Befaco Even VCO

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zorglub76
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Post by zorglub76 » Wed Dec 06, 2017 8:37 am

I was under impression that they updated the board and presoldered components when they announced this:

Image

But now I see that they didn't update BOM, upon which I was sourcing the components. Not sure what to think...

metabaron24
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Post by metabaron24 » Wed Dec 06, 2017 9:28 am

I didn't buy mine from them directly but from a shop in the Netherlands, which must have had a pre-upgrade version. My PCB also says V 0.3.3. wich still doesn't mean the temp sensor is the updated one. My component bags also had the old resistor selection. These are the only changes regarding parts: the SMT sensor and a few resistors (5 I think)

I contacted them and they were super helpful. In my case it is relatively easy because I haven't started building yet. I'm going to send in my main PCB and they will replace either the temp sensor or just sent me an updated one instead. (plus they will send the few updated resistors) So the only downside is that I can't start soldering today.
There's also a fun system of Befaco coins to pay for the postage back to me.

Knowing myself, while I'm at it I'll probably pull the trigger on another PCB/panel combo from them :nana:

metabaron24
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Post by metabaron24 » Wed Dec 06, 2017 9:31 am

Just took a look at the BMO. As far as I can tell it's updated, so if you've sourced your parts recently you should be fine. It's easy to tell by the temp sensor.

metabaron24
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Post by metabaron24 » Wed Dec 06, 2017 9:40 am

Also the question is: If you have an assembled version that is nicely tuned and tracks well, why bother getting an update? It's not that they weren't usable as stable VCOs before the update, at least that's my impression from reading here.

zorglub76
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Post by zorglub76 » Wed Dec 06, 2017 6:46 pm

I bought PCB/Panel on September 26. The BOM I used was from October 17, and that BOM had outdated components....

I actually don't care much for tracking. I do this for a hobby, and I'm interested in using modules for autogenerative music, so, for me unstable VCO is a plus :hihi:

But I'm annoyed by the two problems I mentioned before - getting only ~3 octaves of range and getting triangle wave from sine output. That's why I'd like to rule out any BOM related issues before trying to debug the module.

zorglub76
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Post by zorglub76 » Fri Dec 08, 2017 9:36 am

Looks like I've got good news for you.

I didn't change the tempco that I got on my 0.3.3 board, but changed everything else (IC's and resistors). I didn't want to wait for those two weird resistors (4.22 and 95k3), so I soldered a few in parallel and measured them - I got 4.2 and 94k9.

I tuned the oscillator to C5, and started measuring frequency. This is what I got so far (left is the time in hh:mm, right is the frequency in Hz):

00:00 - 523.2Hz
00:12 - 527.2Hz
00:25 - 526.7Hz
00:38 - 526.6Hz
00:45 - 526.7Hz
00:53 - 526.6Hz
01:00 - 526.6Hz

I guess that it became stable now, but I'll still run it for some time. It drifted for 11.5 cents, and it seems that it takes about half an hour to stabilize, which is exactly what Befaco stated in their tuning manual.

The other good thing is that now (after changing ICs and resistors) the range that I have is much wider than before. The bad thing is that the range is still wrong. Now whenever I turn the switch I get two octaves down or up instead of just one.

This means that already at 4' I'm getting just 32Hz, and at 1/4' it goes ultrasonic. Ref voltage is still 1.500V, and I didn't need to calibrate that one.

metabaron24
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Post by metabaron24 » Sat Dec 09, 2017 4:07 am

What a weird resistor this is, isn't it. 4.22 Ohms is unheard of. But there we go Resistance is just the result of an equation.

@zorglub: What IC's did you replace? IC2 and IC3 with the LF412? I have those in my bag. Or did you take even fancier ones?

Nicely done just doing it and getting stable results. Way to answer a question. I should develop a more experimental approach. Maybe after my fifth build.

zorglub76
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Post by zorglub76 » Sat Dec 09, 2017 7:13 pm

Yes, in the old BOM, IC2 and IC3 were TL072, so I now replaced them with LF412.

Now I see that the schematics file is offering some more ways of checking if everything works properly (exact voltages for each position of the octave switch, oscillator graph in different points etc.). I'll try to check my build using that.

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Richie Witch
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Post by Richie Witch » Mon Dec 11, 2017 9:45 am

metabaron24 wrote:Also the question is: If you have an assembled version that is nicely tuned and tracks well, why bother getting an update? It's not that they weren't usable as stable VCOs before the update, at least that's my impression from reading here.
Yeah, I agree with you. I feel bad for everyone who has had problems, but mine works great after a 10-minute warm up. I built mine about two years ago.

Recently, I was using the square wave output as a test signal for a mixer I refurbished, and only once, over the course of an hour, did the oscillator drift from 1.0k Hz to 999.8 Hz (after the warm-up, of course). That seems pretty stable to me, so I'm gonna pass on the update.
Every new row of Eurorack is going to be my last.

zorglub76
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Post by zorglub76 » Thu Jan 18, 2018 6:13 pm

Had a big progress solving the issues with Even VCO :party:

It turned out that the stability fix also fixed my tuning problems.

Before applying the fix, I had awful tuning (about half the octave for each turn of the switch). Also, changing Width worked the same as changing Init - you set VCO to play C5 note, switch octave and get F5. Turn the width to get G5, set switch back to octave below, and get D5....

Then I changed everything according to Stability Update document EXCEPT tempco. Somehow I thought that the new and the old tempco had the same resistance and different ppm (turned out that the old one was, I think, 10k, and the new one is 100Ohm). Now Width trimmer worked OK, but I was getting 2 octaves on turn of the switch.

Now I changed tempco and also changed all the resistors around it (R1, R3, R6) with 0.1% tolerance ones, and I can finally tune the VCO properly :yay:

Now I have a new problem - V/Oct plays two octaves up. When I play C3, I get C5.

Also, I'm still getting triangle wave instead of sine.

Btw. shout out to Befaco support, which had a lot of patience with me, and helped a lot with debugging.

giantreptile
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volt meter hook up

Post by giantreptile » Mon Feb 12, 2018 12:49 pm

noob question: where/how do I hook up a volt meter to test voltage of even vco? It says hook up to T_P_L GND. but not sure where that ground is if the module is plugged into power supply.

context: updating old version with new upgrade kit supplied by Befaco. wasn't expecting all the de/soldering, but here goes nuthin'!

metabaron24
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Post by metabaron24 » Mon Feb 12, 2018 1:20 pm

It says connect Voltmeter between T_P_1 and GND. T_P_1 is a test point on the PCB very close to the Width trimmer. For ground I use the the metal distance piece next to it. Works fine.

Good luck.

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retoid
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Post by retoid » Sat Mar 31, 2018 8:07 pm

Started building the EVEN VCO recently and have run into a few issues. A couple of the IC sockets had to be dremeled out a little in order to allow them to fit over the pre-mounted SMD components. This was the case for 2 of them.

Image

Another issue I am running into is that this red film cap is supposed to fit into C7 but it looks to have the incorrect footprint on the PCB and the cap legs are super short. Anyone else run into this issue? Any advice?

Image[/img]

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retoid
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Post by retoid » Sun Apr 01, 2018 1:07 am

Ended up barely able to make it fit by using some small needle nose pliers.

gbel
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Post by gbel » Mon Apr 30, 2018 6:15 pm

Damned... just pulled a trigger in one of those... What was the outcome? Did you get it Calibrated easily?

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jfprimeau
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Post by jfprimeau » Mon Apr 30, 2018 7:50 pm

I've finished my build a few weeks ago, and so far I am super happy with it. The calibration process was not too painful, and it is stable as far as I can tell by ear with I use it musically.

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retoid
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Post by retoid » Tue May 01, 2018 1:57 pm

gbel wrote:Damned... just pulled a trigger in one of those... What was the outcome? Did you get it Calibrated easily?
Yeah got it all working and tuning/calibration was a breeze. Not much tuning was needed.
jfprimeau wrote:I've finished my build a few weeks ago, and so far I am super happy with it. The calibration process was not too painful, and it is stable as far as I can tell by ear with I use it musically.
Same here, I really like this VCO a lot.

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HorseyWindpump
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Post by HorseyWindpump » Tue May 22, 2018 1:13 pm

Just finished building my Even VCO (V3.3)

Mostly fairly painless, except for the part where I am meant to mount the main PCB to the control PCB. There is not nearly enough space for both one of the ferrite beads, and the 'INIT' trimmer. My solution was to desolder the ferrite bead and mount it on the other side of the PCB. Has anyone else run into this problem?

Hopefully it's visible enough in the middle of this photo - you can see there's no way the ferrite bead could sit underneath the trimmer:

Image

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oliq
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Post by oliq » Wed Jun 13, 2018 3:16 am

Just finished building an Even VCO too. The kit was very good (from Thonk), clearly labelled parts all well organised and the order of components made sense. First kit I've done that didn't have pictures or diagrams of parts, just the list and part numbers but it was still pretty clear.

It's running, calibrates well and sounds great (huge sawtooth!), but I have one problem...

My sine wave output is silent. The even output also just sounds like a sawtooth an octave up from the saw output. From what I've read here the sine is needed to derive the even waveform so that makes sense. I've located the parts in the sine circuit using the schematic and double check the values and the soldering. The only one I haven't checked is the SMD transistor under the IC. I assumed it was OK as it came pre soldered to the board.

@BigCranberry you posted that this part wasn't soldered correctly on yours, did you have the same problem?

I'm not looking forward to removing the IC socket to get to this part... any other suggestions before I do?

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oliq
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Post by oliq » Mon Jun 18, 2018 5:24 am

Just for anyone else with the same problem I had - I fixed it.

It was indeed the surface mount transistor in the sine circuit (under the IC on the bottom left of the board). I ended up cutting the IC socket so it became two strips, which revealed the surface mount part. I carefully heated each leg to reflow the solder and that fixed it.

Now have a sine wave and the great even waveform - which is actually really sweet with it's bottom end and higher harmonics, so glad I got it working.

gbel
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Waves not what they are supposed to be

Post by gbel » Sun Aug 05, 2018 6:39 pm

Hey guys, I'm having trouble with my build basically everything `works` I was able to calibrate the vco, it tracks quite reasonably, all cvs, inputs and outputs are working but the waveforms are not how they are supposed to be...
The sine wave is almost a squareImage
The triangle is almost the same as sine but with a little peak
Image
Even output is like a double triangle with something at the bottom
Image
Sig Zag seems almost ok
Image
And the Square has a little wiggly
Image
Any Ideas? Thanks in advance.

gbel
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Figured out with the help of Befaco

Post by gbel » Wed Aug 08, 2018 12:30 pm

WOrked out the be the triangle circuit, there was a short underneath the IC socket legs 1 and 2 :bang: which cause the whole Ordeal.

All is good now and I'm an even bigger fan of Befaco :)

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INIT out of spinzzz

Post by TheRealQuestionable » Tue Aug 21, 2018 2:25 pm

Sup guys, im new to the modular world, and electronic world, sooooo SUPER NEWB :miley:
This is my first post, I already read through this whole article to see if similar issue, some similar but none the same. This is my first Modular and i have only been now into modular/known it exists for 5 weeks. so that being said pls excuse my uber n00bness.

SO
I have built, its working all g. In the tuning process now and havnt gotten far till i have troubles LOL
Im stuck on the section of selecting one on the rotary switch and Adjusting INIT to C5
the highest i can Adjust too is Ab4 with 6cent. Litterally wont go any higher no matter how much i spin the INIT trimpot.
So I read through here and saw that someone said Width works the same, so i tried adjust the width, didnt really work the same at all... just upped/downed the tune by a few cent until it too had no more effect.
IM OUTA SPINZ!
i can get the it to C5 when i adjust the TUNE pot to around +3. Buuuut the tuning instructions say to set it at middle. Keen to hear a response. Stoked to be part of this collective. super keen for a life further filled with Modular! (seriously how did i only discover this a few weeks ago?)

THANKS! :bananaguitar:
also if you havnt gathered im very bad at simplifying text. I over explain to avoid confusion. love it baby.

OH also would getting a much bigger Trimpot be the solution? Would defs prefer to not have to pull apart and re solder. but also okay if i have to.

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oliq
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Post by oliq » Sun Sep 09, 2018 5:33 am

Just to add to this thread about the incredible tuning on this thing. I've been using at the main VCO in a lead sound fora track I've been working on on and off for several weeks. In all that time I haven't had to tune it, the tuning is seriously solid on this thing.

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Post by loresdef » Sun Nov 18, 2018 8:56 am

Hi all,

I just wanted to add here that i build the Evenvco (rev 3,3) this week and allthough when calibrating / tuning, it did run off a few 0,1 cents per few seconds (after a few minutes 2/3/4 cents) when calibrating. But after finishing the tuning procedure its really stable and tracks tight over all octaves!


For people wondering about the red film cap (c7), i just squeezed it in there, it should fit when bending the legs!

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