Discussion:
Low distortion sinewave oscillator without big capacitor.
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Edward Rawde
2025-03-30 18:54:56 UTC
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Not long ago JM posted a 1KHz sinewave oscillator with very low distortion.
It used a 470uF non polarized capacitor which in practice would probably be made from two 1000uF capacitors.
There's nothing wrong with that but I wanted to see whether I could make a working circuit without needing such a large capacitor.

What I have so far is below.

Any comments?
What's the best way to control the output level?
Currently it's 5v pk-pk but I rather have half that.

Version 4.1
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TEXT -2792 1560 Left 2 !.tran 0 10 0 1u startup
TEXT -2792 1504 Left 2 !.options plotwinsize=0 numdgt=15
TEXT -2248 -112 Left 2 ;Low distortion 1KHz oscillator. Edward Rawde 30 March 2025.\nBased on designs by JM and BS.
Bill Sloman
2025-03-31 08:00:49 UTC
Reply
Permalink
Post by Edward Rawde
Not long ago JM posted a 1KHz sinewave oscillator with very low distortion.
It used a 470uF non polarized capacitor which in practice would probably be made from two 1000uF capacitors.
There's nothing wrong with that but I wanted to see whether I could make a working circuit without needing such a large capacitor.
What I have so far is below.
Any comments?
It relies on the Analog Devices MAT-02 dual transistor, which is now
obsolete

https://www.analog.com/media/en/technical-documentation/obsolete-data-sheets/mat02.pdf

The .asc file shows eight NPN transistors labelled MAT-02, presumably in
four pairs of the part, but it isn't clear which of the eight
transistors should be paired up.
Post by Edward Rawde
What's the best way to control the output level?
Currently it's 5v pk-pk but I rather have half that.
The rectified currents from the four phased shifted versions of of the
output waveform flow through R13, R14, R15 and R16 into R11 and through
it into the virtual earth set up at the inverting input of U3, where the
summed current is compared with a fixed current drawn from the +15V rail
through D1 and R10.

Doubling R10 from 330k to 680k would roughly halve the output amplitude.
One could be more precise, but it wouudl be hard to justify the extra
effort.
--
Bill Sloman, Sydney
Edward Rawde
2025-04-01 03:09:03 UTC
Reply
Permalink
Post by Edward Rawde
Not long ago JM posted a 1KHz sinewave oscillator with very low distortion.
It used a 470uF non polarized capacitor which in practice would probably be made from two 1000uF capacitors.
There's nothing wrong with that but I wanted to see whether I could make a working circuit without needing such a large
capacitor.
What I have so far is below.
Any comments?
It relies on the Analog Devices MAT-02 dual transistor, which is now obsolete
https://www.analog.com/media/en/technical-documentation/obsolete-data-sheets/mat02.pdf
The .asc file shows eight NPN transistors labelled MAT-02, presumably in four pairs of the part, but it isn't clear which of the
eight transistors should be paired up.
BCM61B is available and very reasonably priced.
https://www.digikey.ca/en/products/detail/nexperia-usa-inc/BCM61B-215/2119400
It can be used for Q1 Q2 and Q3 Q4 in the circuit below.

The remaining four transistors can use MAT14
https://www.digikey.be/en/products/detail/analog-devices-inc/MAT14ARZ-R7/2510588
which although a bit pricey has four independent matched transistors.
I can't find an LTSpice model for MAT14 so MAT02 is still shown in the circuit below.
Post by Edward Rawde
What's the best way to control the output level?
Currently it's 5v pk-pk but I rather have half that.
The rectified currents from the four phased shifted versions of of the output waveform flow through R13, R14, R15 and R16 into R11
and through it into the virtual earth set up at the inverting input of U3, where the summed current is compared with a fixed
current drawn from the +15V rail through D1 and R10.
Doubling R10 from 330k to 680k would roughly halve the output amplitude.
One could be more precise, but it wouudl be hard to justify the extra effort.
Ah yes, that takes care of the output level.
The revised circuit is below.
Line 459 will need to be unwrapped.
--
Bill Sloman, Sydney
Version 4.1
SHEET 1 3020 2792
WIRE 80 -208 -288 -208
WIRE 800 -208 160 -208
WIRE -288 -96 -288 -208
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FLAG 288 192 vee
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FLAG -816 336 0
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FLAG -1664 1040 vcc
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FLAG -2544 864 0
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FLAG -1904 1648 0
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WINDOW 0 0 56 VBottom 2
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SYMATTR Value 10K
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WINDOW 0 0 56 VBottom 2
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WINDOW 0 0 56 VBottom 2
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SYMATTR Value 16K
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SYMATTR Value 10n
SYMBOL cap 720 16 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C2
SYMATTR Value 10n
SYMBOL res 176 -224 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R4
SYMATTR Value 10K
SYMBOL res 176 -80 M270
WINDOW 0 32 56 VTop 2
WINDOW 3 0 56 VBottom 2
SYMATTR InstName R5
SYMATTR Value 82k
SYMBOL cap -256 976 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C3
SYMATTR Value 1000n
SYMBOL res 32 1200 R270
WINDOW 0 32 56 VTop 2
WINDOW 3 0 56 VBottom 2
SYMATTR InstName R10
SYMATTR Value 820k
SYMBOL diode 240 1168 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName D1
SYMATTR Value 1N914
SYMBOL res -48 960 R0
SYMATTR InstName R11
SYMATTR Value 47k
SYMBOL res 560 592 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R18
SYMATTR Value 10K
SYMBOL res 416 432 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R19
SYMATTR Value 10k
SYMBOL diode -48 720 M180
WINDOW 0 24 64 Left 2
WINDOW 3 24 0 Left 2
SYMATTR InstName D2
SYMATTR Value 1N914
SYMBOL diode 192 720 M180
WINDOW 0 24 64 Left 2
WINDOW 3 24 0 Left 2
SYMATTR InstName D12
SYMATTR Value 1N914
SYMBOL diode 400 720 R180
WINDOW 0 24 64 Left 2
WINDOW 3 24 0 Left 2
SYMATTR InstName D13
SYMATTR Value 1N914
SYMBOL diode 784 720 M180
WINDOW 0 24 64 Left 2
WINDOW 3 24 0 Left 2
SYMATTR InstName D14
SYMATTR Value 1N914
SYMBOL res -48 736 R0
SYMATTR InstName R13
SYMATTR Value 68k
SYMBOL res 192 736 R0
SYMATTR InstName R14
SYMATTR Value 68k
SYMBOL res 400 736 M0
SYMATTR InstName R15
SYMATTR Value 68k
SYMBOL res 784 736 R0
SYMATTR InstName R16
SYMATTR Value 68k
SYMBOL voltage -2544 1824 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value 15
SYMBOL voltage -2544 1968 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V4
SYMATTR Value 15
SYMBOL OpAmps\\LT1679 -144 160 R0
SYMATTR InstName U5
SYMBOL OpAmps\\LT1679 288 160 R0
SYMATTR InstName U6
SYMBOL OpAmps\\LT1679 688 160 R0
SYMATTR InstName U8
SYMBOL res -112 272 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R8
SYMATTR Value 10k
SYMBOL res -320 272 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R9
SYMATTR Value 560
SYMBOL cap -480 272 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C8
SYMATTR Value 1000n
SYMBOL res -272 1088 R270
WINDOW 0 32 56 VTop 2
WINDOW 3 0 56 VBottom 2
SYMATTR InstName R6
SYMATTR Value 47k
SYMBOL cap -304 1056 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C4
SYMATTR Value 10000n
SYMBOL OpAmps\\LT1679 384 528 R90
WINDOW 3 37 22 VRight 2
SYMATTR InstName U1
SYMBOL pnp -2032 736 M180
WINDOW 3 84 0 Left 2
SYMATTR Value 2N3906
SYMATTR InstName Q9
SYMBOL res -1984 208 R0
SYMATTR InstName R12
SYMATTR Value 56k
SYMBOL res -1760 384 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R25
SYMATTR Value 2.7Meg
SYMBOL cap -2176 544 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C7
SYMATTR Value 10p
SYMBOL npn -2096 1152 M0
SYMATTR InstName Q5
SYMATTR Value MAT-02
SYMBOL npn -1728 1152 R0
SYMATTR InstName Q7
SYMATTR Value MAT-02
SYMBOL npn -1424 1408 R0
SYMATTR InstName Q8
SYMATTR Value MAT-02
SYMBOL npn -1968 1408 R0
SYMATTR InstName Q6
SYMATTR Value MAT-02
SYMBOL res -1552 2112 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R28
SYMATTR Value 120k
SYMBOL res -1376 1120 R0
SYMATTR InstName R29
SYMATTR Value 100k
SYMBOL res -2448 528 R0
SYMATTR InstName R32
SYMATTR Value 10k
SYMBOL res -2448 752 R0
SYMATTR InstName R33
SYMATTR Value 15k
SYMBOL cap -944 256 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C12
SYMATTR Value 1000n
SYMBOL res -656 144 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R7
SYMATTR Value 14k
SYMBOL cap -688 32 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C5
SYMATTR Value 10p
SYMBOL cap -1600 384 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C6
SYMATTR Value 100n
SYMBOL OpAmps\\LT1679 -704 288 R0
SYMATTR InstName U2
SYMBOL OpAmps\\LT1679 -272 1200 M0
SYMATTR InstName U3
SYMBOL OpAmps\\LT1679 -2224 688 R0
SYMATTR InstName U4
SYMBOL cap -2560 768 R0
SYMATTR InstName C9
SYMATTR Value 10n
SYMBOL cap 992 128 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C10
SYMATTR Value 10000n
SYMBOL npn -2096 2176 M0
SYMATTR InstName Q1
SYMATTR Value BCM61B
SYMBOL npn -1888 2176 R0
SYMATTR InstName Q2
SYMATTR Value BCM61B
SYMBOL npn -1600 1792 M0
SYMATTR InstName Q3
SYMATTR Value BCM61B
SYMBOL npn -1392 1792 R0
SYMATTR InstName Q4
SYMATTR Value BCM61B
SYMBOL res -1136 1728 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R17
SYMATTR Value 120k
SYMBOL res 1056 256 R0
SYMATTR InstName R21
SYMATTR Value 100k
TEXT -2792 1560 Left 2 !.tran 0 10 0 1u startup
TEXT -2792 1504 Left 2 !.options plotwinsize=0 numdgt=15
TEXT -2248 -112 Left 3 ;Low distortion 1KHz oscillator. Edward Rawde 31 March 2025.\nBased on designs by JM and BS.
TEXT -576 1368 Left 2 !.MODEL BCM61B NPN\n+ IS = 1.822E-14\n+ NF = 0.9932\n+ ISE = 2.894E-16\n+ NE = 1.4\n+ BF = 324.4\n+ IKF =
0.109\n+ VAF = 82\n+ NR = 0.9931\n+ ISC = 9.982E-12\n+ NC = 1.763\n+ BR = 8.29\n+ IKR = 0.09\n+ VAR = 17.9\n+ RB = 10\n+ IRB =
5E-06\n+ RBM = 5\n+ RE = 0.649\n+ RC = 0.7014\n+ CJE = 1.244E-11\n+ VJE = 0.7579\n+ MJE = 0.3656\n+ TF = 4.908E-10\n+ XTF = 9.51\n+
VTF = 2.927\n+ ITF = 0.3131\n+ PTF = 0\n+ CJC = 3.347E-12\n+ VJC = 0.5463\n+ MJC = 0.391\n+ XCJC = 0.6193\n+ TR = 9E-08\n+ CJS =
0\n+ VJS = 0.75\n+ MJS = 0.333\n+ XTB = 0\n+ XTI = 3\n+ EG = 1.11\n+ FC = 0.979
TEXT -2656 1256 Left 3 ;Use MAT14 for Q5-Q8

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