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Sum Mix Pan Channel 4 Left Output Volume Is Low (New Build)

I just finished this build, and everything looks good, but on channel 4 the left audio is lower volume. The left and right channels are equal volume when the knob is at 10 o'clock.

Where should start troubleshooting this? I've tried reflowing the main and VCA boards, but I may have missed something. I plan to go back under the scope and take another look tomorrow.

Sending an envelope to the volume input works on all channels. So does the pan CV, scan, and span.

Because the left channel is of lower volume, the audio isn't equal until the pan knob is at 10 o'clock.

Thank you!

9 comments

Kommentare (9)

st-modular

Dec 08

I don’t see anything suspicious here; it looks good. Could you please send me your email through the contact form on this website? I’ll forward the schematics to you. Hopefully, this will make it a bit easier to trace.

st-modular

Dec 04

Hey Exe,

the ICs involved are U4, U5, U22, U23, U24 and surrounding parts. It could also be one of the resistors R43, R52, R280, R279, R281, R282, R283, R284 and D7 or Q26. It might be worth starting to reflow the parts mentioned above.

Cheers,

Stefan

ExecutiveDysfunction

Dec 05

Replying to

So, measuring JP CON3_4 on the main board, I can see that I get a max of 4.5v on pin 1 when completely panning channel 4 to the right. I get 4.5v on pin 2 when panning to the left. I get the same numbers on pins 3 and 4 when panning channel 3.

JPCON1_2 shows the same for channels 1 and 2.

For JP1234 I can see the signal coming in from the Pan CV inputs on their respective inputs.

If I plug an audio signal into channel 4 I can see the waveform coming in from pin 2 of JIN2.1. I'm measuring these on the mainboard.

On the VCA board, I can see the audio waveform come up through pin 2 of JIN2,1. The iBom shows it go into pin 6 of U1 which I measure 10.7v on. It I can see the waveform coming out of pin 7 of U1.

ExecutiveDysfunction

Dec 07

Replying to

So I'm still trying to find a solution to this issue. I've reflowed every single component on each board. Here are some images of the main board. I'll post pictures of the VCA board in another comment. It was a lot prettier looking before I reflowed everything.

Where does the signal actually get split into left and right? I'm trying to chase it around the board, but can't figure out where it actually gets split.

ExecutiveDysfunction

Dec 07

Replying to

Here are the picture of the VCA board too.