tube pre-amp for active monitors

George makes a good point about impedance compatibility.

The description of your A200 speakers at the AirPulse site **seems** to imply that the balanced analog inputs are received by a Texas Instruments PCM1804 A/D converter chip. The datasheet for that chip indicates that it has an input impedance of "10K single-ended," which may mean that it has a balanced input impedance of 20K. However the website description of the speaker doesn’t explicitly say that there isn’t a buffer chip or other circuitry "ahead" of that chip.

Also, the PCM1802 chip that is described as receiving the unbalanced analog inputs is specified in its datasheet as having an input impedance of 20K.

I wonder if there is a simple stereo tube buffer I can fit between DAC and monitors?

Before anyone can make a suitable recommendation, if in fact one can be made at all, you should contact AirPulse and ask them to clearly state what the input impedances of the balanced and unbalanced analog inputs are.

Regards,
-- Al

@almarg  
The balanced inputs bypass the built-in dac and tone stack

The balanced inputs bypass the built-in dac and tone stack

Thanks.  But how does that relate to what I said in my post?

Regards,
-- Al

ignore everything above 
get a used itube for 100-150$ you can use it at 0 db or 6db gain as a preamp.it's really small  one source rca in and out .great for fighting digital harshness and expanding the soundstage,  the power supply and tube do not require an upgrade they use a nos ge tube which i know from other gear and their  50$  ipower. i'm using the itube with an arcam delta 120 power amp and b&w floorstanders (pc> ipurifier3>nuforce icon hd dac with ifi ipower (>hd700)> ifi itube preamp 0 gain>arcam delta120power amp>?b&w dm580. i am very happy with this set . got the itube from ebay used about a month ago used and a little cosmetically challenged  for a 100. 

Are you using the DAC part of your laptop or do you have a separate one?