Reviews and questions about the entry-level MPC500
By lamalta129 Mon Feb 26, 2018 10:53 pm
Also while we are on this topic, what would be a quality PSU to order and use? Mine is switching and was definitely cheap on amazon. Finding one that I knew would have negative tip etc seemed rough to begin with. I’m finding some with interchanging tips and a switch to reverse tip polarity etc. but just not sure if you guys know a tried and true. I’m just not trying to go through batteries or recharging all the damn time and last I checked I had the noise with them regardless.
By lamalta129 Mon Feb 26, 2018 11:40 pm
Or even another prudent question to ask is, if these caps are already going bad and are prone to noise, I wonder is there good enough reason to replace any that are on the input recording sampling side before they start generating noise as well?
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By DjDiskmachine Tue Feb 27, 2018 2:24 pm
lamalta129 wrote:This is great news. Thank you so much.

So it was only the 5 caps, C907 to 912 that you replaced in the end?

I’m not completely inept at soldering but was wondering if you could circle which caps those are in your image?

Do you suspect it would be those 5 or would only a few be the main culprits? I’m getting the whining from the headphone and line outs. Mostly concerned with the line outs.



Yo!
That's actually 6 caps, but let's not get into a fight over arithmetic ;)
Jokes aside, there's an image on my instagram here: https://www.instagram.com/p/BZCS0jpH9cw ... iskmachine hope it helps!
There are markings next to the caps on the silk screen of the PCB so it shouldn't be too much of a hassle figuring out what is what. ^_^

As per my analysis, these were the caps (C907 to C912) that were responsible for DC filtering (removing noise on the VCC and VDD rails). I guess it wouldn't harm to re-cap some of the SMD components that also share this responsibility, but I don't have a hot air soldering gun so I just left them in place.
I was happy with the result - no piece of electronics at this price point is completely noise-free, but the positive change I personally experienced was quite dramatic.

One thing tho, I found the solder job to be a bit tedious as the pads are very tiny and hard to get to. If you decide to do this thing, I'd recommend a very fine chisel tip and to use a generous amount of liquid flux.

Another thing, these caps are of different values, be sure to replace them with the correct value!

About PSUs - get one from your local music shop. Reversing polarity is as simple as just cutting off the leads and swapping them around if they don't have it in stock. :D

I haven't done any line-in sampling after my mod, but my conclusion to of the nature of the problem would be related to the actual power supply rails and that this re-cap should solve problems on both input and output. :)
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By richie Tue Feb 27, 2018 5:39 pm
DjDiskmachine, what about using SMD caps to work around the space constraints?

I realize that the SMD will have different ripple response and am asking because you seem to have the actual equipment (based on your IG) to verify such a question.
By lamalta129 Tue Feb 27, 2018 11:26 pm
I’ll take your word that these are the ones worth doing. I’m not feeling crazy enough to try the surface mount stuff.

Just to clarify before I get in the guts though, was the nature of the noise you had the higher pitched whine that attenuated somewhat when the volume knob was set around 2 o clock? This is what seems to be a consistent shared problem among certain units judging from comments and what I’m really trying to mitigate. I don’t think I’m getting much in the way of pinkish noise, just this whining noise.

If I set the master output to max I admit it’s negligible enough but then I get digital distortion if I’m running enough samples. Setting master out at -6db is enough to bother an anal retentive jerk like me for quiet passages.

I want to run some experiments to see if it shows up in samples direct to the line in. Will probably transfer samples to a computer to listen. Ideally it wouldn’t and only be on the outputs but even then I find this worth an experiment.
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By DjDiskmachine Wed Feb 28, 2018 7:09 am
richie wrote:DjDiskmachine, what about using SMD caps to work around the space constraints?

I realize that the SMD will have different ripple response and am asking because you seem to have the actual equipment (based on your IG) to verify such a question.


Oi richie!
Didn't consider it, wouldn't put SMD components in a place that's designed for thru hole really. ^_^'

richie wrote:
I’ll take your word that these are the ones worth doing. I’m not feeling crazy enough to try the surface mount stuff.

One note tho, maybe a first step would be to get yourself a better PSU? I'd vote on improving the peripherals before disassembling a machine - it's a bit of a hassle and if a PSU turns out to make enough of a difference maybe you can save yourself some time? :)
How does it sound while on fresh batteries?

Can't remember if the noise was attenuated when turning the knob down, but that kind of behaviour definitely sounds like you have some problems with decoupling / noise on the voltage rails..
what happens when going below 2 o clock? Is that the point where the noise is at it lowest?
By lamalta129 Wed Feb 28, 2018 1:58 pm
Between 1 and 3 o’ clock is a sweet spot where the whine noise is somewhat attenuated versus the output signal level. Below and beyond that area you can definitely notice an increase. Obviously going below that spot the noise just swamps the sample levels. Going above is probably a wash between a gain in noise and output level.

Last I tried batteries I did not notice a difference. I will try with a fresh pack. I would preferably not have to keep charging or changing batteries and use a PSU so I’m just trying to narrow it down before I open her up and play with the guts.
By lamalta129 Wed Feb 28, 2018 4:59 pm
I’m pulling the trigger and ordering caps. So C907 C908 and C909 are 100uf, and C910 C911 and C912 are 220uf according to your post.

I’m willing to give it a whirl and will let you guys know if I can possibly find time in a few weeks to do it.
By lamalta129 Sat Mar 03, 2018 4:10 am
Minor update (I still haven’t had time to order caps...):

I did try fresh batteries. The whine is still there roughly same volume as with PSU but is slightly higher pitched. Does the battery power go through the DC filtering too? It is interesting to note that it seems like with batteries the backlight doesn’t have an effect on or off. With power supply it does.

I don’t know very much about this. My fear would be if batteries supply cleaner power then the PSU but I’m still getting the noise... then would changing these caps still produce a quieter noise?

I also updated the OS. Still no change.

I will order caps eventually just making sure I’m getting the right ones. 16v 100 and 220uf radial... polarized?
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By DjDiskmachine Sun Mar 04, 2018 8:58 pm
lamalta129 wrote:Minor update (I still haven’t had time to order caps...):
Does the battery power go through the DC filtering too?

Yes: this can be seen in the top right corner, last page of the MPC service manual: http://www.synfo.nl/servicemanuals/Akai ... MANUAL.pdf
As you see, both the power jack and the battery line will be led through three ICs; IC901-903. These are LM2674M-ADJ, adjustable step-down switching voltage regulators that produce the 1.7, 3.3 and 5V power lines that all need filtering. Maybe you will find a familiar component in this area..? ;)

lamalta129 wrote:It is interesting to note that it seems like with batteries the backlight doesn’t have an effect on or off. With power supply it does.

Fresh batteries? This means your PSU is struggling to keep a constant voltage output and probably due to the current draw being to high from the machine. This is actually a bit hazardous for your work flow, the machine might brown out and reboot if the PSU can't supply enough current, Say you're having a big project with a lot of samples and then deciding to load another big project on top of it, causing the machine to need even more current and then the PSU can't provide any more.. Not to worry you, just using a reasonable example top of my head.

lamalta129 wrote:I don’t know very much about this. My fear would be if batteries supply cleaner power then the PSU but I’m still getting the noise... then would changing these caps still produce a quieter noise?

I'd say yes. The problem isn't the power source so much as the filtering after the ICs 901-903 I mentioned earlier.

lamalta129 wrote:I also updated the OS. Still no change.

Wouldn't expect it to, this is an electrical issue.
lamalta129 wrote:I will order caps eventually just making sure I’m getting the right ones. 16v 100 and 220uf radial... polarized?

I think this translates to electrolytic capacitors in my language. =D I used this brand, and they should look similarly cylindrical with a black striped end: https://www.aliexpress.com/item/10PCS-N ... 61564.html