank you for the patience!

[the bad producer]

Looks great! But surely it's a "multi-turn" pot, not a "dual-gang" (ie stereo) pot? Or have I missed something!

[synthcube]

thank you

post edited accordingly

need more coffee

[ChartreKhan]

could sum1 share a link to the build guide? It wont let me download on the website

[synthcube]

posted here also

[moogah]

I just finished assembling one of these and the kit had another resistor included for R19. The BOM shows 470K and this one was 680K. I'm wondering if that's on purpose? I partly ask because right now it's not working right, I get a rather slow saw (down ramp, is that right) and triangle but no sine.. and neither the init freq or coarse tune knobs affect the frequency. No obvious soldering issues or mis-stuffed parts found yet, I'm done DIY for the night and will pick up tomorrow after studying the schem a bit more.

EDIT to say the way these kits are packed with each component in a bag with the PCB designations printed right there on the bag made this a breeze of a build

[synthcube]

R19 should be 470K per the latest BOM and schematic from Ian.

[moogah]

Ok cool, the 470K was included along with everything else and it's what I stuffed in there

[moogah]

Got one out of two of these calibrated tonight. The issues I ran into earlier were a bad 3280 and I had the Init potiometer wired up wrong. The legs are organized 2, 1, 3 and I had wired them up 1, 2, 3.

Tuning was a bit confusing at first, until I stopped and took a minute about to think what I was doing. I ended up using this process:

Set the coarse and fine tune so it was at 200hz with 0 volts at the CV input.
Apply 1v to the cv input and measure the frequency. Let's say it was 225hz.
Determine the ratio of the two frequencies. 225/200 = 1.125. An octave would equal 1 in this equation, so this tuning is too wide.
Adjust the V/O trimmer, repeat the measurements and calculate the ratio again. If the resulting ratio moved closer to 1 (say 1.100) then the direction I turned the V/O trimmer was correct, if it moved away (say 1.150) then I'd adjusted V/O in the wrong direction.

Repeat these adjustments and measurements until you get a ratio of exactly one (in practice 1.001 or less is pretty good for a VCO).

Given the small adjustments involved you may find it easier to get it close, then repeat the tuning adjustments across multiple octaves with it mixed with a solid digital oscillator and using your ears.

The waveshape trimming was easy, just a matter of having some patience and checking the results at each end of the init trimmer.


I tweaked it a bit with black aluminum knobs from love my switches

[ChartreKhan]

I finally managed to get one of these up and running, woohoo! I just noticed the LM311s are getting a bit warm - not burning, just warm, I'm wondering if this is normal behaviour? I'm using LM311Ps but I installed the 100pf capacitors to reduce chaotic behaviour as suggested on the synthcube website.

[ChartreKhan]

I just fried mine by accidentally shorting a voltage rail (idk which ones) , and now it looks like most of the zeners are shot. Somehow I'm reading 4.85v at one side of D204 which is supposed to be regulating -7v, very confused about how it's somehow turning the voltage positive?

But that brings me to another question, probably borne of my relative lack of experience with electronics. How are these zeners functioning as power supplies without a current limiting resistor? All the 1n5226 / 1n5231s I can find are 0.5 watt. Shouldn't it need a current limiting resistor to work without blowing up the diode?

[elmegil]

Look at where -7V connects. The zener is actually a 5.1V, so the -7V is -12V + 5V = -7V. The place I see it is feeding U2 & U3 (LM311) power pins, but those are actual loads, not just dead to ground or anything, so that's what's limiting the current.

I would imagine the reason it's a + voltage now is that it's fried to the point it's an open circuit (test with diode test on your meter), and something else connected to those op amps is bringing their power pins up to positive voltages.

[ChartreKhan]

Ah thank you, I thought maybe it was the case that the opamps were limiting the current. And you were 100% correct - i tested the diode today and it was totally broke in both directions. Managed to bring it back to life just by replacing the zeners! am happy now

[maxxximiliano]

Hello friends, I bought 4 teezer vco pcb last year from synthcube. I was just starting to build it when I realized that the building documents doesn't match the board they sent me. C10 and C11 are not on my board, instead, I have Rop1 and Rop2. Why is that? is my board wrong? or the documents need to change? thank you!

My board:


The one in the docs:

[elmegil]

The teezer had some revisions after the beta builds. I'm not sure if the docs got updated with the revised layout. My "day job" work day is under way, but I will try to dig out my beta PCB and my final PCB and compare them to what you're showing later ....

[elmegil]

I see Ian responded on the other thread, so ... that would be the thing then.

[ChartreKhan]

Hi i'm back with another question.

I finally got both my Teezers to operate properly tuning-wise, however I can't get the waveforms accurate on either of them. Both VCOs have good waveforms when the linear offset is negative, but when it's positive they get really skewed. The triangle on VCO A looks like a sawtooth that has clipped the positive rail. VCO B's triangle looks better, but I can't get the tips to connect. Also, the "inj" trimmer on VCO B is doing some weird stuff, when it gets beyond a certain points it creates a glitch in all waveforms (like a spike shape, more prominent at lower frequencies). this doesn't happen at all on VCO A.

I noticed the +-5v rails are very far from 5v on both VCOs. They are closer to 4.9v, and the positive rail on VCO B is about 3.8v. How accurate are these voltages supposed to be? I feel like 3.8v is very far from 5v and i'm not sure why it is so low.

Of course I need to match D12 and D13 better but it is hard to come by those diodes at my location and level of income, so I'm looking to see if there might be other factors at play first.

EDIT day later (solved? probably not):
I've narrowed down the problem. I think A4B is supposed to output a +ve voltage when the sawtooth is -ve and vice versa. But on both of my builds, A4B never changes voltage, on one build it is always positive and on the other it is always negative. A4A is outputting kind of a pulse wave on both, which i guess is correct.

I managed to sorta fix it by reducing the value of R38, so that there is less hysteresis on A4B (specifically, I soldered a 120k resistor in series to produce ~22k) But now i get a bit of a pulse on the output as well (mostly at subaudio frequency). It would be cool if someone could help explain what this part of the circuit is doing and how it is supposed to behave - I can see that A4A and A4B are both acting as comparators, but what is the purpose of putting two comparators in series like that? couldn't we just put more hysteresis on A4A and remove A4B entirely? Also would like to know exactly what the "Inj" trimmer is doing because I can't really tell given the other issues I've been having