I recently bought a used pair of Mackie HR824 MK2 active speakers. After listening to them for a while I noticed what sounds like low level distortion while music is playing, but the distortion peaks don't seem to be following the peaks of the music. I used a tone generator in my DAW software and isolated the distortion to 60 hz and below, and it sounds to be coming from both the woofer and tweeter. Wondering if the distortion is from a driver or the plate amp I swapped the plate amps on the speakers, and the distortion follows one amp. I also noticed that the auto power on feature isn't working on that amp, which may be related (or maybe a separate issue). Any ideas on what could be the cause of the distortion? Maybe a bad electrolytic cap? The power supply filter caps are Jianghai brand, and the other electrolytics are JH brand. I know little about electronics, and help on what to look for is appreciated. If it's a simple fix I would like to keep the speakers, else they can be returned.
Owner's manual with block diagram on page 18
https://mackie.com/img/file_resources/HR824mk2_OM.pdf
Schematic (download link at bottom right)
https://www.audioservicemanuals.com/m/mackie/mackie-hr824/4208092-mackie-hr824-mkii-schematics
Owner's manual with block diagram on page 18
https://mackie.com/img/file_resources/HR824mk2_OM.pdf
Schematic (download link at bottom right)
https://www.audioservicemanuals.com/m/mackie/mackie-hr824/4208092-mackie-hr824-mkii-schematics
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Hi
I would replace those Filter caps for a known good brand. Anyway.
Find a Multimeter.
Take the Amp out.
With safety in mind. First.!!!
Measure for DCV at the speaker terminals of the Amp.
Be better to clip the leads on if you can then switch the amp on. But just be safe.
Post the results.
A good test to do anyway.
Cheers
I would replace those Filter caps for a known good brand. Anyway.
Find a Multimeter.
Take the Amp out.
With safety in mind. First.!!!
Measure for DCV at the speaker terminals of the Amp.
Be better to clip the leads on if you can then switch the amp on. But just be safe.
Post the results.
A good test to do anyway.
Cheers
Last edited:
Those numbers seem OK.
Have you searched anywhere else as there might be a known problem with them.?
You’re saying it isn’t the music causing it but something else is being mixed into the sound.?
If it’s on both amps then it has to be something common to both. I just watched a video on it. Those amps are totally isolated from each other. So it might be power related. In the video the speaker was muting on and off caused by a bad cap which resulted in a square wave on one of the transistors. The one next to the diode near the rectifier on the transformer end was causing it.
I’d change the caps related to power. Check out the schematic for it to find the ones to change. If you have to.
Get some Kontakt cleaner for the auto power switches. Try that first.
Cheap parts causing problems.
Have you searched anywhere else as there might be a known problem with them.?
You’re saying it isn’t the music causing it but something else is being mixed into the sound.?
If it’s on both amps then it has to be something common to both. I just watched a video on it. Those amps are totally isolated from each other. So it might be power related. In the video the speaker was muting on and off caused by a bad cap which resulted in a square wave on one of the transistors. The one next to the diode near the rectifier on the transformer end was causing it.
I’d change the caps related to power. Check out the schematic for it to find the ones to change. If you have to.
Get some Kontakt cleaner for the auto power switches. Try that first.
Cheap parts causing problems.
Yes. I have searched, but I didn't find anyone describing this problem. It's a very low volume distortion. I should have mentioned that the volume of the distortion doesn't seem to change with volume of playback content. And I suspect that when hearing it during playback it may be following some low frequency content that I'm not hearing. I may be able to watch for that on a spectrogram or spectrum analyzer.
I do need a few odd components, and I may as well add some electrolytic caps to the order to see if swapping any out takes care of the problem. Since there is the the problem of distortion that doesn't seem to follow playback volume, the distortion happens at 60 hz and below content, and the auto power on mode isn't working, I'm wondering how likely it might be of something at fault near the inputs in the low frequency gain trim (B8-B7 on page 1 of the schematic), just after which the signal is tapped for the auto power on detection (power mode switch is at D6). And I guess it wouldn't hurt to check voltages at the test points listed on page 3 at B7.
I didn't think of it before, but I changed the input trim volume, and the distortion isn't changing at all when playing a test tone at different trim volumes. I might be chasing my tail here, with the distortion problem actually being a mechanical buzz at the front baffle that is only being brought on by low frequency content. Maybe I assumed that since 60 hz and below brings it on that it was an electrical problem. And it could be that the auto power on feature not working is completely unrelated.
60hz is AC.
Yea ,test for voltages etc first. Everything that’s free. That’s why they’re there.
They’re all cheap caps in there I think as well.
Yea ,test for voltages etc first. Everything that’s free. That’s why they’re there.
They’re all cheap caps in there I think as well.
All jumper points tested ok. Maybe +15v was a little low at 14.8 v. And listening more to the distortion, it's not mechanical. Definitely electrical, and the volume of it does change when changing the volume of the test tone.
Other than the big filter caps, all the other electrolytics look to be of just a few values, so I suppose I could order those values and try some swapping out.
Other than the big filter caps, all the other electrolytics look to be of just a few values, so I suppose I could order those values and try some swapping out.
I did find today someone else mentioning this same problem. Unfortunately he never reported back.
https://www.soundonsound.com/forum/viewtopic.php?t=26826
I think I'll contact the store tomorrow, describe the problems, and see if they are willing to discount the price. If they are, I'll order and replace the electrolytic caps, starting with the Housekeeping and Eq section. Else, I'm sending them back. I made a list of the electrolytic caps from the schematic, starting at page 1, A8, left to right:
Page 1, Housekeeping and EQ
C43 47uF 25V
C117 47uF 25V
C114 4.7uF 63V
C127 47uF 25V
C133 47uF 25V
C56 10uF 50V
C55 4.7uF 63V
C116 47uF 25V
C141 470uF 25V
C72 22uF 25V
C64 22uF 25V
Page 2, Power Amplifiers
C128 22uF 25V
C138 47uF 25V
C139 1000uF 6.3V
C145 100uF 50V
C51 4.7uF 63V
C52 47uF 25V
C29 10uF 50V
Page 3, Power Supply
C92 47uF 25V
C94 47uF 25V
C152 47uF 25V
C12 47uF 25V
C123 470uF 25V
C82 10,000uF 63V
C115 10,000uF 63V
C124 470uF 25V
Totals
3 4.7uF 63V
2 10uF 50V
3 22uF 25V
11 47uF 25V
1 100uF 50V
3 470uF 25V
1 1000uF 6.3V
2 10,000uF 63V
https://www.soundonsound.com/forum/viewtopic.php?t=26826
I think I'll contact the store tomorrow, describe the problems, and see if they are willing to discount the price. If they are, I'll order and replace the electrolytic caps, starting with the Housekeeping and Eq section. Else, I'm sending them back. I made a list of the electrolytic caps from the schematic, starting at page 1, A8, left to right:
Page 1, Housekeeping and EQ
C43 47uF 25V
C117 47uF 25V
C114 4.7uF 63V
C127 47uF 25V
C133 47uF 25V
C56 10uF 50V
C55 4.7uF 63V
C116 47uF 25V
C141 470uF 25V
C72 22uF 25V
C64 22uF 25V
Page 2, Power Amplifiers
C128 22uF 25V
C138 47uF 25V
C139 1000uF 6.3V
C145 100uF 50V
C51 4.7uF 63V
C52 47uF 25V
C29 10uF 50V
Page 3, Power Supply
C92 47uF 25V
C94 47uF 25V
C152 47uF 25V
C12 47uF 25V
C123 470uF 25V
C82 10,000uF 63V
C115 10,000uF 63V
C124 470uF 25V
Totals
3 4.7uF 63V
2 10uF 50V
3 22uF 25V
11 47uF 25V
1 100uF 50V
3 470uF 25V
1 1000uF 6.3V
2 10,000uF 63V