I'm using them as output transistors in a diamond buffer output stage of a headphone amp. They don't sound worse than the BD137/138 they replaced, maybe better, but they distort whith heavy loads and the BD's did not. The bias current is 20 - 25 mA and supply is only 10V. Their Hfe values are about 150 and the BD's about 100.
I had to change the input transistors emitter resistors to 56R. Should I play with the output transistors emitter resistors instead?
I had to change the input transistors emitter resistors to 56R. Should I play with the output transistors emitter resistors instead?
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Nelson,
this pair is one of those astonishingly nice video devices from Sanyo, optimized for high-voltage low-current voltage amplification. Generally, video transistors lose linearity rapidly with increasing current. In fact, according to the datasheet, these particular types should be linear at 30 mA, nevertheless, are not meant for use in current stages, requiring different properties.
this pair is one of those astonishingly nice video devices from Sanyo, optimized for high-voltage low-current voltage amplification. Generally, video transistors lose linearity rapidly with increasing current. In fact, according to the datasheet, these particular types should be linear at 30 mA, nevertheless, are not meant for use in current stages, requiring different properties.
I would try to find dedicated types.
Thanks for your comments. I think you're right. After I've listened to them for a while, I find them too smooth. The BD137/138 from ONSemi were better. I hope I can use them in another amp later on.
These are great transistors to swap for to-92 devices. They have ultra-low capacitances, high ft and reasonable beta, but I wouldn't drive them close to maximum current.
Jacco,
that`s another beautiful type for VAS. For CAS something like 2SC3421/2SA1358, even the good old 2SD669/2SB649 are better than the BD fellows.
that`s another beautiful type for VAS. For CAS something like 2SC3421/2SA1358, even the good old 2SD669/2SB649 are better than the BD fellows.
Just an example that video transistors are little good for delivering current.
Toshiba 2SA1184/2SC2824 are nice and pretty cheap in the EC.
Toshiba 2SA1184/2SC2824 are nice and pretty cheap in the EC.
Same same, the lower numbers handle a bit more power.
Better derated SOA at higher rail/bias levels, not interesting for 10Vdc rails and biased at 25mA.
Better derated SOA at higher rail/bias levels, not interesting for 10Vdc rails and biased at 25mA.
I've lowered the bias currents to 5 mA. Some of the softness and glaze is gone. It's drier and less colored. Even though this is a failure, it's interesting to learn things.
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