The first input resistor in the tube stage should probably be around 47k. 33k makes output signal from CD player much too high, otherwise the stage sounds a lot better than the original one.Hello
My modification:
Analogue stage:
Power supply:
Enjoy!
An externally hosted image should be here but it was not working when we last tested it.
In this pic you can see the two diodes removed and the L78L33ACZ 3.3V voltage regulator put in place for DAC Vdd+ supply - it gives steady 3.3 unlike diode solution that fluctuates the voltage depending on current draw. There are two wima's underneath the PCB bypassing the input and output of the regulator. Input bypass cap also tames +5V supply oscillations that were significant.
Filtering caps were replaced by Oscons and Nichicons.
All these modifications resulted in significant improvement in sound.
Here a picture from a modification with a pcm1798 dac. And a passive mod. Bypassing the ad827 opamps on the dac board. Straight from the I/V resistor to the MHZS tube stage.
An externally hosted image should be here but it was not working when we last tested it.
The modified player on the photo had a defect DAC ic. it had already the passive mod from page 1 and played good for 3 years. Replacing the origenal DAC was not a option because there are much better dac's . I toke a lampucera type2 dac board and connected it to the sdpif out from the player, i removed the opamps(3 x AD827) from the dac board. Put in 470 ohm resistors in pin 2 and 3 for I/V conversion in the first two dipsockets and connect pin 2 to the input capacitors of the mhzs tubestage. The powersupply i have got from the mhzs pcb, one 5V for analoge circuit and one 5V for digital circuit. +/- 12V i do not need because i removed the opamps.
Now the player has a pcm1798 dac like the 88G.
Now the player has a pcm1798 dac like the 88G.
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There is easier way to connect output caps. One can fit caps of bigger size and better quality. And what you think about that little passive filter I aded after dac? Where 2n caps should go - after or before 1k resistor?
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I think with PSM1798 current out you could bypass coupling caps and go directly to tube grids. 470R resistor then would be RG...
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Ronny-
Is a cracking noise heard when very low level signals are played , caused by that oscilation you have mentioned?
That is possible, but it can also be the cable to the dsplay. try to move the cable or place a ferritcore on the cable.
I can recommend to ad the four capacitors. The voltageregulators stays much cooler.
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I put a ferritcore on that cable but that did't help.
I'll do the 4 caps and see what happens.
That cracking noise with low level signal is kind of characteristic for this player, isn't it. Try to play last 30 seconds of Phil Collins' Face Value record , you will hear it. I would be suprised if your player is quiet playing that. Let me know if it is.
An externally hosted image should be here but it was not working when we last tested it.
Going to try this schematic for PCM1798...
It's my schematic. Where did You get it?
And be aware that is for PCM1798 wchich is CURRENT output DAC. And MHZS has PCM1742 wchich is VOLTAGE output DAC.
Ronny , on your picture it shows you decouple Vin and Vout to the ground for 7808 , but in case of LM317 you decouple them to adj that goes to the ground too but through a resistor. Is that correct?
I found it at diyaudio.com, I believe, in one of your posts. I bought PCM1798 dac board and I'm going to do some further experimenting.
I installed modified CS4397 DAC board into Pioneer DV-59avi player and it sounds very good.
I suggest You to make a standalone tube output DAC based on this PCB. If well done, it sounds excellent.
Yesterday I had possibility to compare my PCM1798 DAC called The Protagonist with Audio Note DAC 1.1x. The difference in sound quality was HUGE, my DAC sounded far better.
Yesterday I had possibility to compare my PCM1798 DAC called The Protagonist with Audio Note DAC 1.1x. The difference in sound quality was HUGE, my DAC sounded far better.
Ronny,
I want to discuss that again.
You wrote this: " Chef chef, i hope you did also the mod on the Voltagestabeliser for the DAC. Because these things oscillate like hell. After a while they will quit working and destroy the DAC."
I beleve you were wrong saying that they feed the dac. These two have nothing to do with the dac. They supply 5V[LM317] and 8V[7808] to the other board[transport control].
And in case of decoupling LM317 , you should decouple it rather directly to the ground, not through resistor when you go to ADJ .
Could you please comment on that.
I was following your posts on other sites RE dac and tube output stages. If all goes well with cd66 experiment I will make a decent DAC for myself. I am trying to source out some lundahl transformers and russian tubes. I might even try BBC LL/88 to see if they work.I suggest You to make a standalone tube output DAC based on this PCB. If well done, it sounds excellent.
Yesterday I had possibility to compare my PCM1798 DAC called The Protagonist with Audio Note DAC 1.1x. The difference in sound quality was HUGE, my DAC sounded far better.
my cd66 tube output stage was modified according to your schema with ECC88. I didn't like the sound of it, maybe because of the tubes I have, or maybe because of the significant attenuation that is required for the original DAC chip - it sounded a bit weiled. At the moment I feed 1742 output directly to the cathode follower and it sounds better, although with some digital glare.
I tried both. And PCM1798 works excellent with output wired directly to tube's grid and only a conversion resistor to the ground. So I sold my Sowters and Lundahls.