Marantz CD63 & CD67 mods list

[6h5c]

Ok, well that's quite an advanced setup you've got there! I reckon the opamps will suffer a bit from HF stuff then anyway. Using the DOS for the summing is a great solution.

I recall there are some discrete I/V solutions, FET-based, was it from Pedja? You could also use the DOS as an opamp, and connect the non-inverting input to ground. That way it will become a trans-impedance input stage. Dunno if it works o.k. but you could give it a try.

Regards,

Ray

[guido]

Originally Posted by 6h5c

This configuration is more linear and produces less distortion compared to a single input device, and that is a good thing of course! It is often used to linearize the input stage of power amps, so why not use it in the DOS!

I did put my pcb together and did some testing. And i did notice quite a bit of distortion on my SA. So i'll try this too and take some before/after pictures.

Probably sunday as tomorrow is the radio/electronics market here in the netherlands which will take most of my day. I'll figure out what i'm missing in a moment and then i can look for parts tomorrow if i do not have them lying around here.

Haven't had much time lately to do anything, personal loss in the family..

[Thomo]

Originally Posted by guido

Haven't had much time lately to do anything, personal loss in the family..

Really sorry to hear that, Guido.

Lee.

[Thomo]

Ray, that's a great idea. I remember I did that once for my TDA1541 dac now

Just done the schematic and starting board design now.

Lee.

[stvnharr]

Originally Posted by 6h5c

Wow, it's awfully quiet here, with so little posts in one week!

Let's stir things up a little: there's a new tweak for the DOS available!!

This tweak was kindly brought to my attention by Steve (stvnharr) from this forum, thanks a lot Steve!

Now what is it? There's no how-to yet, only this PDF, so it's highly DIY . The tweak consists of two extra transistors (BC560C) and two resistors that are added to the DOS' input stage. Together with the existing transistor or FET, they form a Complementary Feedback Pair. This configuration is more linear and produces less distortion compared to a single input device, and that is a good thing of course! It is often used to linearize the input stage of power amps, so why not use it in the DOS!

I haven't tried it myself yet (gathering parts at the moment...) but Steve reports a major upgrade in sound. In time, there will be a page dedicated to this tweak on my website, and I will probably adapt the DOS boards to fit this tweak. Untill then, it's happy soldering

Regards,

Ray

Hello out there, Steve here,

The Complementary Feedback Pair that I installed into the original DOS input long tailed pair is a major improvement in sound quality. The CS 4397 dac chip outputs a fairly highish voltage at somewhere around 1.25V, I believe. With the long tailed pair as input, there are very high voltage swings between + and - signals, and this leads to a lot of music signal compression. The addition of the slave transistor and resistor, which now make the long tailed pair into a complementary feedback pair, stabilizes the voltage swings to a very constant voltage across the long tailed pair. This leads to music as heard live, and with seemingly no signal compression. And after some simulations and trials suggested by Ray, I found the near perfect value for the resistor to the slave transistor which has the effect of a vast increase in bass signal, and perhaps the best bass out of a cd player that doesn't cost as much as a new car.

The addition of just these four parts is quite easily accomplished under the board of the existing DOS. You also have to change some of the resistors allowing for more current into the input stage. This all will not be hard to do once Ray gets the information on a new web page.
A new board with the four extra parts requires a near complete redesign of the pcb, and is a lot of work that took me a long time.

I would urge everyone with a DOS to do this simple modification to your existing board. Eventually you can get a new board, which will be much neater of course with nothing underneath.

Thus far I am the only one to do this. But once some others do it, you don't just have to take my word for it. All I can firmly write is that this modification was a super improvement for me in my application in my SA 8260 player.

[Malefoda]

Shepp you are not alone, I also feel out of place
Anyway, nice try for always better... I'll keep in the "good" range ( le mieux est l'ennemi du bien ). I've fixed my "forgotten" digital decoupling cap issue and some mis-routed 5Vs, that "dead" highs are gone. A 68µF/20V OsCon there.
The best CD-43 of the world is back!

Matthieu

[Thomo]

Excellent news Matthieu.

By the way, last night I saw that I had some private messages sent through this forum. These weren't forwarded to my email and I had no idea they were there. I apologise to everyone for ignoring them, it wasn't intentional.

Lee.

[RCruz]

Update the DOS.... I was not expecting this... Here I go again

Would you send us a revised schematic with real resistor values ?

What about some pics of the underside of your DOS ?

[shepperd]

I probably should be banned Mathieu, for my utter and complete ignorance, if that's what you mean! I read all these pages like they were in a some alien tongue, for which I have a working vocabulary of maybe 50 words . I latch on to "better" though! and I'm totally psyched by the prospect of the DOS board (with, I hope, these latest wonders installed). At some point, when my poor battered '67 settles down from it's post-operative stress, I will humbly attempt to describe the transformation. I can't contribute anything but some dosh (as apposed to DOS) and unflagging admiration for the masses of work that have been done.

[RCruz]

Originally Posted by Malefoda

The best CD-43 of the world is back!

Matthieu

This time it is not a CD53 so I can rest