Looking for a DIY way to boost CV level

[aspertime]

You are right, of course. I was looking at the wrong connections. So I will solder a new ic and check again.

[Haralds:Werk]

Very good. Hope that works. OpAmp from the same Batch? Mind the orientation!

[aspertime]

Checked all Opamp connections (pins to GND, pins to resistors, 4,8 pins' voltage), all checks out fine on the multimeter.
Replaced Opamp with a new one, got same result, no amplification.

[Haralds:Werk]

That is strange. You have done all the usual tests and everything looks fine. There must be something we have overlooked. Time to use your scope. Feed in an audio signal and follow the signal path. Start with the whipper and then move back or forth depending on the result.

[aspertime]

I checked the audio and got amplification even by connecting "regularly", as in input to output through the whole circuit.
Next I checked the CV amplification from within a synth (internal LFO to filter cutoff) and it's also amplifying.
What doesn't work is amplifying the CV signal from my audio interface. It only attenuates. I tried replacing the cable but got the same result.
What could be different between the CV coming from the audio interface and the one which comes from a synth?

[Haralds:Werk]

So finally it is working and we chased a phantom.

Strange. Does your audio interface use balanced output? What is the output impedance?

As workaround patch the output of one channel to the input of the next channel.

[aspertime]

The audio interface has both balanced and unbalanced outs. I could not get an impedance info anywhere, can I do that using a multimeter?
Connecting the out of one channel to the in of the next channel does produces some amplification, however still not up to a full +-5.
What if I change the R2, R7, R12 resistors' value, can I increase the amplification to x4 that way?

[Haralds:Werk]

Yes you can increase R2, R7 and R12 for more amplification.

Balanced and unbalanced on the same output? You can measure this when using a stereo cable. Measure signal between tip and middle contact. And then between tip and GND. Tip and middle contact should have double voltage as tip against GND. Do connect to your modular with mono or stereo cable?
When your audio interface is rated +/-2.5V for the balanced output and uses the same output for unbalanced out you will get only 1.25V at the unbalanced out.

[aspertime]

I see. So I'll try replacing one of the 20k resistors with a 100k one and see if I get x10 amplification.
I'm connecting to the eurorack with mono connectors.

[Haralds:Werk]

First try the mono connection and see if you can get amplification on one channel. Then increase resistors for your needs.

[aspertime]

I did get some amplification but not enough. So I switched to 100k resistors and it did the trick.
I guess I can panel it up and use it it my rack now.
Thank you so much for all your help, I really appreciate your assistance and encouragement.
I learned so much from you and from this build that I'm actually a bit sorry that it works
Well, I can always try out your 36db filter or trapezoid VCO if I want more challenges. (joking, but actually they do seem really attractive)
Maybe after I build some simpler modules.
Thank again for everything.

[Haralds:Werk]

It was me a pleasure to help. Now you gained some experience and move on from here. Happy building.

[aspertime]

Hello again, I have another question for you , Harald.
Now I would like to fabricate a panel. I saw on your website that you're offering .fpd files for panels.
The fabrication company needs Gerber files, and I looked around and it seems that converting .fpd to Gerber files is quite a convoluted process, involving multiple programs and plug-ins, so there's plenty of room for error.
What do you do when you want to fabricate your panels?

[Haralds:Werk]

I buy from Schaeffer.

[Haralds:Werk]

When I started DIY I bought blank panels. Printed the *.fpd files on colored paper and laminated it wit adhesive foil Then glued it to the panel. Panel drilled before with the drill marks of a other *.fpd print. This worked very well for me for a long time. Looking at the prices for milled panels today I might go back to this method or go for PCB material as front panel.

[aspertime]

Thanks. It is strange how some panel designs are more costly than identically-sized ones, at least as it appears when getting an instant quote on the fabrication site.
I guess that size isn't the only factor, might be the amount of drilling as well.

[Haralds:Werk]

When you look at the *.fpd software from Schaeffer you can see the cost listed for every single drill and milled engraving and the common costs as well. It adds up quickly.