Share your knowledge on these two classic MPCs
By Paulau Tue Jan 24, 2023 10:33 pm
Hi guys,

I used to work only with the right stereo out. I tried to use both to split the instruments while recording and of course to have the full stereo out.

The problem is that when play my sequence, the right stereo channel plays perfect even if I play the stereo volume at the maximum or the sample in full level, it's not cracking at all.

While during I use the left stereo channel it is crackling when I press louder on the pad of the Kick drum for exemple. If I use a lower velocity, this is not cracking but this is really to tricky and not comfortable :Sigh:

I read all the topics I could find here, like maybe there is a need to do some soldering, but mostly speaks about those issue during the sampling.

Anyone as any experience related to this problem?

I hope I was clear enough :worthy:
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By Telefunky Thu Jan 26, 2023 3:15 pm
Does the crackling appear on all pads when higher velocity values are generated ?
If that‘s the case make a 1 bar sequence and set velocity in step edit.
Say 4 notes with 31, 63, 95, 127 as velocity. Check at which bound crackling starts and then use higher values to get to the exact point.
If 31 and 63 work it tells you that the lower 8bits are ok, then extend from 95 on.
You may find a point at which crackling definitely sets in.

It doesn‘t tell you about the exact source of the problem, though, but narrows the region in which to look.
The output converter PCM69 receives a bitstream, splits it up into left and right channel data and does a 2 stage processing before it outputs left and right audio.

There‘s a good chance that 1 section of this chip has an internal flaw, it‘s relatively easy to exchange and probably a cheap part.
But if the bitstream is messed up before the converter, things get more complicated.
It might also be the cap between the 1st output opamp and PCM69.
Get the data sheet of the PCM96 to identify left and right output on your board.

ps: if you‘ve never done something similar or have few soldering experience find someone to do it for you. A MPC3K is an expensive item today... ;)
By Paulau Sun Jan 29, 2023 9:18 pm

Thanks for your reply, i just saw it.

So I've tried what you advise me to do. Yes this is happening on all pads.

For exemple :

-I tried with a kick drum, it starts to crackle after 28%
-Then I tried with a snare drum and it cracks around 34%
By Paulau Sun Jan 29, 2023 9:21 pm
Does it tells you more about where could be located the problem ?

It's okay i've soldered many times, it's quiet necessary to know when you have old gears I think :)
a week ago I change most of the switch. Let me know, and thanks again for your time.

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By Telefunky Mon Jan 30, 2023 4:05 am
that‘s good to know...
here‘s the pcm69 schematic (you probably have the 16 pin version) ... PCM69.html
left output is pin 2, inverted pin 3, check these with a on oscilloscope, if available
(the pins next to 5V supply, which is top left pin if the connector side is left)

let a bar loop a sustained stereo sample of 50/60 Hz at almost full level
(the left channel is expected to distort, while the right one plays clean)
then set a multimeter to AC and measure pin 2 and pin 7 (right output)
if there‘s a significant difference, the PCM96 most likely has an internal problem
if both voltages are absolutely identical, the flaw is probably elsewhere
(this is a crude approach assuming that a voltage difference occurs in case of a conversion error, as both channels receive identical signals)