Sony MZ-E33 - Modification audio output

On Instagram I was chatting with a keen MiniDisc portable modifier.
He informed me that my favorite Sony player, the MZ-E33, could be easily modified to improve the audio output.
Since I have 3 of these, I decided to use the one
I bought as junk and first of all see if it would turn on.
The previous owner left the battery in the unit a couple of years too long, see picture of the edge of the housing.
Some IPA, vinegar and contact cleaner did the trick - it works fine now.
The modification is simple: remove D352 from the circuit.




And here is the silver ‘junk’ player with the simple modification done:


(The component closest to the corner edge has been desoldered.
Luckily it was not directly surrounded by other SMD components of the same scale.)

I’ll post my subjective findings about the audio improvement when I’ve had some time to compare a few albums.

 

Do you have the schematic of the unit ? I would like to see what purpose those 2 diodes have.

 

I have the service manual @Valentin , find it attached. I can’t recall the source of the manual.

 

The 2 components are zener diodes placed in parallel with the output to clamp the output voltage swing, possibly to protect the included headphones from too much power at the cost of clipping at high volumes. Or to protect from a DC voltage at the output in case the output caps go short-circuit.

What I would expect to hear by removing those 2 diodes is a little higher output power without distorsion. To be more precise higher volumes with less distorsion, at low volumes there won't be any difference.
The Vcc of the headphone amp is only 2.7V, which might generate a 2Vpp output swing. If the zeners are 4V (MA4Z), that's double the maximum output swing and in this case removing them won't make any difference. Could not find a datasheet for that diode, for can't draw any conclusion.

Curious if you hear any difference: try to crank the volume all the way to the max and listen for distorsions.

 

I listened to a fresh Use your illusion 1, recorded from Apple Music on iPad.
Seems that there is a bit more power indeed with volume at maximum when using passive Sony Walkman speakers.
The player can’t drive them (SRS-7) to the levels of distortion it seems, need to pick another set of Walkman speakers like the active SRS-58 this week.
With my IEMs I can’t objectively establish a difference without permanent hearing loss at that volume level.
I need to record a second, identical disc so I can run the two E33’s side by side, allowing me to quicker switch between original - modified.