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Hi there,

Thank you for your attention!

I've built a 1000Hz Wien bridge oscillator according to the following schametic,




and got a THD around -70dB.


The hurdle right now is that I couldn't find a model for the light bulb in the LTspice component lib.


In an online literature about ultra-pure sine-wave oscillator,
there's a linear optocoupler "Silonex NSL32R3". I couldn't find similar model in the LTspice component lib either.




I'm wondering if any forerunners could shed some light?

Thank you again for your kindness!


73,
xe3po

--- In LTspice@..., "xe3po" <xe3po@...> wrote:

Hi there,

Thank you for your attention!

I've built a 1000Hz Wien bridge oscillator according to the following schametic,




and got a THD around -70dB.


The hurdle right now is that I couldn't find a model for the light bulb in the LTspice component lib.


In an online literature about ultra-pure sine-wave oscillator,
there's a linear optocoupler "Silonex NSL32R3". I couldn't find similar model in the LTspice component lib either.




I'm wondering if any forerunners could shed some light?

Thank you again for your kindness!


73,
xe3po

Here's a behavioral model originated by a former employee of mine at GenRad...

****
** SPELLMAN LAMP SUBCIRCUIT
*VO=NOMINAL OPERATING VOLTAGE
*IO=NOMINAL STEADY STATE OPERATING CURRENT
*RCOLD=FILAMEMT RESISTANCE MEASURED AT ROOM TEMP (300K)
*TAU=CURRENT TIME CONSTANT AFTER A 0 (zero) TO VO STEP IS APPLIED
.SUBCKT LAMP 1 2 PARAMS: VO=28 IO=25m RCOLD=112 TAU=22m TAMB=300
H1 6 0 VML 1
RH1 6 0 1
GP 0 4 VALUE={V(6)*V(1,2)}
*V(4,0) = FILAMENT TEMPERATURE IN KELVINS
RT 4 5 {300*(VO-IO*RCOLD)/(IO*IO*VO*RCOLD)}
CT 4 5 {TAU*IO*IO*VO*RCOLD/(300*(VO-IO*RCOLD))}
VAMB 5 0 {TAMB}
El 7 0 1 2 300
R1 7 0 1
E2 8 0 VALUE={V(4)*RCOLD}
R2 8 0 1
E3 10 0 7 9 10MEG
R3 10 0 1
E4 9 0 VALUE={V(8)*V(10)}
R4 9 0 1
GR 1 3 10 0 1
VML 3 2 0
.ENDS LAMP
****

You'll have to scale it to your particular lamp. Do some testing >:-}

-Jim Thompson

Hi xe3po:

There is really no exact model for lamp or model for this sort of stuff however, you can do the equivalent math B-source for it. For example the basic incandescent lamp is governed by a non-linear relationship between current I flowing into the filament and V or EMF to effect this. The relationship is approximated by:

V=C*I^n

Its the non-linearity that help starts your oscillator and as well as sustain it. Starting the oscillator could also quite a challenge - in the past I had to ramp the supply voltage and check if kicks into oscillation or pulse or step the supply to see the effect and do also some spice hacks.

Regards,
Berns B.
Dept.of Physics - USC Cebu,Philippines

--- In LTspice@..., "xe3po" <xe3po@> wrote:

Hi there,

Thank you for your attention!

I've built a 1000Hz Wien bridge oscillator according to the following schametic,




and got a THD around -70dB.


The hurdle right now is that I couldn't find a model for the light bulb in the LTspice component lib.


In an online literature about ultra-pure sine-wave oscillator,
there's a linear optocoupler "Silonex NSL32R3". I couldn't find similar model in the LTspice component lib either.




I'm wondering if any forerunners could shed some light?

Thank you again for your kindness!


73,
xe3po

In message <knhohb+fa48@...>, dated Wed, 22 May 2013, xe3po
<xe3po@...> writes:

The hurdle right now is that I couldn't find a model for the light bulb
in the LTspice component lib.

If this really is a 120 V 4 W lamp, it isn't a good choice, because the
very limited input power hardly raises the filament temperature above
ambient, so as the ambient temperature varies, the output voltage
varies. That lamp was probably good for Hewlett and Packard, because
they were using tubes.
--
OOO - Own Opinions Only. See www.jmwa.demon.co.uk
They took me to a specialist burns unit - and made me learn 'To a haggis'.

John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

--- In LTspice@..., "xe3po" <xe3po@> wrote:

Hi there,

Thank you for your attention!

I've built a 1000Hz Wien bridge oscillator according to the following schametic,




and got a THD around -70dB.


The hurdle right now is that I couldn't find a model for the light bulb in the LTspice component lib.


In an online literature about ultra-pure sine-wave oscillator,
there's a linear optocoupler "Silonex NSL32R3". I couldn't find similar model in the LTspice component lib either.




I'm wondering if any forerunners could shed some light?

Thank you again for your kindness!


73,
xe3po

Here's a behavioral model originated by a former employee of mine at GenRad...

****
** SPELLMAN LAMP SUBCIRCUIT
*VO=NOMINAL OPERATING VOLTAGE
*IO=NOMINAL STEADY STATE OPERATING CURRENT
*RCOLD=FILAMEMT RESISTANCE MEASURED AT ROOM TEMP (300K)
*TAU=CURRENT TIME CONSTANT AFTER A 0 (zero) TO VO STEP IS APPLIED
.SUBCKT LAMP 1 2 PARAMS: VO=28 IO=25m RCOLD=112 TAU=22m TAMB=300
H1 6 0 VML 1
RH1 6 0 1
GP 0 4 VALUE={V(6)*V(1,2)}
*V(4,0) = FILAMENT TEMPERATURE IN KELVINS
RT 4 5 {300*(VO-IO*RCOLD)/(IO*IO*VO*RCOLD)}
CT 4 5 {TAU*IO*IO*VO*RCOLD/(300*(VO-IO*RCOLD))}
VAMB 5 0 {TAMB}
El 7 0 1 2 300
R1 7 0 1
E2 8 0 VALUE={V(4)*RCOLD}
R2 8 0 1
E3 10 0 7 9 10MEG
R3 10 0 1
E4 9 0 VALUE={V(8)*V(10)}
R4 9 0 1
GR 1 3 10 0 1
VML 3 2 0
.ENDS LAMP
****

You'll have to scale it to your particular lamp. Do some testing >:-}

-Jim Thompson

--- In LTspice@..., "jtanalog" <ltlist@> wrote:

Here's a behavioral model originated by a former employee of
mine at GenRad... [cut model text]

Here is a simpler one specifically for LTspice (probably works
better, too).

* Incandescent Lamp Model by analog-at-ieee-dot-org
* input: Kc = conductance constant of filament
* input: Kr = radiation constant of filament
* input: CTf = filament thermal capacitance
* input: RTf = filament thermal resistance
* n = numerical dynamic range scale factor
* Cf = filament conductance
* Pf = filament power (electrical input)
* Pr = radiated power (electromagnetic output)
* Tf = filament temperature (in degrees K)
* Ta = ambient temperature (converted to deg K)
.subckt Lamp 1 2
.param Kc=120 Kr=.7p CTf=5m RTf=10k Ta=temp-kelvin
.param n=1m ; this is for the simulator, not the lamp
BCf 1 2 I=V(1,2)*Kc/V(Tf)**1.2
BPf 0 Tf I=V(1,2)*I(BCf)*n
BPr Tf 0 I=Kr*(V(Tf)**4-Ta**4)*n
Cfa Tf Ta {CTf*n} Rpar={RTf/n}
VTa Ta 0 {Ta}
.ends Lamp

Thank you very much for your input!
120V 4W is the lowest rating I could find locally.
It worked, with a LM741 opamp, and yielded 6Vp-p 1000HZ
output while THD is lower than -70dB.
I just want to get a better THD result like -100dB.

Hi Xe

The wein bridge has poor harmonic rejection.

Try the double integrator state variable oscillator.
Take the output from the 2nd integrator.
2 stages of integration Greatly attenuates harmonics.

Amplitude stability can be gotten with a Soft clipper in the summing
stage, or
you can use the usual jfet method.

Very stable / wide range.
Easy to get a decade with a stereo pot.
Switch ranges by changing capacitors.


On 05/22/2013 07:15 PM, xe3po wrote:

Thank you very much for your input!
120V 4W is the lowest rating I could find locally.
It worked, with a LM741 opamp, and yielded 6Vp-p 1000HZ
output while THD is lower than -70dB.
I just want to get a better THD result like -100dB.

--


AC2CL

I do not think there is any thrill that
can go through the human heart like that felt by the inventor as
he sees some creation of the brain unfolding to success...
Such emotions make a man forget food, sleep, friends, love, everything.

- Nikola Tesla

Hi Guys,

I had a similar problem building a low distortion oscillator last year and fell back on the good 'ol Wien Bridge. I also did the State Variable 2nd stage integrator at the same time. Both in LT.

Before I go too far, I read an article yesterday on how an EE pulled a Wien just a Hertz or so, to lock it to a frequency standard and gain the advantage of both low distortion and accurate frequency.

Back to the light bulb. There was an article in the same pile of yesterday's back reading - can't find it - using a 5W, 120VAC bulb as a leveler instead of the original Hewlett and Packard's 6V bulb. Some of those tiny and rapidly disappearing series-string Christmas bulbs might work well.

The problem with the JFET is assymetrical voltage modulation of the JFET's channel resistance. It will generally limit you to around - 70 to - 80 dBFS. The bulb doesn't do assymetrical distortion. One way is to build your own symmetrical differential Variable Gain Amplifier.

The FET secret is on page 21 of an old (1981? it's not dated) Electronics Magazine Designer's Casebook - using a matched JFET pair connected differentially across the op-amp's + and - inputs. They don't see any more than +/- Voffset. Great idea. No modulation. I used it to model both a - 120 dBFS Wien and State Variable in LT.

Designing low distortion oscillators requires a great bag of tricks and healthy design paranoia. Everything matters. When I find time, I'll try for - 140 dBFS (or is it - 140 dBc?)

I'll look for the links and figure out how to add Attachments to this
Forum.

Regards,

Ron




--- In LTspice@..., alzie <alzie@> wrote:

Hi Xe

The wein bridge has poor harmonic rejection.

Try the double integrator state variable oscillator.
Take the output from the 2nd integrator.
2 stages of integration Greatly attenuates harmonics.

Amplitude stability can be gotten with a Soft clipper in the summing
stage, or
you can use the usual jfet method.

Very stable / wide range.
Easy to get a decade with a stereo pot.
Switch ranges by changing capacitors.


On 05/22/2013 07:15 PM, xe3po wrote:

Thank you very much for your input!
120V 4W is the lowest rating I could find locally.
It worked, with a LM741 opamp, and yielded 6Vp-p 1000HZ
output while THD is lower than -70dB.
I just want to get a better THD result like -100dB.

--


AC2CL

I do not think there is any thrill that
can go through the human heart like that felt by the inventor as
he sees some creation of the brain unfolding to success...
Such emotions make a man forget food, sleep, friends, love, everything.

- Nikola Tesla

There is also the Commutating Filter, followed by a dual integrator.
How about a low distortion audio op amp (National Semi/TI) and a 20 bit Delta Sigma DAC? ~ 1 ppm ~ 120 dB.

xe3po <xe3po@...> wrote:

120V 4W is the lowest rating I could find locally.

Nothing less than 120V? I think you want a much lower *voltage* bulb. Do
you have any electronics shops near you? They ought to have bulbs that run
on 6V, 12V, etc. Those used to be found as pilot lights or dial lights in
radios.

I don't know what would be suitable, but I believe the idea is to warm up
the filament but much less than normal brightness. The glow might be just
barely visible.

Andy


[Non-text portions of this message have been removed]

There is also the Commutating Filter, followed by a dual integrator.
How about a low distortion audio op amp (National Semi/TI) and a 20 bit Delta Sigma DAC? ~ 1 ppm ~ 120 dB.

Ron


--- In LTspice@..., "ron_ck722" <ron_ck722@> wrote:

Hi Guys,

I had a similar problem building a low distortion oscillator last year and fell back on the good 'ol Wien Bridge. I also did the State Variable 2nd stage integrator at the same time. Both in LT.

Before I go too far, I read an article yesterday on how an EE pulled a Wien just a Hertz or so, to lock it to a frequency standard and gain the advantage of both low distortion and accurate frequency.

Back to the light bulb. There was an article in the same pile of yesterday's back reading - can't find it - using a 5W, 120VAC bulb as a leveler instead of the original Hewlett and Packard's 6V bulb. Some of those tiny and rapidly disappearing series-string Christmas bulbs might work well.

The problem with the JFET is assymetrical voltage modulation of the JFET's channel resistance. It will generally limit you to around - 70 to - 80 dBFS. The bulb doesn't do assymetrical distortion. One way is to build your own symmetrical differential Variable Gain Amplifier.

The FET secret is on page 21 of an old (1981? it's not dated) Electronics Magazine Designer's Casebook - using a matched JFET pair connected differentially across the op-amp's + and - inputs. They don't see any more than +/- Voffset. Great idea. No modulation. I used it to model both a - 120 dBFS Wien and State Variable in LT.

Designing low distortion oscillators requires a great bag of tricks and healthy design paranoia. Everything matters. When I find time, I'll try for - 140 dBFS (or is it - 140 dBc?)

I'll look for the links and figure out how to add Attachments to this
Forum.

Regards,

Ron




--- In LTspice@..., alzie <alzie@> wrote:

Hi Xe

The wein bridge has poor harmonic rejection.

Try the double integrator state variable oscillator.
Take the output from the 2nd integrator.
2 stages of integration Greatly attenuates harmonics.

Amplitude stability can be gotten with a Soft clipper in the summing
stage, or
you can use the usual jfet method.

Very stable / wide range.
Easy to get a decade with a stereo pot.
Switch ranges by changing capacitors.


On 05/22/2013 07:15 PM, xe3po wrote:

Thank you very much for your input!
120V 4W is the lowest rating I could find locally.
It worked, with a LM741 opamp, and yielded 6Vp-p 1000HZ
output while THD is lower than -70dB.
I just want to get a better THD result like -100dB.

--


AC2CL

I do not think there is any thrill that
can go through the human heart like that felt by the inventor as
he sees some creation of the brain unfolding to success...
Such emotions make a man forget food, sleep, friends, love, everything.

- Nikola Tesla