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Old 7th April 2012, 08:51 PM   #7501
Salas is offline Salas  Greece
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In your version Vce is at about 10V and in MC version at 5-6V so that base is covered for all those BJTs discussed since the signal is miniscule in that stage. From the easier available ones, the 2SC2240BL and BC337/338-40 combine desirable traits of high hfe, high impedance Ic/Vce characteristics and low internal resistance. Not champion low, but low. Both will be nice to pitch against BC550C which is largely adequate in that position and see if you can actually feel any change. Kean is welcome to comment further.
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Old 8th April 2012, 07:30 AM   #7502
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The BC337-25 are better than the BC550 at the qualities I mentioned. I know this because my Kmultiplier requires very good Vcesat characteristics. One much overlooked issue with BJTs is that a changing Vce not only causes base leakage, but it also causes changes in Vbe. This was the problem with my Kmultipliers; base leakage was not a problem because source impedance was low; but that didn't matter because when the BJT enters the quasi-saturation region, Vbe starts to wander much with Vce.

This perspective might not matter so much for BJTs with 5V Vce, although it still applies. It may be that the C2240 beats all these categories, but I don't think so because it is a high-voltage transistor and my experience is that low-voltage transistors have the best collector impedance.

Salas has more practical experience so I would go with his advice. The one thing I stress is that any time there is base leakage, Vbe also wanders, so Vcesat be more important than you think.

An excellent low-voltage transistor with good Hfe characteristics is the PEMZ7 from NXP, and it's family. That negative collector impedance region could be dangerous though...
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Old 8th April 2012, 10:03 PM   #7503
Djinn is offline Djinn  Norway
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I checked around a little and the BC338-40 has even lover voltage 30V vs. BC337 that has 50V, and the 40 indicates higher hfe and that should be good?

I will in the end try both some off the high voltage versions of the Q5 transistor in question and some off the lower ones, and see if I can hear any difference with the Stax lamda pro earphones toghether with the driver SRM-717. I will both try out some of the 2sc's and the BC's.

All off this will take it's time off course, because I will do a good Hfe matching, and of cource getting a hold of them at a reasonable price. The results I find will be posted. :-)

With kind regards

Martin
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Old 8th April 2012, 10:35 PM   #7504
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Niko kalispera

Could you please have a look at the IDSS values below?
Can any of those be used on the pre-pre stepup? (7ma IDSS required per the pdf)

Thanks in advance

Quote:
Originally Posted by dimkasta View Post
7,22
8,47
8,76
8,95
9,01
9,21
9,4
9,44
9,49
9,49
9,52
9,68
9,68
9,72
9,72
9,76
9,77
9,8
9,8
9,81
9,91
9,92
10,04
10,05
10,1
10,15
10,2
10,21
10,3
10,3
10,3
10,32
10,33
10,34
10,4
10,42
10,42
10,45
10,48
10,49
10,52
10,62
10,64
10,67
10,75
10,76
10,8
10,93
11,04
11,12

Thanks again
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Old 8th April 2012, 10:36 PM   #7505
Salas is offline Salas  Greece
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@ Martin

Higher hfe is good.
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Old 8th April 2012, 10:52 PM   #7506
Salas is offline Salas  Greece
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Quote:
Originally Posted by dimkasta View Post
Niko kalispera

Could you please have a look at the IDSS values below?
Can any of those be used on the pre-pre stepup? (7ma IDSS required per the pdf)

Thanks in advance
You can certainly make two channels by using this group in first+last pair, middles pair.

8,47
8,76
8,95
9,01

Add 3R3 source pin resistor to each one before it meets the common ground.
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Old 8th April 2012, 11:02 PM   #7507
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Thanks a lot Niko

About the source resistor, that is one for each jfet? or one for each pair/channel?
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Old 8th April 2012, 11:15 PM   #7508
Salas is offline Salas  Greece
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One for each to balance them out and cut on Id and temp. Its only 1.65R equivalent bcs in parallel, no significant noise worries it will add.
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Old 9th April 2012, 12:46 AM   #7509
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Quote:
Originally Posted by Djinn View Post
I checked around a little and the BC338-40 has even lover voltage 30V vs. BC337 that has 50V, and the 40 indicates higher hfe and that should be good?

Martin
Got a 1000 BC337-40 fresh from Fairchild
how many do you need?
how well matched?

Some how my Simplistic second build gone in back burner....
And got BC337 for other project now on back burner as well
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Old 9th April 2012, 02:35 AM   #7510
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If it were me, I'd choose the lowest Hfe grade I could get away with, as Vcesat characteristics get worse with higher Hfe. From the datasheet curves it seems that different voltage parts of the same family, like the BC546 and BC550, have the same Vcesat characteristics, so I do not worry about voltage grades as much as I do about Hfe grades within a family of BJTs. But I don't know for sure. It will be interesting if there are audible differences.
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