MAC Rack kit Build Thread from October 2016 with slow attack led

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Re: MAC Rack kit Build Thread from October 2016 with slow attack led

Post by Joe Malone »

ghaudio wrote:Hi Joe, have you had a chance to review the picture? Is there something else I can send to make this easier to resolve?
Do you have +24v between 0v and +V on the dingo?

Do you have -24v between 0v and -V on the dingo?

If you remove the 4 x 99v on the dingos and power up do both VU meters go back to -20dB?

Does the 1k trim measure 1k when fully turned down?

Send me a photo of the two dingo top without opamps fitted
Joe :-)
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ghaudio
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Re: MAC Rack kit Build Thread from October 2016 with slow attack led

Post by ghaudio »

Finally found a moment to get to testing this out. I discovered that the positive power line into Ch 1 dingo had worked itself loose so there was no connection. I corrected that.

I removed the 4x 99v opamps and didn't see the VU's go back to -20db on power up. Then I encountered a new problem.

Couldn't complete the rest of your test's because I did something to cause the power on the unit to start flickering. All the power connections look to have a good solid connection, the fuse looks good, but now the power and power LED's are flashing on and off at about 1 second intervals. I suspect that I plugged the opamps back in with the power on. With the opamps in, or with the opamps out, the power flickers. Do you suspect I blew something up by plugging those back in while powered up?

Pictures and answers to your questions for the original issue below.
Do you have +24v between 0v and +V on the dingo?
unable to test

Do you have -24v between 0v and -V on the dingo?
unable to test

If you remove the 4 x 99v on the dingos and power up do both VU meters go back to -20dB?
The VU Meters did not return to -20db

Does the 1k trim measure 1k when fully turned down?
unable to test

Send me a photo of the two dingo top without opamps fitted
Dingo_L_Ch.jpg
Dingo_R_Ch.jpg
PCB's look fine. If power supply is hiccuping one or more of the 4 x 24v 1w zeners will be short circuit.

Replace short circuit zeners and you should be going again.

When going again do the above volts test with opamps fitted.

If the meter never turns down even with no input on VU then there will be a power rail down or opamp dead on LA500sc or solder short under the LA500sc pcb.
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RAPHAEL
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Re: MAC Rack kit Build Thread from October 2016 with slow attack led

Post by RAPHAEL »

https://photos.app.goo.gl/IWe87jhtfcYTYDCp2
on the LA500POTv4 the thread doesnt show the 120k resistors being installed. do i not need to uses them?
also on the LA500SCv3 the thread shows a different version of the board. mine has 2x transistors and 2x 1 uF caps where the 2x 10R resistors are also the 1 uF cap just below the leds has been omitted. if i could get a point in the right direction that be great

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Re: MAC Rack kit Build Thread from October 2016 with slow attack led

Post by Joe Malone »

RAPHAEL wrote:https://photos.app.goo.gl/IWe87jhtfcYTYDCp2
on the LA500POTv4 the thread doesnt show the 120k resistors being installed. do i not need to uses them?
Yes as blue led is not used so 2 x 120k are not fitted but if you have fitted them it is also ok as they are not used.
also on the LA500SCv3 the thread shows a different version of the board. mine has 2x transistors and 2x 1 uF caps where the 2x 10R resistors are also the 1 uF cap just below the leds has been omitted. if i could get a point in the right direction that be great
Due to OPA2604AP opamp being unavailable and our stock running out recently the pcb has a been changed in that corner to use 78L12 +12v and 79L12 -12v reg instead of the 78L05 +5v reg.

Just fit all the parts as shown on the overlay of the PCB so no 10R no 78L05 instead fit 78L12 and 79L12 and 3k3 resistor as shown and it will work fine.

Let me know if you have any more questions
Joe :-)
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RAPHAEL
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Re: MAC Rack kit Build Thread from October 2016 with slow attack led

Post by RAPHAEL »

Im in the diagnostic and calibration phase of my build and I am getting a 30kHz resonance in channel 1 any suggestions?

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Re: MAC Rack kit Build Thread from October 2016 with slow attack led

Post by Joe Malone »

RAPHAEL wrote:Im in the diagnostic and calibration phase of my build and I am getting a 30kHz resonance in channel 1 any suggestions?
Please explain more? Do you have a bump in the frequency response at 30khz? Or do you mean you have oscillation at 30khz?
Joe :-)
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fistman
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Re: MAC Rack kit Build Thread from October 2016 with slow attack led

Post by fistman »

Hi Joe,

Just getting going on the dingo and saw the note about avoiding using the () and [] components when using your 99v opamps. Wanted to verify that I should NOT place R17, R18, R20, C11, C13. You have those installed in the pictures, and you seem to be using the 99v opamps in those photos as well, so I was a little bit confused. I see there are no components in the dingo kit for the () values, but it seems you installed the components labeled with []. I already soldered the resistors 17,18,20... oops, but could easily just cut them off heh :mrgreen:

Thanks in advance!

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Re: MAC Rack kit Build Thread from October 2016 with slow attack led

Post by Joe Malone »

fistman wrote:Hi Joe,

Just getting going on the dingo and saw the note about avoiding using the () and [] components when using your 99v opamps. Wanted to verify that I should NOT place R17, R18, R20, C11, C13. You have those installed in the pictures, and you seem to be using the 99v opamps in those photos as well, so I was a little bit confused. I see there are no components in the dingo kit for the () values, but it seems you installed the components labeled with []. I already soldered the resistors 17,18,20... oops, but could easily just cut them off heh :mrgreen:

Thanks in advance!
It is fine to fit all of those parts as it doesn't make any difference to the working of the dingo with JLM99v. So no need to take them off.

We just build the dingo up universally so they work with JLM99v and normal DIP8 opamps which is why we fit all the extra parts.
Joe :-)
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fistman
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Re: MAC Rack kit Build Thread from October 2016 with slow attack led

Post by fistman »

Joe Malone wrote:
It is fine to fit all of those parts as it doesn't make any difference to the working of the dingo with JLM99v. So no need to take them off.

We just build the dingo up universally so they work with JLM99v and normal DIP8 opamps which is why we fit all the extra parts.
Understood. May as well solder in the other caps too then, as they're already placed. Thanks for the quick reply!

fistman
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Re: MAC Rack kit Build Thread from October 2016 with slow attack led

Post by fistman »

Hey again Joe,

Got to the calibration stage - the first side went well. Then got to the second side and had 1.67v output... after some investigation, I noticed I somehow missed installing a 100k resistor on the dingo :roll: That side is reading around 1.25v output now with 1.23v input (I assume this is close enough, as the other output reads 1.21v ?). Mostly just wondering if I could've damaged anything by having it up and running for a couple hours or so without the 100k resistor installed (located between the two op amps), but also if the voltage discrepancies are any problem.

I've done some mic pre kits, but still relatively green when it comes to calibrations etc. so after realizing I wasn't sure how to figure out my reference levels for my converters, I tested and trimmed all my output channels individually to get as close to 1.228v as possible. Hopefully my multimeter is calibrated well heh.

Anyway, I'm trudging forward with the calibration on the side I fixed. Just looking for a little reassurance I haven't strayed too far from the path.

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Re: MAC Rack kit Build Thread from October 2016 with slow attack led

Post by Joe Malone »

fistman wrote:Hey again Joe,

Got to the calibration stage - the first side went well. Then got to the second side and had 1.67v output... after some investigation, I noticed I somehow missed installing a 100k resistor on the dingo :roll: That side is reading around 1.25v output now with 1.23v input (I assume this is close enough, as the other output reads 1.21v ?). Mostly just wondering if I could've damaged anything by having it up and running for a couple hours or so without the 100k resistor installed (located between the two op amps), but also if the voltage discrepancies are any problem.

I've done some mic pre kits, but still relatively green when it comes to calibrations etc. so after realizing I wasn't sure how to figure out my reference levels for my converters, I tested and trimmed all my output channels individually to get as close to 1.228v as possible. Hopefully my multimeter is calibrated well heh.

Anyway, I'm trudging forward with the calibration on the side I fixed. Just looking for a little reassurance I haven't strayed too far from the path.
Leaving the 100k out won't damage anything but would put the cal out between the 2 channels if calibrated that way.

The output level of 1.23v isn't very critical so 1.21v to 1.25v etc is fine. But if you can get the same value for both channels is good.
You can use the makeup pot to trim the level when a bit calibrating.
Joe :-)
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GaryE
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Mac Rack Calibration

Post by GaryE »

Hello. First time here .I have been assembling a Mac Rack kit for a friend. I have reached the calibration stage and got everything set up perfectly on each channel separately but when I try to link the two channels I have had minor problems.
I have a tone generator at 1Kh and 2 Voltmeters setup .They are reading 1.23 volts each within .04VAC of each other
Turning the Gain reduction knobs to -5db on the Vu's drops the voltage to about.860 VAC on each meter.I am assuming that is correct.
When I set both channels to -5db and flip the link switch ,ChA drops to -7db and ChB rises to -4.5 db on Vu setting.
I move the jumper on ChA over to match and turn ChB gain reduction knob CCW .I get -1db on ChA and -0.5db on ChB.I can't get any closer than that using the ChA St match pot.Is there a trick to matching these more closely or have I missed something?

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Re: Mac Rack Calibration

Post by Joe Malone »

GaryE wrote:
Fri Apr 16, 2021 11:04 am
Hello. First time here .I have been assembling a Mac Rack kit for a friend. I have reached the calibration stage and got everything set up perfectly on each channel separately but when I try to link the two channels I have had minor problems.
I have a tone generator at 1Kh and 2 Voltmeters setup .They are reading 1.23 volts each within .04VAC of each other
Turning the Gain reduction knobs to -5db on the Vu's drops the voltage to about.860 VAC on each meter.I am assuming that is correct.
When I set both channels to -5db and flip the link switch ,ChA drops to -7db and ChB rises to -4.5 db on Vu setting.
I move the jumper on ChA over to match and turn ChB gain reduction knob CCW .I get -1db on ChA and -0.5db on ChB.I can't get any closer than that using the ChA St match pot.Is there a trick to matching these more closely or have I missed something?
If the optos have been split correctly between U1 and U2 in each comp as the sticker on them explains the extra match trimpot should not need to be used and both comp should push away from each other less than 1dB. Best to always do the alignment twice or more to get it tighter tolerance.

First before alignment with the MAC comp off check the needle is sitting on -20 on both meters. If not use the front meter flat screwdriver adjust to set needle to -20 before calibration.

Make sure the 2 meter 0VU setting are with the same output level of 1.23vac (+4dbu) as the overall gain of each LA500A may be slightly different due to makeup pot value variation.

Let me know if you are still having problems.

I moved this post to the MAC build thread
Joe :-)
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GaryE
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Re: MAC Rack kit Build Thread from October 2016 with slow attack led

Post by GaryE »

Ok, I believe I have mixed up the opto pairs . 2 U1s in one comp and 2 U2s in the other.. Damn..How can this be rectified? Is there a test procedure I can do to tell which is which?
I thought I was being careful but I obviously mis read these instructions.

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Re: MAC Rack kit Build Thread from October 2016 with slow attack led

Post by Joe Malone »

GaryE wrote:
Sat Apr 17, 2021 1:31 am
Ok, I believe I have mixed up the opto pairs . 2 U1s in one comp and 2 U2s in the other.. Damn..How can this be rectified? Is there a test procedure I can do to tell which is which?
I thought I was being careful but I obviously mis read these instructions.
I would try realigning again just to be sure you cannot get the 1dB push between the comps.

But if you cannot and you are sure you have both U1 in one comp and both U2 in the other comp.

Just gentle unsolder one opto from each comp and swap them and realign.
Joe :-)
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