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Old

B1

Posted 29th January 2010 at 07:58 PM by Cro maniac

I finally gathered some will to deal with my Pass B1 project. I drawed the board in Protel and bought the components at Farnell almost 6 months ago, but never got time/mood/will to assemble it. Wednesday was my day off at work and I had nothing to do at home so I decided it is the Pass B1 day . I printed and made the boards, drilled the holes and lacquered them. Couple of hours later they were ready for soldering the components.
But hey, there is a bag full of 2SK170's that need to be matched prior to soldering ! I managed to get 3 matched pairs and I need only 2. Good enough
My version is the one with Salas regulator with R6 mod so I used the leftovers from matching in supply.
Now, everything is soldered and in place except input coupling 1uF caps and pot that I yet need to buy.

Now when it's nearly completed I don't sleep thinking how should the case for the preamp look like. I would really like to make it from wood.
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Old

Matching BJT's

Posted 27th January 2010 at 08:27 AM by Cro maniac

Yeah, my first blog entry !

I have spent whole day in matching output transistors for poweramp I'm building for a friend.
I found out that Vbe tracks gain pretty good (the transistors with higher gain have proportionally higher Vbe), so I think the painful matching of Vbe at various collector currents is pretty much useless because Vbe spread can be already seen in DC current gain.

If I think of Vbe tracking gain, it is good, because transistor that needs more Vbe will be less opened, but it has higher gain, so collector current will be more equal between devices.
I have 10 pairs of MJ21193 / MJ21194 and plan to use 4 pairs per channel.
Transistors are ordered directly from Onsemi and the NPN's all come from the same batch but PNP's are from 2 different batches and that can be clearly seen from measurements because there is a big mismatch in gain between the 2 batches.

Fortunately, the ones from the same batch are pretty...
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