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Old 20th December 2012, 08:57 AM   #581
Marra is offline Marra  United Kingdom
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Quote:
Originally Posted by deadhead View Post
Where can we buy Diotec from?

Conrad

Diotec BC327/40 Transistor PNP TO 92 1AA -45VV from Conrad Electronic UK
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Old 20th December 2012, 09:02 AM   #582
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BC337-40TAPE DIOTEC | SOS electronic
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Old 20th December 2012, 10:32 AM   #583
hesener is offline hesener  Germany
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Quote:
Originally Posted by deadhead View Post

I would like the designers to write down in simple terms what values I should aim for and what should match what.
Hi everybody, the matching is not really that critical or difficult.

On the input stages, the absolute BEST would be to have 8 PNPs and 8 NPNs that have matched gain, collector-base leakage current and no noise issues.

Unfortunately that will require expert equipment, so we can make do with just matching 8N and 8P with current gain, that is good enough in 99.9999% of the cases. To match the current gain between the left and right channel input stages will help to remove gain differences between the channels, helping imaging. If that cannot be done, at least the NPNs and PNPs of the input stage should match between each other (within N and within P separately, that is).

This input stage is the key piece of the amplifier, so spending time to make the match as good as possible is definitely worth it. While you are at it, you may want to match the 33Ohm resistors as well, their influence is less (and 1% resistors are already pretty good), so that may be borderline to overdoing it.

How good is good enough? If you can get the matching down to +/-10% that is good. More precise is better of course but obviously tends to be a little difficult. My recommendation would be to try and achieve closest possible matching for the input stages, and then match every other subcircuit within itself.

For the other subcircuits of the amplifier, take a look at the schematic in the assembly guide, it has circles around sections of the circuit in which the transistors should match to each other. They do not necessarily have to match to the other devices. This is because the transistors in these subcircuits work closely with each other, and outside of those the absolute parameters don't matter much for the function of that subcircuit, thanks to the great design that MiiB did.

On the absolute numbers, the circuit will work with pretty much all the values in the -40 grade, so thats not an issue. The team has a feeling that if the current gain gets very high (above 550 or so), the amplifier may have a tendency to oscillate, but we did not perform all the tests to make sure that that REALLY is the reason. It is clear though that with lower values it should not oscillate. My recommendation would be to use values around 400 for both N and P for the input stage, whereas the other parts of the circuit can use higher gains (but please make sure you have those decoupling caps in place on the bottom side of the PCB).

Hope that makes it clearer!
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Old 20th December 2012, 11:52 AM   #584
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Originally Posted by hesener View Post

Hope that makes it clearer!

Brilliant.... many thanks.
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Old 20th December 2012, 12:36 PM   #585
Max1410 is offline Max1410  Germany
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@Heesener
for example: hfe 400 +/- 10% that is between hfe360 till hfe 44, is that enought, really??? You are sure?
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Old 20th December 2012, 12:43 PM   #586
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Yes, that will work.
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Old 20th December 2012, 01:31 PM   #587
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Quote:
Originally Posted by Max1410 View Post
@Heesener
for example: hfe 400 +/- 10% that is between hfe360 till hfe 44, is that enought, really??? You are sure?
Told you so in post 568

Sems that placing spelling mistakes on my posts to keep you lot attentive does not work anymore

YEA HE IS blipping blopping sure

10 % is cooooooooooooool but 5 is beter but not so cooooooooooooooool if it get you worry

Last edited by Bksabath; 20th December 2012 at 01:34 PM.
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Old 20th December 2012, 02:12 PM   #588
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Well, the emitter resistors in the input stage and in the mirrors are decent sized. That provides local current feedback and erodes small differences in Hfe anyway. 10% match and Hfe of 400 is really fine.
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Old 20th December 2012, 02:36 PM   #589
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Thanks Alfred and Joachim.

That should be no problem... I find octets within 2% matching at hfe of 470, and octets within 1% at 490-500.
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Old 20th December 2012, 02:37 PM   #590
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Very good.
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