JimL

So, if I understand this, it looks like this design really likes to be driven balanced. If you have an unbalanced input (e.g. RCA) the negative input is grounded and the stator gets no signal, unlike the differential input designs which become a long-tailed phase splitter if you ground the negative input, thus providing a balanced output. Correct?

WOW! That's 113 dB SPL. Definitely won't like my SRX Plus either. It'll be a clipping machine at those levels. As someone said, "That ringing in your ears is the scream of a dying nerve cell."

Either way I'm thinking that the input transformer could be contributing to the HF roll-off as well to get -0.8 dB at 20 kHz. I'm just not clear on the benefits of an input transformer in the first place, unless it's to filter out HF crap from the DAC (NB, totally uninformed wild ass speculation).

Um, hang on. The SR-009 is specified as 110 pf capacitative load. With an output impedance of 6500 ohms, the high frequency -3 dB roll-off should be around 222 kHz, and -0.8 dB should be around 100 kHz, not 20 kHz.

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See, this is the real idea behind the Stax mafia. They pat you on the back for building one of their designs while they're sucking money out of your pocket by posting a new one.

Very nice!

Sure makes this statement 100% credible: "I spoke with MSB, as I expected they confirmed that they did all of the engineering work on the amp themselves, no outside source was used at any stage, contrary to some rumours here." BTW, anyone see any sign of a regulated power supply, or is it just lots of big electrolytic caps?

Yikes, no need for room heaters with those!

Hey, Kerry, I used to live on the Upper East Side in another life (504 E 81st studio apt) when I was a fellow at MSKCC. I've had Quads for years, even managed to squeeze them into the studio apt with a Hartley subwoofer, but my HT set-up has used Tannoy System 8 NFM II speakers which are stand mounted and reasonable size. Needs a subwoofer though as they only go down to about 55 Hz. A bit industrial looking with gray matte cabinets and black grilles, as they were designed as studio monitors, but sound pretty good. The late JGH used System 10 DMT II monitors in a 5.1 system for a number of years, which is what I have now, but with an 8 as a center speaker - I still have a pair of 8s sitting around, but w/o grilles. I think the 10s may have been his last system. They are obsolete but show up from time to time on ebay within your budget.

The board layout uses all TO220 MOSFETs for both the DN2540 and 10M90S, so the 10M90S should be a direct drop in for the top DN2540.

Now, that's an interesting design! If I were rebuilding it and wanted to keep the phono preamp I'd probably hardwire the phono input to the phono board, hardwire the phono EQ in place and convert the tape and mic inputs to more line inputs, but that's just me. BTW, are those green resistors Kiwame (Koa)?

Haven't heard of any problems with the amp. One change I made is to feed the input tail CCS with separate resistors from B- for each channel. This eliminates the need for a -15-20 volt PS.

Haven't done anything with my PS as I am out of town this weekend. AFAIK, three people have completed an SRX Plus, Congo5, mwl168 and Straw Hat recently wrote me that he completed his. I believe Congo5 used the original KGBH PS, mwl168 used a KGSSHV PSU and Straw Hat used my PSU design. So far, nobody has written me any e-mails complaining I wasted their time and money.

On what?

Joking (subtle reference to Wayne's World). On a serious note, I tried rebuilding my PS to make it quieter and discovered it is significantly noisier than I had thought. OTOH, a friend built a KGST using the KGSSHV PS and it is definitely quieter.

Probably can build an SRX Plus for under $1000, although I've had some problems with the PS recently - the full KGSSHV PS is an excellent substitute. But I'm biased, and as Kevin says, it's not worthy.

Very, very nice, George!

And as I recall, with all that weight and bulk it didn't even have a regulated power supply, just caps and resistors.

Only worth it if you're smuggling $46k worth of diamonds inside it.

Actually, the microZOTL 2.0 is licensed from Berning by Linear Tube Audio, who also build a number of Berning's other designs. I used a Berning EA-230 amp for a number of years for my Quad electrostatics - nice amp. The big thread on H-F is largely about substituting better power supplies for the original switching PS. I heard a demo of different power supplies at the Albuquerque Head-Fi meet earlier this year, and it does make a difference, but it also gets expensive pretty fast.

Well, except that for tubes this is a measurable phenomenon. In Glass Audio, Vol 1, No.2, Charles King has an article on extending tube life, and it has a graph from GE that shows the transconductance of a tube declining gradually by about 20% during the first 1500 hours, then stable over the next 3500 hours. And from an old post from Kevin Gilmore on biasing replacement tubes in a Stax SRM-T1, "... new tubes drift like crazy." That means the parameters in a new tube change as it is run in. Now whether this is audible or not I can't say, but it certainly is measurable.

Yup. Here's a pic. Note that this is for my point-to-point wired unit. For the KG board, the heatsinks are spaced so that there is enough space for the ceramic insulators to fit between the 10M90S TO2220 and the heatsink.

Incredible build John! I'd ask you to adopt me but I'm probably older than you are.

Yep, usual gain for SPEAKER amps is around 10-20 (20-26 dB). Headphones generally need less, which is why in the bad old days the headphone jacks on integrated amps and receivers often had a resistor in series to cut down the gain, and possibly also to prevent the amp from blowing out the headphones.