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Old 2nd July 2013, 09:31 AM   #61
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Quote:
Originally Posted by borys View Post

Can someone can give me some advice please, would be better off to replace the vas transistors with the same as in driver stage - I mean 2SC4793/2SA1837 pairs in vas and in driver stage ??



Thanks
I believe that this could be good option for BJT outputs version. You should try them.
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Old 2nd July 2013, 01:54 PM   #62
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Originally Posted by ivanlukic View Post
In fact, John Linsley Hood proved these vertical mosfets by Toshiba to be the most linear devices, more linear than BJT and LatMosfet, when used in circuits (not per se) in his famous experiment with classic Lin topology.
I would not contradict JLH, (which would be silly), but I think the rest of us often do not interpret correctly what people like JLH or Nelson Pass say and write. I very much doubt that when he said "in circuits", he meant in every kind of circuit imaginable.

Having said that, I agree that this would be worth exploring, and in fact I bought 4 each from NicMac with something like that in mind. Except for the cost of shipping them from Italy to the US, the price seems reasonable for what you get, in terms of tested and matched parts, and he ships VERY promptly, and well packaged.

The main issue I see is controlling a layout and the rest of the parts well enough for a valid experiment which is repeatable by other people, and consistent in comparison testing...

Although my experience with audio is limited, I have been through this in other (instrumentation-type) applications, and getting consistent, and repeatable results that depend on the linearity of power semiconductors, and especially complementary pairs of power transistors, is a big job. By that I mean an order of magnitude bigger that the effort I have put into the through-hole version of VSSA/PeeCeeBee.

Not trying to be discouraging, b/c I would like to do it myself, , but just realistic...
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Old 2nd July 2013, 06:04 PM   #63
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Originally Posted by PMI View Post
I would not contradict JLH, (which would be silly), but I think the rest of us often do not interpret correctly what people like JLH or Nelson Pass say and write. I very much doubt that when he said "in circuits", he meant in every kind of circuit imaginable.

Having said that, I agree that this would be worth exploring, and in fact I bought 4 each from NicMac with something like that in mind. Except for the cost of shipping them from Italy to the US, the price seems reasonable for what you get, in terms of tested and matched parts, and he ships VERY promptly, and well packaged.

The main issue I see is controlling a layout and the rest of the parts well enough for a valid experiment which is repeatable by other people, and consistent in comparison testing...

Although my experience with audio is limited, I have been through this in other (instrumentation-type) applications, and getting consistent, and repeatable results that depend on the linearity of power semiconductors, and especially complementary pairs of power transistors, is a big job. By that I mean an order of magnitude bigger that the effort I have put into the through-hole version of VSSA/PeeCeeBee.

Not trying to be discouraging, b/c I would like to do it myself, , but just realistic...
Pete,

That's good (critical) thinking. I am just retelling some old stories. JLH did that experiment because people like Doug Self claimed that vertical mosfets (and mosfets in general) are unsuitable for linear applications like audio power amps because of low basic linearity. Doug used some simulation programs and JLH wanted to see for himself so he built the same circuit with different output tranies, measured and showed that Toshiba's vertical mosfets are more linear in that particular circuit than both excellent BJTs and IGBTs by the very same Toshiba. The whole thing started because Toshiba wanted to prove that (than) new IGBTs are the best.
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Old 2nd July 2013, 08:10 PM   #64
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Originally Posted by borys View Post
As I promissed. Prototype schematic bellow.
The C15 and C16 are not required (100pF), only the 33p are needed (reducing small overshoot on pulse response).
I have try some higher voltage transistors for vas and input stage.
Hi Borys, what is C5 C6 (1mF) voltage rating?

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Old 2nd July 2013, 09:31 PM   #65
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Originally Posted by Idefixes View Post
Hi Borys, what is C5 C6 (1mF) voltage rating?

Marc
There is around 0.85v on them so 6,3V 10V will do the job.
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Old 3rd July 2013, 08:04 AM   #66
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Today I have soldered vas - 2sc4793/2sa1837 with 22pF compensation cap, results bellow.
Attached Images
File Type: png vas 2sc 2sa 22pf.png (126.3 KB, 787 views)
File Type: png vas 2sc 2sa step 20kHz 22pf.png (112.6 KB, 768 views)
File Type: png vas 2sc 2sa.png (132.2 KB, 747 views)
File Type: png bjt vs fet.png (388.3 KB, 723 views)

Last edited by borys; 3rd July 2013 at 08:11 AM.
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Old 3rd July 2013, 08:43 AM   #67
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Originally Posted by borys View Post
Today I have soldered vas - 2sc4793/2sa1837 with 22pF compensation cap, results bellow.
Instead of BD139/140 than...

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Old 3rd July 2013, 10:37 AM   #68
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Originally Posted by Idefixes View Post
Instead of BD139/140 than...

Marc
Yes instead off bd139/140, so I have putted same transistors in vas and driver stage
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Old 3rd July 2013, 12:51 PM   #69
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Originally Posted by borys View Post
Yes instead off bd139/140...
These come in different speeds (see suffix), so it would be helpful if you posted which ones you are using. So, BD139/14016STU are fairly fast, and available from Fairchild. Without the -16 suffix, perhaps not so fast, but they still seem to give a good result in your test. KSA1220/KSC2690 is also available, and proposed in the PeeCeeBee thread as alternative to KSA1381/KSC3503.

I built my version of PeeCeeBee with unmatched KSA1381/KSC3503, with good results so far (although I would prefer to use a true complementary pair in the future).

Here is a link to some test results, and below my post there are more scope pics from another through-hole VSSA version by Nikosokey.

(My tests were done with 47uF compensation cap)

Square Wave Test
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Old 3rd July 2013, 02:52 PM   #70
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Quote:
Originally Posted by PMI View Post
These come in different speeds (see suffix), so it would be helpful if you posted which ones you are using. So, BD139/14016STU are fairly fast, and available from Fairchild. Without the -16 suffix, perhaps not so fast, but they still seem to give a good result in your test. KSA1220/KSC2690 is also available, and proposed in the PeeCeeBee thread as alternative to KSA1381/KSC3503.

I built my version of PeeCeeBee with unmatched KSA1381/KSC3503, with good results so far (although I would prefer to use a true complementary pair in the future).

Here is a link to some test results, and below my post there are more scope pics from another through-hole VSSA version by Nikosokey.

(My tests were done with 47uF compensation cap)

Square Wave Test
Yes bd were -16 the high gain ones, they are doing good job but only up to +/-40V
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