Talk to ZM. His IXFN hocky puck Singing Bush PCBs looks like theres a jumper between
the buffer and the gain stage...which looks to my untrained eye an exact copy of this.
You can input signal directly to the other side of the jumper. With the upper Mu PCB, and the
Peasant half (as he calls it)...you essentially have the BAF2015 amp. The biggest hurdle I
had was ensuring the input transformer was connected properly. After that, the bias supply.
ZM modified Nelson's original, I used that initially, but apparently I needed lower than 4.7V.
Changed the 1K pot to 5k based on Soundhappy's suggestion. Initial startup was slow, but
after an hour, everything stayed where I set it.
the buffer and the gain stage...which looks to my untrained eye an exact copy of this.
You can input signal directly to the other side of the jumper. With the upper Mu PCB, and the
Peasant half (as he calls it)...you essentially have the BAF2015 amp. The biggest hurdle I
had was ensuring the input transformer was connected properly. After that, the bias supply.
ZM modified Nelson's original, I used that initially, but apparently I needed lower than 4.7V.
Changed the 1K pot to 5k based on Soundhappy's suggestion. Initial startup was slow, but
after an hour, everything stayed where I set it.
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I have some boards I made. I got an amp working but it currently has more distortion than I expect. Probably havs something to do with my source impedance though as the circuit seems to work just fine. I only built genergs variant for IRFP240 / R100 though but apart from swapping som values here and there the wirings should be the same.
Only error I found so far is that the cap CCS_C3 has the wrong polarity. The transformer silk screen is also wrong one some pin winding polarities but If I remember correctly the actual wirings are correct.
The schematic is more complicated as I wanted it to support using mixed mode feedback (which also worked great). Also I wanted to test different biasing networks hence all the jumpers so I can test for example depletion mosfets without needing a new PCB.
The transformer I used is the JT123 FLPCH. I used a standoff board for the transformer. CCS_JP is also something I copied from the incorrect schematic and should not be connected =)
Input can also be configured to use balanced input or single ended depending on which jumpers are connected.
While I can't guarantee the quality of the boards as I am no board expert I do have an excess of boards (price for 10 was same as 2) and can send you some for shipping costs if you are interested. I'll get access to my work bench next weekend and I can start digging in the PCB shelf to see if I can dig up some transformer boards, I should have an excess of them too. Those boards should not be absolutely needed though as the transformer can be soldered directly to the board but personally I liked having the option to swap around.
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Another error is that B_R3 should not be connected to B_J2, so if someone uses this board make sure to drill away that trace. If you do want a set I can fix this before posting them.
I have finally finished my THF-51S version of the BAF2015 amp. It took a while because I managed to destroy a THF-51S and a IXFN140N20P, and getting a replacement THF-51S from Pras in China was slow because of shipping problems due to the pandemic.
The device failures were not caused by wiring error but by layout issues. The amp was running for a while before things came to an end. The case of the capacitor across the emitter and collector of the 4N37 was too close to the metalwork and eventually shorted to ground which overbiased the IXFN140N20P. It then failed and shorted, which in turn caused the THF-51S to fail. Another learning experience.
A quick review of the amps. They have forced air cooling using 3 computer cooling fans per monoblock running at low voltage. They are very quiet and the amps run cool. I've added a B1 R2 buffer at the input so I can use these amps with a variety of preamps. The main power supply is CLC and the amps are very quiet.
I have not installed them in my main system yet. Ultimately, I will use them to drive JBL 2226 in 9 cu. ft. boxes in a biamped system.
The device failures were not caused by wiring error but by layout issues. The amp was running for a while before things came to an end. The case of the capacitor across the emitter and collector of the 4N37 was too close to the metalwork and eventually shorted to ground which overbiased the IXFN140N20P. It then failed and shorted, which in turn caused the THF-51S to fail. Another learning experience.
A quick review of the amps. They have forced air cooling using 3 computer cooling fans per monoblock running at low voltage. They are very quiet and the amps run cool. I've added a B1 R2 buffer at the input so I can use these amps with a variety of preamps. The main power supply is CLC and the amps are very quiet.
I have not installed them in my main system yet. Ultimately, I will use them to drive JBL 2226 in 9 cu. ft. boxes in a biamped system.
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Beautiful 
CongratulationsReally really awesome - well done for a beautiful build. There's something about these amps that evokes memories of valve amps...
Separately, I was advised by a Japanese hobbyists that they commonly place a 5A quick blow use in line with the SITs. Otherwise even a mains power trip can blow these rare devices (if for example, bias disappears before the main rail caps discharge) - or when the protection methods fail for whatever reason...
The THF-51S amps are in my system and are making music. I was a little bit worried about how they would perform doing the lower frequency duties in a biamped system. I had a 50 watt/channel Sony TAN-5550 VFET amp on the low end previously, and it worked very well.
The bottom line is, I did not need to worry. The amps are certainly no worse than the TAN-5550, and I think are better in a number of ways. It is difficult to do a fair comparison, but one thing jumps out. The transients, such as percussion, seem better.
One bonus that I didn't expect is that these amps run cooler than the TAN-5550. That is one hot running amp. I guess I'll be one of the few who considers the BAF2015 amps as summer amps.
I ran some tests on the new amps and measured distortion at 1 watt output. Both amps were very similar.
Other picture shows my JBL speaker system. I use a modified LX-Mini for crossover and response shaping. The top end is powered by a 2SJ28 L'Amp with 193V inductors. Preamp is 01A tube.
The bottom line is, I did not need to worry. The amps are certainly no worse than the TAN-5550, and I think are better in a number of ways. It is difficult to do a fair comparison, but one thing jumps out. The transients, such as percussion, seem better.
One bonus that I didn't expect is that these amps run cooler than the TAN-5550. That is one hot running amp. I guess I'll be one of the few who considers the BAF2015 amps as summer amps.
I ran some tests on the new amps and measured distortion at 1 watt output. Both amps were very similar.
Other picture shows my JBL speaker system. I use a modified LX-Mini for crossover and response shaping. The top end is powered by a 2SJ28 L'Amp with 193V inductors. Preamp is 01A tube.
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