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Got a Mopho Keyboard and want it to sound better?
MUFF WIGGLER Forum Index -> General Gear  
Author Got a Mopho Keyboard and want it to sound better?
50quidsoundboy
yeah but character
Karg
While I do not have a Mopho 4x, in the Tetr4 it is also two DACs. Each of them covering two voices. Here the mod works equally well.

Locations are the following:


Text description is posted elsewhere: http://karg-music.blogspot.de/2016/06/tetra-morphosis.html

, Karg
catzrcool
Allright, thanks a lot for the help!
Synthbuilder
catzrcool wrote:
But is there any technical reason to use a tantalum cap?


None at all. You can use any decent quality electrolytic too. I just used tantalum because I had a bag full at the time. One good thing about them is they do have a resin case which makes it less likely to melt when soldering them - which is quite easy to do when soldering the device from the topside of the board.

Tony
catzrcool
Great tip on the DAC-filtering, I'll have to get around to doing it on my Mopho. But is there any technical reason to use a tantalum cap?

The thing is, there are some pretty strong ethical reasons to forego tantalum whenever possible, it's mined under horrible conditions and the ecological impact is bad.

One poster mentioned that he used a regular cap, if that works the same, that's what I'll do, and that's what should be recommended imo.
Ahinga
did anyone do this mod with an mopho x4?
i have not opened it yet, but discovered at least 2 dacs on pictures...
Karg
Hi,

inspired by Tony's mod, I improved my Mopho Desktop. Sound is much cleaner now! Thanks for sharing your insights!

I also added a USB port, indicator LEDs for clock and notes played, and as a bonus some wooden sides.



Detailed instructions are published on my blog: http://karg-music.blogspot.de/2016/01/mopho-morphosis.html

, Karg
brokensolderingiron
Quote:
[quote="Synthbuilder"]
lvoemachine wrote:
This is cool. I forwarded this on to Carson Day at DSI. They might find this kind of interesting.

They already know about it. I've been in contact with them all last week. The support lady was very kind and helpful and has forwarded my e-mails onto the technical department. We'll see what they say but I haven't heard personally back from anyone yet.
Tony

Great find and solution!

Wat's puzzling is despite DSI designed in RC smoothing filters on most CVs and the DAC is 16bit yet PW was rattling that bad and clearly no more within specification of the 16bit DAC rendering to 9 10 bits was fixed to a lot healthier state with a simple cap.
Did DSI fix the Mopho desktop "dead oscillator cycles" that was found on SDIY list 6 years ago?(Most noticeable with bass sounds)
dafus
Thank you Tony for this post. I just did it and it definitely sounds much better than before.
At least for the high Pulse range. Not sure it affects other OSC shapes too but it certainly "feels" better. hihi
60€-cent for the Tantalum and 15 minutes unscrewing, soldering and screwing it back on - totally worth it!
wavehead
damn that looks like some serious corner cutting, but i guess anybody mass producing this stuff at "competitive prices" is going to have a hard time not cutting corners.

makes me wonder what else is going on in some of the DSI stuff that might be partly the reason some of their gear gets a bad rep.
computer controlled
Huh, i never noticed this before. I don't have a Mopho anymore, but if i end up with one again, i'll most certainly do this. If anyone does this with the desktop, post a pic!
pre55ure
Wow

I'd love to know if this type of thing is a problem on any of their other boards as well. I have an Evolver that I've always noticed has sort of a weird "extra modulation" happening on the analog waves. I wonder if it might be related to something like this. hmmm.....
JohnLRice
That's awesome, Tony! applause we're not worthy
widdly
Just did the mod on my mopho and it sounds good. Before with the pwm at 99 it sounded like the sample Tony posted. Now with PWM set at 99 it sounds about the same as when the PWM is set at 1. I used an electrolytic because I didn't have a tantalum.

thumbs up
flo
Synthbuilder wrote:
flo wrote:
Any idea about their other stuff, Tetra etc.?

I've not seen the insides of any of the other stuff or had one to play with long enough to investigate further. I would hope they haven't repeated the same thing.

But just listen to the pulse wave at 99. If it sounds nasty and garbled like the wav file above then it could well have the same noisy DAC reference.

Tony


Will check this on my Tetra and report back...
Synthbuilder
Skaput wrote:
By the way what type of solder did you use for the modification, lead free or the good stuff. Just wondering if it would make much difference.

With my own gear I always use Pb/Sn solder - it's just easier to use especially if I'm moving things on and off several times which I need to do for comparison* purposes. For a customer I'd stick with whatever was used by the manufacturer.

* No wave files for the 'after' comparison from me for a while. I've not got time to do it this week. But dabbing that cap on and off while listening to the output made it perfectly clear it is a worthwhile mod to do.

Tony
Synthbuilder
lvoemachine wrote:
This is cool. I forwarded this on to Carson Day at DSI. They might find this kind of interesting.

They already know about it. I've been in contact with them all last week. The support lady was very kind and helpful and has forwarded my e-mails onto the technical department. We'll see what they say but I haven't heard personally back from anyone yet.

Tony
Synthbuilder
flo wrote:
Any idea about their other stuff, Tetra etc.?

I've not seen the insides of any of the other stuff or had one to play with long enough to investigate further. I would hope they haven't repeated the same thing.

But just listen to the pulse wave at 99. If it sounds nasty and garbled like the wav file above then it could well have the same noisy DAC reference.

Tony
Paraphonique
Another vote for an "after" sound test. I'd really want do this mod on my Tetra.
-P
lvoemachine
This is cool. I forwarded this on to Carson Day at DSI. They might find this kind of interesting.
Skaput
Interesting, going to listen to mine now.

By the way what type of solder did you use for the modification, lead free or the good stuff. Just wondering if it would make much difference.
mattysal
This is crazy! I always noticed this on my mopho keyboard, gonna get my tech to do this upgraded as i am super not cable of doing this myself!

I wonder if the dsi tempest has a similar "issue"?

thanks for the great work! I'm excited to see the response of DSI support team! I've heard great things about them so I wonder what they will say!
flo
Wow, thanks for that! Any idea about their other stuff, Tetra etc.?
Synthbuilder
Tombola wrote:
Do you have an 'after' sound sample?

Not yet. But in some ways there's not a lot to hear. The Mopho now behaves as it should - with the pulse sounding clear even at the extremes and not grainy like you hear in the above wav file.

Tony
Tombola
I don't have a Mopho, but this is a great post.

Do you have an 'after' sound sample?
Synthbuilder
I posted this on Gearslutz but it may be useful to some of you wigglers:

I've got a Mopho keyboard and it's a great little thing. But one thing puzzles me; when listening to any patch using a pulse wave, I notice the overall sound somewhat dirty sounding. It's not very nice really.

You can hear what mine sounds like here:

http://www.oakleysound.com/Mopho&Pulse.wav

I popped the hood and found that it is caused by the internal CVs to the voice chip that control the pulse wdith having some sort of randomised voltage added to them.

However, it is not only the pulse width control voltages that have this unwanted randomisation. All of the CVs do, but it is most noticeable on the pulse widths. What got me onto the right track was the fact that all the CVs had worse noise when they were set to high values. This points the finger towards a noisy reference voltage to the system's DAC.

The DAC used on the Mopho Keyboard appears to use a 5V reference derived from the +12V supply. Now, the 12V supply gets tainted by noise from the other parts of the electronics of the Mopho - but in particular from the -5V charge pump power supply which generates horrible 80kHz perturbations.

However, the real problem is that the Mopho creates the 5V reference by simply dividing the +12V rail with a pair of resistors (R67 and R71). This divided down signal, complete with a portion of the noise from the +12V rail, gets sent to a voltage follower (U18b) and then sent to the DAC. Oh dear... because this noise now ends up on the CVs. The higher the CV the more noise gets through.

Solution: Filter the +5V reference voltage before it goes to the voltage follower. I did it with a 10uF tantalum cap soldered directly across R71. The reference voltage is now nice and quiet. The Mopho behaves better, not only with respect to the pulse wave, but also seems smoother in general tone too.

The Mopho Keyboard is primarily built from surface mount components using lead free solder. This makes it slightly more awkward to work on than older through hole designs. However, it is quite possible to do a nice job if you take care.

You'll need one 10uF, 16V tantalum capacitor. You can use a decent quality electrolytic if you wish, and in that case, a 10uF, 25V will suffice.

Solder the cap across the resistor R71. With the keyboard to the front of the unit, the positive terminal of the cap should be facing left. That is the negative end should go to the ground plane which is attached to the end of R71 that is nearest to the number 1 of its name.



And a closer view:



Don't pull too hard on the cap once it is soldered in place because you might pull off the solder pads of R71.

For the Mopho Desktop:

This seems to be built in much the same way with the DAC reference being taken off the +12V line. I am guessing it too will have the same unwanted noise on the DAC reference. However, the board is different in several other respects and the parts numbering is different.

Now I haven't tried this but from online photographs I can assume that you will need to solder the 10uF cap across R52. This is situated, again above the DAC, near U12. The negative pin of the cap should be soldered towards the front of the unit, ie. the positive pin will be mounted nearest the R52 legending.

Tony
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