JLM AUDIO

Ok 98.8k in parallel with 831k = 88.3k. So you can try a 1Meg pot. Since pots are +/20% it will not guarantee the pots will be at the same point in the turn of the pot due to the log curve mismatch but can help. Once you balance the ac volts at these 2 points you will need to redo the makeup balanc...

Ok here are the measurements CH A had .316 vac and 98.8k ohms with pcb cables unplugged. Ch B had .307 vac and 88.3k ohms with pcb cables unplugged. Settings are, y cable with 1.23vac at inputs. 1.3 ratio, VU, and flat. Do people tend to just build these units and not fine tune them at all? Have peo...

Cool. With Y cable and thresholds CCW measure the voltage across the outside threshold pot tags again. If one is higher voltage a resistor can be added to bring it down to match the lower voltage side and then the makeup trim will need to be redone. This can sometimes balance the threshold pot mid ...

I found the culprit, not sure how this got checked on or if it is set this way by default in REW but I went back to not using the Y cable and then I unchecked this and the link switch works perfectly. Such a stupid waste of time trying to troubleshoot a problem that really wasn’t there. IMG_6982.jpeg

The only thing I can see that would do this out of the blue is if one channel is out of phase with the other as then they cancel when joined together. Have you got both channels in phase (preferably using a Y cable in so both channels have identical input level)? Are both phase jumpers behind the i...

OK that looks ok. The clue will be what ac volts you are getting at pin 6 on each IDC 10 pin header on the mac link pcb when separate and when linked measured to 0v while -5dB GR is on each channel. Make sure the switch and threshold settings on both comps are the same. Ok, So just and FYI that I w...

Yes trimpot spot is correct across makeup pot. This is very seperate from the link area of the circuit. Did the link switch work before? Do you have a photo of the link pcb? Yes the link switch used to work just fine only a slight difference between the two -5db readings on the meters when engaged....

Ok never seen this before and the trimmer if done correctly will not affect this. Check the mac link pcb has the 10 pin headers and cables the correct way around and no shorts to 0v. With link switched on unplug one ribbon cable from the link pcb at a time to see if both comps come back to -5dB wit...

Ok, I just got done adding the trimmer pot to balance the two output pots. It wound up being 98.6K and I got the outputs VAC to be equal now when you switch on the VU meter. Thanks so much. I have done the calibration again and made some slight tweeks to adjustments trimmers but now have something w...

Thanks Joe,
Once I get them equal should I drop the output of my daw so that I get 1.23vac on both opto outputs so I can zero out the meter when I recalibrate? So is channel A already adding some gain even though it is already fully CCW?

Hi Joe, I have started to work with figuring out what exact resistor size I would need. I have not made any changes or soldered anything yet. In doing that I decided to setup my Apogee duet interface to use for the REW Signal generator because both outputs are equal on that. With that said I sent 1....

Thanks for the explanation Joe, I really appreciate it. I will try to get this done soon, can I solder the resistors to the outside pads that are closer to the middle of the pcb since they are connected to the ones closer to the edge that are under and covered by the case’s edge.
Thanks
-Scott

Thanks again for all you help Joe. You can add a resistor across channel B makeup pot outside pads to balance the outputs exactly. Somewhere between 240k and 330k should balance it perfectly at the minimum makeup setting. When you have it balanced adjust the interface so both MAC outputs are 1.23vac...

Ok I now know what to measure now thanks so much. Here are the answers from the previous post. Are those out-of-alignment interface outputs going to drive the comp always? Y/N. No, it is just what I have available but now that I know there are discrepancies I will be checking all the outputs of the...

Sorry but I am still confused on the inside / outside part. Before I pull these boards out because I can’t reach the front six soldering points cause they are covered by the case lip. Can I measure from the back 6 solder pads on each pot? Are these part of the switch or the potentiometer? I have cir...