The Workbench

Re: Beogram CD 5500 Non-Oversampling Mod

yachadm — Mon, 10 Aug 2009 13:58:03 GMT

Hi Martin,

Of course you're right about the high-freq distortion and noise.

But I did a test on a few CD's before I did the mod - I have a few original CD's which were not well recorded (by the factory), and before the mod, I could hear high-freq distortion.

And, I checked on some other top-quality CD's, which have no high-freq distortion.

Then I did the mod, and I checked on all these CD's immediately.

The poor quality ones still have high-freq distortion, definitely a bit worse now.

But the good quality ones still have no distortion or noise at all.

So, on the whole I like to listen to my good-quality CD's even more now, and I probably just won't listen to the lousy ones!!!!

Cats - We have lots of cats outside - we don't let them inside - their job is to take care of the snakes. So I guess they haven't time to listen to CD's!!

Re: Beogram CD 5500 Non-Oversampling Mod

Die_Bogener — Sun, 09 Aug 2009 11:30:34 GMT

The idea is very interesting, but there is a problem: distortions.

No oversampling produces a very clear bass, low noise and the impression, that the DAC produces a very nice sound. But this is wrong!

The problem is, that the distortions in high frequencies increase, but usually not all people can hear them... but they are existing.

The sampling rate is 44,1kHz, 16bit per channel. Just imagine, there was a 20kHz signal, full range with value 0 to 65535. Without oversampling and no filters there would be a full digital signal output... in reality the signal would be a sinus signal because digital signals do not exist in a real music. So there would be a lot of harmonic distortions. With 4x oversampling these distortions are reduced... but in lower frequencies this oversampling makes a softer bass. This is exactly what you hear with this mod: a crystal clear punchy bass and very sharp trebles. But the trebles consist of very high disharmonics, which you dont can hear... at least me, 18kHz is my limit.

I beleave you, this mod makes a very good sound impression. But after some time you will find out, that something is wrong with this sound.

But one thing is right: the oszillator of the TDA7220 chip is not really good. If it would be replaced by a good seperate quartz oszillator, it would improve a lot.

This mod improves the oszillator a lot, but switching off the oversampling makes it worse again.

CD players are really difficult...

Hmmmm, you have a cat? Test it. My cat left the room when i also made this test with another cd player. Marantz + non-oversampling mod. The player is very similar to B&O, uses the same drive and the same chips. My cat could not stand it and was gone everytime i played it. With the B&O CD7000 modified just with caps and OPA-chips she stayed on the sofa :)

Beogram CD 5500 Non-Oversampling Mod

yachadm — Fri, 07 Aug 2009 04:32:31 GMT

Hi all,

Just completed a simple non-oversampling mod on the famous and well-regarded Philips TDA1541 DAC-based CD.

This DAC uses the filter IC SAA7220P/A or B, which is very noisy, and corrupts the clock timing.

Net Audio, http://www.net-audio.co.uk/tda1541nos.html, offers a plug-in replacement for the original IC, which includes a high-precision clock.

The soundstage is vastly improved, bass is clean, trebles are sharp, and it justs sounds superb all-round!!!!

Menahem