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

[Patchen]

FWIW I turned the trimmers hundreds of times and they never hit an end stop.

[Joe Malone]

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

Ok when you said pinned I was thinking they went high off the scale. If they don’t move of -20 then check you have fitted the 0.1uF cap to the dingo-T pcb as shown in the attachment below with black box around it.

IMG_8434.jpeg

[Patchen]

I’ll check. I did not install any components that had brackets or parenthesis as I understood those to be the instructions to follow. Good to know if the fix is that simple however.

[Patchen]

Thanks for all your help to get here, Joe. Cap in and now it's behaving much better! I am still having some trouble with the last step of the calibration however.

"Check that with both channels set the same and link switch on meters both still read -5dB. If not realign both comps again." -After running this calibration several times, and with good results up to this point, I'm still getting a discrepancy when flicking the link switch on. With both channels starting at -5db, channel A changes to -7db and channel B changes to about -4dB.

My unit has a channel mismatch of about .3 db with all controls CCW. I've tried this test running the same Oscillator output to both channels evenly but I've also tried compensating for Channel A's lower output by increasing the signal to that channels input. Results seem the same either way.

There is also a discrepancy on the GR knobs to get -5db of about 3 degrees. These numbers seem normal to me for basic pots but thought it worth mentioning just in case it might be relevant.

I'm still not sure what the Pull knobs on the Outputs are for but those don't seem to change anything here either. What do those do btw??

Thanks again.

[Joe Malone]

Thanks for all your help to get here, Joe. Cap in and now it's behaving much better! I am still having some trouble with the last step of the calibration however.

"Check that with both channels set the same and link switch on meters both still read -5dB. If not realign both comps again." -After running this calibration several times, and with good results up to this point, I'm still getting a discrepancy when flicking the link switch on. With both channels starting at -5db, channel A changes to -7db and channel B changes to about -4dB.

My unit has a channel mismatch of about .3 db with all controls CCW. I've tried this test running the same Oscillator output to both channels evenly but I've also tried compensating for Channel A's lower output by increasing the signal to that channels input. Results seem the same either way.

There is also a discrepancy on the GR knobs to get -5db of about 3 degrees. These numbers seem normal to me for basic pots but thought it worth mentioning just in case it might be relevant.

I'm still not sure what the Pull knobs on the Outputs are for but those don't seem to change anything here either. What do those do btw??

Thanks again.

If you want to go extreme match then with all pot CCW measure 1khz ac volts across the threshold pot outside terminals. If one measures higher volts add a resistor across the outside terminals of that pot until both channels are the same ac volts. Then check the mismatch on the output level and which ever channel is low like the -0.3dB you mention then add a resistor across the low output channel makeup pot until both output levels match.

LA500A opto comp stereo matching mode.
Ok first check with the channels both in off that the meter sits on -20 exactly. If not use the front meter screws to set to -20. If you had to adjust then redo the alignment.
1. Check Both comp alignments are correct.
2. With 1k tone of the same level into both comps set 0VU on meter switched to VU and turn up Threshold pot to get -5dB on the meter and switch to GR to check you have -5dB showing on both meters.
3. Link the comps. If meters move away from each other by more than a +/-1dB move jumper to MATCH end on the compressor which shows more gain reduction on the meter.

Original balance trim pot will now adjust GR meter level when switched to GR (U2 meter opto) and new ST Match trim pot R18 will adjust VU meter level when switched to VU (U1 audio opto)
Image

1. Setup both comp with 1k tone and set 0VU on meter switched to VU and turn up Threshold pot to get -5dB on the meter.
2. Turn threshold pot off on modified comp (fully CCW)
3. Link the comps. Adjust modified comp STEREO MATCH VU trim pot until both comps show the same VU meter readings.
4. Switch both comps to GR and adjust modified comp BALANCE / GR pot until both comps show the same GR meter readings.
5. Your comps should be matched.

To check match
1. With 1k tone of the same level into both comps set 0VU on meter switched to VU and turn up Threshold pot to get -5dB on the meter and switch to GR to check you have -5dB showing on both meters.
2. Link the comps. If meters move away from each other by more than a +/-0.5dB trim modified comps New GR & New VU trim pot until perfect match when linked.

[Patchen]

Ok, Joe. The Stereo match mode worked, thanks again for all the help. I had to futz around with it a bit beyond the steps outlined but I got there somehow. Now that that's all out of the way: THIS THING SOUNDS FANTASTIC. I love how the different ratios completely change the character of the compressor. It's like 3 different opto comps in one. Love it!!

Probably a long shot, but would you ever consider making a tightly matched version of this comp with rotary switches instead of pots? I'd love to use this for mixing but recall would be important. Might be cost prohibitive I guess. Anyhow, love it the way it is. Thanks for giving it life and thanks for letting us build it.

Cheers!
Patchen

[Patchen]

P.S. The casework on this thing is masterful. My complements to you or whoever made the enclosure. It's better than just about anything I've ever seen.

[Joe Malone]

Ok, Joe. The Stereo match mode worked, thanks again for all the help. I had to futz around with it a bit beyond the steps outlined but I got there somehow. Now that that's all out of the way: THIS THING SOUNDS FANTASTIC. I love how the different ratios completely change the character of the compressor. It's like 3 different opto comps in one. Love it!!

Probably a long shot, but would you ever consider making a tightly matched version of this comp with rotary switches instead of pots? I'd love to use this for mixing but recall would be important. Might be cost prohibitive I guess. Anyhow, love it the way it is. Thanks for giving it life and thanks for letting us build it.

Cheers!
Patchen

HI Cool great to hear you got it working and like the sound Please spread the word and send me any links to photos on social media etc so I can share them

I have looked at doing a 2 unit high metering version of the MAC with several more complete features but it is down the list a bit but slowly working on it.

The rack cases we use are hard to cnc as they are anodized already but I really like the solidness of the extruded front panel and rest of the case. We laser the black anodising on the front panel to make the white text and dials so it will never rub off ever. And then we CNC them in house for exact fit all controls. Its more work but lasts forever.

[Patchen]

I’ll spread the word . Look forward to see what you come up with.