OK, Thanks.
ISTR Win used a bunch of bipolars to get the noise down to pV/root(Hz) for
ribbon microphones. This required an extremely large input coupling
capacitor to prevent shorting out the base bias and still pass the low
frequencies needed.
I am working on a different approach that DC-couples the input signal to an
op amp, or several in parallel for low noise. There is no couping capacitor
needed, and the op amp eliminates the risk of blowing out the base due to
the high surge current from a power supply. The capacitors in the feedback
network need to be insulated or covered to minimize low frequency voltage
shift due to random air currents affecting the tempco of the capacitors.
Thanks to P. Hobbs for this observation.
I am also working on high attenuation ripple filters for the op amp power
supplies. I'd appreciate your comments.
Here is the ASC file for the input stage:
Version 4
SHEET 1 1888 724
WIRE 544 32 480 32
WIRE 672 32 608 32
WIRE 480 112 480 32
WIRE 528 112 480 112
WIRE 672 112 672 32
WIRE 672 112 608 112
WIRE 720 160 576 160
WIRE 864 160 720 160
WIRE 576 176 576 160
WIRE 720 176 720 160
WIRE 864 176 864 160
WIRE 480 192 480 112
WIRE 512 192 480 192
WIRE 544 192 512 192
WIRE 640 208 608 208
WIRE 672 208 672 112
WIRE 672 208 640 208
WIRE 400 224 384 224
WIRE 544 224 400 224
WIRE 384 240 384 224
WIRE 480 256 480 192
WIRE 576 256 576 240
WIRE 784 256 576 256
WIRE 784 272 784 256
WIRE 864 272 864 256
WIRE 384 336 384 320
WIRE 480 368 480 336
WIRE 528 368 480 368
WIRE 576 368 528 368
WIRE 672 368 576 368
WIRE 720 368 720 240
WIRE 720 368 672 368
WIRE 784 368 784 352
WIRE 480 384 480 368
WIRE 576 384 576 368
WIRE 672 384 672 368
WIRE 480 464 480 448
WIRE 576 464 576 448
WIRE 672 480 672 464
FLAG 384 336 0
FLAG 400 224 Vin
FLAG 640 208 U1O
FLAG 480 464 0
FLAG 528 368 R1C1
FLAG 784 368 0
FLAG 864 272 0
FLAG 512 192 U1N
FLAG 576 464 0
FLAG 672 480 0
SYMBOL voltage 384 224 R0
WINDOW 0 33 22 Left 2
WINDOW 3 37 77 Left 2
WINDOW 123 35 103 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V1
SYMATTR Value 10
SYMATTR Value2 AC 1
SYMBOL opamps\\lt1028 576 144 R0
SYMATTR InstName U1
SYMBOL res 624 96 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R2
SYMATTR Value 4950
SYMBOL res 464 240 R0
SYMATTR InstName R1
SYMATTR Value 50
SYMBOL cap 464 384 R0
SYMATTR InstName C1
SYMATTR Value 10mf
SYMATTR SpiceLine Rser=25m Lser=2n
SYMBOL voltage 784 368 M180
WINDOW 0 33 22 Left 2
WINDOW 3 33 44 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V2
SYMATTR Value 15
SYMBOL voltage 864 160 R0
WINDOW 0 33 22 Left 2
WINDOW 3 33 44 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V3
SYMATTR Value 15
SYMBOL cap 608 48 M270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName C2
SYMATTR Value 100p
SYMBOL cap 560 384 R0
SYMATTR InstName C3
SYMATTR Value 10mf
SYMATTR SpiceLine Rser=25m Lser=2n
SYMBOL res 656 368 R0
SYMATTR InstName Rleak
SYMATTR Value 1e6
SYMBOL diode 704 240 M180
WINDOW 0 24 64 Left 2
WINDOW 3 24 0 Left 2
SYMATTR InstName D1
SYMATTR Value 1N4001
TEXT 368 -96 Left 2 ;'Measure Power Supply, Zener, LED Noise
TEXT 368 -64 Left 2 !.ac dec 500 1m 1e8\n;.tran 2
Here is the frequency response:
[AC Analysis]
{
Npanes: 1
{
traces: 1 {524290,0,"V(u1o)"}
X: ('M',1,0.001,0,1e+008)
Y[0]: (' ',0,0.125892541179417,6,125.892541179417)
Y[1]: (' ',0,-280,40,80)
Volts: (' ',0,0,3,9.99,0.002,10.012)
Log: 1 2 0
GridStyle: 1
PltMag: 1
}
}
[Transient Analysis]
{
Npanes: 1
{
traces: 3 {524290,0,"V(m1s)"} {589828,0,"V(m1g)"} {524291,0,"V(vdc)"}
X: (' ',1,0,0.2,2)
Y[0]: (' ',1,-0.9,0.9,9)
Y[1]: (' ',0,1e+308,30,-1e+308)
Volts: (' ',0,0,0,-0.9,0.9,9)
Log: 0 0 0
GridStyle: 1
PltMag: 1
PltPhi: 1 0
}
}
Here are different versions of the power supply ripple filters.
Version 4
SHEET 1 1888 1296
WIRE -48 48 -64 48
WIRE 16 48 -48 48
WIRE 144 48 16 48
WIRE 288 48 240 48
WIRE 320 48 288 48
WIRE 448 48 320 48
WIRE 576 48 448 48
WIRE 768 48 672 48
WIRE 864 48 768 48
WIRE 896 48 864 48
WIRE -64 64 -64 48
WIRE 768 64 768 48
WIRE 896 64 896 48
WIRE 288 80 288 48
WIRE 16 128 16 48
WIRE 32 128 16 128
WIRE 160 128 112 128
WIRE 192 128 192 112
WIRE 192 128 160 128
WIRE 448 128 448 48
WIRE 464 128 448 128
WIRE 592 128 544 128
WIRE 624 128 624 112
WIRE 624 128 592 128
WIRE 192 144 192 128
WIRE 624 144 624 128
WIRE 768 144 768 128
WIRE -64 160 -64 144
WIRE 288 160 288 144
WIRE 896 160 896 144
WIRE 192 224 192 208
WIRE 624 224 624 208
WIRE -16 256 -64 256
WIRE 144 256 -16 256
WIRE 288 256 240 256
WIRE 320 256 288 256
WIRE 448 256 320 256
WIRE 576 256 448 256
WIRE 768 256 672 256
WIRE 864 256 768 256
WIRE 896 256 864 256
WIRE -64 272 -64 256
WIRE 768 272 768 256
WIRE 896 272 896 256
WIRE 288 288 288 256
WIRE -16 336 -16 256
WIRE 32 336 -16 336
WIRE 160 336 112 336
WIRE 192 336 192 320
WIRE 192 336 160 336
WIRE 448 336 448 256
WIRE 464 336 448 336
WIRE 592 336 544 336
WIRE 624 336 624 320
WIRE 624 336 592 336
WIRE 192 352 192 336
WIRE 624 352 624 336
WIRE 768 352 768 336
WIRE -64 368 -64 352
WIRE 288 368 288 352
WIRE 896 368 896 352
WIRE 192 432 192 416
WIRE 624 432 624 416
WIRE 16 464 16 128
WIRE 144 464 16 464
WIRE 288 464 240 464
WIRE 368 464 288 464
WIRE 400 464 368 464
WIRE 448 464 400 464
WIRE 576 464 448 464
WIRE 736 464 672 464
WIRE 768 464 736 464
WIRE 880 464 768 464
WIRE 896 464 880 464
WIRE 768 480 768 464
WIRE 896 480 896 464
WIRE 368 496 368 464
WIRE 16 544 16 464
WIRE 32 544 16 544
WIRE 160 544 112 544
WIRE 192 544 192 528
WIRE 192 544 160 544
WIRE 208 544 192 544
WIRE 288 544 288 464
WIRE 288 544 272 544
WIRE 448 544 448 464
WIRE 464 544 448 544
WIRE 592 544 544 544
WIRE 624 544 624 528
WIRE 624 544 592 544
WIRE 656 544 624 544
WIRE 736 544 736 464
WIRE 736 544 720 544
WIRE 768 560 768 544
WIRE 368 576 368 560
WIRE 896 576 896 560
WIRE 16 656 16 544
WIRE 144 656 16 656
WIRE 304 656 240 656
WIRE 368 656 304 656
WIRE 400 656 368 656
WIRE 448 656 400 656
WIRE 576 656 448 656
WIRE 736 656 672 656
WIRE 768 656 736 656
WIRE 880 656 768 656
WIRE 896 656 880 656
WIRE 768 672 768 656
WIRE 896 672 896 656
WIRE 368 688 368 656
WIRE 16 736 16 656
WIRE 48 736 16 736
WIRE 160 736 112 736
WIRE 192 736 192 720
WIRE 192 736 160 736
WIRE 208 736 192 736
WIRE 304 736 304 656
WIRE 304 736 288 736
WIRE 448 736 448 656
WIRE 480 736 448 736
WIRE 592 736 544 736
WIRE 624 736 624 720
WIRE 624 736 592 736
WIRE 640 736 624 736
WIRE 736 736 736 656
WIRE 736 736 720 736
WIRE 768 752 768 736
WIRE 368 768 368 752
WIRE 896 768 896 752
WIRE 16 864 16 736
WIRE 144 864 16 864
WIRE 272 864 240 864
WIRE 288 864 272 864
WIRE 352 864 288 864
WIRE 448 864 352 864
WIRE 576 864 448 864
WIRE 720 864 672 864
WIRE 784 864 720 864
WIRE 864 864 784 864
WIRE 896 864 864 864
WIRE 896 880 896 864
WIRE 352 896 352 864
WIRE 784 896 784 864
WIRE 192 944 192 928
WIRE 288 944 288 864
WIRE 624 944 624 928
WIRE 720 944 720 864
WIRE 352 976 352 960
WIRE 784 976 784 960
WIRE 896 976 896 960
WIRE 16 1040 16 864
WIRE 32 1040 16 1040
WIRE 208 1040 112 1040
WIRE 240 1040 240 1008
WIRE 240 1040 208 1040
WIRE 448 1040 448 864
WIRE 464 1040 448 1040
WIRE 640 1040 544 1040
WIRE 672 1040 672 1008
WIRE 672 1040 640 1040
WIRE 240 1056 240 1040
WIRE 672 1056 672 1040
WIRE 240 1136 240 1120
WIRE 672 1136 672 1120
FLAG -64 160 0
FLAG -48 48 VCC
FLAG 192 224 0
FLAG 320 48 Q1E
FLAG 288 160 0
FLAG 160 128 Q1B
FLAG 592 128 Q2B
FLAG 768 144 0
FLAG 864 48 Classic
FLAG 624 224 0
FLAG 896 160 0
FLAG 400 464 Q7E
FLAG 368 576 0
FLAG 160 544 Q7B
FLAG 592 544 Q8B
FLAG 768 560 0
FLAG 880 464 NPN
FLAG 896 576 0
FLAG 352 976 0
FLAG 240 1136 0
FLAG 272 864 Q3C
FLAG 208 1040 Q4B
FLAG 784 976 0
FLAG 672 1136 0
FLAG 864 864 Sziklai
FLAG 640 1040 Q6B
FLAG 896 976 0
FLAG 400 656 Q9C
FLAG 368 768 0
FLAG 160 736 Q9B
FLAG 592 736 Q10B
FLAG 768 752 0
FLAG 880 656 PNP
FLAG 896 768 0
FLAG 192 432 0
FLAG 320 256 Q11E
FLAG 288 368 0
FLAG 160 336 Q11B
FLAG 592 336 Q12B
FLAG 768 352 0
FLAG 864 256 NegVolt
FLAG 624 432 0
FLAG 896 368 0
FLAG -64 368 0
SYMBOL voltage -64 48 R0
WINDOW 0 33 22 Left 2
WINDOW 3 37 77 Left 2
WINDOW 123 35 103 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V1
SYMATTR Value 15
SYMATTR Value2 AC 1
SYMBOL npn 144 112 R270
WINDOW 0 43 35 VRight 2
WINDOW 3 65 27 VRight 2
SYMATTR InstName Q1
SYMATTR Value 2N3904
SYMBOL res 128 112 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 10k
SYMBOL cap 176 144 R0
WINDOW 0 34 15 Left 2
WINDOW 3 34 52 Left 2
SYMATTR InstName C1
SYMATTR Value 470uf
SYMATTR SpiceLine Rser=17m Lser=10n
SYMBOL cap 272 80 R0
WINDOW 0 34 15 Left 2
WINDOW 3 34 52 Left 2
SYMATTR InstName C2
SYMATTR Value 470uf
SYMATTR SpiceLine Rser=17m Lser=10n
SYMBOL npn 576 112 R270
WINDOW 0 43 35 VRight 2
WINDOW 3 69 25 VRight 2
SYMATTR InstName Q2
SYMATTR Value 2N3904
SYMBOL res 560 112 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R2
SYMATTR Value 10k
SYMBOL cap 608 144 R0
WINDOW 0 34 15 Left 2
WINDOW 3 34 52 Left 2
SYMATTR InstName C3
SYMATTR Value 470uf
SYMATTR SpiceLine Rser=17m Lser=10n
SYMBOL cap 752 64 R0
WINDOW 0 34 15 Left 2
WINDOW 3 34 52 Left 2
SYMATTR InstName C4
SYMATTR Value 470uf
SYMATTR SpiceLine Rser=17m Lser=10n
SYMBOL res 880 48 R0
SYMATTR InstName R3
SYMATTR Value 1k
SYMBOL res 128 528 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R4
SYMATTR Value 10k
SYMBOL cap 272 528 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C5
SYMATTR Value 1000uf
SYMATTR SpiceLine Rser=17m Lser=10n
SYMBOL cap 352 496 R0
WINDOW 0 34 15 Left 2
WINDOW 3 34 52 Left 2
SYMATTR InstName C6
SYMATTR Value 470uf
SYMATTR SpiceLine Rser=17m Lser=10n
SYMBOL res 560 528 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R5
SYMATTR Value 10k
SYMBOL cap 752 480 R0
WINDOW 0 34 15 Left 2
WINDOW 3 34 52 Left 2
SYMATTR InstName C7
SYMATTR Value 470uf
SYMATTR SpiceLine Rser=17m Lser=10n
SYMBOL res 880 464 R0
SYMATTR InstName R6
SYMATTR Value 1k
SYMBOL pnp 240 928 M270
WINDOW 0 60 59 VLeft 2
WINDOW 3 97 68 VLeft 2
SYMATTR InstName Q3
SYMATTR Value 2N3906
SYMBOL npn 192 1008 R270
WINDOW 0 43 35 VRight 2
WINDOW 3 80 25 VRight 2
SYMATTR InstName Q4
SYMATTR Value 2N3904
SYMBOL res 128 1024 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R7
SYMATTR Value 47k
SYMBOL cap 224 1056 R0
WINDOW 0 34 15 Left 2
WINDOW 3 34 52 Left 2
SYMATTR InstName C8
SYMATTR Value 470uf
SYMATTR SpiceLine Rser=17m Lser=10n
SYMBOL cap 336 896 R0
WINDOW 0 34 15 Left 2
WINDOW 3 34 52 Left 2
SYMATTR InstName C9
SYMATTR Value 470uf
SYMATTR SpiceLine Rser=17m Lser=10n
SYMBOL pnp 672 928 M270
WINDOW 0 60 59 VLeft 2
WINDOW 3 97 68 VLeft 2
SYMATTR InstName Q5
SYMATTR Value 2N3906
SYMBOL npn 624 1008 R270
WINDOW 0 43 35 VRight 2
WINDOW 3 80 25 VRight 2
SYMATTR InstName Q6
SYMATTR Value 2N3904
SYMBOL res 560 1024 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R8
SYMATTR Value 47k
SYMBOL cap 656 1056 R0
WINDOW 0 34 15 Left 2
WINDOW 3 34 52 Left 2
SYMATTR InstName C10
SYMATTR Value 470uf
SYMATTR SpiceLine Rser=17m Lser=10n
SYMBOL cap 768 896 R0
WINDOW 0 34 15 Left 2
WINDOW 3 34 52 Left 2
SYMATTR InstName C11
SYMATTR Value 470uf
SYMATTR SpiceLine Rser=17m Lser=10n
SYMBOL res 880 864 R0
SYMATTR InstName R9
SYMATTR Value 1k
SYMBOL npn 144 528 R270
WINDOW 0 43 35 VRight 2
WINDOW 3 64 27 VRight 2
SYMATTR InstName Q7
SYMATTR Value 2N3904
SYMBOL npn 576 528 R270
WINDOW 0 43 35 VRight 2
WINDOW 3 63 29 VRight 2
SYMATTR InstName Q8
SYMATTR Value 2N3904
SYMBOL cap 720 528 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C12
SYMATTR Value 1000uf
SYMATTR SpiceLine Rser=17m Lser=10n
SYMBOL res 304 720 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R10
SYMATTR Value 10k
SYMBOL cap 112 720 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C13
SYMATTR Value 1000uf
SYMATTR SpiceLine Rser=17m Lser=10n
SYMBOL cap 352 688 R0
WINDOW 0 34 15 Left 2
WINDOW 3 34 52 Left 2
SYMATTR InstName C14
SYMATTR Value 470uf
SYMATTR SpiceLine Rser=17m Lser=10n
SYMBOL res 736 720 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R11
SYMATTR Value 10k
SYMBOL cap 752 672 R0
WINDOW 0 34 15 Left 2
WINDOW 3 34 52 Left 2
SYMATTR InstName C15
SYMATTR Value 470uf
SYMATTR SpiceLine Rser=17m Lser=10n
SYMBOL res 880 656 R0
SYMATTR InstName R12
SYMATTR Value 1k
SYMBOL cap 544 720 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C16
SYMATTR Value 1000uf
SYMATTR SpiceLine Rser=17m Lser=10n
SYMBOL pnp 240 720 M270
WINDOW 0 60 59 VLeft 2
WINDOW 3 97 68 VLeft 2
SYMATTR InstName Q9
SYMATTR Value 2N3906
SYMBOL pnp 672 720 M270
WINDOW 0 60 59 VLeft 2
WINDOW 3 97 68 VLeft 2
SYMATTR InstName Q10
SYMATTR Value 2N3906
SYMBOL cap 176 352 R0
WINDOW 0 34 15 Left 2
WINDOW 3 34 52 Left 2
SYMATTR InstName C17
SYMATTR Value 470uf
SYMATTR SpiceLine Rser=17m Lser=10n
SYMBOL cap 272 288 R0
WINDOW 0 34 15 Left 2
WINDOW 3 34 52 Left 2
SYMATTR InstName C18
SYMATTR Value 470uf
SYMATTR SpiceLine Rser=17m Lser=10n
SYMBOL res 560 320 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R13
SYMATTR Value 10k
SYMBOL cap 608 352 R0
WINDOW 0 34 15 Left 2
WINDOW 3 34 52 Left 2
SYMATTR InstName C19
SYMATTR Value 470uf
SYMATTR SpiceLine Rser=17m Lser=10n
SYMBOL cap 752 272 R0
WINDOW 0 34 15 Left 2
WINDOW 3 34 52 Left 2
SYMATTR InstName C20
SYMATTR Value 470uf
SYMATTR SpiceLine Rser=17m Lser=10n
SYMBOL res 880 256 R0
SYMATTR InstName R14
SYMATTR Value 1k
SYMBOL pnp 144 320 R270
WINDOW 0 40 38 VRight 2
WINDOW 3 60 26 VRight 2
SYMATTR InstName Q11
SYMATTR Value 2N3906
SYMBOL pnp 576 320 R270
WINDOW 0 40 38 VRight 2
WINDOW 3 60 26 VRight 2
SYMATTR InstName Q12
SYMATTR Value 2N3906
SYMBOL voltage -64 368 R180
WINDOW 0 33 22 Left 2
WINDOW 3 37 77 Left 2
WINDOW 123 35 103 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V2
SYMATTR Value 15
SYMATTR Value2 AC 1
SYMBOL res 128 320 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R15
SYMATTR Value 10k
TEXT 200 -96 Left 2 ;'Low Noise Ripple Filter for Opamps
TEXT 200 -64 Left 2 !.ac dec 500 1m 1e6
TEXT 120 1216 Left 2 ;Capacitors are Kemet Solid Polymer, 470uF 25V, 17mohm
ESR
Here's the PLT files. Watch the wrap:
[AC Analysis]
{
Npanes: 1
{
traces: 5 {524290,0,"V(classic)"} {524291,0,"V(negvolt)"}
{524292,0,"V(npn)"} {524293,0,"V(pnp)"} {524294,0,"V(sziklai)"}
X: ('M',0,0.001,0,1e+006)
Y[0]: (' ',0,1e-012,20,10)
Y[1]: (' ',0,-400,80,480)
Volts: (' ',0,0,3,5.864,0.001,5.876)
Log: 1 2 0
GridStyle: 1
PltMag: 1