Marantz CD63 & CD67 mods list

[Thomo]

Originally posted by pzogal
another thing about output stage, this time Ray's discreete.
how about substituting R11 with a pot ?
couldn't one adjust DC offset this way and get rid of the output cap ??

greetings,
Pawel

I have been meaning to ask this for a while. It would be nice to do away with the cap altogether.

Lee.

[avr300]

Originally posted by rowemeister
....(or you are holding the remote the wrong way round )

Brent

[6h5c]

Originally posted by pzogal
another thing about output stage, this time Ray's discreete.
how about substituting R11 with a pot ?
couldn't one adjust DC offset this way and get rid of the output cap ??

greetings,
Pawel

Nope, not possible this way. The only result of a pot is that there will be more or less current running through the output transistor and the pot, but the voltage will not change much.

Take a good look at the circuit. Where does the voltage across R11 come from? T5 acts as an emitter-follower, so any voltage at the base, will appear on the emitter, minus Ube (= ~0.7V). So the voltage originates at R6/T2. To make the output voltage exactly 0V, the voltage at that point has to be about 0.7V, and thus 11.3V has to be dropped by R6, because the supply is +12V. At 4k7, this means a current of approx. 2.4mA has to flow through it, instead of 1mA now.

So maybe the current setting resistor can be made variable. Let's see what happens when you increase the current. The collectors of the differential amp will be at ~0.7V at some point and the voltage at the output should drop to zero. You have to lower R11 to 1k2 to keep 10mA running through the output transistor.

BUT... now there is no voltage left for both transistors to work on! If you want to have an output that swings to both positive and negative sides, you need HEADROOM, or in this case some voltage left ACROSS the transistor so it can swing up and down. The voltage at both bases of the differential transistors is about 1.2V, that's the DC voltage coming from the passive filter. The emitters will be 0.7V lower, so about 0.5V. With 0.7V on the collector, that makes only 1.2V Uce! That's not enough to produce a decent output signal.

Here's a pic of the circuit with the correct voltages included. Oh, how I love my simulation program.

This concludes the analog electronics lesson for today!

Ray

[Thomo]

Originally posted by 6h5c



This concludes the analog electronics lesson for today!

Ray

Excellent and informative reply Ray, especially for noobs like me! Thank you.

Lee.

[6h5c]

You're welcome! I just kept on writing, I don't know what got into me...

[avr300]

Ray, the attached circuit and the description are out-of-sync. I have attached a file which seems to match the lesson - more or less, if you compensate for the BJT / FET.

[6h5c]

Thanks, avr.

I decided to post the picture later, but the version you posted can't be simulated, as it is optimized for publishing. I didn't want to draw another one...

Ray

[RCruz]

Originally posted by 6h5c
Try an electrolytic (10...47u/16V) in parallel with CY01 on the front panel PCB, worked for me. I noticed the IR receiver somehow becomes less sensitive when RY11 is replaced by an inductor.

Originally posted by rowemeister

If these things mentioned in the thread do not not cure the problem then you may have a duff connector (or you are holding the remote the wrong way round )

I used a 10uF 35v (saved for the ocasion).

Problem fixed...... I can remote from afar again....

Note: I did not try it backwards yet

Ricardo

[SimontY]

Excellent news. It makes little difference where I point my remote, my player's still 30 miles away LOL

[RCruz]

Originally posted by SimontY
Excellent news. It makes little difference where I point my remote, my player's still 30 miles away LOL

As I said before, I believe you are very lucky Simon... You can even drive your CDP directly to the Doctor.

Imagine what would be my situation... having to dismantle everything, pack it carefully and send it by air mail...

What type of output have you on your machine ?
With all this detail, I believe I need discrete outputs... but good ones are so expensive.

Ricardo