Yusynth ARP VCF BC557 version issues

KarolisV · Last edited by KarolisV on Wed Apr 07, 2021 9:34 am; edited 1 time in total

Hello, All!

I just made ARP VCF BC557 version, all values matched as required, calibrated it as well. I am having some issues the internet is silent about, so hope you can help me.

1. When nothing is connected to the input, all knobs fully CCW, I get Hum on the output. I will put recording sample as attachment (frequency know CCW to CW and back to CCW).
This hum gets filtrated when Frequency knob is turned CW.

2. Not sure if the filter should behave like this or not: when passing signal without any adjustments: Frequency fully CW (filter is open), Resonance fully CCW, I get pretty hardly filtered sound. Just checked with pink noise, so I get rollof from 3K and up. Is that how it supose to work? My MS20 and Polivoks filters passes full signal when frequency is fully CW.

Here are some photos of my PCB
https://www.dropbox.com/s/1ekinulun6nnxgp/2021-02-03%2022.37.53.jpg?dl=0
https://www.dropbox.com/s/1ekinulun6nnxgp/2021-02-03%2022.37.53.jpg?dl=0

ArpVCFhum_1003.wav

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2021-02-03 22.38.48.jpg

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2021-02-03 22.37.53.jpg

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KarolisV · Posted: Sun Feb 14, 2021 11:55 am Post subject:

No ideas?

AlanP · Posted: Sun Feb 14, 2021 11:49 pm Post subject:

I'd suggest checking your board very carefully for shorts across tracks where there shouldn't be -- it's hard to tell, but I suspect there may be a couple. Try cleaning the solder side (not the component side) with isopropyl alcohol and a small brush to clean off some of the flux, to make it easier to check.

phobos · Posted: Mon Feb 15, 2021 2:17 am Post subject:

also measure the tracks themselves for continuity, or better measure between the components
as that could also show any bad solder connections. I do see a small crack in the bottom trace
but that loops around so one crack shouldn't matter much.

KarolisV · Posted: Wed Apr 07, 2021 9:32 am Post subject:

So, came back to it.

Cleaned the solder side, inspected by eye, checked all components for continuity and "neighboor" traces for shorts - nothing.

Could this be caused by calibration and should I do it again?