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CDX reverse engineering

It may be that they do it to justify the price difference between the CDX and CDS...

I have no idea what's inside the CDS but since it's also HDCD (and there isonly one chip type that decodeds HDCD), and knowing how Naim use to work, I would be tempted to assume that the CDS is basically the same circuit as the CDX with better components.

Teddy
 
The CDS is very like the CDi, CD2 - and uses opamps and polystyrene caps. The CDS2 not something I've had a look at, aand while I would expect the filter 'design' to be similar note it is an entirely discrete design - no opamps.
 
Interesting! I just was thinking of the possibility to use a preamp TA circuit for the CDX instead of the op-amp based filter. Obviously capacitor/resistor values should be changed accordingly, but the circuit has a lot in common.

Teddy
 
teddy_pardo said:
A message to all CDX owners:

Get rid of these SMT capacitors and replace them with polystyrenes. The difference is very audible!!!

The interesting thing is that Naim thought about it, and there are holes in the PCB to allow polystyrene capacitors. These SMTs probably save some on the cost, but at a cost...

I have also replaced the twelve 1K and the two 5.6K resistors with Welwyn, which is another worthwhile thing to do, but not as much as the capacitors.

Teddy
Click to expand...

Hi Teddy,

Finally obtained some polystyrene caps with the correct values - before I venture further and start ripping apart the CDX (again) I am also considering a few other changes at the same time. One that comes to mind would be to add a VBE to the +/- supplies on the output opamps. I was considering this only for the supply that feeds the last few opamps closest to the output (don't have the circuit in front of me - but it appears that they all share a pair of 117/317 regs.)

Do you feel that this would be a worthwhile mod or should I just do that cap substitution?

Any comments appreciated,

Cheers

Martin
 
Hi Matrin,

I'm using a couple of TeddyRegs to power the opamps, one positive and one negative common to all othem, and it's definitely worthwhile. Just remove the 317/337 pair and connect them instead.

Teddy
 
Hi Teddy,

Thanks for the (super quick) reply, I'll plan to wip up a couple of 'TeddyReg Clones' to go in at the same time.

Regards

Martin
 
BTW, they have great effect on the DACs as well. Use smaller capacitors (up to 20K) though, as the DACs don't like to be powered in delay.
 
Hi there,
i have just discovered this thread. Is there someone here ?:cool:
I bought a CDX few month ago and my "DIY passion" leads me to open the player and after to check what i can do inside !!!!:D
I have 6 OPA LM49710 and also DIL support. I will change the 6 OP42 to try.
 
Hi Martin.
Thank you for the advice !!!! I will order OP627....:) Just have to find where...

Regarding the ALW-SR, any address, plan, etc......?

Thx.
Olivier
 
I will order OP627.... Just have to find where...
Click to expand...
No need. Stick with the OP42s already fitted... these are not a limiting factor.

OP42 vs others has been discussed before here, it might be worth trying a search of this forum if you're interested.
 
All the signal filter caps in Naim's analogue stages are already polystyrene...

(but yes, this is definitely worth trying when modding budget players)
 
So it seems that there is nothing to change :D !!!!

I am looking for the SR first and after i will test something else. Soon i will remove the 6 AOP and put DIP sockets. I can test differents OPA....;)

Any BOM for the ALW-SR for our need ?

See you here soon..... :cool:
 
Hi there, I am back with my questions !!! :D

I have ALWSR +/- PCB and also TeddyReg PCB. So, what i have to put for the last 2 OPA ? ALWR or TR ????

I want to do a external PSU, a XPS-like. Maybe i should keep the ALWR for this.

What do you think ?

Thx
 
Hi,

On the CDX there are 6 OP42s, all connected to the same rails. When you say 2 OPAs do you mean you've replaces the OP42 with OPA627? Also do you mean that you have cut the rails of the last two and separated them from the other four?

I've used ALWSRs in the past, and now I'm using TeddyRegs instead. I prefer them over the ALWSR (but both do a great job, and are better than the original XPS circuit). Note that if you are powering just a single pair of OPAs the load may be insufficient for the TeddyReg and in this case it is recommended to add a 2K resistor in parallel to the TeddyReg output.

BTW, here is a preview of the new, soon-available-on-ebay TeddyXPS:

Front-side.jpg


Internal-top.jpg


Internal-side.jpg



Cheers, Teddy
 
Hi Teddy,

i have changed the last 2 OPA by LME49710 (just to hear...). I will remove the 4 others and put them on DIL support. I will by buy OPA627 to try them.

When you them "cut the rail of the last two and separated them from the other four", what do you mean ? Do you mean that i have to connect the TR direct ti the OPA from an outside PS ?
Or can i use the "original" supply from the CDX and just replace the LM317/317 with the TR ?
Can you draw me the place of the 2k resistor ?:confused:

I have 6 +Ve TR and 2 -Ve. Could you tell me me the better place to place them ? And same question for the ALWSR if i can use them !:D

Thx.;)And your Teddy XPS looks nice.:eek:
 
I only meant to say that whatever you use to power the last two op-amps will also power the other four as they are connected.

You can use the TR to replace the 317/337, but in this case set the TRs to +/- 16 instead of +/- 18V to allow sufficient dropout.

There are many regulators inside the CDX, the most critical are the op-amps and the DAC. If you use TRs for the DAC use the accelerated version, as the DAC will not tolerate the slow start time of the TR.

Teddy
 
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