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I hesitate to call it a kit because the board comes fully assembled but you still wire the transformer to it and mount it in your DAC (if there is space).
So what, you might ask, am I strapping this tube output stage to?? Well, it is my Kinergetics KCD-55 Ultra DAC. The output stage died on it and I decided that rather than try to have the solid state output replaced I would go with a tube output stage.
Why do I think this will be special? Because Lampizator has been getting a great reputation for making truly great sounding DACs and my Kinergetics has arguably the greatest commercial DAC chipset ever put on the market, the Ultra Analog D20400 20 bit DAC module. I have a feeling it will be right up there with the all-time great DACs because it was already better than most but with just a bit more SS "bite" than one should hear.
I have never heard a STAX X-1T or other top end tube DAC with this chipset but I have been so impressed with the Kinergetics with SS output that I really think I might get something to rival good analog.
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The UltraAnalog DAC does not need an output stage. It has a built in I-V converter (AD844) and also has a single pole filter across the feedback resistor. It puts out 3.5 Volts. In my Handmade DAC (circa 1995) I just used a 20 ohm Vishay resistor directly to the output jack. So, you could A/B a single resistor versus your tube output stage. No doubt you will like the tube stage better (more juicy, bigger, more liquid)...ah, nice coloration! I am assuming you have a "normal" UltraAnalog DAC and not a custom one.
Yes, they are the normal ones. It actually has two DAC modules that seems to be running dual differential even though the output stage was not balanced.
I measured them with my digital scope and each + and - leg of each module was putting out a 5V sine wave (I was feeding a 1Khz digital test tone). I just wasn't sure what the output impedance and/or current drive capability of this signal was. I would guess that it is not so great and into a lowish input impedance that might make a problem with dynamics.
I tested another point just before the output transistors that was 1V, so clearly the stepped it down somewhere (wasn't able to find that where yet). I was going to take the signal off that transistor input to the tube stage. I could do a direct out but what about a transformer to step down the voltage to 1V and boost the current a bit instead of a resistor??
I am not so sure it is about colorations...low signal level tubes often have distortion not much higher than FETs and almost always more benign forms (low order harmonics).
Thanks for your input, I will try it without the tubes, either a resistor or maybe a transformer.
"I measured them with my digital scope and each + and - leg of each module was putting out a 5V sine wave (I was feeding a 1Khz digital test tone). I just wasn't sure what the output impedance and/or current drive capability of this signal was."
So why didn't you measure the Zo while you were at it? All you need to do for the real part is hang a resistor on the output and see how much the V drops. Ohm's law is your friend... You can even do the imaginary too if you just trigger off the input or use one channel for it and the other channel for the output and plot the delay vs F into the load of your choice. It's like having your own AP except it would stand for "audiophile precision"...
Audio, at least the in-band signals, are really rather easy to quantify. Mapping the results to our aural perceptions is still tricky, very tricky, but that's what makes it interesting. I'm pleased as punch that you are trying. The notion that the factors that affect our enjoyment are beyond quantification is simply absurd.
Best, Rick
Ordered a Lampi Amber DAC today. Have high expectations.
News at 11. ;-)
Very cool! I look forward to your report...I will have one as well :)
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