G8MNY > TECH 23.04.22 08:23z 68 Lines 2643 Bytes #6 (0) @ WW
BID : 646_GB7CIP
Subj: Dual phase AF AMP explained
Sent: 220423/0821Z @:GB7CIP.#32.GBR.EURO #:646 [Caterham Surrey GBR] $:646_GB7C
To : TECH@WW
By G8MNY (Updated May 06)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
/'\./ ³\ /'\./ \./'\ /³
ÚÄÄÄ³ '>ÄÄÄÄÄÄ L S ÄÄÄÄÄÄ<' ÃÄÄÄ¿
³ ³/' `\³ ³
/'\./ ÚÄÄÄÄÄÄÄÄ¿ ³ ³
______³ PHASE ÃÄÙ ³
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....
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)
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 2V peak to peak can be handled.
But it is more usual to attenuate the output of the 1st amplifier by the gain
of the 2nd amplifier & feed it into the inverting input of the 2nd amplifier.
/'\./ ³\ 1 /'\./ \./'\ 2 /³ R1+R2
I/P ÄÄÄÄ´ `>ÄÄÂÄÄÄÄÄ L S ÄÄÄÄÄÄ<'-ÃÄ¿ AMP2 GAIN = ÄÄÄÄÄ
³/' ³ `\³ ³ R2
But with this simple method you do get 2x the distortion out of the 2nd
N.B. If on single power rail (eg. 12V car radio) these amplifiers often DC on
the LS rails!
Why don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
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