Modification of MHZS CD players

[ClefChef]

I measured other voltages as well, you know, just to see what's there...
For instance required +6.3V for tube heaters measures +5.8V, quite underpowered I'd say.
It's a wonder this player IS working (when it actually does). The best thing about it that I'm able to find is its weight - a real brick.
Maybe the technical plan (I mean design as it was related in some construction biuro meeting) was good, but the implementation and technical details make me wonder if engineers really new what they were doing.
What made them put High Voltage PS and digital transport control on one board next to each other? Tubes and DAC on the same board as well.
1. Power supply.
2. Digital circuits.
3. Analog circuits.

[ThorstenL]

Hi,

Originally Posted by ClefChef

For instance required +6.3V for tube heaters measures +5.8V, quite underpowered I'd say.

Not necessarily bad, low heater voltage extends tube life, IF the cathode current is de-rated.

Originally Posted by ClefChef

the implementation and technical details make me wonder if engineers really new what they were doing.

They probably did not, based on my experience.

Ciao T

[Koifarm]

Chef chef, if the dac chip is defect, you can ad the hongkong Dac board inside the player. You got a upgrade with the cs4397 chip.

[McGyver]

Originally Posted by Koifarm

Chef chef, if the dac chip is defect, you can ad the hongkong Dac board inside the player. You got a upgrade with the cs4397 chip.

There is also latest version of this DAC board based on PCM198 chip. This new version is far better than old, and easier to integrate with tube output stage. I have done several tube output DACs based on this chip and I'm amazed with sound quality wchich is outstanding.

[ClefChef]

Originally Posted by McGyver

There is also latest version of this DAC board based on PCM198 chip. This new version is far better than old, and easier to integrate with tube output stage. I have done several tube output DACs based on this chip and I'm amazed with sound quality wchich is outstanding.

You mean PCM1798

[McGyver]

Yes, indeed. Sorry for mess.

[ClefChef]

Originally Posted by Koifarm

Chef chef, if the dac chip is defect, you can ad the hongkong Dac board inside the player. You got a upgrade with the cs4397 chip.

Where do you tap the digital signal from?

[Koifarm]

From the dig. coax out connector on the back

[ClefChef]

I'm back to the DAC chip Vcc and Vdd supply. As I mentioned before I get +5.01 to leg 6 (OK), and +4.7V to leg 5 (needs to be +3.3V). There are two diodes (zener?) that these voltages are coming from. QUESTION: would changing the value of zener diode help lower +4.8 to +3.3?
I know it's a shitty way to regulate supply voltages for DAC chip, but it's not my design...

[ClefChef]

Originally Posted by Koifarm

Chef chef, if the dac chip is defect, you can ad the hongkong Dac board inside the player. You got a upgrade with the cs4397 chip.

I ordered this board today.
I read Lukasz Fikus aka Lampizator website, I like the stuff that he does a lot. He used this board on several of his "Lamipsized" players. The newer PCM1798 version uses 3 OpAmp chips instead of only 1 in the original.
I will try to repair the original DAC chip circuitry on my player and also install the Lampucera board for comparison. I already changed tube stage to single tube cathode follower - much better solution.