Anyone compared BAT Rex vs. Atmasphere MP-1?

Raquel, yes, those old 'chrome dome' tubes are pretty impressive- I've seen them as original parts in equipment that is over 50 years old, still testing as strong as new tubes. We have seen them go over 50,000 hours in our stuff and I would not be surprised to find out that some of them could do over 100,000 hours in the right circuit. They sound nice too :)

Raquel, the way the MP-1 works is it has a direct-coupled output. The output impedance is low enough that it can drive 32-ohm headphones easily. It is designed to drive 600 ohms without effort; obviously its output impedance has to be well below that in order to do so.

Because its outputs are direct-coupled, the output impedance is flat from 1Hz to 200KHz or thereabouts. So it really can drive 200 foot interconnects without difficulty.

It my opinion that getting rid of the output coupling caps is the single best thing you can do with a tube preamp to improve transparency and bandwidth.

The MP-1 was/is the first balanced line preamp for high end audio. Victor's business partner bought one of the first production units before they went into business together. He had some of our MA-1 amplifiers too- we still have his warranty forms on file.

The preamp is designed for 24/7 operation. IMO you get better bang for the buck when the preamp is operated when you are playing music, rather than using up the tubes while you are at work or asleep in bed.

It warms up quickly, much faster than in years past, due to better regulation and better coupling caps. Two hours is more than enough for the preamp to settle out so 24/7 operation really doens't win you anything with it like it did 10-15 years ago.

The power supplies (8 of them) are all tightly regulated so the use of SS or tube rectification isn't relevent; the rectification is all handled by HEXFREDs. The highest voltage drop on any tube in the unit is about 150 Volts, the B+ and B- are both regulated at +/- 250V.

The 6SN7s in the unit tend to last about 10,000 to 30,000 hours (GT, GTA or GTB, although seriously we don't know how long the 6SN7s last; some seem to last literally for years). The 12AT7s (used only in the phono) tend not to last as long. IF you run the preamp 24/7 we used to recommend replacement of the 12AT7s every 4-5 months; in the Mk 3.1 (the latest version IOW) they seem to last considerably longer but the preamp is so recent (came out a year ago) that we don't have good numbers on that.

Raquel, I think with older tubes the quote might be accurate. But with modern signal tubes, particularly low level miniatures, there is a phenomena of grid contamination that has to do with the inclusion of contaminates during the assembly process. An excellent example is fingerprints when workers are not given latex gloves or the like for assembly.

In such cases (if you are using tubes with this or similar issues) leaving the preamp/amp on 24/7 is not really all that helpful, as when the grid contaminates the transconductance will fall off sharply.

Its really not a good idea to design for tubes that are out of production, unless as a manufacturer you have no concerns about the owner being able to find tubes for the unit 20 years down the road. IOW its a good idea to design for tubes that are currently being made, so using such tubes has become a fact of life.

We have seen this contamination problem with 6SN7s, 12AT7s, 12AX7s, 6DJ8/6922 and a few others. It is considerably more rare with NOS types.

I'm just pointing this out because 24/7 as a generalization is not always the panacea for best performance.

As an additional FWIW, the issue of cathode stripping is far more pronounced with power tubes. It is a matter of controversy as to whether its a problem for small signal tubes.

Talk2me, There is no power amp made that has an input impedance too low for the MP-1 (it can drive 32-ohm headphones directly from the same outputs that drive the power amps). The Burmester is completely balanced, so no worries.