Kenwood DP-7090

November 20 2006, updated on November 20 2007 and July 2008

This is the last model of the great XX90 Kenwood family which I haven't yet tried to lampize so far. So when I finally laid my hands on it I could not wait to peek inside. 8 times PCM1702? That sets expectations high. One of the best DAC chips ever made, and they used EIGHT of them?!? They got a bulk discount or something? Economies of scale?
Is it 8 times better than simple one PCM1702?  Or is it 8 bit better? Apparently they claim to squeeze 22 bits out of 20 bit chip by the way of 8x config and 32 x over sampling. Is it high end or what?






The front panel is a direct cousin of DP 4090 //  DP 5090 units, minus the super cool drawer with extra doors like the cheaper models have. And minus CD-TEXT.
Everything else is identical.
The hood is a thin and flimsy one, not highendish at all. No balanced outputs. Cheap plastic remote etc, etc. So we are dealing with a simple standard CD machine which for some reason has 8 top DAC chips inside. Kind of equivalent of Golf VR6.







What a joy to do lampization - this player has THE BIGGEST  amount of empty space inside (at 3U height !) and what's more - it is evenly split for two parts - left (for power supply) and right - for tubes and stuff. Easily accommodating fully balanced 4 tube output.




All the player fits on one PCB - a big and neat one. There is no doubt where the burr browns reside - 8 of them in two rows makes good impression.







Why 8 ? Nobody knows. While one is needed to make a mono DAC, we need 2 to make stereo set. Adding 2 more enables us to have mirrored balanced signal which still makes a lot of sense. But in this player all that has been doubled and paralleled - what for? To get more output? Or to average errors by SQRT2 ?  Sqrt 2 anybody ? Extra bit of analog resolution? Impressing customers at the cost of 10 bucks? I don't know. Anyway, to use this player properly the only way is to add a balanced transformers from sowter and utilize all 8 chips at once.  THAT WOULD MAKE A KILLER PLAYER. With tubes of course.

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FOLLOW UP

Three years later -in July 2008  I discovered the 6N2P tube and now I would recommend to Kenwood DP7090 to hook-up their PCM1702  DACs to 6N2P only.

Back to lampization of DP-7090 Kenwood

On the photo above you will see capacitors with a double dot - yellow and red for better legibility, which I think should be replaced with much better, low esr caps. Blackgates are unnecessary, but TEAPO or JACKCON  low ESR type will do. Os-cons are marvellous here ! There is over 30 of them but the bass and space improves a lot.


  A portrait of the cheap JRC op-amp (dual one). They had to go away, sorry.




Biggest and most expenceive SOWTER transformers installed - they play important role. They convert  current outputs of the DAC (useless in original form) plus they summarize positive and negative signals from symmetrical set-up plus they amplify the voltage by the factor of turn ratio (5x). On top of that - the transformers  isolate DC offset of DAC output - the DC component. And galvanically isolate DAC from tube grid.

After 1 year more experience I suggest to save money and go for resistor type of I/U conversion. Just add a 100 Ohm resistor from leg 7 to 9 of tube base (no more 250 K there) and wire the isolated DAC outputs to the leg 7. For SE system - only 2 per channel will be used, 2 will remain unused.

The Sowter transformers

Updated 12 months later:
the second time around I decided to try a "sowterless" lampization by means of a resistor output.


The photo above is so huge on purpose to keep resolution.


Since I wanted only RCA outputs I used every OTHER dac chip - positive ones.





Power supply lines installed.




Here is an AC stealing point (after switch)





Installed toroidal transformer and two CRC filters. red wire supplies AC to lampizator, note the black fuse fitting on one wire.








Output RCA's and capacitors (paper in oil Polish military 4uF/160 plus styroflex 5nF bypass which improves "air".


Red dots indicate the electrolytic capacitors which I upgraded as usual with at least 2 x size, 2 x rating and ESR type (for PC motherboard).
These are responsible for power delivery to the DAC chips and to the digital filter Os-cons or even Tantals would have been even better.

RESULT of lampizator and tuning: