kevin gilmore

Depends on which version of the power supply board you have, but 24 volt zeners across the gate to source prevents the pass transistor from blowing up. The fairchild part used in the T2 is way better anyway.FQPF8N80C or FQP8N80C and they are cheap. Probably still out of stock at mouser, so get them at futureelectronics.

In all 3 cases above, its the current source that is the problem. Has to have 1000 volts compliance. This requires stacked pnp's similar to the original circuit. And the capacitor (c1,c2,c3) necessary to stabilize the circuit is going to affect the quality of the current source at higher frequencies. the devil is in the details. Build it and test at appropriate voltages, then let me know. The SiC devices work great on paper. In practice, there are all sorts of other issues because they don't like to work at low currents for example.

Well i'm 30+ lbs LESS buddha than i was when i started this project 19 months ago. You can be pretty sure that if you do a spice analysis, and the results are poor, then if you actually build and test the device, it will be poor or worse. But a good spice result does not necessarily translate to a wonderful sounding amplifier. The ixys10m90s devices sound just fine, but blow up at about 925 volts. Rather consistently. Anything else at 1000 volts does not sound as good. Replacing the 2sc3675's with 2sc4686's does in fact work fine, and sound the same but you have to turn up the bias currents a bit. Same thing with the active batteries. The open loop gain is plenty high already. Anything over 15db of headroom seems to make lots of different amplifiers sound bad. Many of the portable opamp based toys with 50db+ of extra gain are a good example. The slew rate is more than sufficient with a rise time of under a microsecond large signal. Replacing the input tubes is still open to discussion.

My T2 is just about 1 year old now. The hundreds of hours of joy it has given me and will continue to give me in the future is something i will remember forever. I just don't see any way to improve on the design. Maybe ways to make it a bit cheaper and easier to build, but doing anything to increase the slew rate, or further lower the distortion does not seem to be possible.

yup

over the years i have seen bunches of torroid transformers burn up. And not just on audio gear. If we could find a video of them being wound, you would see all the issues that can cause trouble. You spec the transformers as best you can, and hope the manufacturer has a clue. But i know of one well known manufacturer that still to this day has very little clue what they are doing.

i love mine, too bad its not anti-magnetic but is 18k gold http://gilmore.chem.northwestern.edu/dsc_0752.jpg

Not a black circuit board. just reflections from the scanner or camera from the solder mask.

center tap on the high voltage windings is optional.

Someone loan this guy a T2. Has more parts than any other headphone amplifier ever. Or a krell master reference amplifier.

already had the charlie parker, its great music.

Singlepower ran dc filament current all over the boards. Trouble was the significant AC content due to the diodes got into just about everything. The diy T2 does absolutely the minimum amount of filament on the board for this reason.

more fine work by kerry http://gilmore.chem.northwestern.edu/BlueHawaii-AB-T2-Servo-v1-0.zip

First time (well at least so far) that the snow plow has not sent my mailbox into oblivion in 15 years. Sure toasted a few others however. They must have been going at least 30 mph down the street. I have the mailbox on an old single piece of a truck spring, so you whack the thing and it just springs back. Whenever i hear the snow plow barrel down the street, i'm out there 5 minutes later to clean the slush off the end of the driveway before it turns into one solid chunk of ice. The new snowblower i have has this extra feature that turns ice and wet mush into water which it throws out of the way at least 40 feet. Absolutely no problems getting to work and back with the vette the last 2 days.

No... No... Grande Champaigne... The good stuff. Delamain cognac, the 60 year old stuff. Glad my roof is steep enough that the snow does not stick. No way i'm getting up 3 stories...

updated spreadsheet. if there are any other errors let me know. fqpf8n80c... lots in stock at future electronics. If you want to be fancy about it, on the small heatsinks, remove the pins, use them upside down, thread the area on the other side where the pins used to be, and then drill and tap a new #4-40 hole for the transistor. Use ceramic insulator, bushing and stainless screw.

here are a couple more pictures http://gilmore.chem.northwestern.edu/dsc_1799.jpg http://gilmore.chem.northwestern.edu/dsc_1800.jpg

They finally plowed the street, so i'm good to go if i have to. But really a few more hours for the rest of the main streets to be plowed seems prudent.

I'm assuming its acceptable to begin the drinking of the grand champaigne after the blowing of the snow sure hope so even if it is 10am. Had to blow snow 4 times since 2 am. picture at 6am with natural lighting thru second story window. http://gilmore.chem.northwestern.edu/dsc_1792.jpg

18 inches in wheeling, with drifts up to 5 feet high. Took about 2 hours to blow all the snow away. Unfortunately the streets are not plowed yet. Snow day

HR2? design is on headwize

OK, for all that asked, the current board files. Someone should check them to make sure that i did not make any mistakes when i fixed previous errors. amp board http://gilmore.chem.northwestern.edu/staxt2nc3fdh5.zip flipped resistors in servo feedback changed hole sizes on 2sc3381 moved 100k feedback resistor and added compensation caps change pinout for dact power supply board http://gilmore.chem.northwestern.edu/staxt2rev0power1-14.zip backwards diode in low voltage supply correct wiring of 110/220 volt for universal transformers .1uf and 10k resistors in the 4 power supplies. and the multi-page pdf's http://gilmore.chem.northwestern.edu/staxt2nc3fdh5.pdf http://gilmore.chem.northwestern.edu/staxt2rev0power-14.pdf

Although there will not be another board run unless someone else wants to do it, i have fixed the layout to incorporate this and all other fixes. Same with the power supply. If people want, i can post the gerbers.

Yep, and once you terminate the cables in their characteristic impedances, the significant sound differences between even the most different cables become so small that you will have serious trouble telling the cables apart. Something the cable companies obviously do not want to happen as their business will fall into the trash. Also makes it harder for outside interferrence to effect the sound. 50 ohms (or really 46 to 110 ohms) is not a problem for properly designed audio equipment. Even buf634's or the elantec equivalent are actually designed to do video over 50 ohms. Even the toy opamps that drive many headphone amps can drive grado's which are 32 ohms. If the impedance really bothers you, you can always make up some ultra trendy 300 ohm twinline. Made from pure silver, with a large diameter silver shield. Can't do that with OTL tube gear however. Requires a matching transformer.

About 25pf for the fet is right. Add in wire and connector and its 30 pf for sure. There is likely nothing left available in solid state that is going to do any better and still have an extended frequency response. I run a 50 ohm system with 50 ohm correctly terminated cables. The krell stuff is designed for this. So is the Ayre stuff. Anything with significantly lower capacitance has to be tubes.