Befaco Even VCO

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Post by guest » Sat Feb 16, 2019 5:06 am

and suprise, suprise, thats exactly a ratio of 1:100, or 1k to 100k. you might be able to recalibrate it so its more than 1V/octave, but then it wont work with VCOs that buffer the CV. you could also put a buffer in either the M32 or the VCO. but i guess the external buffered mult is the easiest solution, if available.
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Post by rsholmes » Sat Mar 16, 2019 12:54 pm

Update: I built a horstronic buffmult, it works, but the same problem exists: the M-32 KB CV sags to less than 1 V/Oct when plugged into it. But the buffmult outputs have trimmer pots to adjust the gain. So I intentionally miscalibrated one of the outputs for slightly higher than unity gain, just enough to compensate, and now the VCO can track the keyboard CV properly. It's a kludge but it works.

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Post by wavi » Tue Jun 11, 2019 4:04 pm

Hi everyone!

I just built this module and everything else seems to works great, except the octave selector. The waveforms, pitch control etc work but the octave selector simply does nothing. Has anyone had this issue or any have any idea what might be wrong? It seems like the oscillator is stuck at a very low octave.

I'm a bit disappointed as I felt that the build went very well. I only had one issue, which was that I placed one diode the wrong way round. I managed to fix that without too much hassle. I've already built two other modules but I'm just getting into eurorack so maybe I'm missing something obvious?

I have visually checked all my solder joints and all of them look nice and I can't see any shorts or cold joints anywhere. I can't seem to visually locate any issues on the boards. At this point I really don't know what to do.

Anyone have any pointers for what I should check or do now? Thanks!

EDIT:
I read through the manual again, and **** me... I had missed one crucial point:
R115 – This resistor is no longer used so we must bridge the solder points with the leg of a resistor or wire.
I just left it unsoldered and forgot about it. :doh: I'll fix it in the morning and report back. I'm pretty sure this is exactly what my issue must be.
Last edited by wavi on Tue Jun 11, 2019 5:12 pm, edited 1 time in total.

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Post by rsholmes » Tue Jun 11, 2019 4:29 pm

As part of the calibration procedure you should have checked you have 1.5V between TP1 and ground. Do you?

Do you have 5V between R122 (the end further from R125) and ground?

And generally, the voltages on the switch contacts that connect to the resistors should range from 0.5V to 5V. Then the voltage on the other side of the switch should reflect whichever position has been chosen with the switch.

Is all of that correct?

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Post by wavi » Tue Jun 11, 2019 5:16 pm

rsholmes wrote:As part of the calibration procedure you should have checked you have 1.5V between TP1 and ground. Do you?

Do you have 5V between R122 (the end further from R125) and ground?

And generally, the voltages on the switch contacts that connect to the resistors should range from 0.5V to 5V. Then the voltage on the other side of the switch should reflect whichever position has been chosen with the switch.

Is all of that correct?
I calibrated the 1.5 voltage but didn't go further than that. See my edit above (very dumb thing indeed :hmm: ). Sorry to come here that clueless, but I'll fix my mistake and let you know if that helped. Thanks a lot for the quick reply too! Much appreciated!

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Post by rsholmes » Tue Jun 11, 2019 8:39 pm

Yep, leaving out that R115 bridge would explain it. Good luck!

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Post by wavi » Wed Jun 12, 2019 3:09 am

Yeah, that did it. I feel so dumb for missing that. Now I just need to calibrate it :)

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Post by 7C » Thu Jun 20, 2019 11:49 am

chapelier fou wrote:The octave switch isn't cv controlled, is it ?
this...

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Re: Befaco Even VCO

Post by Bodo1967 » Sun Mar 15, 2020 4:05 pm

I am currently troubleshooting my Even VCO v. 3.3, and am encountering very strange problems.

The waveforms as such are absolutely perfect on the oscilloscope, every single one of them. I had first made a mistake and had used an LM336Z25 (2.5V regulator), which led to having only about 0.76 - 0.8 V at TP1. Also, the sine looked more like a second triangle. Anyway, that's solved and was due to the wrong LM336. I replaced it with an LM336Z5, and now I have clean 1.500V at TP1, and the sine looks nice as it should.

However, calibrating the thing is simply not possible. The fine tune pot apparently behaves normally, but turning the octave switch produces weird (to say the least) results. I can calibrate C5 to about 520 Hz in 1" position. When i change the switch setting to 1/2", this results in a frequency jump of maybe seven (!) octaves up, way beyond audible range. My frequency meter detects something like 66 k(!)Hz. On the other hand, when I switch from 1" to 2",the frequency does another seven octave (or so) jump and becomes a slow LFO checking out at about 3.something Hz (yep, that's three Hertz, no typo).

Thou shalt measure voltages, and alas I did.

befaco measured values.jpg

The switch itself provides clean increments of 0.5V per position. The voltages at IC2A pin 1 are reliable as well. I put my measured values in the blue box in the schematic - they are a bit off, but that's probably because the width trim pot is not yet properly calibrated. And there's an eleventh value (-4.9V) mentioned in the schematic which I can't quite figure out - the switch has only 10 positions, so where does an 11th value come from :hmm: ?

Anyway, now it starts to get crazy. The values at the connection between R1 and R3 are completely off (also in the blue box, on the right side. I used a 4R3 parallel to 240R instead of the 4R22 since I couldn't find one, but that imho doesn't provide any reason for the deviances.

Which made me disconnect the module from the PSU and check resistance values at points (A), (B) and (C).

A-ha!

A - B checks out at a bit over 4 Ohms. Fine.
A - C checks out at about 965 Ohms WTF? That should be 104 Ohms or so.
B - C checks out at 961 Ohms. Should be about 100.
That leads me to the conclusion that there is a 1k SMD resistor ("T_SENS") underneath the IC instead of a 100R one.

Did anyone else experience this, and how do I fix this? Replace R 1 and R3 (and possibly R6) with their original values, as in 10k instead of 6.2k for R1; 390R instead of 4R22 for R3, and 10k instead of 95k3 for R6?

Thanks for any help - as I said above, the oscillator section as such seems to be working flawlessly.

Edit - typos corrected
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Last edited by Bodo1967 on Mon Mar 16, 2020 4:22 am, edited 6 times in total.
... why buy it for $100 when you can build it yourself for $150?

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Re: Befaco Even VCO

Post by sduck » Sun Mar 15, 2020 5:06 pm

I realize the danger of measuring resistors once they're in a circuit, but just for fun I put a DMM across the T-Sens resistor of the even vco 3.3 I'm currently building and it reads as a 100R - approximately 108R according to the DMM. Don't know if that helps.
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Re: Befaco Even VCO

Post by Bodo1967 » Mon Mar 16, 2020 2:24 am

sduck wrote:
Sun Mar 15, 2020 5:06 pm
I realize the danger of measuring resistors once they're in a circuit
Sure, but usually you tend to get lower readings and not 9 or 10 times higher than it should, so...
sduck wrote:
Sun Mar 15, 2020 5:06 pm
but just for fun I put a DMM across the T-Sens resistor of the even vco 3.3 I'm currently building and it reads as a 100R - approximately 108R according to the DMM. Don't know if that helps.
... it definitely does, as it confirms my assumption. Thanks!
... why buy it for $100 when you can build it yourself for $150?

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Re: Befaco Even VCO

Post by whyfarer » Sun Mar 22, 2020 9:35 am

I built an even vco v0.3.3 back in the day as one of my first modules. Now that I've been in modular land for a while I'm revisiting and fixing up modules that I never got 100% functional.

My even vco never tracked quite properly and I've just seen in this thread that there is a fix for my pcb/kit version!

The problem is the link to the upgrade instructions on the befaco site seems to be broken. I've reached out to befaco but have yet to hear back. Anyone here still have a copy of the upgrade instructions (or at least the parts list since I'm looking to place a mouser order soon )?

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Re: Befaco Even VCO

Post by sduck » Sun Mar 22, 2020 12:30 pm

I think what you're looking for is at the end of the current build manual - that's still available on their site. Edit: checked it, I'm wrong. Hopefully they'll get back to you soon.
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Re: Befaco Even VCO

Post by whyfarer » Sun Mar 22, 2020 12:39 pm

sduck wrote:
Sun Mar 22, 2020 12:30 pm
I think what you're looking for is at the end of the current build manual - that's still available on their site. Edit: checked it, I'm wrong. Hopefully they'll get back to you soon.
I may be missing it, but I only see build instructions, calibration instructions and schematics. Nothing about the stability/tuning upgrade.

Thanks for taking a look

edit: whoops, i see your edit now

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Re: Befaco Even VCO

Post by sduck » Sun Mar 22, 2020 12:41 pm

You must have replied before I edited my post, Sorry!
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Re: Befaco Even VCO

Post by whyfarer » Sun Mar 22, 2020 12:48 pm

no problem - I appreciate the help!

Since I want to place my mouser order to get going on other projects, I'm going to purchase the currently T-sens resistor currently listed in the BOM:
Tempco 100 OHM 3500ppm SMD 0805 T_SENS PTS0805M1B100RP100

From this thread, it seems like that was what needed to be changed plus some supporting resistors which I hope I'll have on hand.

When I do get this sorted I'll report back for any other slowpokes (like myself) to find later.

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Re: Befaco Even VCO

Post by Bodo1967 » Mon Mar 23, 2020 7:10 am

whyfarer wrote:
Sun Mar 22, 2020 12:48 pm
Since I want to place my mouser order to get going on other projects, I'm going to purchase the currently T-sens resistor currently listed in the BOM:
Tempco 100 OHM 3500ppm SMD 0805 T_SENS PTS0805M1B100RP100
You aren't by accident located in Europe and would be willing to order one more and send it to me, are you? (I'll pay for the resistor and postage of course.)

I don't need anything from Mouser right now, and having one SMD part sent to Germany is... erm... well, just don't even consider it ;)
... why buy it for $100 when you can build it yourself for $150?

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Re: Befaco Even VCO

Post by whyfarer » Mon Mar 23, 2020 12:51 pm

Bodo1967 wrote:
Mon Mar 23, 2020 7:10 am
whyfarer wrote:
Sun Mar 22, 2020 12:48 pm
Since I want to place my mouser order to get going on other projects, I'm going to purchase the currently T-sens resistor currently listed in the BOM:
Tempco 100 OHM 3500ppm SMD 0805 T_SENS PTS0805M1B100RP100
You aren't by accident located in Europe and would be willing to order one more and send it to me, are you? (I'll pay for the resistor and postage of course.)

I don't need anything from Mouser right now, and having one SMD part sent to Germany is... erm... well, just don't even consider it ;)
I'm in the states. Befaco may be able to hook you up if you reach out to them. G'luck sourcing it.

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Re: Befaco Even VCO

Post by Bodo1967 » Mon Mar 23, 2020 1:22 pm

whyfarer wrote:
Mon Mar 23, 2020 12:51 pm
Befaco may be able to hook you up if you reach out to them.
Haven't heard of them in over a week now. I guess right now they have other problems in Barcelona than a customer's wrong SMD resistor :-/.
whyfarer wrote:
Mon Mar 23, 2020 12:51 pm
G'luck sourcing it.
Thanks anyway. Think I'll (have to) postpone this VCO until all this COVID-19 shit is over :deadbanana: .
... why buy it for $100 when you can build it yourself for $150?

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Re: Befaco Even VCO

Post by Befacosynth » Tue Mar 24, 2020 8:30 am

Bodo1967 wrote:
Mon Mar 23, 2020 1:22 pm
whyfarer wrote:
Mon Mar 23, 2020 12:51 pm
Befaco may be able to hook you up if you reach out to them.
Haven't heard of them in over a week now. I guess right now they have other problems in Barcelona than a customer's wrong SMD resistor :-/.
.
Where are you writting? This sounds strange and cannot see any mail from you... sorry for the mess.
Please, for any support inquiry always use support@befaco.org
www.befaco.org
support((at))befaco.org

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Re: Befaco Even VCO

Post by Bodo1967 » Tue Mar 24, 2020 8:39 am

Thanks for getting back :) :tu: !
Befacosynth wrote:
Tue Mar 24, 2020 8:30 am
Where are you writting?
I used the contact form since I didn't find the support e-mail address on your site: https://shop.befaco.org/contact-us

And I also got an automated reply:
befacomail.png
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Last edited by Bodo1967 on Tue Mar 24, 2020 9:47 am, edited 1 time in total.
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Re: Befaco Even VCO

Post by whyfarer » Tue Mar 24, 2020 9:40 am

Befacosynth wrote:
Tue Mar 24, 2020 8:30 am
Bodo1967 wrote:
Mon Mar 23, 2020 1:22 pm
whyfarer wrote:
Mon Mar 23, 2020 12:51 pm
Befaco may be able to hook you up if you reach out to them.
Haven't heard of them in over a week now. I guess right now they have other problems in Barcelona than a customer's wrong SMD resistor :-/.
.
Where are you writting? This sounds strange and cannot see any mail from you... sorry for the mess.
Please, for any support inquiry always use support@befaco.org
I also sent my question to your store contact. I couldn't find the support email on your website - maybe it's a bit hidden at the moment?

I've now sent an email to the correct support email. Thanks for chiming in.

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Re: Befaco Even VCO

Post by Befacosynth » Tue Mar 24, 2020 11:44 am

Hey! Thanks a bunch for the heads up, the contact forms were malfunctioning BIG TIME.
So we have placed pics and texts with our mailing info. :goo:
www.befaco.org
support((at))befaco.org

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Re: Befaco Even VCO

Post by sduck » Tue Mar 24, 2020 12:28 pm

I've posted these guys elsewhere, but should add them here also. These are one of the things that have happened during a long period of social distancing - what a cute couple!
IMG_5641.JPG
IMG_2810.JPG
The zip ties - I wasn't sure if I had the right size standoffs, and the 2 pcbs seemed to be staying together pretty well on their own, so just added the zip ties quickly as a reminder to stay together.
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Re: Befaco Even VCO

Post by whyfarer » Tue Mar 24, 2020 4:11 pm

Befacosynth wrote:
Tue Mar 24, 2020 11:44 am
Hey! Thanks a bunch for the heads up, the contact forms were malfunctioning BIG TIME.
So we have placed pics and texts with our mailing info. :goo:
I see the emails - thanks!

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