Спасибо!В теме Худа, надеюсь теперь споры про KD503 VS современные транзисторы уйдут .
Повествование ведёт сам JLH :
The use of more modern ‘audio’ power transistors with a high current gain-bandwidth product (fT), such as the 2SC5200, 2SC3281 and MJL3281A, is not recommended at present. The >30MHz fT of these devices causes the open-loop gain to remain above unity when the phase shift through the amp reaches 180°. This results in instability and oscillation, which requires additional compensation such as a dominant pole capacitor. In a simple circuit such as this, the provision of a compensation capacitor can significantly increase distortion levels unless other circuit changes are made (which perhaps defeats the object of this simple design). However, I will be investigating various possible options for solving the instability problems since I would really like to try the highly linear MJL3281A device. I have received feedback from one constructor, Tim Andrew, who has been trying alternative output transistors in his JLH 1996 version. The MJL3281A gave clearly audible oscillation. The MJ21194 gave a noticeable improvement in sound quality, but introduced a low frequency hum, the cause of which has yet to be determined. The MJ15003 gave a significant improvement in sound quality, similar to the MJ21194 but without the side effects. Tim’s opinion is that, when compared to the 2N3055, the bass is tauter and faster and the top end less ‘splashy’. In a subsequent email about the MJ15003, Tim went on to say: “It's no good, I just had to email you again to say how good these transistors are. Recordings that were previously hard and bright are now sumptuous with crystal clarity, while recordings that were dull are now alive with a new sense of vibrancy. They seem to go particularly well with the tantalum film resistors that I have just fitted. I know you plan at some point to change to full range speakers, but I would seriously recommend that instead, you try these transistors with paper-in-oil caps, preferably copper foil on the input. Audio Note are introducing large value 50 volt P-in-Os for speaker crossovers. If you try these too, I would say you would be very happy indeed. It seems people just don't realise what they are missing with these P-in-Os. They have a total lack of hardness that has to be heard to be believed. My tweeters are metal domes, people say they don't like them because they sound metallic, but here they have a smoothness and clarity that is difficult to describe. Anyway, thanks again for the suggestion of these transistors, they are a big step up from the 2N3055s and I wouldn't go back now.“ Following Tim’s successful trial of the MJ15003, another constructor, Jason Wou, tried the substitution and sent me the following feedback: “I just replaced 2N3055 with MJ15003. It was direct swap. I didn't really have to adjust anything, it was basically a one-to-one swap. I had lots of MJ15003 to build a Leach Amp. My impression is the MJ15003 is DEFINITLY better!! I was getting goosebumps.
Sounded so real. Smoother highs and midrange (I won't comment on bass since I use a subwoofer). It improved the already superb sounding amplifier even more! I guess I won't be using those transistors for the Leach Amp any more! The MJ15003 is more expensive than the 2N3055, but not by much. Maybe a dollar or two more. From now on if there's any amp project with 2N3055 in it, I will be using the MJ15003!
Для тех ,кто не в курсе KD503=MJ15003
В этом вложении поста 876 ,Худ пишет и о 15 Омах,и о том,что желательно усил делать навесным монтажём,как я раньше и писал.
ldsound.club
