Marantz CD63 & CD67 mods list

[philpoole]

Hi Ray,

Didn't realise there was a second page. D'oh!

I did do a port of your tubestage to transistors a while back.
Its refreshing to see I wasn't too far off.
It was like yours, but without the buffering. My current source used two transistors, one replacing your two diodes (akin to the ultranalog) and the current source resistance I calculated was 300ohms.
I didn't worry about a buffer output in my design, but realise now it might be useful, considering the signal does need to travel down an interconnect.

I think the outout stage could be improved with a series complimentary pair (although, it might be similar already to that darlington-esque arrangement {showing my ignorance there!}) using a current source. I saw great improvements with a headphone amplifier by improving a simple emitter follower this way - but it was driving a very different load.

I'm really distracted with decorating and stuff, but REALLY want to give this a try.

Glad it sounds better than the opamps. 'ear witness' reports to back up a hypothesis are always welcome.

Cheers,
Phil

[philpoole]

Hi Ray,

Just looking at your schematic, and desperately trying to remember theory...
I think R17 is redundant. Mainly because Q2 and Q3 are trying to follow each other's base voltage(I know that description is wrong!) and R20 and R21 can be removed in some circumstances. My design didn't have them. I can't remember the benefits of keeping R20 and R21 (there are situations when useful, and some when not, perhaps frequency dependent).
I'm going to have to dig out my books tonight to back up my feeble statements with some real facts! However, there is potentially room for some tweaks.

I love transistors (the active circuit here potentially sounds better than a £15 op amp, but costs maybe 75p in parts), but I can never do anything with them without a textbook by my side!

Cheers,
Phil

[6h5c]

Originally posted by philpoole
I think R17 is redundant. Mainly because Q2 and Q3 are trying to follow each other's base voltage(I know that description is wrong!) and R20 and R21 can be removed in some circumstances. My design didn't have them. I can't remember the benefits of keeping R20 and R21 (there are situations when useful, and some when not, perhaps frequency dependent).
Cheers,
Phil

Hi Phil,

Yes, this stage is cheap and simple, and it sounds good too! It's a lot less efford compared to a tubestage.....

R17 is not needed to keep the circuit working, that's true. BUT....the voltage across Q2 will not be the same as Q3, because the voltage drop across R17 is gone. As you may know, the point a transistor is biased in also is influenced by it's Vce, so for symmetry reasons I tend to keep this 'redundant' resistor, just like in the tubestage.

R20 and R21 can also be removed theoretically, but you will find the circuit then amplifies way too much (140x/43dB in my simulation). These resistors act as a local current feedback, and can be used to set the amplification. As you may have noticed, the original SACD Enhancer uses a higher 8k2 and a 5k pot there, and therefore it has less amplification. The passive filter attenuates the signal with some 6.4dB, so I lowered them to 820R to maintain 2Vrms output level.

Regards,

Ray.

[Fidelity Audio]

I wonder if some nice descrete component cards could be made up to plug direct into the opamp sockets.

[6h5c]

Originally posted by rowemeister
I wonder if some nice descrete component cards could be made up to plug direct into the opamp sockets.

Hi Brent,

I suppose it could be done, especially if you use SMD. But if you use the passive filter you can bypass the opamps and use the modified HDAM instead. Whatdoyouknow....maybe HDAM will become useful after all.....

Ray.

[SimontY]

Originally posted by rowemeister
I wonder if some nice descrete component cards could be made up to plug direct into the opamp sockets.

I'll take two

[Fidelity Audio]

Originally posted by 6h5c


Hi Brent,

I suppose it could be done, especially if you use SMD. But if you use the passive filter you can bypass the opamps and use the modified HDAM instead. Whatdoyouknow....maybe HDAM will become useful after all.....

Ray.

Having not spent any time working with the HDAM and just bypassing it. What would it sound like with no opamp and DAC straight to HDAM?

Will the gain and filtering be all wrong

Brent

[6h5c]

Hi Brent,

You will have some signal, but the first opamp amplifies 2.7x, so it will be a bit low. There will probably be some noise residue because the filter part around the second opamp is missing.

Just yank out the opamps and jumper pins 3 and 7. You'll have to use a coupling cap then, because of the DAC's offet voltage. You should try my passive filter part + modified HDAM .

Ray.

[Fidelity Audio]

Originally posted by 6h5c
Hi Brent,

You will have some signal, but the first opamp amplifies 2.7x, so it will be a bit low. There will probably be some noise residue because the filter part around the second opamp is missing.

Just yank out the opamps and jumper pins 3 and 7. You'll have to use a coupling cap then, because of the DAC's offet voltage. You should try my passive filter part + modified HDAM .

Ray.

Just looked at the op amp circuit, the gain of 2.7x is from the 27K and 10K resistors then

I'll have to have a go with the passive filter

Brent

[Luke]

Hi Ray,

would your discrete output stage work on a cd6000? Think the main difference between the two is that the cd6000 has two dacs not one. If it should be ok to use, should I proceed it with the filter you have designed, or will it not be appropriate for cd6000?
Wher do you get the inductors from, and should they be high precision, or matched components?


Cheers arthur