If the SJ74 is 2mA, then it is fake i would bet. It would be in the GR range, not BL. Buy from FetAudio.
ZM,
On the Dac you just finished with line trafos and OPA1632, did you have a buffer in front of OPA? with such a high Zin, I would assume in would be necessary. What trafo you use. THanks and sorry for off topic. Didn't want to start new thread.
ZM,
On the Dac you just finished with line trafos and OPA1632, did you have a buffer in front of OPA? with such a high Zin, I would assume in would be necessary. What trafo you use. THanks and sorry for off topic. Didn't want to start new thread.
you can go to Pub , to keep clean this thread for BA3 related technical info and usual Off Topic distractions ( not technical ones)
I also had a problem with my 2SK74, posted about it in the thread Fake or Original. Had big problems in getting correct balance.
From AudioFet (the ebay shop run by alweit) I bought very good originals, excellently matched pairs to better than 1%. These were crucial to get the high performance from my F5.
albert
I have about 20 good pairs, but glad to find out that FetAudio is not only source.
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Biasing
I had to add 330 ohm resistors on the back of the board to get past 0.85V on one side as well.
I also added 10uF capacitors across the power supply in the BA-3 box as per Nelson's latest schematics. Result of these changes is a smoother sound that appears a touch rolled off in the treble until I play something like harpsichord or percussion, when it becomes obvious that there's plenty of treble when needed.
I'm biasing mine at 1.1V across R10 and R11 (higher quiescent current helps with a slightly too-high power supply voltage). The heatsinks get faintly warm.
I had to add 330 ohm resistors on the back of the board to get past 0.85V on one side as well.
I also added 10uF capacitors across the power supply in the BA-3 box as per Nelson's latest schematics. Result of these changes is a smoother sound that appears a touch rolled off in the treble until I play something like harpsichord or percussion, when it becomes obvious that there's plenty of treble when needed.
EDITOR'S NOTE:
ALL info on the BA-3b, the Balanced BA-3, are moved here:
http://www.diyaudio.com/forums/pass-labs/201281-burning-amp-ba-3b-balanced.html
ALL info on the BA-3b, the Balanced BA-3, are moved here:
http://www.diyaudio.com/forums/pass-labs/201281-burning-amp-ba-3b-balanced.html
where ?
on output of FE or on output stage itself ?
in both cases - more than good
4mV across the 330ohm resistor of the output of the BA-3.
congratulation....... ! your J-Fets now seem to work......
Thanks to you.
I let the amp run for about 45 minutes, during which the DC offset swung between +60mV and -100mV until with a few adjustments it settled between -6mV and +6mV. R10 and R11 settled in at about 1.07V and R3 and R4 were both 0.058V with P3 set dead centre.
I plugged this unit (this is the left channel monoblock) into the system last night and I'm running it again this morning. Quite distinct from the BA-2 on the right channel but comparisons are not easy because the left BA-3 is powered by the Salas voltage regulator and the right one is not (not yet anyway). On first listening the slight chestiness to voices on the BA2 has been replaced by a more even and open sound. Percussion on cymbals is more distinct in the sense I can hear a clearer sense of impact and decay and a clearer sense of position. Instruments are easier to separate from the mix. However, some of this will be the upgraded voltage reg I am sure. I am certainly getting more detail from the amp at lower output levels than I was whilst there is no sense of hardness to the sound (not that there was any on the BA2).
I think we need to let those who are building for the first time that the BA2 is an outstanding amp in its own right. I hadn't heard anything as good as the BA2 even after years spent auditioning some very expensive amps and there will be those who prefer the BA2 sound. For those building for the first time I would go for the BA2 because I found the front end easier to build and set up. I have had a lot more problems with the BA3 and I think I might have given up had it been my first build.
Of course I wouldn't have given up; you guys would have sorted it out.
Of course I wouldn't have given up; you guys would have sorted it out.