Filter before Transformer Primary in 80´s Sony /Toshiba /Philips CD-Players

[Salar]

I found this kind of inductive filtering before the AC transformer primary in some early CD-players from Sony like CDP-103 / 102 / 502.
Did find it also on contemporary Toshiba XR-Z70 model (250µH), Philips CD-100, (25mH)

I did not find this kind of filtering in the very first Sony CDP-101, or many contemporary (Like Nakamichi, based on Sony and Philips design) and later (expensive) CD-players.

What was the purpose at the dawn of the CD? And is it something for us DIYers to rediscover for our designs?

Images from left to right:
CDP-102 schematic, CDP-102 parts list,Toshiba XR-Z70 schematic, Philips CD-100 schematic, Sony CDP-101 schematic (filter is missing there)

All the best,
Salar

 

[DF96]

The purpose of filtering is to filter i.e. remove unwanted stuff. Well-engineered systems generally include it, unless it is clearly unnecessary. 'Audiophile' fashion is currently suspicious of mains filters, unless they are extremely expensive, but fashion is not driven by facts but by opinion formers.

 

[simon7000]

It is there to comply with regulations on noise emmisions. Noise doesn't just come in on the power line it also goes back out on it. So since there are standards on EMI compatibility the earlier units created enough noise the power line filters were needed to meet some of the standards. As the digital signal processing improved and went to lower power along with a different power transformer design the filters were no longer required.

 

[Salar]

Thanks a lot for your answers!

Audiophile' fashion is currently suspicious of mains filters, unless they are extremely expensive, but fashion is not driven by facts but by opinion formers.

Well, those units were not sold as High End for sure. (Besides the fact that the compact disc was probably regarded as High End)

t is there to comply with regulations on noise emmisions. Noise doesn't just come in on the power line it also goes back out on it. So since there are standards on EMI compatibility the earlier units created enough noise the power line filters were needed to meet some of the standards. As the digital signal processing improved and went to lower power along with a different power transformer design the filters were no longer required.

The IC from the players using coils on the AC mains (CX23035 / CX20108) also were used in second gen. Nakamichi Players, also Philips ICs were to nbe found in first gen. Nakamichi Players.
But no filtering on the AC mains in Nak players even though emissions should be roughly the same. In first gen. CDP-101 they are missing.
So maybe one designer had an implementation, that financial department scrapped after some time?

What effect on which frequency do 250µH on the AC mains have?

All the best,
Salar

 

[stephensank]

Specifically, what you see there are common mode chokes, used to differentially cancel noise accross the ac line by the coils being wound on the same core, much, much more effective than two separate inductors that would merely filter each according to purely their inductance value.

 

[Salar]

Thanks! Is the inductance dependent on the power drawn, i.e. could it be used for a 100W amp as wells as for a 20W CD-Player? Wat I m also wondering about:
The payers mentined are 30 years old, from times before PCs/laptops or smartphones with switching power supplies, no mobile networks at work. Should be AC cleaning from high not be more necessary than ever? Or is this a myth?

 

[TonyTecson]

i would harvest them from atx psu's these filters and incorporate them in my builds along with the NTC resistors.....

 

[Ken Newton]

The payers mentined are 30 years old, from times before PCs/laptops or smartphones with switching power supplies, no mobile networks at work. Should be AC cleaning from high not be more necessary than ever? Or is this a myth?

As stephensank said, these are called common-mode chokes.

They are intended to impede current flow that's of common phase to both HOT and NEUTRAL power mains conductors. This is as compared to normal-mode current flow, which is of complementary phase between mains conductors. Such current flow is an error and represents undesired noise that can easily couple across component boxes via any unbalanced signal interfaces. So-called ground loop hum is a familiar example of power mains generated common-mode noise.

While the degree of benefit obtained will vary depending on the common-mode noise presented by a given power mains connection, my experience is that they more often than not make an audible improvement to the sound. Some common-mode filters are too small to be very effective at impeding 60Hz hum, being optimally sized to impede much higher frequency noise such as is generated by electical equipment having switching power supplies. If a discrete common-mode filter isn't located somewhere on a component's PCB, then one may be located within the IEC power inlet module if that component features such a module.