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G8MNY > TECH 16.06.08 07:12l 65 Lines 2530 Bytes #999 (0) @ WW
BID : 59184_GB7CIP
Read: GUEST
Subj: Dual phase AF AMP explained
Path: IZ3LSV<IK2XDE<DB0RES<ON0AR<GB7CIP
Sent: 080615/2200Z @:GB7CIP.#32.GBR.EU #:59184 [Caterham] $:59184_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
By G8MNY (Updated May 06)
(8 Bit ASCII Graphics use code page 437 or 850)
/'\./ ³\ /'\./ \./'\ /³
ÚÄÄij '>ÄÄÄÄÄÄ L S ÄÄÄÄÄÄ<' ÃÄÄÄ¿
³ ³/' `\³ ³
/'\./ ÚÄÄÄÄÄÄÄÄ¿ ³ ³
______³ PHASE ÃÄÙ ³
³INVERTERÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ
ÀÄÄÄÄÄÄÄÄÙ \./'\
(phase splitter)
The LS sees 2x the voltage of a normal single amplifier arrangement. That is 4
times the power! e.g. a 4ê LS with 0V & 13V DC on the amplifier may give ñ 12V
peaks to the LS. Peak crest power = 12 x 12 / 4 = 36W peak, = 18W RMS.
Or for typical commercial disco amplifier may use ñ90V @ 22A PSU to power a
pair of amplifiers in bridged to 8ê LS load, to give a peak power of
179 x 179 / 8 = 4kW peak crest power (USA rating), or 2kW RMS. Although this
sounds big they are made this size! But the power rails usually dip a lot under
heavy load, but 4kW peak pulse is what the loud speaker system has to handle!
The phase inverter/splitter could be just this....
ÚÄÄÄÄÄÄÄÄÄÄÄsmoothed +ve
1kê
ÚÄÄÄÄ´ 1uF
220kê ÃÄÄÄÄ´ÃÄÄÄÄÄ phase inverted by 180ø
/'\./ ³ ³/ + \./'\
Input ÄÄÄÄÄ´ÃÄÁÄÄ´ NPN
0.1uF ³\e 1uF /'\./
ÃÄÄÄÄ´ÃÄÄÄÄÄNON inverted (sames as I/P)
1kê +
ÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄ
The identical 1kê in emitter & collector give the same output if there are no
significant following different circuit loads. The bias 220kê should be
selected to give about 1/2 the voltage across the transistor. e.g. on a 12V
supply emitter = 3V, collector = 9V, so there is 6V across the transistor, then
about 4V peak to peak can be handled.
But it is more usual to attenuate the O/P of the 1st amplifier by the gain of
the 2nd amplifier & feed it into the inverting input of the 2nd amplifier.
AMP AMP
/'\./ ³\ 1 /'\./ \./'\ 2 /³ R1+R2
I/P ÄÄÄÄ´ `>ÄÄÂÄÄÄÄÄ L S ÄÄÄÄÄÄ<'-ÃÄ¿ AMP2 GAIN = ÄÄÄÄÄ
³/' ³ `\³ ³ R2
R1 ³
ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ
R2
_³_
////
But with this simple method you do get 2x the distortion out of the 2nd
amplifier!
Why don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
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