Reviews and questions about the entry-level MPC500
User avatar
By DjDiskmachine Sat Jan 05, 2019 4:54 pm
Bad luck you managed to pinch the cable, I recommend shrinkwrap or electrical tape to fix that!

Hmm what caps did you replace again? I'm not having any problems with my inputs, they used to have a bad noise problem but now they are pretty much transparent.
I can't see any evidence that the line in caps should need replacement, the ones I see in the Service Manual are only there for DC blocking and perform no filtering.
The line in circuitry uses a different OP amp than the outputs (IC19 as opposed to IC11 for outs). It uses the same rail (5V) as the one supplying the output amplification circuitry. Are you sure you replaced all the caps? Are you sure you got the right values in the right place?

The only thing different between the input OP and the output OP is they have their own cap for HF filtering (on the input OP that's C46, seen way at the bottom right of the last page in the Service Manual).
This doesn't seem like a likely cause of the problem to me, but can't be ruled out of course since I can't perform any measurements ;)

This sentence got my attention now when I read your post again, can you elaborate, please?
NearTao wrote:"If a sound is playing it is okay and the noise floor seems to cut out"

Do you mean that the noise is supressed, like when doing compression -eg the louder sound "pushes" the quieter noise down then the noise is louder again after the sound stops playing?

User avatar
By NearTao Tue Jan 15, 2019 1:33 pm
The noise you quoted would best be described as ducking I suppose. There is a low level noise that goes nearly silent while playing a sample.

One thing I believe I have narrowed down the problem to seems to be that when plugged into the outlet I have tons of noise issues, but when on battery power they all appear to go away. I suspect the next piece of the puzzle is to get a new power pack, the one I have is Sino-American model:A31250. I'll try to keep narrowing down the issues :)

As to the capacitors I used Nichicon ULD1C101MED1TD/493-14722-1-ND and UVY1C221MED1TD/493-12895-1-ND that I ordered from DigiKey.
User avatar
By DjDiskmachine Wed Jan 16, 2019 9:11 am
OK I guess that a badly filtered PSU might be the cause of this problem, get one that's a little less cheap and report your results! :)
Please double-check your Cap values for C907 & C910, these are the ones that perform filtering for the rail Mainpow +5V in the service manual and they should be able to take care of this.