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IC: Group Buy Monofied Sijosae Buffer PCBs - Page 7

post #91 of 102
8/4/09 at 12:45pm
Not a function of bias, I mean keep same bias and sound quality gets worse as transistor warms, after running awhile versus first turned on. I don't recall the bias I was using at the time but it was definitely more than 30mA. Keeping it cool would help but I couldn't hear a difference between initial/cool transistors at higher bias and running lower bias so they didn't get hot so there seemed no need to bias so much.
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post #92 of 102
8/4/09 at 5:58pm
Not that I'm the kind of person who obsesses about Class-A operation and owns a half-dozen monoblock JLH, Zen, or "le Monstre" amps or anything, but if you wanted to ensure true Class-A operation of these buffers as outputs for headphone amps, wouldn't you want to bias 'em up around 25-30ma or so? (With a J310, presumably.)

Obviously we're no longer looking at something even remotely suitable for a portable amp, but for a desktop amp, on the other hand...
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post #93 of 102
9/17/09 at 11:19am
I wonder what other NPN-PNP pair we can use in a battery-powered amp apart from BC337/327.

Pls advise. Thanks in advance.
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post #94 of 102
9/17/09 at 1:23pm
This buffer is class AB and the bias is only 2.7mA per side as set by the CCS.

With that considered, your battery time will be mostly dependent on how much of a load you've given the buffer and your voltage swing. If you are going to limit current to save battery you might as well not use the buffer at all.
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post #95 of 102
9/17/09 at 3:37pm
MPS751/MPS651 is one replacement, but they're harder to find, I think. 2N2222 and 2N2907 might also work, but I'm not sure the pinout is the same, and they'd probably sound worse.

Seeed seem to be out of stock on the PCBs at the moment; I don't know if/when they'll have more, but if you need some in a hurry, PM or email me - I've still got a dozen or so left over from the first production run.
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post #96 of 102
9/17/09 at 3:51pm
Quote:
Originally Posted by Nemo de Monet View Post
<snip> 2N2222 and 2N2907 might also work, but I'm not sure the pinout is the same, and they'd probably sound worse.<snip>.
Good guess I've also tried 2SA1015/2SC1815 which sounded close but I preferred the BC327/337. 2SA970/2SC2240 might be worth trying (for portable use, not for current capability).
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post #97 of 102
9/17/09 at 5:16pm
You can use many many complimentary pairs of transistors, but my general impression is if you use those with lower current rating you end up with a more harsh sound and less controlled bass. The BC327/337 happen to have high current for TO-92 size, but if your amp case has enough clearance you might go with 1A to 3A transistors instead, noting the orientation/pinout used.

Pick the bias level you want, easy enough to swap in a different resistor up to the max with a jumper instead of resistor.

Even in class AB with low CCS, I find a buffer sounds quite better than bufferless direct drive from an opamp, but use as much bias as the battery capacity vs runtime will allow.
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post #98 of 102
2/3/10 at 7:18pm
Quote:
Originally Posted by Pars View Post
Good guess I've also tried 2SA1015/2SC1815 which sounded close but I preferred the BC327/337. 2SA970/2SC2240 might be worth trying (for portable use, not for current capability).
I have couple 2SA1015/2SC1815 and I want to use them

But the different pinout makes me wonder how to put those transistors in the circuit. Just mirror image or what?

Sijosae's component placement is easy to read
as in here: http://www.headphoneamp.co.kr/bbs/da...SimpleAB_1.gif
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post #99 of 102
2/3/10 at 8:16pm
Not quite. You'd need to twist things around a bit and probably insulate the leads, as well. From the bottom, with the flat side facing up, the BC327/BC337 leads are C-B-E (collector/base/emitter), from left to right. The 2SA1015 and 2SC1815 in the same position are E-C-B.
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post #100 of 102
2/3/10 at 8:26pm
Quote:
Originally Posted by Nemo de Monet View Post
Not quite. You'd need to twist things around a bit and probably insulate the leads, as well. From the bottom, with the flat side facing up, the BC327/BC337 leads are C-B-E (collector/base/emitter), from left to right. The 2SA1015 and 2SC1815 in the same position are E-C-B.
Yeah I was quite disappointed when I noticed that I just cannot use them there without extensive modification.

I have quite many of those Japanese transistors, but I cannot find any use for them... If somebody would help with similar picture as Sijosae has done.
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post #101 of 102
2/3/10 at 11:53pm
Uhhhmmm...


The right hand side version is using E-B-C transistors and you have E-C-B, so put them in in that orientation, but use teflon tubing and flip the B and C pins. Note that the 4 inner transistors are only used as diodes, with their B and C connected together, so you don't really need to do anything on those. Not really an extensive modification.
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post #102 of 102
2/8/10 at 6:52pm
Quote:
Originally Posted by cobaltmute View Post
I was reading this thread where FallenAngel was biasing BD139s with 100mA. You need heatsinks but you can go alot deeper on the bias.

I heard tell elsewhere of using J309 as a constant current source. Idss can get up ~30mA. Or you can look at J310 which the datasheet shows as a Idss of 24mA to 60mA. I suspect you can drop either of these in on the board.
I was hunting around a bit on this, if anyone cares, and the Fairchild PN5482 is pin-compatible with the 2N5486, J309, and J310, and per the datasheet has a minimum Idss of, ahem, 150ma. It's also actually stocked by Mouser, yay. Might be worth playing around with, for people who like their transistors warm.
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