Befaco Even VCO

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Varthdader
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Post by Varthdader » Thu Mar 30, 2017 9:18 am

So, one more case of an EvenVCO not being able to calibrate properly.

I get to C5 on the ´1 octave by having my Freq. knob out of center, running out of turns on the trimmer pot. Center of freq pot gives me C4.

I go though the calibration chart provided in the last page of the build doc, and manage to get the `1 and `8 steps tracking C, but can´t tune `1/4, the trim pot runs out of turns between G and A

Tried contacting Befaco, but had no reply so figured maybe somebody around Muff´s had a clue as to how to tune this pup.

Varthdader
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Post by Varthdader » Mon Apr 03, 2017 9:26 am

So, Befaco are still silent on how to properly tune my Even.

I am about to get some 100k trimmers to replace the ones in the kit in the hope this gives me enough adjustment to be able to dial in the tuning.

I hope I don´t damage anything with this, my Even is working fully (apart from not being calibrated)

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destroysound
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Post by destroysound » Fri Apr 07, 2017 4:33 pm

drmarble wrote:I didn't have any "heat sink compound" around, so I decided to build a "breeze shield" around IC2. Got the idea from here:
http://musicfromouterspace.com/analogsy ... Tempco.php
Also having pretty drastic temperature drift problems here:

- Take it out of the case and the tracking immediately gets wonky and the pitch drops at least 50 ct.
- Tune it up and adjust the tracking outside of the case, everything is good until I put it back in.

I've been letting it warm up periodically between taking it out and making fine adjustments which gives me a couple of octaves of tracking. But it sure would help not to have to do this little dance. drmarble, did this fix help you at all?

drmarble
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Post by drmarble » Fri Apr 07, 2017 4:47 pm

destroysound wrote:
drmarble wrote:I didn't have any "heat sink compound" around, so I decided to build a "breeze shield" around IC2. Got the idea from here:
http://musicfromouterspace.com/analogsy ... Tempco.php
Also having pretty drastic temperature drift problems here:

- Take it out of the case and the tracking immediately gets wonky and the pitch drops at least 50 ct.
- Tune it up and adjust the tracking outside of the case, everything is good until I put it back in.

I've been letting it warm up periodically between taking it out and making fine adjustments which gives me a couple of octaves of tracking. But it sure would help not to have to do this little dance. drmarble, did this fix help you at all?
Ah, that fix didn't really help a ton. It just slows down the effect of cool air a little bit, but the drift itself isn't improved over the longer term.

There's a bunch more about my attempts to understand the tempco circuit used by the Befaco VCO here:
viewtopic.php?t=177712

I haven't had time to revisit the troubleshooting for a while, but with the help of Muffwiggler member "guest", I am basically re-engineering that part of the VCO, and will be replacing the tempco resistor and some other supporting parts.

It's all a bunch more time and effort than I had planned spending on a VCO which was supposed to be super accurate and stable. It has great features but a massive Achilles heel. Oh well, at least it's an education...

RawMaterial
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Tracking issue: v/oct cv or octave rotary switch, not both

Post by RawMaterial » Tue Apr 11, 2017 12:20 am

Just built a kit from Synthcube. Had no trouble building the kit, all the parts were present and instructions were clear. I was able to calibrate the module by following the instructions, however when I plug in a v/oct cv source, it does not track accurately. It would only track the octave rotary switch. I then calibrated again using the instructions, but instead switched between c1-c5 using v/oct cv rather than the octave rotary and got it to track perfectly, but then it would not track the octave rotary switch. So it seems I can track one or the other, but not both. What am I doing wrong?

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Re: Tracking issue: v/oct cv or octave rotary switch, not bo

Post by donpachi » Tue Apr 11, 2017 10:56 am

RawMaterial wrote:when I plug in a v/oct cv source, it does not track accurately. It would only track the octave rotary switch. I then calibrated again using the instructions, but instead switched between c1-c5 using v/oct cv rather than the octave rotary and got it to track perfectly, but then it would not track the octave rotary switch. So it seems I can track one or the other, but not both.
Don't know if you saw this on page 1 --- did you jumper (short out) R115?
float32 wrote:I had the same tracking issue - calibrate for the octave selector, but then v/oct is sharp ~20c per octave. I think I've figured it out. The v/oct summing resistors are 100k, and the octave selector is .5v/oct, so its summing resistor should be 50k. The v/oct inputs have 100k 0.1% resistors but the selector has a 50k 0.1% in series with a normal 1k 1% (R115). I just jumped R115 and recalibrated and now I'm getting much better tracking, about +/- 15c across 10 octaves.
praise the carp

drmarble
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Re: Tracking issue: v/oct cv or octave rotary switch, not bo

Post by drmarble » Tue Apr 11, 2017 1:30 pm

donpachi wrote: Don't know if you saw this on page 1 --- did you jumper (short out) R115?
That was my 1st thought too...

If the pitch is tracking well with an external V/oct CV source, then congrats, you got a tempco circuit that is performing reasonably well. Luck of the draw I guess.

RawMaterial
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Fixed! Thank you

Post by RawMaterial » Sun Apr 16, 2017 10:49 pm

Total bonehead move on my part. I had read up on the tracking issue and jumping R115 before I even received the kit, then promptly forgot all about it, as the build went so flawlessly. It didn't even occur to me that I missed that step until you guys mentioned it. Thanks!
:banana:

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Randy
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Post by Randy » Sun Apr 30, 2017 11:06 am

I did the R115 mod, still no luck on this. It worked for awhile 'though. Now, I can't get better than a major 6th interval out of the octave switching and less than 2.45V from TP1.

I have replaced the LM336 as well. Befaco tells me the centre pin of the LM336 should be 5V but it is also 2.45V. This is an odd one.

Randy

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Oblivion
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Post by Oblivion » Fri Jun 09, 2017 4:09 pm

So . .. what's the consensus on this module? Go or no-go? Looks awesome at first blush, but then a bunch of problems cropped up. All solved?
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drmarble
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Post by drmarble » Fri Jun 09, 2017 5:39 pm

Oblivion wrote:So . .. what's the consensus on this module? Go or no-go? Looks awesome at first blush, but then a bunch of problems cropped up. All solved?
Tuning problems not solved yet. See details here: viewtopic.php?t=177712

Manufacturer expressed to me that they want to revisit the design, to address these issues... so I'd check in with them to see where they are in that process, before ordering one.

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Oblivion
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Post by Oblivion » Fri Jun 09, 2017 8:20 pm

Thanks, drmarble. Had a line, but I'll pass for now. I've got enough wonky gear.
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Cloudstache
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Post by Cloudstache » Mon Jul 03, 2017 3:05 pm

drmarble wrote:
Manufacturer expressed to me that they want to revisit the design, to address these issues... so I'd check in with them to see where they are in that process, before ordering one.
If there's a serious design flaw, it's not cool that it hasn't been announced more openly by Befaco and that these are still being sold today. I'm sure I'm not the only sucker who bought a second kit to try to figure out what went wrong with his first build.

Are there a lot of people building it and having no tuning problems?

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bchampion96
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Post by bchampion96 » Thu Sep 14, 2017 3:32 pm

Cloudstache wrote:
drmarble wrote:
Manufacturer expressed to me that they want to revisit the design, to address these issues... so I'd check in with them to see where they are in that process, before ordering one.
If there's a serious design flaw, it's not cool that it hasn't been announced more openly by Befaco and that these are still being sold today. I'm sure I'm not the only sucker who bought a second kit to try to figure out what went wrong with his first build.

Are there a lot of people building it and having no tuning problems?
Tuning on mine hasn't been completely perfect. I've got the tracking reasonable, but it does go out of tune when out of my case/with temperature. Using the fine tune, fixes it mostly. Definitely not 100% accurate, but for sequences spanning 3 octaves, it'll do okay for me! Just finished uploading my video on the chap!


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bchampion96
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Post by bchampion96 » Tue Sep 19, 2017 11:55 am

Just got an email through from Thonk that Befaco are sending out (free of charge) an add on to Even VCOs for better temperature stability. Will update when mine arrives! :)

Dancing_Bananas
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Post by Dancing_Bananas » Tue Sep 19, 2017 12:42 pm

Cloudstache wrote:
Are there a lot of people building it and having no tuning problems?
I built one in a workshop, two more were also build, and all three worked fine. Calibration took a little longer than expected maybe, but that's it.
bchampion96 wrote:
Just got an email through from Thonk that Befaco are sending out (free of charge) an add on to Even VCOs for better temperature stability. Will update when mine arrives! smile
Please do, I'm surprised this hasn't been announced louder.

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bchampion96
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Post by bchampion96 » Tue Sep 19, 2017 3:26 pm

Dancing_Bananas wrote:
Cloudstache wrote:
Are there a lot of people building it and having no tuning problems?
I built one in a workshop, two more were also build, and all three worked fine. Calibration took a little longer than expected maybe, but that's it.
bchampion96 wrote:
Just got an email through from Thonk that Befaco are sending out (free of charge) an add on to Even VCOs for better temperature stability. Will update when mine arrives! smile
Please do, I'm surprised this hasn't been announced louder.
Yeah, I can't find anything about it on befaco's website. Just the email I got from thonk

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Richie Witch
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Post by Richie Witch » Wed Sep 20, 2017 9:42 am

Dancing_Bananas wrote:I built one in a workshop, two more were also build, and all three worked fine. Calibration took a little longer than expected maybe, but that's it.
This was my experience as well. The module has worked perfectly since I found the bus pin I forgot to solder. :hihi: Calibration took about an hour. Yes, it's long and tedious and I had to cycle through the flow chart about 20 times, but patience paid off. The thing tracks perfectly (+/- 2 cents across 8 octaves) after a 20-minute warm up. I have an L-1 tuner that I keep connected to it just to be sure.

During the warm-up, I've seen as much as a two-and-a-half semitone drift, but once it's warm, I've had no further issues.
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bchampion96
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Post by bchampion96 » Fri Oct 06, 2017 8:15 am

Here's a link to the changes you need to make with the upgrade kit (which hasn't arrived yet). SMT stuff in there as well which is not good news for me. Never done any before :(

https://www.befaco.org/docs/Even%20VCO/ ... pgrade.pdf

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Uvula_Fluorentine
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Post by Uvula_Fluorentine » Thu Oct 19, 2017 3:18 pm

I just received a new Even VCO kit from Modular Addict and it included the components for the thermal stability upgrade. It looks like it still involves changing out the SMT resistor.

It came with pre-mod instructions. The proper instructions for full assembly with the upgrade are at:

https://www.befaco.org/docs/Even%20VCO/ ... grade_.pdf

imre
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Post by imre » Wed Nov 22, 2017 4:13 pm

Does anyone have a check on the current situation with the kit?
I don't really feel like picking up this kit on the basis of what I've read here, but the situation might've changed?

zorglub76
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Post by zorglub76 » Tue Dec 05, 2017 1:58 am

Hi guys,

I've just finished building the new version of Even VCO, and I'm having problems with calibrating it. It looks like the range is ~3 octaves whatever I do with WIDTH trimmer.

Also, it looks like the trimmers INIT and WIDTH are doing the same job. I set C5 on 1' with INIT, then go to 8' and turn WIDTH all the way to lower the current tone by 5-6 semitones. But when I switch to 1' again C5 is now lowered by the same 5-6 semitones - so WIDTH does not change the range but just shifts the tuning the same way as INIT.

Can anyone suggest what might have gotten wrong with this build? (Btw. I was able to adjust ref. voltage to 1.500V)

zorglub76
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Post by zorglub76 » Tue Dec 05, 2017 5:15 am

And now I found another problem - sine output outputs triangle signal at half the voltage of that from the actual triangle output (square and sawtooth are ok):
Image

Image

I thought that maybe my cheap oscilloscope messed something, so I let Humpback self-oscillate, and I got a nice sine wave:
Image

metabaron24
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Post by metabaron24 » Wed Dec 06, 2017 4:34 am

I am about to build the Even VCO from a full kit. I'm a little nervous about it, it's only my second build and I've read all the stuff about tracking problems and there are a number of revisions to the assembly.

The latest one is for the temperature stability update and it calls for an SMT part to be replaced, it's the temperature sensor under the IC. All the other changes are resistors which is easy.

Now I don't think I can do that myself, too scared of SMT :sad:

Is that part critical for the update?
Or put differently: Does it even make sense to use the other resistors of the update version and not change the temperature sensor or would I mess up more that way?

Just at the beginning of my journey :help:

zorglub76
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Post by zorglub76 » Wed Dec 06, 2017 7:58 am

metabaron24 wrote: Now I don't think I can do that myself, too scared of SMT :sad:
No worries. All the SMT stuff came presoldered (at least on my board). You should find tempco at the place where some IC should go, and there should also be several smd resistors around the rotary switch.

EDIT: Do worry.
I've just taken a second look at that update document, and it seems that I'm screwed up. I thought that my version (3.3) came with already updated sensor and all... How on earth will I desolder a smd that is already below the IC socket.....

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