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Old 9th January 2004, 08:57 PM   #11
esl is offline esl  Poland
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BTW. what's your opinion on these transistors?

Greetz

esl
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Old 10th January 2004, 01:44 AM   #12
jcx is online now jcx  United States
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Hugh,

are you talking npn - npn, pnp - pnp matching? could you comment on npn - pnp matching? do the parameters overlap at all?
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Old 10th January 2004, 02:42 AM   #13
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ESL,

I'd try with 10 pairs of each to begin with, and focus first on Vbe at the same collector current/temperature, then test within each sample on beta. Measure Vbe at the same collector current as the bias setting, and at a constant, low Vce voltage (say 6V); this is important. And do it quickly; it changes 1.5mV/degree C as the devices warm up. Use a rapid sampling DMM like a Fluke.

Of course matching also depends on the tolerance you choose; looser tolerance will mean less devices need be purchased. I try for only 1mV on Vbe (like devices) and 2% on beta, but if you relax the beta tolerance, possible with larger 0R47 emitter resistors, you might find matching easier....

These are very good transistors, extremely linear, very fast, acceptable SOAR, and inexpensive. I like 'em a lot, and feel that they easily best the MJL21193 series. You will find most contemporary high end amps use these devices.

JCX,

I don't even try to match NPN versus PNP. The argument is spurious in my view; I use the Self Type II DEF output stage with charge suckout and believe it's fatuous to match unlike devices. However, matching like devices is VERY important, as the slightest mishap as the musical baton is passed along at crossover is very readily audible. Any differences in beta or Vbe with Ic are absorbed relatively well in the NFB loop; but crossover disjunctions are poorly corrected, and thus all four NPNs should turn off at the same time as the four PNPs are turning on (and vice versa!). This is one reason why large power amplifiers with multiple output pairs never sound as good as little amps with only a single pair.

Cheers,

Hugh
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Old 14th January 2004, 12:10 PM   #14
esl is offline esl  Poland
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Hello,
thanks Hugh 4 your input. Yes, I am going to order 10 pairs
of Toshibas for starters and then match them as you said.

There's however one thing that I don't get. The fact, that when
the signal crosses the point where "NPNs should turn off at the
same time as the four PNPs are turning on". Does it means that
the more the amp is biased into Class-A the less is it susceptible
to these distortions. I mean - can I use more less precisely
matched devices biased at higher quiescent current ot not?

Could also anyone provide me with a shematic of power supply
consisting of two transforers per channel? (ie. one transformer
per rail as far as I remember, there was some trich used by
Electrompaniet in their higher-end amps with double transformers,
could anyone have any input on this?)

Which rectifier diodes are better: slow ones or fast ones? Is it
dependable on PWR supply configuration etc. etc. ?

Thanks,

esl
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Old 14th January 2004, 12:30 PM   #15
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Default Matching

In my 400 W amp I am using six pair of these transistors without any matching ( only take this from one plastic transport tube ). Balast resistors are 0,47 R. Maximal current difference between each currents is about 2 % (measured as voltage on balast resistors at full load ) = all transistors ( from one series ) are practicaly the same.
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Old 14th January 2004, 12:35 PM   #16
esl is offline esl  Poland
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Hello,
I was told that all the transistors I am going to buy are
from the same batch, so as far as I'm concerned precise matching
is good but not crucial?

btw. how does your amp sounds? any likt to schematics?

esl
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Old 14th January 2004, 12:51 PM   #17
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To esl : " Stop blowing your own trumpet " - how it sounded, it must say other. Schematic is know how of one firm, so I am sorry. Matching is good in case, if transistors have low value balast resistors - with 0,47 R isn't necessary.
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Old 3rd February 2004, 09:09 AM   #18
esl is offline esl  Poland
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Finally...
... I got some output transistors, form the same batch, gonna
match them ASAP... some new ideas...

Since my Martin Logans are rated at 200W/channel with
impedance ranging form 4 ohm (1KHz) to 2.5 ohm (15 KHz),
I wonder how many pairs to go for a single channel so that:
- it goes into Class - A as far as it's reasonable (30 W??? 50W???)
- I get 80 W@8ohm/160@4ohm and about 200@2 ohm and
still transistors work in their SOA

What about using a tube in the input stage?

What about drivers? FETs or BJTs? And what topology?

As for the power supply - I can but some 68000uf/63V Kendeil
caps (four of them)... would it be good or maybe such a huge
capacitance would be an overkill? Shouldn't I stick to smaller
values conected in parallel?
Is there anything more than a trafo, caps and bridge required
in a good power supply? Any filtration?


Thanks

esl
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Old 3rd February 2004, 04:12 PM   #19
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Its all very well having all these matched pairs of trannies but what about the amp design?? Surely it would be a good idea to find a design first. No?
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Old 3rd February 2004, 04:19 PM   #20
esl is offline esl  Poland
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Yes, but bear in mind that I want to use tube as an input stage, followed by fet and then these 2sa5200/2sc1943...
... is there any design that I could use and make some changes so
that it can have a tube as an input stage?

Sorry for so lame question, but I just want to know whether does
it take a lot of reworking some orginal schematics to get rid of
(usual) diff input pair and use tube instead...

Or maybe sth like that... say, 6992 input tube, then jfet diff pair and
then Toshibas as a follower?

What do you think?

esl
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