[BUILD] SEM VCF

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Emalot
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Post by Emalot » Thu Jan 28, 2016 9:34 am

SOmething strange, i just finish this SEM filter and it looks working, but the frequency pot don't have any effect.
I try to put CV in the freq input, and the frequency didn't change.
The NOTCH pot and the resonance works fine.
ANy idea??

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roglok
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Post by roglok » Thu Jan 28, 2016 9:44 am

what PCB revision? Have you flipped the rogue transistor?

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Emalot
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Post by Emalot » Thu Jan 28, 2016 9:46 am

yes i flip the 2N3906.
THe PCB is the BLUE one.

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roglok
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Post by roglok » Thu Jan 28, 2016 9:52 am

are you absolutely sure that your PCB version requires the fix? look at my post
two years ago:
viewtopic.php?p=1219467#1219467

sounds just like yours, eh?

i'd follow the PCB traces and compare with the original schematics...

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Emalot
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Post by Emalot » Thu Jan 28, 2016 9:56 am

SO you mean i didn't have to switch the 2N3906?

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Post by roglok » Thu Jan 28, 2016 9:59 am

Emalot wrote:SO you mean i didn't have to switch the 2N3906?
No, I mean that the documentation for this project is not very good and that you need to make sure you know what you are doing.

I was merely pointing out that it could be related to the 2N3906, since it was a problem in the first revision of PCBs. I don't know how many subsequent revisions there were, what colour those PCBs are and if they had the errors fixed. Hence I advise you to check your build against the original schematics since they are known to be 100% correct and working.

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Emalot
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Post by Emalot » Thu Jan 28, 2016 10:10 am

OK.
I switch the 2N3906 (i put it like in the silkscreen) but freqpot doesn't work too.
I already built one of this filter, and i remember that i switched the 2n3906, so, the problem is something else.
MAybe an IC? but i don't know wich IC is for frequency?

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roglok
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Post by roglok » Thu Jan 28, 2016 1:28 pm

that's the problem with PCBs without parts designators - you can't tell the parts apart. in order to debug you need to map the signal path to the PCB traces...

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Post by galingong » Fri Feb 05, 2016 5:19 am

I'm building the old version of this filter as I don't need CV input for Resonance. I'm making some changes though.

Would it be ok if I swapped the LM301 and the 3 pieces of LM741 for a single TL074?
I'm also planning to use 13700 instead of 3080s (for some reason I have a bag of 13700s, I'd like to put some to use.)

Any input on this? I've successfully replaced older OTAs for 13700 in the past, but I'm not quite sure about those single opamps. Thanks!

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Post by CliffordMilk » Wed Feb 24, 2016 8:52 am

(delete)

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CliffordMilk
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Post by CliffordMilk » Wed Feb 24, 2016 9:07 am

Could someone please help with the calibration process? Simply put, where do I connect the multimeter when trimming T9 and T10 to 0V?

Any help would be grately appreciated. It sounds as though it'll be a great filter once set up correctly.

Thanks

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Post by keninverse » Thu Feb 25, 2016 10:48 am

I'm pretty sure both of those are just set up as dividers so just measure wiper (middle pin) to ground. If you really want to make sure hook up a probe to ground and make sure one side is the same as the V- supply and the other is your V+ supply. Then zero out the center pin.

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Post by CliffordMilk » Sun Feb 28, 2016 8:57 am

All done. Thanks. It sounds great.

I do have one issue that I can't figure out: I built two of these and one one of them, the vari output has a fault. When I turn the notch pot, there is no change to the sound and about 3/4 of the way into the pot turn, the audio cuts out completely. The individual outputs all seem good but all cut out if I turn the notch pot. My first thought was that it was probably a short but close inspection showed nothing. Totally stumped. Has anyone experienced similar or has anyone got any suggestions as to what the culprit might be?

Thanks

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Post by raph36 » Tue Apr 12, 2016 4:09 pm

this is like the worst board i've ever had to build....why the F*** would you sell a board without testing it first.....nothing works like it should there's no f*** part numbers on the board...so i can go to hell with the schematics... well i feel like i've been fooled!

really.... man, prototyping is just 25 bucks!

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Post by woodster » Tue Apr 12, 2016 4:21 pm

raph36 wrote:this is like the worst board i've ever had to build....why the F*** would you sell a board without testing it first.....nothing works like it should there's no f*** part numbers on the board...so i can go to hell with the schematics... well i feel like i've been fooled!

really.... man, prototyping is just 25 bucks!
?

What's the issue with your board ?

Have a look at the 1st post of this thread, there is an image of the pcb with all component values listed...

I built 2 quite early on in my SDIY days, both worked on 1st power up, and both are really fantastic VCF's !

Yes there is a trace cut or two, but nothing complicated really, plus there is a good build document freely available from Synthcube with accurate info and BOM etc.

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Post by raph36 » Tue Apr 12, 2016 4:43 pm

well, i don't know if someone had the same problem, but at one point of the frequency pot, all the sound disappears, resonance and doesn't seem to work as it should, overall the effect is weak

it's just that it really feels like the board has not been fully tested prior to distribution
i ran onto the synthcube doc.. my pcb is green (dont know which version it is) it seems like everything has bee done as it should

so let me summarize what i did just to see if i havent forgotten something
-one 2N3906 backwards
-i used two 2N5458, right next to the silkscreen pointing in the same direction
-2 trace cuts on notch pot and jumpers to the op-amps (as in the doc)
-keep the TL074
-only two LM3080

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CliffordMilk
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Post by CliffordMilk » Wed Apr 13, 2016 12:55 am

This may be a long shot but try removing the nuts on the pots that secure them to the panel and testing the pots again. Sometimes they can cut out if they aren't aligned properly. I had that issue with my resonance pot.

Stick with it though man, you will get there and when you do, you'll have the best filter of it's kind in Euro.

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Post by Flareless » Wed Apr 13, 2016 7:29 am

CliffordMilk wrote:Stick with it though man, you will get there and when you do, you'll have the best filter of it's kind in Euro.
I totally agree! The filter is really excellent.

The build is admittedly extremely tricky. I found that thoroughly reading this thread and the documentation prior to starting was a huge help. Even still I ran into a problem due to the docs being Euro specific while my rig is MU (I soldered the pots to the board rather than using flying wires for the Synthcube panel).

Good luck!
Rich

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What can this strange device be? When I touch it, it gives forth a sound - Neil Peart

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Emalot
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Post by Emalot » Thu Jul 28, 2016 3:08 pm

My VCF SEM doesn't work.
EVerything is OK, but the FREQ pot and FREQ CV in doesn't work.
I changed all IC's, i change the 2N5458, (orientation is OK), offset FREQ trimpot.
I already built the same filter, and it 's working, but i cant find what is the probleme on this one.
How to do to find the problem? I don't have schems, i don't know which components are for FREQ or not...
Raaaahhhhh....

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Post by roglok » Thu Jul 28, 2016 3:42 pm

Emalot wrote:My VCF SEM doesn't work.
EVerything is OK, but the FREQ pot and FREQ CV in doesn't work.
I changed all IC's, i change the 2N5458, (orientation is OK), offset FREQ trimpot.
I already built the same filter, and it 's working, but i cant find what is the probleme on this one.
How to do to find the problem? I don't have schems, i don't know which components are for FREQ or not...
Raaaahhhhh....
schematics are in the first post of this thread. i just reviewed this and found another issue i had earlier regarding CV response - check my post here:

viewtopic.php?p=1221194#1221194

IOW: have you wired up the CV attenuverter?

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Emalot
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Post by Emalot » Thu Jul 28, 2016 4:06 pm

NO
I just put off the TL074 (after 4 month on this fucking problem)
And it's working!!!
It was the attenuverter.
Thanks Roglok, because i found it when i read your post page 5.

How i have to do to build this filter without attenuverter?
A resistor of 50K between the pin of CV2?

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Post by roglok » Thu Jul 28, 2016 4:14 pm

Ha, that's great!
:yay:

Sorry, I had totally forgotten about the issue with the attenuverter when you first asked in January! Only after I re-read my own post I remembered.

This project is a real challenge, but very satisfying when completed. I use the filter a lot and love it to bits.

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Emalot
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Post by Emalot » Thu Jul 28, 2016 5:10 pm

oh, finally it's not too simple.
When i put off the TL074 it's working, but i wired 50K attenuverter, i put the TL074, and it's not working.
HUm???

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Post by Barcode » Sat Aug 20, 2016 11:19 am

Control PCB's that line up with the Clark panel are coming! They will be available from Synthcube really soon.

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Post by sammy123 » Sun Aug 21, 2016 12:23 pm

Oh hell yeah!! Thank you!!!!

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