MAC Rack kit Build Thread from October 2023 with slow attack led

[Patchen]

Thank you Joe. This is helpful. Although I still think an update would be helpful, I've managed to get through most of it. It might be worth mentioning how the new switch spacer is supposed to work. I think I did it slightly wrong as my switches only sit just flush with the circuit board but oh well.

[Patchen]

Hi Joe,
I'm to the calibration phase and without having adjusted any trimmers I'm seeing a different voltage at one output vs the other. I also see there is one trimmer that is not mentioned in your instructions that is perhaps decided by the balance/match jumper? What does "St Match VU" do?
Also, I have a scope and know just enough to be dangerous with it. Could I get more accurate calibration using the scope and if so how? The base and top voltages on the scope seem to differ from the RMS reading on my multimeter.

thank you,
Patchen

[Patchen]

Unfortunately I’ve run into a problem. I'm finding that meter vu trimpots don't seem to be doing anything for either channel. Meter is always pegged full left in VU mode. They both seem to turn freely and never hit an endpoint.

Also finding that at the 3:1 setting full gain reduction on one channel equals about 60% gain reduction on the other channel. according to an rms meter sending pink noise. Very large difference. Any tips here?
Also, what are the pull knobs for on the output knobs?

thank you!

[Patchen]

I wanted to test that the compressor is working even though I'm having problems with calibration. The compressor seems to work, however the action of the two channels is wildly different with the same settings, with or without the link switch on. One channel is very 'smashy' and the other seems to have much more relaxed time constraints. Not sure if this is related.

[Joe Malone]

I wanted to test that the compressor is working even though I'm having problems with calibration. The compressor seems to work, however the action of the two channels is wildly different with the same settings, with or without the link switch on. One channel is very 'smashy' and the other seems to have much more relaxed time constraints. Not sure if this is related.

Just yes or no answers to the below questions will help me to help you.

Were the Optos in each bag split to the correct U1 and U2 opto positions ? Does the compressor compress harder when switching from 3:1 to the other ratios ?

Check is both dingo-T are working with unity gain. With threshold and makeup fully CCW does the audio level stay the same when switching from off to VU or GR?

If not remove the ribbon cables from the link switch pcb and sc pcb and try the loop test into any of the plugs to see both dingo-T are unity gain when relay bypass is switched off. It both are unity gain. Then plug the sidechain pcbs in and check the meter lights in VU or GR and you can hear the relay on the dingo-T switch on and off?

Check the NE5532A on the sidechain pcbs has +12v on pin 8 and -12v on pin 4? If both have +/-12v? If comps are still not matching let me know where in the calibration does the alignment go wrong? The opto match is very tight these days so very rare the jumper for stereo match would be need to be moved.

[Patchen]

Checking other things but just to make sure. I have a mean well 48v adapter that came with this kit. Is that correct? Voltage on Ti Opamp is way out of spec

36.5v on Pin 8
12.35 on 4
Readings on both channels are comparable.

[Patchen]

Were the Optos in each bag split to the correct U1 and U2 opto positions ? Does the compressor compress harder when switching from 3:1 to the other ratios ? -Yes and Yes.

Check is both dingo-T are working with unity gain. With threshold and makeup fully CCW does the audio level stay the same when switching from off to VU or GR? -YES +\- .5db

If not remove the ribbon cables from the link switch pcb and sc pcb and try the loop test into any of the plugs to see both dingo-T are unity gain when relay bypass is switched off. It both are unity gain. Then plug the sidechain pcbs in and check the meter lights in VU or GR and you can hear the relay on the dingo-T switch on and off? -Relay is working did not perform rest of these tests because above is working

Check the NE5532A on the sidechain pcbs has +12v on pin 8 and -12v on pin 4? If both have +/-12v? -> +36.5v on Pin 8
+12.35 on 4 Readings on both channels are comparable.

If comps are still not matching let me know where in the calibration does the alignment go wrong? The opto match is very tight these days so very rare the jumper for stereo match would be need to be moved. -I can only do the second step, calibrate GR. Other trimmers seem to have no effect.

[Joe Malone]

Check the NE5532A on the sidechain pcbs has +12v on pin 8 and -12v on pin 4? If both have +/-12v? -> +36.5v on Pin 8
+12.35 on 4 Readings on both channels are comparable.

Seems like you are measuring from -v of the plug pack not actual ground 0v audio pin 1 XLR

If comps are still not matching let me know where in the calibration does the alignment go wrong? The opto match is very tight these days so very rare the jumper for stereo match would be need to be moved. -I can only do the second step, calibrate GR. Other trimmers seem to have no effect.

So send me photos of the top of the sidechain pcbs. No need to remove them at all. So putting in a 1kHz tone and the meter showing 0VU and turning up the threshold until the meter shows -5dB does happen ?

[Patchen]

Thank you Joe. I’ve left the studio for the night so won’t be able to check or send photos again until tomorrow. You are correct on the ground measurement. I didn’t know where to get ground from. I’ll try pin 1 xlr next.
From memory yes, I could set the GR trim to show 0db and then adjust the threshold and the needle would move as expected. It’s just in VU mode the meters are pegged hard left no matter what I’ve tried so far.

[Patchen]

I can confirm voltages are correct on op-amp +/- .3 volts. Here are the photos. Thank you!

[Joe Malone]

Thank you Joe. I’ve left the studio for the night so won’t be able to check or send photos again until tomorrow. You are correct on the ground measurement. I didn’t know where to get ground from. I’ll try pin 1 xlr next.
From memory yes, I could set the GR trim to show 0db and then adjust the threshold and the needle would move as expected. It’s just in VU mode the meters are pegged hard left no matter what I’ve tried so far.

Ok build looks correct from on top from what I can see in the photos.

So with no input plugged in and switched to VU do the meters sit on -20? Normally before alignment with 1kHz tone reading 1.23vac between the output XLR pin 2 and pin3 the meter would read about -2 until the trimpot was turned several full turns up to get the meter to 0VU. These pots are 25full turns end to end. Do you get 1.23vac on the output XLR ?

[Patchen]

Yes, I can get 1.23vac on output. Meters always full left in vu mode.

[Joe Malone]

Yes, I can get 1.23vac on output. Meters always full left in vu mode.

So with nothing plugged into the input the meters are pinned above +4db?

[Patchen]

They are pinned full left usually. I’ll double check tonight but I’m pretty sure yes. In vu mode always full left

[Patchen]

Confirmed, always full left in vu mode. So I guess it seems like they are never seeing signal or something? So not above 4dbu. Other side