Newbie to cassette players, is it possible to reduce the "hiss" by modifying the PCB?

Greetings,

I recently bought a used Sony WM-EX631 from Akihabara, Tokyo to listen to the cassette released by one of my favorite band. (Realizing I did not get the remote control with it afterwards, sheesh!)

I grown up in the CD era so let's say I'm very unfamiliar of how cassettes should sound like, and the constant "hiss" or white noise is making me a bit unable to focus on the music that's playing.

I Googled a bit and it seems that the hiss is pretty much unavoidable due to cassette tape's analog nature, which I could understand but still wanted to try to reduce it as much as possible.

I have some experience of modifying the feedback resistor value of the opamp in a radio player to lower the amplification level, reducing the noise with the trade off of max output volume. (Which was way too loud for my headphone anyways.)

So, I disassembled my WM-EX631 and found the service manual of it.
https://elektrotanya.com/sony_wm-ex631.pdf/download.html

This player uses Toshiba TA2123AF as the power amp, which is quite more complicated than usual opamp.

From its datasheet and schematics in the service manual, I can't really tell if it's possible to lower the amplification level with this chip. So, I'd like to ask if there are any folks here who's familiar with how this chip works and may shed some light on how I could proceed to reduce the hissing noise. Any advice is much appreciated!

 

The whole point of Dolby Noise Reduction (simply referred to as Dolby for most of its life) is to reduce tape hiss. https://en.wikipedia.org/wiki/Dolby_noise-reduction_system#Dolby_B
For it to work the tape needs to be recorded with Dolby (most pre-recorded ones were) and the Tape Player needs to have Dolby circuitry and it needs to be switched on.

What I don't understand is why Sony stopped fitting Dolby to high end models like the one you have. In the mid 1990s it literally added about £5 to the cost of a player. Back then I bought a cheap Aiwa for about £20 as that seemed like a bargain for a player with Dolby new retail in WH Smith.

 

There are players with Dolby B noise reduction, like the WM-EX910, although like @Longman states, plenty of later Sony units came without Dolby noise reduction.
However, on the players with RV (revitalize) I tend not to use Dolby noise reduction, in favor of RV.
On the EX631 you will need the remote to change the sound settings (RV, MB, GRV), similar to the https://walkman.land/sony/WM-EX651.

 

I have in front of me Sony Walkmans WM-BF49 and WM-FX479. The only thing special about either of them is that they have Dolby. With those I recall finding them in a catalogue and it was about £10 extra to get the versions with Dolby. @CDV is the expert on black plastic Walkmans like the WM-BF49.

 

More specific: there were enough mid to high end players released with Dolby noise reduction even after the mid 90s.
It looks to me like Sony was doing what Samsung did too, around 2010 only with mobile phones.
Many models, small differences in features and functionality, just to ensure they could cater to anyone’s needs.
Even so, with RV on I find most tapes sound pretty good, especially with tapes that were recorded without noise reduction.

 

How to reduce hiss.
Make a really good recording using Chrome tape, using your quality home deck. Not peaking any higher with digital LEDs no higher than plus three decibels or with vu meters, not much more than barely above 0 DB.
Do not use Dolby when recording.
And lastly, turn down your volume on your player to a low level and enjoy.

 

@UN1C0RN The output power amps have fixed gain (feedback resistors are internal), while modifying the gain of the preamp is something I would not recommend.
That's because modifying the feedback network will change the frequency response and the reference voltage going to the head.
So not as simple as changing some resistors to differnt values. On a cassette player we need a certain EQ (120us/70us) in order to have an overall flat response for the entire system.

Noise depends on a lot of factors, not just the gain of the amplifier. The head itself and how noisy are the transistors in the amps play a much bigger role. Not to mention tape itself which is the main source of noise.
Bias noise of the tape will also depend a great deal on how well the tape is recorded. If it's recorded on a deck with generic calibration, results won't be great.
If recorder is calibrated on the tape (ideally bias, level and EQ), performance can be improved significantly. On best recorders, EQ on recording is fine adjusted for particular tape forumulation used, not fixed on 120/70us.

A good tape must also be used for the lowest noise possible. Doesn't necessarily have to be a TYPE II, can be any type if it's a good tape.
Some low quality tapes are just very noisy and noise will be audible even with Dolby C, while others will be almost noise free with Dolby B.

As far as recording levels, to be noted the 0dB mentioned above doesn't tell us much, because 0dB means different things on different scales: https://walkman-archive.com/articles/guide-excellent-recordings_05.html
How hot a tape can be recorded without distorsion will depend on the tape's MOL (which can vary significantly), Dolby NR and HX Pro.
Dolby C has headroom extension so a tape recorded with C will allow hotter recording (with same distorsion) than B or Dolby OFF.
HX Pro alters the bias in real time, so SOL of the tapes improves dramatically. This way, high frequencies can be recorded hotter without distorison.
If we are to take the old Philips scale as the reference, most good tapes can be recorded as hot as +8dB with HX Pro and proper calibration.
The most notable exception to this are pure chrome tapes (like BASF Chromdioxid, Chrome Maxima), which have degraded MOL and won't take more than 0dB (typically less). However these are extremely low noise.

 

Really grateful for all of you sharing your invaluable experiences and knowledge, it seems the best option for me is to let my walkman be and enjoy the retro feeling it provides
It is still tons of fun to listen to and to admire its mechanical designs!

 

Me I'm a visual person. I just can't stand reading about numbers and letters in a posting somewhere without actually seeing the actual item. Because then I have to go and search the internet and find out just what in the world we're talking about and sometimes people don't even know what they're talking about because they'll have a inaccurate item or texting and it won't be about the actual item at all. So to clarify, here's a picture of the actual item talked about in this thread.
Walkman wm-ex631 and I'm showing hopefully the model number of the remote that came with mine. Although I'm not exactly sure if it is exactly correct model remote for this unit and so that's all I know

 

That is the right remote according to the service manual:

 

Thank you for that information.