Sony Walkman motor buzzing fixing

[Makymak]

Hello!

I had bought 5-6 years ago a bpc Sony Walkman (WM-FX407) very cheap because it needed a new belt. Since I serviced it (there's nothing fancy you can do with these models - cleaning - lubrication - belt - speed correction) it's working fine. The only problem I found is some motor buzzing at the headphones when I use it with rechargeable batteries or when the alkaline are worn out. In other words, when it gets lower than 3V, it buzzes. Not something huge but when I use type II and Dolby B it's quite heard. I thought it was a capacitor going bad but this model has only two electrolytics and replacing them didn't improved the buzzing. Grounding the motor didn't helped. So, I left it as it was.

Fast forward, a few days ago, I bought an other bpc Aiwa portable (HS-JS445) in non working condition (the known belt + an elco going bad) and I was impressed with the quietness of the sound. No buzzing at all. I remembered the Sony and I was furious to find a solution; and I found it.

Well... the solution was very very expensive for Sony to had implemented it at first place......

I put an electrolytic 100μf at the power supply and the buzzing went away. No negative impact at the sound (and how a capacitor at the battery terminals could impact the sound?).

I think this cap can't be harmful in any way...

What I can't think out is why Sony didn't placed this cap at first place or any other motor filtering. I know, cost cutting. But, c'mon, it's a simple capacitor....

 

[20tajk7]

Hi, noticed the same issue on the FX475 I've used back then in high school.
It seems like the motor control circuit doesn't like low voltages.
That's why I always used powerful alkalines, lasted a week in the Walkman and still enough power to play with the GameBoy for 2 or 3 weeks.

 

[mr_rye89]

Huh, I've only had em buzz if the capacitors were rotten (or lifted ground)

 

[Makymak]

If we were talking about some serious models, yes.

But this plastic crap has only two caps, none of them being at the signal path, neither at the power supply. Not a single trace of noise filtering for the motor other than what its driver ic provides internally. And ofcourse there is no motor grounding by design...

Go figure, the Sony being a Dolby B deck, there is no way to adjust the levels. They are predefined by design... The Aiwa is worse at this aspect, since it is also a recorder (God help make it a recorder) but at least Aiwa has a noise filter AND grounds...

 

[J!m]

I thought my old Aiwa was decent but I just listened to tapes on it in 86.

 

[Makymak]

An '80s Aiwa should be indeed decent enough, not to say excellent.

The above Aiwa and Sony are of mid-late' 90s. Read their specs and cry... The Aiwa fr is 26Hz - 8kHz @ ±5 dB for type I and reaches the magnificent... 10kHz for type II and IV! W&f is something above 0.5% peak (I suspect something about 0.2 - 0.25% din).
The recording part is worse. It uses a permanent magnet for erasing but surprisingly it is ac bias. But the magnet induces such a noise that makes it suitable only for speaking recordings...

The Sony is similar, though it's not a recorder (thank God!!!)...

Ofcourse they have their pros but sound wise they are mediocre.