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Old 10th February 2003, 08:43 AM   #1
JoMY is offline JoMY  United Kingdom
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Default Philips CD450 mods

Hi everyone,
This is my first posting so please forgive me if I am posting a topic which has been said many times before.

I've recently revived my aged Philips CD450 CD player (fairly basic dual 16 bit DAC, 4x oversampling unit, so old I cant remember when I bought it!). I've put in LM317/LM337 regulators for +/- 15V lines improved decoupling on the other supply lines and swapped the LM833 op amps in the analog stage to OPA2134 and am very impressed by the results. Although still not a match for my Linn LP12 it is getting embarrasingly close in some respects - I cant believe how good an early generation CD player can be improved by fairly simple changes. Inspired by this, I am now considering re-clocking it with an external clock. The existing 11.289MHz clock is the standard circuit using the CMOS inverter in the SAA7220 digital filter. I am interested in building a simple external oscillator and would be interested to know if anyone has any views on whether this is a worthwhile pursuit on this type of CD player [I assume that the SAA7210 decoder/SAA7220 filter/TDA1541 DAC is a generic circuit?]. I get the impression that the Kwak clock is a very impressive mod. Would this be appropriate, if so I would appreciate it anyone could tell me how I could find out more details on this or any other DIY clocks,or indeed any other worthwhile mods I could consider on my Cd player.

Thanks


John
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Old 10th February 2003, 12:06 PM   #2
guido is offline guido  Netherlands
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John,

You might also try to 'upgrade' the digital chips. In the 450 are the first versions of the chipset.
(i have a 650 and there they are). Swapping the 7220 for a 7220B and the DAC for a 1541A could be
beneficial (i never tried). Carefull with the DAC, the newer version needs a cap between pin 16 and 17
which the old one does not. However, the cap is also in my 650...?

As a clock, you could also use G. Tent's clock. Can't comment on which one is better, but it is easier
to implement (only a canned osc). I am using the G.Tent clock in my DAC and i am using the 650 as I2S
source. As for the Kwak clock, if you email Elso he will sent you the schematic. When my DAC is finished,
i am going to try his design to see if it is a further improvement.

I think the 450 also has the CD2 transport. It is probably hard to find if it brakes down.
You might consider to get a newer player with the modern 16bit chipset and CD4.

Regards,
Guido B.
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Old 10th February 2003, 07:55 PM   #3
JoMY is offline JoMY  United Kingdom
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Guido,

Thanks very much for advice. I will contact Elso as you suggest. As for the G. Tent Clock, are details of this in previous postings as I cant find any more details by searchin the forum?

Regarding the DAC, according to the CD450 schematic, my Cd also has 680pF across pins 16 & 17, maybe the player already has upgraded ics? I'll have to look at actual board.

You are right the the 450 has the CDM2 transport. So bearing this in mind you are right I should upgrade to a better machine, so its probably not worthwhile upgrading digital chips. Neverthless I am still keen to see what re-clocking does.


Regards
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Old 10th February 2003, 10:29 PM   #4
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Default CD450 mod

John,

If you are interested in my clocks, drop me a mail off line.

evaguido@iae.nl

Guido
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Old 10th February 2003, 11:27 PM   #5
Asen is offline Asen  Bulgaria
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Remove the muting transistors, disconnect the headphone amp from the main circuit, put more good caps (main and near the DAC), replace the PSU diodes with shotkey diodes, add a AC filter in front of the trafo, replace the interconnect cable if it's fixed (mine was). I use vdHul D-102 Hybrid MkIII.
I think the most significant results come from the mute transistors and the PSU diodes. I'm not sure what helped more because I added the AC filter together with changing the diodes with 1N5819. Anyway - these were the mods that sent the CD player in another, higher class.
I have CD721, but after all it had to suffer I'm not sure that something in the 600-700$ range could outperform it.
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Old 11th February 2003, 07:46 PM   #6
JoMY is offline JoMY  United Kingdom
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Asen,

Thanks for suggestions. One thing puzzles me though. You say:

<Remove the muting transistors....I think the most significant results come from the mute transistors and the PSU diodes...>

The muting transistors connect across the outputs right after the low impedance output op amps (albeit via a couple of 100ohm resistors) - I can't believe that the small parasistic capacitance of the OFF transistors have an effect. Am I missing something, would someone care to explain why the transistors should have an effect?

Regards
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Old 11th February 2003, 07:48 PM   #7
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The problem is their varying capacitance ( with the varying output voltage ) when OFF.

Please see:

http://www.audio.nl/tipseng.html
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Old 11th February 2003, 07:58 PM   #8
Asen is offline Asen  Bulgaria
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Actually I don't know. Just remove them and see for yourself.
I also was suspicious just like you. So I cut only one leg of the 4 transistors - the one connected to the signal path. After half a minute of listening I removed them all. There was no doubt it was a radical improvement. These little devils were bc337 (if I recall correctly). This mod didn't bring an improvement on the CD player of a friend of mine - Denon. So he put the muting transistors back in. This is not the case with Philips, though. I can garantee.
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Old 13th August 2005, 05:29 PM   #9
Quaid is offline Quaid  United Kingdom
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HI, my grandfather has passed a philips cd450 down to me and I would like to mod it, but I can't find the muting transistors. Are they on the underside of the main pcb? I see 4 surface mount transistors on the underside of the pcb near the outputs, are these the ones to remove? Also are 1N4148 shotkey diodes ok to replace the originals?


I found a service bulletin which says you can replace the cdm2 transport with the cdm4.
here it is;

MODEL: CD450
SYMPTOM: Set will not go into PLAY mode with replacement CDM4 deck
CURE: It is possible that some early production versions of the above models which have a MAB8441P T012 microprocessor mounted on a sub-panel will not operate correctly when fitted with a replacement CDM4 deck (4822 691 30211). If the player is unable to find the first track and go into PLAY mode the servo microprocessor should be replaced with type MAB8441P T082, code number 4822 209 11416. This is carried out as follows: (i) Remove the decoder PCB from the cabinet. (ii)Remove the sub-panel and connector from the decoder. (iii) Unsolder the two leads from pins 6 and 7 of IC6304. (iv)Carefully transfer the crystal 1451 from the sub-panel to position 1301 on the decoder. (v) Check that surface mounted capacitors 2301 and 2302 are fitted on the decoder. (vi)Fit replacement IC MAB8441P T082 on the decoder and replace the panel in the cabinet.

Thought that may be of interest to you guys.

Any help regarding the muting transistors would be great.

Regards,
Nick
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Old 16th August 2005, 12:23 PM   #10
Quaid is offline Quaid  United Kingdom
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anyone?
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