Hi,
This I most emphatically second.
Buy some cheap 2nd hand stuff that you do not care one way or another first to hack up, so if it dies you chalk it up to experience.
Ciao T
This I most emphatically second.
Buy some cheap 2nd hand stuff that you do not care one way or another first to hack up, so if it dies you chalk it up to experience.
Ciao T
Well, I found that the best sound without wrecking the player much is DAC -> coupling caps -> second tube (cathode follower), bypassing OpAmp and the first tube. I ran it through the scope - no visible sine distortions, spectrum analyzer and sweep signal shows flat line across the frequency spectrum, the sound coming out of it beat Virtue Audio Piano M-1...
I also learned (the hard way) that DAC chip is rather flimsy, something happened to it while doing all those tweaks and it died on me - had to remove the sarcophagus with all the toys in it - the chip was not properly attached to the board, waiting for replacement DAC to arrive.
I also learned (the hard way) that DAC chip is rather flimsy, something happened to it while doing all those tweaks and it died on me - had to remove the sarcophagus with all the toys in it - the chip was not properly attached to the board, waiting for replacement DAC to arrive.
Hi,
I would tend to agree, though with respect, my scheme shown above whould likely improve the situation further, as it allows DC coupling between DAC and tube and raises the output level back to the "standard" around 2V RMS, while DAC & Follower leave you at 1V (this at least makes direct comparisons with other players problematic).
Well, with the DAC Chip dead, here is a chance to upgrade to something better... The DAC in the MHZS range you deal with is really about as low as you can go in terms of price.
Ciao T
I would tend to agree, though with respect, my scheme shown above whould likely improve the situation further, as it allows DC coupling between DAC and tube and raises the output level back to the "standard" around 2V RMS, while DAC & Follower leave you at 1V (this at least makes direct comparisons with other players problematic).
Well, with the DAC Chip dead, here is a chance to upgrade to something better... The DAC in the MHZS range you deal with is really about as low as you can go in terms of price.
Ciao T
That would require my building a new tube buffer board or floating existing board connections, something I am not ready to do on this player.
What would be the direct replacement for PCM1742KE? I admit it is not the best but for this player it is enough. Outboard DAC is a much better option.
I was checking the board and PCM1742 connection points and leg 5 (Vdd) is 4.8V (Max 3.6 according to TI), leg 6 (Vcc) shows normal 5.07V. What could be the problem?
It is difficult to get under the PCB with multiple connections required from trafo and PS, it has to stay in. There are two regulators there: 7808 and LM317. The 317 runs very hot while 7808 is not even warm...I need some assistance here.
Hi,
Actually, if you look hard enough you may find that it takes a minimal number of parts replacements and cut/jumps to achieve my circuit. But your call.
No direct replacements, just buy a decent board with a good DAC of ebay and just make sure the input formats are the same.
Not really, as that entails a SPDIF connection which in most cases causes more trouble than the "DAC Chip Upgrade" compensates for. Fitting the DAC internal and using 3/4 wire serial as input is a MUCH better choice.
Either the Regulator for the 3.3V line has failed (which would have zapped the DAC Chip) or it does not like to work without load or MHZS simply made a bad design that exceeds manufacturers ratings and makes the Chip suceptible to damage.
In chinese "design" they often seem to consider "absolute design max" as 'below minimum recommendations", both on solid state stuff and tubes, based on what I have encountered...
Start by either getting a schematic from the manufacturer or by tracing the circuit.
Ciao T
Actually, if you look hard enough you may find that it takes a minimal number of parts replacements and cut/jumps to achieve my circuit. But your call.
No direct replacements, just buy a decent board with a good DAC of ebay and just make sure the input formats are the same.
Not really, as that entails a SPDIF connection which in most cases causes more trouble than the "DAC Chip Upgrade" compensates for. Fitting the DAC internal and using 3/4 wire serial as input is a MUCH better choice.
Either the Regulator for the 3.3V line has failed (which would have zapped the DAC Chip) or it does not like to work without load or MHZS simply made a bad design that exceeds manufacturers ratings and makes the Chip suceptible to damage.
In chinese "design" they often seem to consider "absolute design max" as 'below minimum recommendations", both on solid state stuff and tubes, based on what I have encountered...
Start by either getting a schematic from the manufacturer or by tracing the circuit.
Ciao T
Haha, I put a load resistor on leg 5 and V started dropping down a little, but still nowhere near the 3.3+.
From what I am able to see both +5 and +3.3 run from the same regulator. It looks like voltage difference is achieved by using two different voltage zener diodes.
This is proving to be an interesting project...
From what I am able to see both +5 and +3.3 run from the same regulator. It looks like voltage difference is achieved by using two different voltage zener diodes.
This is proving to be an interesting project...
Hi,
That sounds majorly dodgy.
Maybe just add a nice 3.3V Fixed Voltage reg for the 3.3V? Or a shunt reg using TL/LM431 with a suitable series resistor.
Ciao T
That sounds majorly dodgy.
Maybe just add a nice 3.3V Fixed Voltage reg for the 3.3V? Or a shunt reg using TL/LM431 with a suitable series resistor.
Ciao T
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.
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.
Hi,
Not necessarily bad, low heater voltage extends tube life, IF the cathode current is de-rated.
They probably did not, based on my experience.
Ciao T
Not necessarily bad, low heater voltage extends tube life, IF the cathode current is de-rated.
They probably did not, based on my experience.
Ciao T
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.
An externally hosted image should be here but it was not working when we last tested it.
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.
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...
I know it's a shitty way to regulate supply voltages for DAC chip, but it's not my design...
An externally hosted image should be here but it was not working when we last tested it.
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.