[IN STOCK] Eurorack: Discrete State-Variable VCF v1.4

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Jumbuktu
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Post by Jumbuktu » Thu May 24, 2018 8:57 am

khakifridge wrote:Get your DMM out and check for shorts between the power rails and 0V.
Thanks! That is the kind of guidance I was hoping for.

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Post by donpachi » Sun May 27, 2018 6:05 am

After several years, I finally built this filter. It sounds ace :party:
negativspace wrote:
sammy123 wrote:Jason, did you ever try with the 2N5089/5087 or 2SC945/2SA733? I used the pn100a/5158 and it was amazing. Now it's time to build my second.
No, but it's certainly worth a try! I have the 945/733s here and also a giant pile of 5089s (and also of 5088s) but I haven't given them a go in this circuit yet. I'm interested in your results if you do. 8-)
Did anyone build this with transistors other than 2N3904&2N3906 (I used 2SC1815&2SA1015, which should be very similar) or PN100&PN5138? Have another main PCB and would like to try something different. I think Jop reported that there were some problems with the behavior of the circuit with 2SA733&2SC945 in his build, possibly due to bending of the legs to fit the pinout, but cannot find the post.
Thanks :tu:
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Jumbuktu
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Post by Jumbuktu » Sun May 27, 2018 7:26 am

khakifridge wrote:Get your DMM out and check for shorts between the power rails and 0V.
I checked this. No shorts between Gnd and either +12v or -12v on the power header pins. However, +12v is shorted to -12v? Not sure what is causing it though.

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Post by khakifridge » Tue May 29, 2018 3:49 am

Jumbuktu wrote:I checked this. No shorts between Gnd and either +12v or -12v on the power header pins. However, +12v is shorted to -12v? Not sure what is causing it though.
Do these apparent shorts and not-shorts register no matter which way round you have the DMM test leads? The circuit is protected with diodes which will conduct in one direction.

If you do still have a real short between +12V and -12V, get out a magnifying glass and go hunting. It'll be a whisker of solder or a stray wire strand...

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Post by negativspace » Tue May 29, 2018 5:48 pm

Double-check the upper header, the top 2 pins bring + and -12V to the SMT circuit on the control board. Also don't forget to check the SMT section itself.

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Post by Jumbuktu » Wed May 30, 2018 2:57 am

negativspace wrote:Double-check the upper header, the top 2 pins bring + and -12V to the SMT circuit on the control board. Also don't forget to check the SMT section itself.
I separated the boards and got the same issue.

I am wondering if my soldering of one of the SMT caps on the back of the main board might have bridged the pads?

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Post by negativspace » Wed May 30, 2018 3:31 am

Definitely not impossible. :hihi:

(I've done that once or twice...)

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Post by Jumbuktu » Mon Jun 04, 2018 5:08 am

negativspace wrote:Definitely not impossible. :hihi:

(I've done that once or twice...)
Ok, I lost most of the last week with an emergency visit to hospital to have my gall bladder removed. Back home now and I was able to sort this out today.

I had to remove both of the SMT capacitors from the back of the main board to get it to power up with no dramas. However, with the control board attached, I still had power problems - but some modules were now getting enough power to light some LEDs.

Suspecting a pattern here, I removed both of the 0.1uF SMT capacitors from the control board, and the module powered up Ok. After some calibration, I had a fully-functioning filter. The resonance is a bit ratty, but I am not sure the missing caps are affecting it much.

I can't believe I bridged the solder pads on EVERY 0.1uF cap (and still managed to solder the other SMT components properly). I must have mistakely been given or picked up a pack of resistors instead of caps.

Now my question is - what do the caps do? And does it matter if I don't replace them? I am relieved that I now have a working module, but I would like to finish the whole build off properly.

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Post by negativspace » Mon Jun 04, 2018 7:09 am

Ugh, sorry to hear about that one. I had emergency surgery to remove my necrotic gall bladder a little more than a decade ago, so... been there. Not fun. :deadbanana:

Those caps are all for decoupling. The module should work ok without them, but to be on the safe side I'd get some replacements with your next parts order and install them when you can.

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Post by GregorSmith » Sun Jun 24, 2018 11:47 pm

Hi Jason,
I purchased and built the 1.4 version and I've got a couple issues that hopefully you can help get to the bottom of. The filter section plays at extremely low volumes and the resonance is not working properly either. The mixer works just fine though. I'm including a few pictures and an audio file so maybe that will make it easier to troubleshoot. It seems when I close the cutoff frq I get some pops towards the bottom(closed) position on the way down from opened. Ive triple checked all trans and they are in the right position and with the proper value. I used red wima caps for the 10u instead of the silver ones in case I screwed up doing that and that might be an issue as well. On the posted soundcloud link I started with the lp with no resonance and then moved the res all the way up. I then moved to the BP, HP, and finally notch with the res maxed. At the end I switch to the mixer which works fine so you can hear the volume difference. Thanks!

i was playing with the resonance knob a little some during the middle of that sample.
Edit:
https://soundcloud.com/djgregorsmith/6-15-18a/s-Dpb0a
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Last edited by GregorSmith on Mon Jun 25, 2018 1:21 am, edited 1 time in total.

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Post by Jumbuktu » Sun Jun 24, 2018 11:53 pm

GregorSmith wrote:Hi Jason,
I purchased and built the 1.4 version and I've got a couple issues that hopefully you can help get to the bottom of. The filter section plays at extremely low volumes and the resonance is not working properly either. The mixer works just fine though. I'm including a few pictures and an audio file so maybe that will make it easier to troubleshoot. It seems when I close the cutoff frq I get some pops towards the bottom(closed) position on the way down from opened. Ive triple checked all trans and they are in the right position and with the proper value. I used red wima caps for the 10u instead of the silver ones in case I screwed up doing that and that might be an issue as well. On the posted soundcloud link I started with the lp with no resonance and then moved the res all the way up. I then moved to the BP, HP, and finally notch with the res maxed. At the end I switch to the mixer which works fine so you can hear the volume difference. Thanks!

https://soundcloud.com/djgregorsmith/6-15-18a/s-Dpb0a
Hi, did you calibrate the voltages as per the build guide? Mine didn't work properly until I got that right.

PS the red box caps look like the same ones I used. Should be fine.

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Post by GregorSmith » Mon Jun 25, 2018 1:29 am

Thanks for the reply. Everything is calibrated nicely. I adjusted until I got 6 volts then moved on to the + and -. The first one was the minus and I think it was + .10v so I adjusted the other to match at -.10v. The 5v is right on at 5v.

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Post by Jumbuktu » Mon Jun 25, 2018 2:45 am

GregorSmith wrote:Thanks for the reply. Everything is calibrated nicely. I adjusted until I got 6 volts then moved on to the + and -. The first one was the minus and I think it was + .10v so I adjusted the other to match at -.10v. The 5v is right on at 5v.
OK rules that out then.

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Post by Jumbuktu » Tue Jun 26, 2018 6:18 pm

GregorSmith wrote:Thanks for the reply. Everything is calibrated nicely. I adjusted until I got 6 volts then moved on to the + and -. The first one was the minus and I think it was + .10v so I adjusted the other to match at -.10v. The 5v is right on at 5v.
Since no one else is chiming in, let me add a few obvious checks. I don't know much about electronics, but having just completed a build with problems, I feel your pain and I have been through some of the troubleshooting processes myself.

The images you posted are a bit fuzzy and perhaps too close up - parts of the boards are cropped off at the edges. So it's pretty difficult for me to check component values, IC orientation etc. Things i would check:

- The values of the capacitors on the main board. As you probably discovered, the BOM has the resistors coded R1, R2 etc, but for some reason it doesn't say which capacitors are which. I had to refer back to the schematic to work out a few of them. You might just check you have them in the correct place.

- Obvious things: correct orientation for diodes, electrolytics, transistors and ICs.

- The two regulators - are they in the right places? I was confused about the one on the left at first - the thread said that it was solk-screened the wrong way round, but in later boards (like mine) it was correct.

- Correct values for pots. It's easy to mix them up.

- Correct orientation of the SMT IC (although I don't think this would create the issue you are getting, since I think the SMT section just handles the notch behaviour).

Hopefully someone with a bit more knowledge will have a look at your build.

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Post by jgb » Wed Jun 27, 2018 9:46 am

Also, double check the resistor values, sometimes I mess up due to misreading values.
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Post by GregorSmith » Thu Jun 28, 2018 1:38 am

Thanks for the reply guys, I’ve checked all the basics already and most likely need to wait until Jason sees my post as he knows this circuit in and out. He most likely has had this symptom show up once during the many. Many builds he’s made.

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Post by Jumbuktu » Thu Jun 28, 2018 4:07 am

GregorSmith wrote:Thanks for the reply guys, I’ve checked all the basics already and most likely need to wait until Jason sees my post as he knows this circuit in and out. He most likely has had this symptom show up once during the many. Many builds he’s made.
Did you pm him? Good luck anyway!

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Post by GregorSmith » Thu Jun 28, 2018 8:02 pm

Thanks man and I really appreciate the help and input. I tried to PM hi but for some reason it didn’t go through. I’m new to posting here at Muff after years of lurking so maybe it’s my post count or something.

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Post by Jumbuktu » Thu Jun 28, 2018 11:54 pm

GregorSmith wrote:Thanks man and I really appreciate the help and input. I tried to PM hi but for some reason it didn’t go through. I’m new to posting here at Muff after years of lurking so maybe it’s my post count or something.
One other thing you should try is swapping out the ICs. I had a similar problem with a Kotelnikov VCO I built last year. It all worked fine, except that the output distorted at a certain point when sweeping the wavetables. Turned out to be a faulty TL074. It's something easy to check, and would at least rule that possibility out.

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Post by GregorSmith » Fri Jun 29, 2018 1:40 pm

Good idea man. I haven’t tried swapping the ic’s so it’s definitely worth a shot. Thanks man I’ll let you know what happened.

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Post by GregorSmith » Sat Jun 30, 2018 12:02 am

Yea I just checked and unfortunately it’s still the same. I hit Jason up with a PM. It went through this time I think.

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Post by jimfowler » Sun Jul 01, 2018 10:48 am

DISCLAIMER: I don't know what the hell I'm doing.

That having been said, I was able to get rid of a lot of the odd behavior (which, for me, was thumping and clicking when moving the cutoff knob quickly and/or controlling it with cv AND no audio out if the cutoff knob was below ~40%) by changing R47 to 220k. It would appear that I've sacrificed a little resonance (no longer self-resonates) but that's ok with me. I might pop a 180k in there and see what happens.

- Jim

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Post by GregorSmith » Sun Jul 01, 2018 1:42 pm

Jim, thanks so much for the reply man. Really appreciate the lead. I’m definitely down for trying that but Jason sent me a PM and before I start desoldering I just wanna wait until he chimes in. I’ll be honest it’s very tempting to do it right now but with my luck something else will happen...lol.. thanks again

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Post by jimfowler » Sun Jul 01, 2018 2:26 pm

Let us know how you make out. Seems like a small group of folks are experiencing somewhat similar misbehavior despite correct assembly.

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Post by GregorSmith » Mon Jul 02, 2018 12:58 am

Jim, wow that personally makes me feel a little better after hearing that though I don’t want anyone else to come into or deal with any issues obviously. I was on quite a good run of builds with
out a single issue. I might go over every resistor value again tomorrow. The thing that really makes it hard for me is that it’s calibrated perfect and I’ve checked everything that I thought of with the multimeter. I’m still drooling though because everyone who has this filter working perfectly just raves about the sound. I’ll definitely let you know what happens either way and thanks for checking in man.

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