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Old 29th September 2002, 02:18 AM   #1
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Default Amp for low impedance ...???

Hello,
sorry for my poor englisch language, but I've some questions:

I can get some amounts of 2N 3773 realy cheap (Price about 0,30 $), but only the NPN not the PNP (2n6609)

-is the 2N3773 suitible for Audio (bass Amp only) or is it useless?
the PDF file looks good so far
here's a link with spec's: http://www.onsemi.com/pub/Collateral/2N3773-D.PDF
(150W @100V, hfe=15@ 8A min, Ic= 16/30 A(peak) 150 W 140V)
-because there are no cheap PNP 2N6609 (complementary of 3773) i've thougt "re"designing a Quasicomplementary Amp
I found a schematic but i want modify it to 2n3773 but lower supply Voltage (+-65 Volts) for lower output impedance (i want achive 2 ohms or so)
-I know Quasi Complementary Designs are from the 70ies but ist the sound realy so bad?
is it suitible for Bass in Bi Amped system?

original Transistor was MJ15024 & much higher Supply but I want to drive low impedance Speakers
so 2x6 of the 2N's I Think are good for driving 1,5... 2 Ohm's @ +-65 Volt ???

any comments? try it oder not???
thank you,
Stefan

edit:schematic simplified to the basics...
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Old 29th September 2002, 07:42 AM   #2
djk is offline djk
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How fast are these 2N3773s? The Motorola (ON) are 4Mhz. I got some $0.30 Solitron 2N3773s, they aren't fast enough for an audio amplifier. In any event I would use a tripple output stage, (pre-driver, driver, and then the outputs) otherwise you won't have enough current gain.
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Old 29th September 2002, 09:06 AM   #3
djdan is offline djdan  Romania
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For 2N3773 Ft = 0.3Mhz so the amp can work only for subbass aplication. If you have good devices made by Motorola or ON Semiconductors ( Toshiba branded are counterfit ) , you will can make a good and very cheap amp.
I used this parts year ago , and I have good impresions .
( Only for general audio , like PA or something like this ).

For pre-drivers I strongly recomend 2SC5200/2SA1943 . If you will use something smaller the fail will be posible.

Please tell us about your progres about this project.

Regards !
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Old 29th September 2002, 09:23 AM   #4
djdan is offline djdan  Romania
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I saw many negative opinions about " low impendance " subject in this forum.

If the power devices are very cheap, what is the problem to use 60 pieces for a single power amp and leave any curent protection away ?

(Only 7w - 8w disipation for tranzistor).

In this case will cost 36 $ for 120 pieces 2N3773 . I saw too many bad schematics with a single pair of power tranzistors selled with 100$ or more.

For somebody how like to make audio amps ( DIY ) it is somethig fun and interestig to built this kind of experiments.

Regards !
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Old 29th September 2002, 01:41 PM   #5
skaara is offline skaara  Slovenia
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ON Semi is part of Motorola company..
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Old 29th September 2002, 06:46 PM   #6
djdan is offline djdan  Romania
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I know that, but I speak about 2N3773 , a very old part made by Motorola 20 years ago . It is posible to buy some old stock or something similar and that is the reason to mention " Motorola" .
On Semiconductors is much younger .

Regards !
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Old 29th September 2002, 06:53 PM   #7
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thank You for so much reply!

Yes I see, the Driver must be very strong because of the small hfe
the base current becomes high of the output stage the driver should deliver it ...

You mentioned the 2SC5200/2SA1943 - I think there is a risk of getting counterfeit transistors (toshiba I think is a very good "chance" to get counterfeit)
what would be alternatives - if there are some one?
BD139/140 ist tooo small i think
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Old 29th September 2002, 07:36 PM   #8
djdan is offline djdan  Romania
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2SC3264/2SA1295

2SC3858/2SA1494

MJL21193/MJL21194

MJW21194/MJW21195

If you want to make something unusual ( but very rugged ) you can put a pre-driver on every power devices and you can used something small like MJ15030/15031 or similar.
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Old 29th September 2002, 08:16 PM   #9
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Stefan, if you don't want speed (was it a bass amp?) why don't you consider MOSFET's? The drive power will be rather small even at low impedances. Four pairs will probely do. 5 to 15 mA is possible as current for the whole driver.
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Old 29th September 2002, 08:57 PM   #10
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Bass amp: It should be for my subwoofer 15...100 Hz active crossover @100 Hz

hm Mosfet Amp: I'm afraid i get an oscilating Amp ???
the 2n3773 are cheap available cheap Mosfet's i've no idea

driver's: hm Ive to visit local electronic shop tomorrow if there are good driver Transistors available

thank you for the Idea with "multiple" dirvers
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