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Old 18th December 2003, 02:55 AM   #1
Fin is offline Fin
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Question CDP Mods

Hi all

I am new to DIY so please forgive some stupidquestions or comments I might make . Over the last few weeks I have learned a lot from the questions and answers many of you have posted here. As a consequence, the bug has bitten and I am well on the modification madness. My humble 1991 Philips CD624 is the first victim and will be undergoing some, hopefully beneficial, changes.


Below is a List of Proposed Modifications:

Replace master clock: (TENTLabs XO2)
Master Clock power supply (TENTLabs XO Supply)
Replace op-amps in output stage: (AD8065, AD8066, OPA627, OPA637, OPA2134, LM6172)
Add extra transformer(s)/psu(s)
Replace power cable with EIC type (filtered & screened)
Replace all 1N4002 and 1N4148 diodes on with Schottky type: SB150/MBR150, should I use bigger ones ie MBR3100?)
Replace 78XX voltage regulators with LM317, LM337
Replace capacitors on power supply with better ones
Replace some resistors (Not sure if they make any difference)
Replace output capacitors
Remove muting transistors (Maybe replace with relays)
Replace metal jumpers with higher quality copper wire (Maybe)
Add a switch to turn off display (Maybe)
Disconnect headphone circuit (Maybe)
Add 75ohm resistor to digital output RCA (I can switch it off or should I disconnect it while CDP is open)
Replace op-amp NMJ4560 on turntable motor control (Not sure what to use)
Add heatsinks to all IC's to reduce vibration??
Shield some components with copper sheets
Add copper sheet to inside cover of player
Add dampening material to top and bottom of case
Add dampening material to transport mechanism
Replace feet (Isopods/Vibropods)


I have read that adding additional transformers and power supplies make a real difference. However, this is where things get a little tricky for me with my lack of electronics experience.

From the schematics, it looks like there is one transformer with two seperate secondary windings. One of these seems to power the display only with about 4V. Could it be AC as there doesn't seem to be a rectifier on this line? The other secondary winding is 60V with a centre tap giving 30 - 0 - 30. There are additional taps for +/-21.2V and +/-10V.

The +/- 21.2V pass through a rectifier and voltage regs giving +/-15V DC. This seems to supply the analogue output stage (one dual opamp) and the headphone section. There is also a connection to the Kill circuit, which I think is the muting system. There is also a tap off this line, before the reg, going to the Kill circuit. So my understanding is that this power supply only runs the analogue stage, except for a few connections which are not active while music is playing.

Q1: Would there be a benefit to adding a seperate transformer for this section? If so, should I just add a small toroidal 18 - 0 - 18 unit to the rectifier after disconnecting the original transformer from this section or is there a better way? What should I do about the centre tap from the new transformer? Does it just connect to the existing ground or does the ground for the entire analogue section now need to be seperated from everything else?


The +/-10V taps from the existing transformer feed to another rectifier and then unregulated to the rest of the main board. Another feed is taken from this rectifier and through some regs to provide +/-5V to the main board.

Q2: Would it be a good idea to add another transformer here, maybe two, one for each voltage? Again, I would like to ask the same questions as above. Also, would it be a good idea to regulate the +/-10V lines?

This would leave the original transformer to power the display and mechanism only.

Q3: Is it generally better to add multiple small transformers for each section or one larger and better quality transformer with multiple seperate output windings?

I know I have asked a lot of questions here and I would really appreciate any assistance some of you experts might be able to give me.

Thanks

Fin
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Old 18th December 2003, 05:52 AM   #2
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Default Anything else that you want to know.....?

Best suggestion:

Only change one thing at a time. Trying to do what you have up your sleeve is something that I would not recommend that someone try all at once. Especially first time out.

Places to start:

Better clock. Has to have a clean supply. A good distribution scheme, too. Maybe Guido will supply some answers.

But power supply......

You can make another transformer/regulator section for the analog: I do it all the time. But if it has all the same mistakes as the stock one, then why bother? Cleaning up all the ground loops can make a big difference just by itself.

You would need good test equipment to do that. Another option would be to make a battery powered amp to drive headphones that you can listen to the rails. Something like a AD797 or so would work.

My bet is that if you hooked that up to all of your supply rails, listen, and get the noise out, you will have lots of stuff to do. And learn.

Jocko
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Old 18th December 2003, 07:12 AM   #3
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You might try to replace all electrolytics first.
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Old 18th December 2003, 09:19 AM   #4
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Quote:
Originally posted by Peter Daniel
You might try to replace all electrolytics first.

Yes, that will help, especially when you maintain the problem Jocko points at.

I'd suggest doing that after solving other issues first
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Old 18th December 2003, 09:32 AM   #5
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Hello,

I have learned a great deal from upgrading my CD63 and a good place to start is the TNT Audio website.

Many of the mods can be carried out on any player.

KevinLee
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Old 18th December 2003, 10:30 AM   #6
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Hi, read your post in the other thread i posted a while back. I was going to say keep it simple - but others have already done that, listen to them, they know a lot lot more than me! Dont try and do too much at once, its a recipe for problems. If it were me i would try some/all of the following, but not necessarily all at once.

1st find schematic for the player. 2nd carefully dismantle the player and become familiar with where everything goes and how it dismantles and how to put it back together. Simple thingss that are good are replacing the mains cable - supra lo-rad is good basic cable for this. I have made little boxes from thin copper sheet to cover ICs in the past. I made these by cutting out a box plan and folding it into a box to put over the IC, the copper edges on the base covered with insulating tape and a strip of blu-tak. This is then soldered by small length wire to the gnd plane. I have had good results with this and it only requires removal of the lid. Covering the digital ICs is good - big microprocessor somewhere near the transport (probably) for example. Damping the case can be beneficial and also perhaps a blob of blu-tak on a few caps.

A new clock is a good thing to do (pref with good supply). New caps are a good thing - uprated parts and maybe slightly larger in the analogue supply. can be good too. Start small and see where you are. Can I make a bold suggestion, leave the op-amps in. Although sometimes good things can be had, i often find that the character i like is changed too much. (unless u dont like it!) Does your player have op-amps external to the ones in the saa7323 itself? Supplying the DAC with a cleaner/seperate 5v is a good thing. Plus better decoupling aronud the DAC and perhaps the decoder too.
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Old 18th December 2003, 11:17 AM   #7
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Fin,

if I remember correctly , your cdp has a groundplane divided in sections.Check this.If true,Jocko's remark about grounding will turn out to be the cheapest and most basic modification to perform.Search the web for some articles.(and read them...)
Guido Tent has a usefull article posted somewhere.Ask him.

Martijn
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Old 18th December 2003, 11:55 AM   #8
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Yes i remember reading Guidos article on bypassing etc and it contained a small reference to this. How would this be achieved? By running connections back to the power supply from the analogue ground plane? Or am i compeltely wrong?
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Old 18th December 2003, 01:19 PM   #9
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Rotellian,

I have never seen the PCB in your Rotel.(My experience with bitstreamers is somewhat limited)In 1990 some of my friends bought the early ones.(Philips).Whe supplied every chip with it's own regulated powersupply,shortened local groundwiring and restored the groundplane.It worked, and without measuring equipment,we didn't come up with any new ideas at that time.
Restoring the grounplane meant:
-soldering all gaps
-connecting every chip to it
-disposing of some groundtracks
(Nowadays I would add some resistors and coils in signal and supplylines(thanks to Guido's article) and use an oscilloscoop.)

martijn
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Old 18th December 2003, 07:18 PM   #10
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Quote:
Originally posted by martijn
Rotellian,

I have never seen the PCB in your Rotel.(My experience with bitstreamers is somewhat limited)In 1990 some of my friends bought the early ones.(Philips).Whe supplied every chip with it's own regulated powersupply,shortened local groundwiring and restored the groundplane.It worked, and without measuring equipment,we didn't come up with any new ideas at that time.
Restoring the grounplane meant:
-soldering all gaps
-connecting every chip to it
-disposing of some groundtracks
(Nowadays I would add some resistors and coils in signal and supplylines(thanks to Guido's article) and use an oscilloscoop.)

martijn
Martijn is right. ONE groundplane, and controlling the currents (bot routing, amplitude and frequency domain)

Ciao
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