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PSS-A50 sounds stereo

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Lionel N:
Hello,

I focussed on this PSS-A50 product because I read many interresting articles from @pjd, on his site (http://sandsoftwaresound.net/yamaha-pss-a50-look-inside/)

I would like to contribute to the discussions about this, and especially share a piece of information, following my first investigations and prototyping on this PSS-A50 : This keyboard has stereo capabilities (the samples are in stereo), but unfortunately, the engineer only used/wired the left channel of the SWLL YMW830-V. They could save some cents on the cost of a dual OpAmp, using a dual instead of a quad.

I wired the DACLPP/DACLMM and DACRPP/DACRMM outputs of the SWLL to an external active Low Pass filter with a basic LM324 and a few resistors/capacitors (same schematics as for PSS-F50, and... indeed, the sound is now a very audible stereo for all samples. (I'm dissapointed because the Motions Effects the programmed are not stereo).

I uploaded a video with sound. Have a look there : https://youtu.be/cwDBfVab3vc

Enjoy,

Lionel

pjd:
Hello Lionel --

Sorry for the late reply -- a hotel wifi ate my first response!

Nice hack!!!

I agree. I don't know why Yamaha didn't make the PSS-A50 stereo...

-- pj

Lionel N:
Hello PJ,

nice article here : http://sandsoftwaresound.net/yamaha-pss-a50-stereo-mod/
Very pedagogic with nice illustrations. I also think the differential approach is relevant in order to lower the noise.

It's funny, because this week, I retro-engineered the Op Amp block, and... I get the same schematics.
Not so a suprise because the global picture is nearly the same as the one we can see in the PSR-F50 service manual.
Unfortunately, I could not find the service manuel for PSS- Remie series; so I wonder if you could find it or if you also re-constructed it from the pcb.
I confirm also the resistors values and the 1µF capacitors, but I could not get a solid value for other small caps; that's why your schematics is interesting, because even if I try to reconstruct using the circuit simulation https://www.circuitlab.com/; it's better to have the good picture.

The only major difference I have on my side is R501 and R502 for which I have 1,5k (instead of 2,2k on your side, which is not dramatic since the divide bridge is still 1/2 in order to add the half direct voltage.

My initial idea with this mod was a kind of proof of concept, in order to identify if its worth going deeper (i.e check if the stereo samples were present and palyed back). Which is the case.
Now, my target is to create a small PCB with the missing op amp, and replicate the mono circuit.
Because of the components shortage, and since I plan to make my PCB via jlcpcb.com, I identified three possible alternatives : TL972, TS462 or MAX4477. For availability and cost reasons, I'll use the TL972.
Now the question is : only replicate a "Right" channel or replicate both in order to have a common design on the same PCB ? Well, I'll replicate only one channel. In case performances is worse (ground loops, noise... it might be easier to fix), and in case performances is better, I will just have to use two PCB (probably stacked, so I have to think about the design) : one for the new right channel and on for the left channel that will go into the headphones amplifier.
The left channel path for the loudspeaker will remain, using the original NJM2740M Op Amp

Most probably, I will unsolder the 4 caps C601 to C604 and wire the outputs of my PCB. TBC.

Regards,
Lionel

pjd:
Hello Lionel --

Great work!

I was thinking about my own mod and started searching for a small stereo preamp board with differential inputs. I think I would connect the SWLL signals to the preamp board and run the board in parallel with the existing electronics. That would minimize impact to the existing Yamaha DM board in case the experiment didn't work out.  ;)

I'm a little nervous about working with SMT devices mainly because my hands aren't as steady as they once were. Nonetheless, those SMT traces are tiny!

Bonne chance -- pj

sm7x7:
Hey, Lionel, how is going there? Any progress with PCB? I have two A50s, one already opened and waiting for modding ))

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