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Old 22nd February 2013, 04:06 PM   #1501
PMA is offline PMA  Europe
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Originally Posted by FdW View Post
This is the first time I have seen proof that the BC's are actually making the thing oscillate, who would have thought. Still we do not know why (Iím still thinking too much gain), or what the defect is (tiny
Parasitic impedances, they differ with manufacturers.
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Old 22nd February 2013, 04:20 PM   #1502
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I don't know which brand, they came with the parts group buy. They where BC337 (Q102, Q104), hFE~470. Large picture here. Replaced by the same type.

Another possible reason for problems - I have purchased 1000 Fairchild BC327 from Mouser because the "group buy BC327" had a too low HfE. Havn't had any issues yet, but one of the transistors in the bag had a totally shattered case. I was wondering what happens if a case has a crack that is small enough to not be noticed.

I have a question - I have removed the RIAA resistors that I used first because I will replace them with Rs that have the more linear curve. While I wait for the new Rs to arrive, is it OK to power the amplifier up and start the process of capacitor forming etc. with no RIAA resistors soldered in?

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Last edited by Abraxas336; 22nd February 2013 at 04:44 PM.
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Old 22nd February 2013, 04:42 PM   #1503
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They look like Continental from India.
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Old 22nd February 2013, 04:45 PM   #1504
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Tanks Sven
I also have 1000 each from Fairchild direct those are all pretty Hi HFE which I have used on the R2 build
My batch of GB is also covering different HFE ranges what brand are those anyone knows?
I just received 200 each from Diotec / Conrad's
which I will measure up when possible.

I have started a forum for swap of transistors my apologies if I have not been to active there but hopefully it will pick up gain.

Paradise BCXXX-40
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Old 22nd February 2013, 05:02 PM   #1505
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Now I understand your question Sandro - in general, the group buy 327 have hFE mostly below 400, very difficult to find anything that matches the group buy 337 which concentrate around 480. The Fairchild 327 are concentrated around 440, however it is some kind of bell curve so finding enough 327 to match with the 337 from the group buy was possible. Biggest overlap in the 460 area, as to be expected .

I edited my last post kind of too late, so again my question - I have removed the RIAA resistors that I used first because I will replace them with Rs that have the more linear curve. While I wait for the new Rs to arrive, is it OK to power the amplifier up and start the process of capacitor forming etc. with no RIAA resistors soldered in?

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Old 22nd February 2013, 06:13 PM   #1506
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Put in a 10kOhm to ground, then you have aprox. the same DC conditions then a fully stuffed RIAA.
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Old 22nd February 2013, 06:38 PM   #1507
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Sorry to know so little but I need to ask - put a 10kOhm to the ground from where?
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Old 22nd February 2013, 07:16 PM   #1508
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From the output of the current mirrors to ground.
There has to be a DC path from the mirrors to ground or the DC point would float wild.
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Old 22nd February 2013, 07:29 PM   #1509
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Quote:
Originally Posted by PMA View Post
Parasitic impedances, they differ with manufacturers.
Yes, I know that, what I intended to make clear is; I still do not know what 'exact' is the reason of oscillation, and I (at this moment) think that a little less gain in the Sziklai pair's may be a cure all
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Old 22nd February 2013, 08:19 PM   #1510
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I agree, a Sziklai's pair has always been a potential problem.
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