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Old 8th October 2010, 10:00 AM   #1
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Default CD player opamp upgrade -advice needed

Hi,
This is my first post on the forum and I am looking for some advice please from you experienced DIYers out there.
I am a keen hifi tweaker and have purchased an old Technics CD player SLPS840 with the intention of improving the sound quality by upgrading the components with newer/better versions now available.
I have succesfully fitted a clock mod - this brought about a big improvement - and also changed the original SMT dual opamps M5238 & M5219 in the buffer/difference amp of DAC O/P stage. To get the replacement LM4562s to work I had to remove the dc blockng caps in the signal path - two in each channel. On advice (thanks Karl) I have also fitted 0.1uf caps across the supply pins Now for the questions.....
1/ Is it OK to leave out the dc blocking caps? I measued 0v at the output of each opamp so assumed this is safe. The payer has been on test for two weeks with no probs and sounding quite a bit better.
2/ Next in the ouput stage is a LP filter amp with two NJM4580, which I understand are bjt. I would also like to change these for the LM4562 (which I like) but don't want to blunder on and wreck what is now a good sounding player. Hopefully the circuit diagram will appear with this post.
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File Type: doc SL-PS840 OUTPUT CCT DIAGRAM.doc (97.0 KB, 141 views)
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Old 8th October 2010, 10:29 AM   #2
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Let me first ask you what has been improved by the clock upgrade ?
I also own a similar cd player that i tweaked last year, but without any clock modifications. About 100 Euros later I couldn't tell the difference.
It is safe to replace the LPF op-amps with any type you wish.
You can leave the DC blocking caps out, i did the same ( power amps have input caps fitted so there shouldn't be any problem).

Last edited by rrrremus; 8th October 2010 at 10:47 AM.
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Old 8th October 2010, 12:07 PM   #3
Mooly is offline Mooly  United Kingdom
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Pleased it's working OK... I don't have office etc installed so can't open .doc files.

The 4562 should be fine... and with opamps, as long as you don't do anything silly such as fitting single for dual, no harm will come to the player... even if there happened to be other issues... which there shouldn't be here.
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Old 8th October 2010, 12:54 PM   #4
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I also like the LM 4562 and they should be fine in the filter stage. The cap "acros the supply pins" is not usefull. It should be fitted between each supply pin and the ground - and usually those are already there.
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Old 8th October 2010, 02:55 PM   #5
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Quote:
Originally Posted by rrrremus View Post
Let me first ask you what has been improved by the clock upgrade ?
I also own a similar cd player that i tweaked last year, but without any clock modifications. About 100 Euros later I couldn't tell the difference.
It is safe to replace the LPF op-amps with any type you wish.
You can leave the DC blocking caps out, i did the same ( power amps have input caps fitted so there shouldn't be any problem).
The clock mod improved just about all areas - better soundstage, more detail, better seperation, tightened up the bass etc. etc. I think the trick here is to make sure you supply a high tolerence clock to the DAC and also the digital processor. The player has seperate crystals for each 33.8688, and 16.9344mhz respectively. I managed to find a clock unit with on board AC power supply and frequency divider to supply both frequencies. It works very well but draws more current than the Technics TXfmr could handle so I added a small TXfmr for 6. The clock module cost 30 on ebay, its looks very well made and I think it is a bargain.
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Old 8th October 2010, 03:12 PM   #6
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Originally Posted by SoNic_real_one View Post
I also like the LM 4562 and they should be fine in the filter stage. The cap "acros the supply pins" is not usefull. It should be fitted between each supply pin and the ground - and usually those are already there.
I understand there is some debate about whether to add caps to ground or across the pins, but I am afraid I do not have the technical know how to be able to comment. I will leave that discussion to the more technical people out there. I am however trying to develop a better understanding of electronics and am currently reading Small signal audio design by Doug Self. (thanks again Karl) Progress is slow but I will persevere
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Old 8th October 2010, 03:21 PM   #7
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Hi Karl - for the cct. diagram what files do you use? Let me know and I will see if i can send it. Cheers, Steve
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Old 8th October 2010, 05:48 PM   #8
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Your circuit
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File Type: gif clip_image002.gif (24.4 KB, 198 views)
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Old 8th October 2010, 06:02 PM   #9
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by stevew7280 View Post
Hi Karl - for the cct. diagram what files do you use? Let me know and I will see if i can send it. Cheers, Steve
Usually pdf's... I've no need for office so don't have it installed... MS Works does all I need lol

Cap to ground or across the supply... from supply to ground can introduce disturbances into the signal path, yes unlikely on tightly regulated low power stuff but across the rails and it can't. It is non the less a real effect that's easily demonstrated on anything with non optimal grounding. Also on the IC itself is a near to the chip as you can get.
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Old 8th October 2010, 06:02 PM   #10
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Thanks Andy...
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