teddy_pardo
Trade: Teddy Pardo
What you see here is still work in progress, (well, you can say that for anything you start modifying...), it will look better finished, just wanted to share some info in the meantime.
Initially I wasn't sure that modifying a CDX is a good idea, after all it's not cheap, and if you fail... The bottom line is that I'm very happy I did it, although it's a lot of work, the final result is a very high end CD player. Nothing to do with the original CDX.
So here is how it looks like now:
In order to understand the modifications please read the acoustica CD3.5 mod page, and the CDX reverse engineering thread first.
I'll describe the modifications in the order I made them, hoping I won't forget anything.
1. Replace the six OP42 opamps by OPA627
This one is very good, it completely transformed the sound of the CDX to be more open, and more detailed. The exaggerated mid bass disappeared. I've used OPA627AU, someday I'll replace them by OPA627BP, which are supposed to be better.
2. Replace the opamp regulators by super regulators
I removed the 317/337 pair located at the left of the PCB and used super regulators instead. In the picture, these the circuits inside the two large shrink sleeves. Later they will go to the place vacated by the transformer.
My super regulators have VBEs instead of preregulators, I'm doing it now everywhere since the improvement is obvious (read here for details).
I also replaced the SMT decoupling capacitors next to each opamp by 10uF tantalums.
This mod is highly recommended too, improvement in sound is very clear (dynamics, etc). My feeling is that it is useless to invest in super regulators in the external PSU (XPS) since they are followed by 317/337 internally.
3. Replace the output coupling tantalum capacitor by BC128
Nothing to write home about...
4. Enhance all the regulators using the "regulator booster" circuit
This one is very worthwhile, it boosts the performance of the CDX in almost every aspect. I have done it in little steps, 2-3 regulators at a time, and each time there was a further improvement read here for more details.
Note that the three regulators near the transformer (those that drop the 15V to 9.5V) carry a large current and requires a darlington transistor if you want to enhance them. The most important are the 6 DAC regulators on the left part of the PCB (and the PMD-100 VDD2 regulator if you don't use a Flea, see mod #10)
5. Add VBEs to the 15V, and +/-10V rails
I added small strip boards with power darlington and 56uF oscon VBEs on the two 15V and on the +/-10V rails (the +/-22V already have VBEs on the modified SRs). It gives another enhancement to the sound (all over).
6. Enhance the DAC rail RC filter
There are eight tantalum capacitors in two rows near the six regulators on the left part of the PCB. With the 3.3R resistors next to them, they form an RC filter. The row which is closer to the regulators if powering the analogue part of the DACs. I replaced the capacitors by 180uF 16V oscons, and added a 1R resistor in parallel to the 3.3R. It's a subtle improvement.
7. Replace the DAC capacitors
There are six 100uF tantalum caps near the DACs, they are used for Vref decoupling etc. I replaced them with 180uF 16V oscons. It's another subtle improvement.
8. Replace the local PSU capacitors (Applicable only if you don't have an external PSU)
I realized that after I added the VBEs there is not much different anymore between the local and the external PSU. I thought that it may be due to the fact that 4700uF for the +/- rail and 10,000uF for the + rail are too small. I replaced them with 15,000uF 25V chemi-com capacitors (SME series, same size). It improved things, but still the external PSU sound a bit better. Besides that I need the space.... so I decided to use the external PSU.
9. Replace the clock by a PFM Flea
When I got the Fleas the CDX already sounded amazingly good, I was sceptical about further improvements, but there are... The Flea+XO added more clarity and detail, Stacy Kent's voice sounds much more natural now. The improvement was obvious, but not as much as other reported. Initially I thought that it is because it's the last mod, and there's not much to improve, but read on the next mod.
To connect the Flea, I bypassed the inverter and connected it with 47R and 330R resistors in a wireless way. That is, one leg of the resistor to the Flea and the other to the CDX PCB, that's as short as you can get. Currently the Flea is powered from the + part of the +/- 22V rail (it will get it's own rail later...)
10. Replace the PMD-100 regulator
While mounting the Flea, I realized that unlike the CD3.5, on the CDX the DACs are getting their clock from the PMD-100 HDCD decoder, not from the main clock (or the Flea). The PMD-100 is reclocking the signal using an internal clock. If that's the case I thought it would probably benefit from a Flea too, and it did, big time. I connected a second XO-less Flea to the VDD2 pin of the PDM-100, and the improvement was even more than the first Flea with the XO. To get the max improvement I replaced the 100uF tant decoupling capacitor by two red 3.3uF Wimas (thanks again Carl), and two 1R resistors.
11. ADD large VBEs for the two Fleas
Since the Fleas are now powered from the +22V rail, I wanted to isolate them, so again a small strip board, a pair of TIP122, 470uF, 1K, and this is it. Another small but nice improvement until they get their own rails.
This is it for now. Next thing is to add two power rails to the PSU, and cleanup things, all the boards which are currently in shrink sleeves will be mounted in the place vacated by the transformer. I'm also considering powering the DACs by four +/- Fleas.
Cheers, Teddy
Initially I wasn't sure that modifying a CDX is a good idea, after all it's not cheap, and if you fail... The bottom line is that I'm very happy I did it, although it's a lot of work, the final result is a very high end CD player. Nothing to do with the original CDX.
So here is how it looks like now:
In order to understand the modifications please read the acoustica CD3.5 mod page, and the CDX reverse engineering thread first.
I'll describe the modifications in the order I made them, hoping I won't forget anything.
1. Replace the six OP42 opamps by OPA627
This one is very good, it completely transformed the sound of the CDX to be more open, and more detailed. The exaggerated mid bass disappeared. I've used OPA627AU, someday I'll replace them by OPA627BP, which are supposed to be better.
2. Replace the opamp regulators by super regulators
I removed the 317/337 pair located at the left of the PCB and used super regulators instead. In the picture, these the circuits inside the two large shrink sleeves. Later they will go to the place vacated by the transformer.
My super regulators have VBEs instead of preregulators, I'm doing it now everywhere since the improvement is obvious (read here for details).
I also replaced the SMT decoupling capacitors next to each opamp by 10uF tantalums.
This mod is highly recommended too, improvement in sound is very clear (dynamics, etc). My feeling is that it is useless to invest in super regulators in the external PSU (XPS) since they are followed by 317/337 internally.
3. Replace the output coupling tantalum capacitor by BC128
Nothing to write home about...
4. Enhance all the regulators using the "regulator booster" circuit
This one is very worthwhile, it boosts the performance of the CDX in almost every aspect. I have done it in little steps, 2-3 regulators at a time, and each time there was a further improvement read here for more details.
Note that the three regulators near the transformer (those that drop the 15V to 9.5V) carry a large current and requires a darlington transistor if you want to enhance them. The most important are the 6 DAC regulators on the left part of the PCB (and the PMD-100 VDD2 regulator if you don't use a Flea, see mod #10)
5. Add VBEs to the 15V, and +/-10V rails
I added small strip boards with power darlington and 56uF oscon VBEs on the two 15V and on the +/-10V rails (the +/-22V already have VBEs on the modified SRs). It gives another enhancement to the sound (all over).
6. Enhance the DAC rail RC filter
There are eight tantalum capacitors in two rows near the six regulators on the left part of the PCB. With the 3.3R resistors next to them, they form an RC filter. The row which is closer to the regulators if powering the analogue part of the DACs. I replaced the capacitors by 180uF 16V oscons, and added a 1R resistor in parallel to the 3.3R. It's a subtle improvement.
7. Replace the DAC capacitors
There are six 100uF tantalum caps near the DACs, they are used for Vref decoupling etc. I replaced them with 180uF 16V oscons. It's another subtle improvement.
8. Replace the local PSU capacitors (Applicable only if you don't have an external PSU)
I realized that after I added the VBEs there is not much different anymore between the local and the external PSU. I thought that it may be due to the fact that 4700uF for the +/- rail and 10,000uF for the + rail are too small. I replaced them with 15,000uF 25V chemi-com capacitors (SME series, same size). It improved things, but still the external PSU sound a bit better. Besides that I need the space.... so I decided to use the external PSU.
9. Replace the clock by a PFM Flea
When I got the Fleas the CDX already sounded amazingly good, I was sceptical about further improvements, but there are... The Flea+XO added more clarity and detail, Stacy Kent's voice sounds much more natural now. The improvement was obvious, but not as much as other reported. Initially I thought that it is because it's the last mod, and there's not much to improve, but read on the next mod.
To connect the Flea, I bypassed the inverter and connected it with 47R and 330R resistors in a wireless way. That is, one leg of the resistor to the Flea and the other to the CDX PCB, that's as short as you can get. Currently the Flea is powered from the + part of the +/- 22V rail (it will get it's own rail later...)
10. Replace the PMD-100 regulator
While mounting the Flea, I realized that unlike the CD3.5, on the CDX the DACs are getting their clock from the PMD-100 HDCD decoder, not from the main clock (or the Flea). The PMD-100 is reclocking the signal using an internal clock. If that's the case I thought it would probably benefit from a Flea too, and it did, big time. I connected a second XO-less Flea to the VDD2 pin of the PDM-100, and the improvement was even more than the first Flea with the XO. To get the max improvement I replaced the 100uF tant decoupling capacitor by two red 3.3uF Wimas (thanks again Carl), and two 1R resistors.
11. ADD large VBEs for the two Fleas
Since the Fleas are now powered from the +22V rail, I wanted to isolate them, so again a small strip board, a pair of TIP122, 470uF, 1K, and this is it. Another small but nice improvement until they get their own rails.
This is it for now. Next thing is to add two power rails to the PSU, and cleanup things, all the boards which are currently in shrink sleeves will be mounted in the place vacated by the transformer. I'm also considering powering the DACs by four +/- Fleas.
Cheers, Teddy
