EFG build issues

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Leverkusen
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EFG build issues

Post by Leverkusen » Mon Jul 13, 2020 6:04 am

Hi there,

I just completed an EFG (board 6, simple version) and it basically seems to work, just not quite right.

What does work is, that an audio signal gets boosted as I would expect and I can grab it from the PRE OUT.

Also a CV signal that is somehow related to the audio amplitude is emmited at CV OUT and the LED goes with the CV amount.

GATE LED ist lighting up as expected too and reacts to THRESHOLD and RESPONSE.



Now what does not to seem right is that on GATE OUT I get something like a very, very fast gate rolls when the LED is on, while I would expect a single gate. This does not react to RESPONSE in a noticable way.

Also the CV OUT is very heavily slewed. There is no way to get a fast response. SPEED control has the effect that at about 8:00 (not fully CCW) there is the shortest resonse, which is still quite slewed but one can recognize the original amplitude flow. Beneath and beyond the slew gets heavier from mid position on it just increases and does not go down anymore until it reaches maximum.


I deviated from the buidling guide at some points but cannot judge how or if this could be related to my issues:

Firstly I ha no 10k lin dual pot for the GAIN control and thought a 50k lin should also work. Then I accidentally got on the deluxe part of the BOM ant some point and populsted the two 2u2 film capacitors at C43, C45. I left them there as I expected them to be not connected to the rest of the ciruit.

Worst mistake was placing U6 in the wron orientation. The whole system did not power up then. I noticed the mistake, turned it around and it worked like described. My first atempt to fix it was replacing the IC with a new one, but with no effect.

Unfortunately the behaviour is too unspecific and my understanding of circuits too basic to find a strating point in the schematics and I would appreciate any ideas where to start. I can't even make out what the misplaced IC could have damaged...

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Synthbuilder
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Re: EFG build issues

Post by Synthbuilder » Tue Jul 14, 2020 4:07 am

Leverkusen wrote:
Mon Jul 13, 2020 6:04 am
Firstly I had no 10k lin dual pot for the GAIN control and thought a 50k lin should also work.
It won't work as it should. You'll get a mismatch of gains between the two stages. You should replace that with a dual 10K linear as soon as possible.
I accidentally got on the deluxe part of the BOM ant some point and populated the two 2u2 film capacitors at C43, C45. I left them there as I expected them to be not connected to the rest of the circuit.
They won't do any harm if you have fitted them. Although you could take them out and use them in another project as they are quite expensive parts to leave doing nothing.
Worst mistake was placing U6 in the wrong orientation....
Since replacing U6 didn't change the fault the problem is likely to be elsewhere. However, U6 does control the V2164 (U5) directly, and maybe when U6 was put in backwards it may have damaged the V2164. The V2164 is configured as a low pass filter. The cut-off frequency of the low pass filter is what the 'speed' control affects. How fast the CV output is allowed to change is controlled by the speed control.

Check that the control voltage to the V2164 is responding correctly. Measure the voltage on pin 1 of U6 and rotate the Speed control. Check that the voltage goes from around +2.5V to 0V. If it does, it could be that the V2164 has been damaged. However, it would be wise to check all the components are correct around U5 just in case.
Now what does not to seem right is that on GATE OUT I get something like a very, very fast gate rolls when the LED is on, while I would expect a single gate.
Check that C17 is a 680nF capacitor and that R27 is 10K.

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Leverkusen
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Re: EFG build issues

Post by Leverkusen » Tue Jul 14, 2020 11:54 am

Thank you Tony, for the support!

What I already tried last night was (apart from desoldering those two caps) exchanging the V2164 (from Coolaudio) with a new one, checking every single part in the filter section and replacing D9. I also tried replacing U4. Voltage at U6 pin 1 goes from 2.2 to 0.0 when turning SPEED clockwise. C17 and R27 are right too.

I ordered a single 10k pot (ouch!) from Banzai and will try again when it is replaced.

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