"Watson A.Name - \"Watt Sun, the Dark Remover\"" wrote in message ...
Opinions on this, especially the 2.5W amp schem at the bottom.
http://www.intio.or.jp/jf10zl/EF.htm
When the amp is idle, and there's no(?) current flowing in either output
transistor because there's no forward bias, then the V drop 'resistance'
of the E-B junction adds to the 100k feedback resistor, so the loop gain
increases to the open loop gain. So it would seem that the amp would
attempt to hunt in this region, possibly oscillating?
I just simulated the circuit in LTSpice using LT1113's instead of
the TL084. It simulates quite nicely. The feedback causes the base
drives to swing through the "crossover" region so that's no problem.
Here's a "cut-n-paste" ASCII file for the input to LTSpice:
Version 4
SHEET 1 880 680
WIRE -16 384 16 384
WIRE 144 144 48 144
WIRE 16 144 16 384
WIRE 16 384 144 384
WIRE 144 112 96 112
WIRE 96 112 96 240
WIRE 96 352 144 352
WIRE 208 128 288 128
WIRE 208 368 288 368
WIRE 352 176 352 240
WIRE 352 416 352 464
WIRE 352 80 352 32
WIRE 96 240 352 240
WIRE 96 240 96 352
WIRE 352 240 352 320
WIRE 496 240 448 240
WIRE 448 512 448 480
WIRE 448 416 448 368
WIRE 448 288 448 240
WIRE 448 240 352 240
WIRE 560 240 592 240
WIRE 624 240 624 336
WIRE 624 416 624 512
WIRE -16 240 96 240
WIRE -96 240 -128 240
WIRE -128 240 -128 368
WIRE -128 368 -160 368
WIRE -80 368 -128 368
WIRE -320 368 -288 368
WIRE -288 432 -288 368
WIRE -288 368 -240 368
WIRE -288 496 -288 528
WIRE -480 416 -480 368
WIRE -480 368 -384 368
WIRE -480 496 -480 528
WIRE -400 0 -400 48
WIRE -256 48 -256 0
WIRE -80 400 -128 400
WIRE -128 400 -128 448
WIRE 592 240 624 240
WIRE 48 144 16 144
FLAG 176 96 +14
FLAG 176 336 +14
FLAG 352 32 +14
FLAG 176 160 0
FLAG 176 400 0
FLAG 352 464 0
FLAG 448 512 0
FLAG 624 512 0
FLAG -288 528 0
FLAG -480 528 0
FLAG -48 352 +14
FLAG -400 0 +14
FLAG -256 0 +7
FLAG -400 128 0
FLAG -256 128 0
FLAG -128 448 +7
FLAG 592 240 out
FLAG 48 144 1st
FLAG -48 416 0
SYMBOL Opamps\\LT1113 176 304 R0
SYMATTR InstName U1
SYMBOL Opamps\\LT1113 176 64 R0
SYMATTR InstName U2
SYMBOL Opamps\\LT1113 -48 320 R0
SYMATTR InstName U3
SYMBOL pnp 288 416 M180
SYMATTR InstName Q1
SYMBOL npn 288 80 R0
SYMATTR InstName Q2
SYMBOL res 432 272 R0
SYMATTR InstName R1
SYMATTR Value 10
SYMBOL cap 432 416 R0
SYMATTR InstName C1
SYMATTR Value .1µ
SYMBOL cap 560 224 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName C2
SYMATTR Value 470µ
SYMBOL res 0 224 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R2
SYMATTR Value 100k
SYMBOL res -144 352 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R3
SYMATTR Value 10k
SYMBOL cap -320 352 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName C3
SYMATTR Value .05µ
SYMBOL cap -272 496 R180
WINDOW 0 24 64 Left 0
WINDOW 3 24 8 Left 0
SYMATTR InstName C4
SYMATTR Value .001µ
SYMBOL res 608 320 R0
SYMATTR InstName R4
SYMATTR Value 4
SYMBOL voltage -480 400 R0
WINDOW 3 -177 -127 Left 0
WINDOW 123 -172 -91 Left 0
WINDOW 39 -128 98 Left 0
SYMATTR InstName V1
SYMATTR Value SINE(0 .5 1000)
SYMATTR Value2 AC .2
SYMATTR SpiceLine Rser=1k
SYMBOL voltage -400 32 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value 14
SYMBOL voltage -256 32 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value 7
TEXT -72 -64 Left 0 !.tran 10m