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Old 10th January 2019, 08:19 PM   #21
rensli is offline rensli  Estonia
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Quote:
there are only the output transistors that are "not too much"
critical.
Sry, but in my opinion, there was nothing better then a pair of 2SC2922 and MJE as it is.

2SC2922 is absolute also

Different outputs means that everything must be replaced
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Old 10th January 2019, 08:32 PM   #22
huggygood is offline huggygood  France
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yes,for sure
real sc2922 but not a chinese sc2922 ...
i used a bd 743c but in low power (nap 110/140) with a big pleasure .
i have a lot of real sc2922 but i do not to use them now,i start collecting a elements for building a nap 90/110
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Old 10th January 2019, 08:32 PM   #23
huggygood is offline huggygood  France
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bd 901 also
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Old 10th January 2019, 08:34 PM   #24
huggygood is offline huggygood  France
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saw how it went, i will end up building a naim resli and naim jeffyoung, i love your work to both
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Old 10th January 2019, 08:40 PM   #25
rensli is offline rensli  Estonia
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Quote:
have a lot of real sc2922
with bd 743c and bd 901 you could make very good sounding small amplifier:

Upper RC filter 27R+33R+470pF, lower RC filter 560R+390R+470pf, dont forget MJE253/243 + use 68uF Solid tants on feedback and bias, ESR of ~0.5 - 0.6R

then i would make small PSU +/- 25V, better if regulated with 300VA toroid.

This setup should give plausable BASS response, very very tight with the inductor at the output.
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Old 10th January 2019, 08:46 PM   #26
huggygood is offline huggygood  France
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I have to look at my 110/140 to see what I did, but I'm already extremely happy.
Thank you for the info
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Old 11th January 2019, 02:35 AM   #27
Ian Finch is offline Ian Finch  Australia
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Reply to Jeff's first draft:
That's very impressive presentation and nice PCB work .
Incidentally, the bias voltage between TP1 and TP2 should be approximately 2 x 7.2mV for a Naim clone.
As you can read in Julian Vereker's interviews, his concern for the type of output transistor was focused on switching speed to reduce crossover artefacts. Power transistors were still quite slow in the 70s and switching types, such as BDY56,58 that were produced for SMPS and similar applications, were preferred - even to more linear power transistors.

Now that we do have very fast power transistors, its possible to switch fast and have good gain linearity - the best of both, as Naim quickly realised when they adopted the fastest Sanken LAPTs back in the 1980s. They haven't stopped there and their latest models continue to exploit more exotic output semis in the push for faster switching speeds, better linearity etc.

I wouldn't seriously consider the slow MJ series of power transistors. BUV20 is more in the medium speed switch category of the early Naim transistor types like BDY56 and 58. However, they are also history in terms of sound quality now and it would be a retrograde step to use them IMHO, when you can still buy OEM 2SC2922 type Sanken LAPT transistors in a TO3P package. 2SC3263 is the direct (same chip) replacement type. Profusion in the UK carry a good range of Sanken power semis including this one and I don't see any dissipation problems using the smaller package, given the realistic power limits for domestic use. A substantial heat spreader bar and thick case is the key to Naim reliability in any event.
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Last edited by Ian Finch; 11th January 2019 at 03:02 AM. Reason: add bias comment
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Old 11th January 2019, 06:49 AM   #28
indianajo is offline indianajo  United States
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I bought some allegro sanken 2SC3263 from newark US in 1/17. That is farnell here. Also 2SA1194. Newark generally sells OEM parts.
2SC3263 measure 36 nf b-c with a parts express C meter, whereas MJ21194 from Newark measure 1.1 nf. It is a little vague to me why the 2SC3263 is supposed to be faster Ft (30 mhz) than the MJ21194 (4 mhz).
People forget that 70's output transistors were 800 khz Ft, not 4 mhz like the 2n3055 datasheet now. Vile sound of ST-120 in reviews was cleaned right up with MJ15015 outputs.
Nice layout JeffYoung. 2 output transistor board is useful. I find it strange that all the kits offered by diyaudio store or vendors on vendors forum here are either class A, 10 W (ampcamp), 400 W (honeybadger) or vacuum tube. My point to point Apex AX6 was 70 W with one pair OT, but it took about 100 hours to build. 35 to 70 W is useful with 8 ohm 102 db @ 1W1m speakers in my music room. AX6 fits on a 3.5" X 5.5" card (external OT) as did the ST-120 PC14. Honeybadger is about 6 times the size.
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Last edited by indianajo; 11th January 2019 at 06:58 AM.
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Old 11th January 2019, 07:35 AM   #29
traderbam is offline traderbam  Canada
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What’s with the silvered mica Miller cap?
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Old 11th January 2019, 07:42 AM   #30
traderbam is offline traderbam  Canada
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C10 must not connect to the input gnd on the PCB. It must be wired directly to the psu star ground.
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