Welcome to my Blog

I'm happy with my integration. I now enjoy a lot playing with my PSS-A50.
It's a real pleasure, especially when playing with headphones.

To begin, have a look on my latest video : I hope you'll enjoy the all world around known "Get Lucky".
Maybe it's the first time this song (kind of intro in fact) is played (at least on youtube) on a Yamaha PSS-A50.
And for sure, it's the first time on a stereo PSS-A50.
https://youtu.be/QGN_a2lWWMY

Please also have a look there (he was inspired by my mod) : https://darekasan-net.hatenablog.com/entry/2022/09/19/045703
(Chrome can translate in case)
DarekaSan implemented an additional jack output using a PCB shield for Raspberry Pico (it seems the PCB is only available in Japan), and cut the PCB shield to isolate the lowpass filter section.
In this implementation, no stereo sound will be connected to built-in PSS-A50 headphones jack.


About my own PCB integration, here are some details :

At first, I soldered two 4 pins male headers (1.27mm) on my PCB (H3 and H4).
Then, I inserted two 4 pins female headers (1.27mm) and soldered two wires : black on female H3 for AGND and red for female H4 +5V


The pins of the female headers have been bended in order to lower the header profile

Also, don't forget to solder on the mod PCB a 6 pins 2.54mm female header (or, in case, only 2 pins may be enough just for the R+ / R- RIGHT channel) in order to plug the wires coming from of the Yamaha SWLL YMW830-V IC.

I also put some "Koptan" (the Chinese low quality Kaptan) in order to have an insulation with the PSS-A50 PCB; because the idea is :


1. Plug the female headers on the Mod PCB male header
2. Put some hot Glue on the PSS-A50 PCB (at the places where the two 4 pins headers will be, once the mod PCB will be pluged on the 2x4pins male header I soldered the last time on the PSS-A50 PCB
3. While the glue is still hot (don't waste time), plug the PCB mod at the right place on the PSS-A50 PCB
4. Solder the red and black wires on the Capacitor C035 pins (on the bottom of the PSS-A50 PCB)


The assembly will look like this :


If you unplug the mod PCB, here's how it looks like :


That way, the mod PCB is mecanically firmly inserted in three locations, which makes it stable from a mecanical point of view.

Anyway, I'm aware the fragile location (or weak point) is the 2x4pins male header soldered on the PSS-A50 PCB, because the original PCB pads are not suited to hold this kind of component. In order to make the meca more robust, it would be relevant to put some cyanoacrylate glue around the PSS-A50 PCB and the bottom of the 2x4pins male header (once soldered of course).

Got the PCB samples ! Last step is now coming !

The PCB design is close to be frozen
On the top left corner, the 2x4 pad for the female header (bottom of the PCB)
In case your iron ability is not proven to solder a 1.27mm header on the PSS PCB, it's still possible to solder just 2 wires from the PSS PCB (near the headphones amp; C601 and C602 to be removed) and the 2.54mm pads on the left side of my PCB (OUT : R- and R+)

Two wires are also needed from the DACRPP/DACRMM pins of the Yamaha SWLL YMW830-V IC; to be soldered on the 2.54mm pads on the bottom side of my PCB (IN : R- and R+)
And last but not least, two wires for the power supply (to get from the capacitor C035 (under the PSS PCB) on the 2.54mm pads on the left side of my PCB (+5D, AGND)



I used two 1x4 pins 1.27mm headers (bottom left and top right) that are used as a spacer (same height as the 4x2 male + female header) in order the PCB keeps well in place (two 4 pins male headers soldered under my PCB, and two 4 pins female headers glued on the PSS PCB)

The PCB has a breakable part in order to be plugged on the male 2x4 header, soldered on the PSS PCB (in case we decide to remov the mod and find the original mono sound configuration.

First step is to remove C601/602/603/604 and adjust and solder a 8 pins 1.27mm male smd header (2x4) in order to have something clean :

The easy way for me to desolder the caps is to use two irons, in order to prevent heating too much. My brand new TS100 with the TS-I tip on the left, and my old good JBC30S with R05D round tip on the right (the smallest available).

This pic is for illustration only (the header is already soldered; The iron tips are on another cap, just for the picture).


Then, the 1.27mm header has to be adjusted before beeing soldered :
The two top-right pins stay at their nominal length
The two pins below are cut at the half length
The four pins on the left are cut that way only one third of the length remains



The picture below is for illustration only, since the header is not located on C601-604. As you can see, bottom parts of the smd header is located exactly on the pads.


Alignment of the header is a crutial operation, because the pads on the PSS-A50 PCB are not exactly designed for this kind of header. It is very risky if you are not experienced or if you don't have the right iron / tip. Don't do it if you are not used or fell uncomfortable.

The result after the soldering operation :
(it looks dirty on the picture because of the flux, but the header is in a well condition and not melted).
During the soldering, it's mandatory to have the female conterpart connected on the header in order to avoid having the pins bent.


I used Kaptan tape in order to protect the headphone amplifier from the heat and avoid any solder projection on the 4 very tiny pins of the chip. This is a chinese "Koptan". The quality is not very good and might melt if heated too much. Once the header was soldered, I removed the tape. I also used a flux gel in order to ease the soldering and ease the capillarity.


Once soldered, check for every pins, and also cross-check that there is no short circuit and no open connection
1 x x 8 ("L OUT-" written on the PCB, from existing OpAmp)
2 x x 7 ("L OUT+"written on the PCB, from existing OpAmp)
3 x x 6
4 x x 5

pins 6 and 7 are shorted, because of the PCB trace, that's normal.
pins 5 and 8 are shorted, because of the PCB trace, that's normal.
pins 1 to 4 are going respectively to the close pins of the headphone amplifier IC
You can use a needle in order to have a thinner test point with your multi-meter in order to check the continuity and absence of short circuit

There's a nice article here from PJD about my experimentation : http://sandsoftwaresound.net/yamaha-pss-a50-stereo-mod/
It is very pedagogic with nice illustrations. I also think the differential approach is relevant in order to lower the noise.

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.
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 the schematics provided by PJD 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, 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 it's worth going deeper (i.e check if the stereo samples were present and played 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 www.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.

Now the Block Diagram with the integration of the Right channel looks like this :

I'm about 50 years old, I live in France, in Paris area.

I work in the automotive field, especially in the infotainment systems.

https://www.linkedin.com/in/lionel-nollet-b780a55b/

My interests are in electronics, hardware, embedded systems programming.
I'm also learning again the piano, on a Yamaha P-125.

I bought a few weeks ago a Yamaha PSS-A50, especially "for fun" but also in order to analyze the HW, and potentially to "mod" it.