OK so I modded my CD723 - but it's still mediocre - diyAudio
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Old 1st June 2004, 04:43 PM   #1
Dave S is offline Dave S  United Kingdom
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Default OK so I modded my CD723 - but it's still mediocre

I have a CD723 with all the "Chris Found" mods plus:
KC-7,
AD826 I/V
Schottky PSU diodes
Separate transformer with emitter follower type power supplies for the OpAmp and DAC (cut down version of the Audionote PSU).
Servo 11V is still supplied off the original unregulated supply.
Output caps 22uF 63V FCs bypassed with 10nF Wima polypropylenes
Chassis damping

In varying amounts, most of the mods made improvements to the sound of the player. However it is still some way behind my lightly modified Arcam Alpha+ player (Trichord clock and a few component upgrades) and a long way behind my friend's Cambridge Audio CD2, both of which are 10+ years old. I reckon the CD723 is comparable with a decent modern 400 CD player.

Any suggestions to make the CD723 better, or have I reached the limit with this very cheap machine???
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Old 1st June 2004, 06:38 PM   #2
Previously: Kuei Yang Wang
 
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Default Re: OK so I modded my CD723 - but it's still mediocre

Konnichiwa,

Quote:
Originally posted by Dave S
I have a CD723 with all the "Chris Found" mods plus:
Hmmm.

Quote:
Originally posted by Dave S
KC-7,
I hope it is well implemented. I would expect the layout to be critical, much more so than the actual circuit.

Quote:
Originally posted by Dave S
AD826 I/V
Why? You like bad sound?

Quote:
Originally posted by Dave S
Schottky PSU diodes
Separate transformer with emitter follower type power supplies for the OpAmp and DAC (cut down version of the Audionote PSU).
Hmmm. Nothing wrong with that, but again implementation is critical.

Quote:
Originally posted by Dave S
Servo 11V is still supplied off the original unregulated supply.
Output caps 22uF 63V FCs bypassed with 10nF Wima polypropylenes
Why? You like bad sound?

Quote:
Originally posted by Dave S
Chassis damping
In what sense?

Quote:
Originally posted by Dave S
Any suggestions to make the CD723 better,
Yes. Analyse the Circuit. identify the weaknesses and address them. You seem to have left most of the in place, the same style it is often done by "boutique" modders who like sell expensive modules and pretend that an excellent clock and analogue stage will makie a world class player out of any mediocre piece of rubbish.

Quote:
Originally posted by Dave S
or have I reached the limit with this very cheap machine???
I don't think so.

Sayonara
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Old 1st June 2004, 07:15 PM   #3
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Cool Re: OK so I modded my CD723 - but it's still mediocre

Quote:
Originally posted by Dave S
I have a CD723 with all the "Chris Found" mods plus:
KC-7,
AD826 I/V
Schottky PSU diodes
Separate transformer with emitter follower type power supplies for the OpAmp and DAC (cut down version of the Audionote PSU).
Servo 11V is still supplied off the original unregulated supply.
Output caps 22uF 63V FCs bypassed with 10nF Wima polypropylenes
Chassis damping

In varying amounts, most of the mods made improvements to the sound of the player. However it is still some way behind my lightly modified Arcam Alpha+ player (Trichord clock and a few component upgrades) and a long way behind my friend's Cambridge Audio CD2, both of which are 10+ years old. I reckon the CD723 is comparable with a decent modern 400 CD player.

Any suggestions to make the CD723 better, or have I reached the limit with this very cheap machine???
Hi Dave,
You could try the OPA2604 or the OP275 for IV.
Jung like regulators seem to better suited for the analog stages in my experience.
A balanced power 1:1 transformer improved the sound of my Philips CD931.
Ultrasoft recovery diodes worked better for me, but this is clearly player dependent as all mods. In the Philips CD650 I heard a big difference, in the CD931 not.
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Old 1st June 2004, 08:21 PM   #4
sreten is offline sreten  United Kingdom
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"you have to be cruel to be kind"

Mods improve matters but there's no way you can expect
to be able to bypass total high quality build practises.

You can't turn a cheap CD player into a giant killer.

sreten.
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Old 1st June 2004, 08:26 PM   #5
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Old 1st June 2004, 09:32 PM   #6
Previously: Kuei Yang Wang
 
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Konnichiwa,

Quote:
Originally posted by sreten
Mods improve matters but there's no way you can expect
to be able to bypass total high quality build practises.

You can't turn a cheap CD player into a giant killer.
Actually, you can. Here is what is wrong with the CD-720/21/22/23:

1) Powersupply - complete joke. Fit seperate transformers/supplies for Analogue Stage & DAC (+/-12V & 5V), one for the Servo circuitry (+/-12V), one for the clock (5V) - use the basic Tent Audio Module - hard to implement it wrong if you use a fully insulated supply, fit correctly & forget and one (5V - might be 3.3V on the later verions) Supply for the main CD processor.

Build well implemented and de-noised supplies and clean up the original supply to only supply "utility" digital circuitry (uP/Display/Remote etc.). All the transformers used to supply especially the digital section should be chosen for minimal leakage between secondary and earth and suitably phased/ploarised to minimise further any leakage. Then add an external 1:1 insulation transformer and filter, non of this needs a lot of power.

2) Chassis - complete joke. For a minimum fit a serious solid wood bottom plate (spruce plywood) and fit some decoupling feet like the String Suspension thingies you get. Add solid hardwood sidecheeks and a plywood rear panel, plus a nice solid vented top cover made from thin spruce ply, for fun make the vent openings in the shape of Violin Vents. C37 laquering of wood and PCB's are optional.

3) Fit a nice superfast Op-Amp (LM6182 is still my choice) in the analog stage (more or less original circuit adjusted for 2mA Full Scale Current), no capacitor in the feedback loop and follow by a simple low impedance 1st Order LPF (I used 100R/15..22nF IIRC) and a suitable (passive) offset adjustment to get rid of the output offset.

Now the above can be done well on a fairly tight budget, within the existing case so on. For more extreme versions a string suspended drive for a toploader might be worth a try.

The Digital Filter and DAC in the CD-723 are "good enough for CD", if you make sure to eliminate the other problems.

Sayonara
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Old 1st June 2004, 09:42 PM   #7
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by jean-paul
Say that again to the Tjoeb guys !

Quote:
Originally posted by Kuei Yang Wang
Konnichiwa,



Actually, you can. Here is what is wrong with the CD-720/21/22/23:

1) Powersupply - complete joke. Fit seperate transformers/supplies for Analogue Stage & DAC (+/-12V & 5V), one for the Servo circuitry (+/-12V), one for the clock (5V) - use the basic Tent Audio Module - hard to implement it wrong if you use a fully insulated supply, fit correctly & forget and one (5V - might be 3.3V on the later verions) Supply for the main CD processor.

Build well implemented and de-noised supplies and clean up the original supply to only supply "utility" digital circuitry (uP/Display/Remote etc.). All the transformers used to supply especially the digital section should be chosen for minimal leakage between secondary and earth and suitably phased/ploarised to minimise further any leakage. Then add an external 1:1 insulation transformer and filter, non of this needs a lot of power.

2) Chassis - complete joke. For a minimum fit a serious solid wood bottom plate (spruce plywood) and fit some decoupling feet like the String Suspension thingies you get. Add solid hardwood sidecheeks and a plywood rear panel, plus a nice solid vented top cover made from thin spruce ply, for fun make the vent openings in the shape of Violin Vents. C37 laquering of wood and PCB's are optional.

3) Fit a nice superfast Op-Amp (LM6182 is still my choice) in the analog stage (more or less original circuit adjusted for 2mA Full Scale Current), no capacitor in the feedback loop and follow by a simple low impedance 1st Order LPF (I used 100R/15..22nF IIRC) and a suitable (passive) offset adjustment to get rid of the output offset.

Now the above can be done well on a fairly tight budget, within the existing case so on. For more extreme versions a string suspended drive for a toploader might be worth a try.

The Digital Filter and DAC in the CD-723 are "good enough for CD", if you make sure to eliminate the other problems.

Sayonara
I simply don't care. My bog standard Cambridge Audio
CD4SE is miles better than any modded cheap CD player,
tubes added or not, and as far as I'm concerned thats it.

sreten.
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Old 1st June 2004, 09:47 PM   #8
Nuuk is offline Nuuk  United Kingdom
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I got clear improvements with thorough mechanical modifications as described HERE .
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Old 1st June 2004, 09:48 PM   #9
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Quote:
Originally posted by sreten


I simply don't care. My bog standard Cambridge Audio
CD4SE is miles better than any modded cheap CD player,
tubes added or not, and as far as I'm concerned thats it.

sreten.
If you don't care why react in this thread ? You can't compare apples and pears but there are really a lot of possibilities with cheap cdplayers. Especially if you dont like to watch tv in your spare time and have a soldering tool waiting.

For bog standard more or less expensive cdplayers without needed work you're on the wrong forum Besides that there are plenty expensive cdplayers with excellent build quality that sound absolutely mediocre. The fun with DIY can be making a very good cdplayer with a cheap basic model and some hard earned knowledge.

I don't want to challenge you but your remark "miles better than any modded cheap CD player" is like walking on thin ice.
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Old 1st June 2004, 09:53 PM   #10
Nuuk is offline Nuuk  United Kingdom
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I had a CD4SE and they are excellent CDP's but I don't know if it is that much better than my modified CD723 (which cost me about half of what the CD4SE did!
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