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patrick-turner patrick-turner is offline
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Default Wien Bridge Oscilator, 1Hz to 1MHz.

Hi folks, people, demons and anyone else hangin around.
I have posted up another page for as 1/2 decent wien bridge oscilator which has 6 F ranges to give 1Hz to 1MHz. Instead of using potentiometers or tuning caps it has a two ganged wafer switches each with 12 pos x 1 pole to give relative F = 1, 1.2, 1.5, 2.0, 2.5, 3.2 3.9, 4.7, 5.6, 6.8, 8.2 and 10..0. These F appear at fairly evenly positioned points around a dial covering 360 degrees with 12 F marks.
A fairly decent Schmitt trigger square wave maker is included.
See
http://www.turneraudio.com.au/Wien-b...scillator.html

Address brick bats carefully, so I may return them with gusto and a better aim than yours !
Patrick Turner.
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Phil Allison[_3_] Phil Allison[_3_] is offline
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Default Wien Bridge Oscilator, 1Hz to 1MHz.


"patrick-turner"

http://www.turneraudio.com.au/Wien-b...scillator.html


** In about 1978, I acquired a used BWD 141 in excellent condition.

Although capable of battery operation, a mains PSU came installed in the
battery compartment. The vast majority of units made had this option fitted.

The custom made, wire wound, reverse log, 15kohm dual potentiometer was the
best thing about it and normally outlasts everything else. I still have two
perfect examples, one in daily use.

Because of using such a beautiful pot, BWD 141s have exceptional frequency
stability.

The typical THD is 0.05% between 100 Hz and 100kHz.

Replacing the original BWD discreet electronics with a pair of NE5532
op-amps and a "phase shifting oscillator" topology reduced the THD to
vanishing levels (circa 0.002% ) at all audio frequencies.

Shame then Turneroid had to butcher his one so badly.





.... Phil



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Phil Allison[_3_] Phil Allison[_3_] is offline
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Default Wien Bridge Oscilator, 1Hz to 1MHz.


"Phil Allison"

** In about 1978, I acquired a used BWD 141 in excellent condition.

Although capable of battery operation, a mains PSU came installed in the
battery compartment. The vast majority of units made had this option
fitted.

The custom made, wire wound, reverse log, 15kohm dual potentiometer was
the best thing about it and normally outlasts everything else. I still
have two perfect examples, one in daily use.

Because of using such a beautiful pot, BWD 141s have exceptional frequency
stability.

The typical THD is 0.05% between 100 Hz and 100kHz.



** Stumbled on this web page that has internal pics ( high res too) and a
link to the schematic.

http://goughlui.com/?p=1343



..... Phil


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patrick-turner patrick-turner is offline
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Default Wien Bridge Oscilator, 1Hz to 1MHz.

Phil mentioned, as I expected, about yet another piece of old junk made in Autrsalia when far better stuff could have been made........

Although capable of battery operation, a mains PSU came installed in the
battery compartment. The vast majority of units made had this option fitted..

The custom made, wire wound, reverse log, 15kohm dual potentiometer was the
best thing about it and normally outlasts everything else. I still have two
perfect examples, one in daily use.

**You are lucky. The pot on the one I have IS ****, intermittent, and you can't pull it apart to clean it and I guess it was worn out. There were other faults in PS, ****ed bjts from having recieved stray excessive voltages from something it was hooked up to.

Because of using such a beautiful pot, BWD 141s have exceptional frequency
stability.

**I have found all pot operated wien bridge oscilators are far less stable than somethig operated by a radio tuning gang and fixed resistances. The HP 33A gear was SO MUCH better, with a beautiful 4 gang C you can get 100pF to 1,000pF. But the amount of C isn't enough to allow sensible R values at 1Hz. There is only room for a suitable replacement for the Comptom pot, or you have switched F where the R says absolutely stable, and when you switch to a selected F, that's what you get.

The typical THD is 0.05% between 100 Hz and 100kHz.

**Yes, not bad, but excessively good for just response testing I have other low THD oscilators for low THD.

Replacing the original BWD discreet electronics with a pair of NE5532
op-amps and a "phase shifting oscillator" topology reduced the THD to
vanishing levels (circa 0.002% ) at all audio frequencies.

**No doubt you could use opamps but They don't go very well at 1MHz. I have not explored using special much wider BW devices. I've just used what everyone can buy at wescomponents.com.au

**My circuit gives no DC offsets, and excellent square waves from 1Hz to 100kHz, quite good enough from 100kHz to 400kHz. Square waves above 400kHz are acceptable for limited use and could be better but I really should put in another emitter follower comp pair buffer after the attenuator switch and pot to create Rout of always 50 ohms to preserved the HF content to maybe 20MHz. I have not explored making a better Schmitt trigger sine to square wave converter. But I do have quite good all round performance and better than the crummy original junk that BEGGED to be BUTCHERED, as it was never ever going to get used as it was, and I came close to putting the junk in the bin.

Shame then Turneroid had to butcher his one so badly.

**Shame Phil likes to stand up for such terrible old junk.

**The fet I use for NFB control is not a perfect solution. Its action creates considerable THD as anyone will find if they put a CRO on the drain terminal of the MPF102, the typical j-fet used in such a situation. What puzzles me is that you have a fet with source at 0V, and gate has negative bias applied, like a vacuum tube, but drain is also at 0Vdc bias and the applied Vac to drain swings above and below 0V, and there is considerable THD created by the action so the Rd looking into the biased fet d terminal is a non linear resistance. I think there should be about +10Vdc at the MPF102 drain, and that this should be supplied by a CCS, using a u-follower cuit with additional MPF02 with fixed 10Vdc appied to its gate, 470k bias R and its gate cap coupled to drain of bottom j-jet. Then the drain to 0V circuit of bottom fet can be cap coupled to other R of NFB network, 2k7, and maybe the Rd with DC bias across the fet may be more linear.
I am also thinking of a light dependant resistance and LED, but that all seems to have circuit impedance that is is too high for MHz operation.
There is actually rather a small amount online abut the real issues involved with fets used in NFB regulation. BUT, I find RS component have type 327 lamps which are rated for just over 1W at 28V and 40mA, giving 700r, so 150r at low levels of an oscillator, and the other R then can be 300r, giving FB R total of 450r, and OK at HF, and not too low to load the amp too much. 327 would be better than 12V "grain of wheat lamps" which are 27r cold, and ideally 60r with a volt. Using a few in series gives starnge results because then you find any batch you buy are all unmatched, and some run with much varying T. Having said that, I have a 1kHz oscillator that gives 8Vrms at THD 0.004% using NE5534, and with just the one 12V lamp which has about 2.67V across it.
Patrick Turner.
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Phil Allison[_3_] Phil Allison[_3_] is offline
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Default Turneroid Menace Strikes back


"patrick-turner"

Phil mentioned, as I expected, about yet another piece of old junk made in
Autrsalia when far better stuff could have been made........

** Wot a pig ignorant, bull****ting old ****.


Although capable of battery operation, a mains PSU came installed in the
battery compartment. The vast majority of units made had this option fitted.

The custom made, wire wound, reverse log, 15kohm dual potentiometer was the
best thing about it and normally outlasts everything else. I still have two
perfect examples, one in daily use.

**You are lucky.

** Bull****.

The pot on the one I have IS ****,

** Very, very unusual.


Because of using such a beautiful pot, BWD 141s have exceptional frequency
stability.

**I have found all pot operated wien bridge oscilators are far less stable
than somethig operated by a radio tuning gang and fixed resistances.


** NOT true when the pot is a precision WW type as is the case here - plus
the electronics are all SS so there is no temp rise.


The typical THD is 0.05% between 100 Hz and 100kHz.

**Yes, not bad, but excessively good for just response testing ...

** Wot a ****ing stupid thing to say.

Wot a ****ing stupid **** just said it.


Replacing the original BWD discreet electronics with a pair of NE5532
op-amps and a "phase shifting oscillator" topology reduced the THD to
vanishing levels (circa 0.002% ) at all audio frequencies.

**No doubt you could use opamps but They don't go very well at 1MHz.


** Never said they did - you bul****ting old ****.


Shame then Turneroid had to butcher his one so badly.


** Shame Phil likes to stand up for such terrible old junk.

The original BWD141 performs way better than ****ing the POS the Turneroid
made out of his.

http://goughlui.com/?p=1343


The Turneroid abortion has horrible, discontinuous frequency adjustment,
massive transients in the output and very high THD. So it is utter garbage
for audio testing.

As I expected, when you throw a Pearl in front of a swine.



.... Phil





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Phil Allison[_3_] Phil Allison[_3_] is offline
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Default Wien Bridge Oscilator, 1Hz to 1MHz.


"patrick-turner is a **** "

http://www.turneraudio.com.au/Wien-b...scillator.html


** In about 1978, I acquired a used BWD 141 in excellent condition.

Although capable of battery operation, a mains PSU came installed in the
battery compartment. The vast majority of units made had this option fitted.

The custom made, wire wound, reverse log, 15kohm dual potentiometer was the
best thing about it and normally outlasts everything else. I still have two
perfect examples, one in daily use.

Because of using such a beautiful pot, BWD 141s have exceptional frequency
stability.

The typical THD is 0.05% between 100 Hz and 100kHz.

Replacing the original BWD discreet electronics with a pair of NE5532
op-amps and a "phase shifting oscillator" topology reduced the THD to
vanishing levels (circa 0.002% ) at all audio frequencies.

Shame then Turneroid had to butcher his one so badly.





.... Phil





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Trevor Wilson Trevor Wilson is offline
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Default Wien Bridge Oscilator, 1Hz to 1MHz.

On 22/08/2013 8:18 PM, patrick-turner wrote:
Hi folks, people, demons and anyone else hangin around.
I have posted up another page for as 1/2 decent wien bridge oscilator which has 6 F ranges to give 1Hz to 1MHz. Instead of using potentiometers or tuning caps it has a two ganged wafer switches each with 12 pos x 1 pole to give relative F = 1, 1.2, 1.5, 2.0, 2.5, 3.2 3.9, 4.7, 5.6, 6.8, 8.2 and 10.0. These F appear at fairly evenly positioned points around a dial covering 360 degrees with 12 F marks.
A fairly decent Schmitt trigger square wave maker is included.
See
http://www.turneraudio.com.au/Wien-b...scillator.html

Address brick bats carefully, so I may return them with gusto and a better aim than yours !
Patrick Turner.


**OT, I know, but I recently acquired a couple of General Radio 1564-A
generator/measurement devices. The mechanical engineering in these
things is simply astonishing. When I get some time, I'll replace the
NiCads and restore them (not that much needs to be done - they look like
they've been build to last a 1,000 years).

--
Trevor Wilson www.rageaudio.com.au
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patrick-turner patrick-turner is offline
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Default Wien Bridge Oscilator, 1Hz to 1MHz.

Phil mentioned this about my butchering of a crummy low quality budget iBWD141 oscilator...

""The Turneroid abortion has horrible, discontinuous frequency adjustment,
massive transients in the output and very high THD. So it is utter garbage
for audio testing.
As I expected, when you throw a Pearl in front of a swine. ""

The original 141 I was given had a ****ed Compton pot, and no amount of fiddling with adjustments would improve it.

Rather than chuck it out, I tried implememting a home brew op-amp using discrete bjts and j-fet input. Such a voltage amp can amplify signals from 0.1Hz to about 4MHz at 3.6Vrms output without slew THD and have low output Vdc offset and have low Rout, and low noise, all better properties than the original 141 amp.

But anyone should feel free to use some of the op-amps available which are not to be found at Jaycar or wescomponents.com.au and which may produce higher F with wien bridge than 1MHZ.

The output on my oscilator amp has a voltage clamp to prevent Vo swinging wildly during switching F ranges, (and unavoidable in the original 141.) The make before break switches used for switched resistors instead of a damned pot prevent noticeable transients. Any transients are so short lived during normal use that any amplifier being tested will cope well with the transients because they have peak voltage of only +/- 1.4db around normal output voltage of 3.6Vrms. If a tested amp doesn't cope with such mild transients then it is a really awful bloody amp which needs serious re-design.
The Turnerized 141 replaces a similar unit I buit from scratch some years ago but which only goes from 2Hz to 200kHz in 5 ranges, and often I wanted to know what happens between 200kHz and 1MHz. That unit has square waves to 470kHz, and not quite as nicely square as the Schmitt trigger I have made, shown at my page on the revised oscillator.

The overall build quality of the original 141 was Bluddy Crummy. Low budget **** quality, and nowhere near what was then being made in USA and which was of much more expensive, and mainly only purchased by government depts, armed forces, universities, but rarely by private service ppl. The original BWD 141 board is a monument to bean counting and penny pinching cost cutting and parts are crammed onto a board that is too small and very low quality like you'd find in really poor quality kits from Jaycar or Dick Smith. Almost anything any one does can be better.

I also have a 161 which is a function generator with sine, square and triangle wave and done using an early function chip with a single pot for F control. Its not bad, but very imprecise and with high THD and varying square wave symmetry and atrociously low Vo level so had to instal a wide band home brew op-amp and do considerable repairs and alterations to make it as usable as my existing totally home brew gear. I did once have a Topward function gene, with far more sophisticated circuitry, and AM and FM functions up to 2MHz, and far less THD than the BWD but the pot wore out, then another wore out, and the output amp burnt out so badly plus many other chips when a lead touched a tube amp B+ that I binned the bloomin thing. Its power tranny hummed loudly, i'd replaced bits so often it was a mess, and time to say farewell. The use of a tubed cathode follower buffer after the unit Vo was a good idea, but I got lazy, forgot to include it, and POOF, smoke, and no sig.
Later, I found diode voltage clamps are OK most of the time.

I have a pair of HP 333A THD testing contraptions and a spare 4 gang tuning cap, and time permitting, I may build up a better unit than the original HP.
But I also have about 6 triple gang tuning caps from old radios and an ex-ham's collection so I can get 400pF to 4,000pF C variation and with low R get up to 5MHz with wien bridge if I wanted to with suitable SS devices. But for 1Hz, the R must be 40Meg, so fixed C and variable R is better for 1Hz to say 100Hz, and then the tuning C for the rest, so TWO oscillators need to be made.

Phil goes on to spit the dummy, and to insist I am a copulating female sex organ. IMHO, he really should stick to electonics, not delve into incorrect personel assessment, lest everyone begin believing all he says is incorrect.
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"patrick-turner is a stinking swine "

http://www.turneraudio.com.au/Wien-b...scillator.html


** In about 1978, I acquired a used BWD 141 in excellent condition.

Although capable of battery operation, a mains PSU came installed in the
battery compartment. The vast majority of units made had this option fitted.

The custom made, wire wound, reverse log, 15kohm dual potentiometer was the
best thing about it and normally outlasts everything else. I still have two
perfect examples, one in daily use.

Because of using such a beautiful pot, BWD 141s have exceptional frequency
stability.

The typical THD is 0.05% between 100 Hz and 100kHz.

Replacing the original BWD discreet electronics with a pair of NE5532
op-amps and a "phase shifting oscillator" topology reduced the THD to
vanishing levels (circa 0.002% ) at all audio frequencies.

Shame the Turneroid Public Menace had to butcher his one so badly.

That is what happens when you give a pearl to a pig ignorant piece of swine.


BTW:

** Stumbled on this web page that has internal pics ( high res too) and a
link to the schematic.

http://goughlui.com/?p=1343




.... Phil




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patrick-turner patrick-turner is offline
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Default Wien Bridge Oscilator, 1Hz to 1MHz.

To all readers, I added more comments about the Wien Bridge oscilator at http://www.turneraudio.com.au/Wien-b...scillator.html

The text explains some minor changes.

I did find that above 500kHz, the square wave became slightly assymetrical so I've added R1a 150r plus C1a 100pF across R1 5k6 feed resistance to input base of Q9 at the Schmitt Trigger circuit.
The square wave at 1MHz now looks much better, and one whole lot better than in the original crummy low budget BWD 141.

But, I still have one problem. Such Wien bridge oscillators usually give their lowest THD and lowest Vo when the NFB ß factor is increased so that oscillations are on the verge of stopping, so that increasing NFB causes stop-start and more NFB makes it stop permanently.
Nobody wants Vo bounce, and everyone wants quick Vo amplitude settlement between F range switching, and in this case, F switching within each F range.
So in this case, I found the balance between low THD of 0.4% at 2.5Vrms output and 4% at 3.7V+ output. At 3.6Vo, I get 1.7% 2H.
It sounds a lot, but its hardly visible on the CRO and it does not alter measurements of amplifiers.
But when the Vo = 3.6Vrms, and THD = 1.7% 2H, -0.81Vdc is the gate bias of fet, abd its Rd measures 302 ohms and the Vd = 0.26Vrms, and the THD at d = 5% approx, mostly 2H. I'm not 100% clear about the properties of the j-fet. We have a voltage at the drain varying +/-0.36Vpk, so current flows positively and negatively, and the Rd in each direction is different.

So I can see that the j-fet has rather non linear drain resistance Rd, and when I get time I will try redesigning the whole NFB loop so there is DC flow in the fet from a second j-fet arranged as a µ-follower. Afaik, bias can be the same as I have it now. The 2k7 plus 1k0 VR1 can be cap coupled to the bottom j-fet drain and then I can see what happens and see if the Rd with Idc and Ed at say +8V is any more linear. The existing 2uF plus 1M0 for control amp Vo DC offset can be removed because of cap coupling of all NFB Rs to the fet drain via a cap.

Elsewhere on the Net you can see j-fets commonly recommended for dynamic ß control used in the FB network to stabilise Vo, but usually, there is **** all mention of the difficulties involved to get good usable operation.

Its also possible to maybe use a voltage clamp of 12 x 1N914 with 6 in series facing each way and with 1k0 trimpot all across my 2k7. The use of 6 such diodes in series means their stray C is minimised and their turn on character is not abrupt, but over a wider V & I range. Then THD should become mainly 3H, and the 3H is not conducted around the PFB loop as much as the 2H.

Its occured to me that anyone could have a single F Wien bridge oscillator with say 3 cascaded wien bridges, each with gain amp of 3x, with two amps having fixed NFB networks. But the last amp has its NFB enclosing the 3 networks with the 2 "buffer" gain amps between the 3 PFB networks. This will increase the Q of the PFB networks and thus any THD of the main amp with variable NFB will be less boosted by the PFB thus allowing NFB to reduce it by about -12dB more than otherwise. Its seems a lot of trouble to go to, but I think that if the PFB network had a higher Q you'd get a lot less THD without needing such a huge amount of open loop amp gain. One is almost tempted to use an LC circuit, or a gyrator used with a C for a parallel resonant circuit.

Keep soldrin', and if you can't stay healthy, try not to go insane.
Patrick Turner.




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Default Wien Bridge Oscilator, 1Hz to 1MHz.

More from me about wien bridge oscilator.

The idea of passing idc through fet does not make any difference to the nature of the effective Rd - it remains a very non linear resistance.

WB oscilators with lamps or thermistors are probably all capable of producing far less THD. But perhaps using current source from a bjt collector with PNP MJE350 to pass some dc through 3 x 12V/50mA lamps to warm them up so R = 100r, so 3 give R = 300r, and then NFB network total R = 900r, and that may work well. The main FB R = 600r approx, and would be cap coupled to lamps, and Idc controlled with rectified voltage to MJE350 base and current limited with say 220r emitter R between +20V and emitter.

"Grain of wheat" 12V lamps have about 27r at 20C and when hot are 240r.

I could get a type 327 lamp, 28Vx40mA = 700r at max on current, and maybe 240r at situation where you wan to use them in WB oscilator, sometimes with cathode Idc flowing through one at V1 cathode of a 2 stage tubes oscilator. I recall HP's first WB oscilator had this.

Patrick Turner.

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Default Wien Bridge Oscilator, 1Hz to 1MHz.

Regarding the wien bridge oscilator.
I deleted the j-fet amplitube regulator. I could not sleep because it produced a huge amout of THD. But at least the Vo did not bounce, and all F between 1Hz and 1MHz had the same amplitude.

But after deleting the j-fet, I tried the ITT P564 thermistor and a an adjust pot to see just how well it worked. I soon saw how badly the darn thing worked with terrible V bounce. But THD was very low. But I could not get all the F in 100kHz to 1MHz range to oscillate. I tried lots of things and had to delete the bloomin thing.

Then I built a high input Z rectifier to produce a max +Vdc of +3Vdc. This is applied to a base of a common emitter stage which inverts the at the collector output so that a Vdc can be derived to power a BC640 bjt with Re 180r so that as it turns on it feeds collector current up to 22mA through 4 series lams each rated for 12V x 50mA.
Suitable R + electro Cs slow down any change in lamp DC current and its the DC though the lamps that causes the most change in their resistance, which varies between 27r cold to up 115r with about 22mA.

I have not tried my 3 bjt Vo regulator yet, but it does seem to behave far better than the j-fet, and up to a slightly higher Vo.

The ß just goes over 0.33 at 3.5Vrms input to my circuit.
But at turn on, ß = 0.1, so oscillations will be max and distorted until lamps warm up SLOWLY.

This NFB is a much lower resistance circuit so I expect no troubles getting all F between 100kHz and 1MHz

I should get far lower THD, because the VNFB produced has no visible THD on my CRO, unlike the j-fet which produced several % 2H.

I removed the PSU from inside the box, and re-built it much better at the rear of the back plate so I have to make a cover to screw over it. This re-arrangment gave me room to put the Vo regulator in a nice board against the inside of the rear panel. The arrangment keeps noise extremely low.

I will ammend the circuit at my website when I try the new Vo reg and iron out any unexpected bugs which always manage to accompany R&D when you get keen.

So, what did anyone else work on today? Or have you given up?

Patrick Turner.
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Default Wien Bridge Oscilator, 1Hz to 1MHz.

Last night I said I had a plan in mind for dc current control of the lamp resistance.............

"""Then I built a high input Z rectifier to produce a max +Vdc of +3Vdc. This is applied to a base of a common emitter stage which inverts the at the collector output so that a Vdc can be derived to power a BC640 bjt with Re 180r so that as it turns on it feeds collector current up to 22mA through 4 series lams each rated for 12V x 50mA.
Suitable R + electro Cs slow down any change in lamp DC current and its the DC though the lamps that causes the most change in their resistance, which varies between 27r cold to up 115r with about 22mA.

I have not tried my 3 bjt Vo regulator yet, but it does seem to behave far better than the j-fet, and up to a slightly higher Vo.

The ß just goes over 0.33 at 3.5Vrms input to my circuit.
But at turn on, ß = 0.1, so oscillations will be max and distorted until lamps warm up SLOWLY.

This NFB is a much lower resistance circuit so I expect no troubles getting all F between 100kHz and 1MHz

I should get far lower THD, because the VNFB produced has no visible THD on my CRO, unlike the j-fet which produced several % 2H.""

This is all very well, and a fabulous plan and while there wasn't any oscilator amp hooked up, the experiment showed it might work, but unfortunately, time constants got me yet again when trying to implement a circuit with long time constants into another amp circuit ( the oscillator amp ) with very high open loop gain, even at near DC.
The result was that the Vo slowly waved up and down like very slow amplitude modulation because the DC servo circuit was acting as a LF oscilator to vary the lamp resistance.
Back to the drawing board. I doubt if any simulation program would tell me it won't work before I built it because I doubt anyobe would know how to enter in so many interactive variables.

But at least it works with a j-fet, except for the highish THD. I will reserach a little more, before returing to the j-fet idea.

Sorry to bore you all to tears. Its OK, but wenya tryta build sumping good, with high aims in mind, then a special Law of Life applies :- COWPAT = 1 / N squared, where COWPAT = Chance Of Working Perfectly Any Time and N is the number of things you didn't know might stop it working, or what you didn't know, or you dropped a spanner, or the dog ate your data notebooks :-)
Patrick Turner
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Default Wien Bridge Oscilator, 1Hz to 1MHz.

Previously, I described my 3 transistor amplitude control circuit, then I said.....

"""This is all very well, and a fabulous plan and while there wasn't any oscillator amp hooked up, the experiment showed it might work, but unfortunately, time constants got me yet again when trying to implement a circuit with long time constants into another amp circuit ( the oscillator amp ) with very high open loop gain, even at near DC.
The result was that the Vo slowly waved up and down like very slow amplitude modulation because the DC servo circuit was acting as a LF oscilator to vary the lamp resistance.
Back to the drawing board. I doubt if any simulation program would tell me it won't work before I built it because I doubt anyobe would know how to enter in so many interactive variables.

But at least I knew the oscillator works with a j-fet Vo reg, except for the highish THD. I will reserach a little more, before returing to the j-fet idea.

Sorry to bore you all to tears. Its OK, but wenya tryta build sumping good, with high aims in mind, then a special Law of Life applies :- COWPAT = 1 / N squared, where COWPAT = Chance Of Working Perfectly Any Time and N is the number of things you didn't know might stop it working, or what you didn't know, or you dropped a spanner, or the dog ate your data notebooks :-)
Patrick Turner"""

Now today I tried a few more mods to time constants around 3 bjts, ie, adding larger coupling C, and finally I got it stable at 1kHz, and I measured THD = 0.015%, not bad. But if I switched anything, the Vo would dissapear and take too much time to re-appear at a different F.

So, I removed the 3 bjt Vo control circuit; I don't have a lifetime to spend on a dodgy idea.

I assembled a j-fet circuit again, but this time added some shunt NFB between drain and gate, just 2 x 10k plus a 220uF and slightly modded rectifier circuit for getting the wanted -1Vdc gate bias.

The revised Vo reg circuit will appear at my website in coming days.

The shunt FB does not much change the j-fet MPF102 Rd which needs to be about 300r at normal op with about -1Vdc gate bias.
Everything became stable and not too critical and I could re-measure THD with the fet Vo control. I got 0.014%, certainly good enough, and better than nearly 2% without the local shunt FB at the fet.

I then built an complementary darlington pair emitter follower buffer output stage to use between 1k0 output pot and output terminals. This lowered Ro to 55 ohms, so that HF content wasn't so easily shunted by cable C after the output pot. I used PN100, PN200 driving BD1390, BD140.

But THD rose to 0.09%, I suspect its the buffer., even though it has 15mAdc idle current so 3.6Vrms can be put into 400r without the stage moving out of class A. No crossover THD at HF.

The effect of the buffer after the attenuator and level pot gave a rather good 1MHz square wave with 104V/uS rise time, ie, the rise time was like 1/2 a 10MHz sine wave which is 10.4Vp-p, and time = 0.1uS.

So the old BWD 141 is now quite a decent unit. Switching F along a selected band causes almost no V0 level bounce, and no long delays before settling and like my other oscillators with switched F it works just fine.

Noise at the output with all attenuators turned to low was mainly stray RF pick up because metal covers are not on yet, but level measured 0.2mV. The only thing in the signal path is the EF output buffer with its input shunted to 0V,
so there isn't much noise.

Patrick Turner.
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patrick-turner patrick-turner is offline
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Posts: 119
Default Wien Bridge Oscilator, 1Hz to 1MHz.

It seems like I am the only ******* left alive on Planet Earth.

Has everyone died?

I have NOT.

Anyway, I have revised my page about the Wien Bridge oscillator with re-done schematics including many new details.
See http://www.turneraudio.com.au/Wien-b...scillator.html

I will estimate its The Most Boring website page ever devised, unless you'd like to make a half decent signal gene.

Of course, I have used a rotary two wafer make-before-break switch that gives 12 F per decade evenly spaced around a dial at enough convenient F to allow plotting most F reponses of any audio gear tested, unless a high Q resonant filter is used, because the adjustablity of a pot of variable C is not present.
For audio amp checking the unit is quite sufficient. Those wanting infinitely varaible F should consider buying a dual gang reverse direction log pot with value 15k. Lord Noze where you'd obtain one, and one that gave you nicely spread out F around 315 degrees of rotation with 1Hz at the max anti clockwise and 10Hz at max clockwise and 3.2Hz at 1/2 rotation.
With a bigger box and slightly more range switch complexity you might incorporate TWO 3 gang AM radio tuning caps with each gang 40 to 440pF thus giving 132pF to 1,320pF which is fine for 100Hz to 1MHz, with fixed R values. The two ranges 1Hz - 10Hz, 10Hz - 100Hz could use a pot with fixed C and values are not difficult to implement. The variable tuning gang as was made in 1950s is hard to beat for a WB oscillator but to get down to 1Hz with max C = 1.320pF the R needs to be 120Meg ohms, an impractical R value. But where you had 6 x 3gang C then C max = 3960pF, and if your lowest range was 2Hz to 20Hz, then R need only be 20Megohms.
The minimum C = 396pF, and R need only be 200r for 2MHz. For stable operation at such a high F you need low value R and C high enough so stray C in devices does not make F adjustment too critical. The j-fet in NFB network for Vo control should work up to 2MHz.

HeeLLLLOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO? anyone there? Ah, they all musta died.

Think I'll go ride a bike, and even being attacked by magpies is just fine.
Patrick Turner.


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John L Stewart John L Stewart is offline
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Location: Toronto
Posts: 301
Smile

Quote:
Originally Posted by patrick-turner View Post
It seems like I am the only ******* left alive on Planet Earth.

Has everyone died?

I have NOT.

Anyway, I have revised my page about the Wien Bridge oscillator with re-done schematics including many new details.
See http://www.turneraudio.com.au/Wien-b...scillator.html

I will estimate its The Most Boring website page ever devised, unless you'd like to make a half decent signal gene.

Of course, I have used a rotary two wafer make-before-break switch that gives 12 F per decade evenly spaced around a dial at enough convenient F to allow plotting most F reponses of any audio gear tested, unless a high Q resonant filter is used, because the adjustablity of a pot of variable C is not present.
For audio amp checking the unit is quite sufficient. Those wanting infinitely varaible F should consider buying a dual gang reverse direction log pot with value 15k. Lord Noze where you'd obtain one, and one that gave you nicely spread out F around 315 degrees of rotation with 1Hz at the max anti clockwise and 10Hz at max clockwise and 3.2Hz at 1/2 rotation.
With a bigger box and slightly more range switch complexity you might incorporate TWO 3 gang AM radio tuning caps with each gang 40 to 440pF thus giving 132pF to 1,320pF which is fine for 100Hz to 1MHz, with fixed R values. The two ranges 1Hz - 10Hz, 10Hz - 100Hz could use a pot with fixed C and values are not difficult to implement. The variable tuning gang as was made in 1950s is hard to beat for a WB oscillator but to get down to 1Hz with max C = 1.320pF the R needs to be 120Meg ohms, an impractical R value. But where you had 6 x 3gang C then C max = 3960pF, and if your lowest range was 2Hz to 20Hz, then R need only be 20Megohms.
The minimum C = 396pF, and R need only be 200r for 2MHz. For stable operation at such a high F you need low value R and C high enough so stray C in devices does not make F adjustment too critical. The j-fet in NFB network for Vo control should work up to 2MHz.

HeeLLLLOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO? anyone there? Ah, they all musta died.

Think I'll go ride a bike, and even being attacked by magpies is just fine.
Patrick Turner.
Still here Patrick & look in every day or two as I'm sure others do. Today is my 81st so I will go out & do 50 km on the bike. Takes about 2h50m these daze. Twenty years ago could easily do 70 km in that time. But August was good for 550 km anyway.

No Magpies here, they are all in Western Canada. But we got their relatives, Crows, Ravens, Jays & so on. The Redwing Blackbird chase in their nesting season. Almost collided with a flying Wild Turkey a few years ago. That would be a mess, they are kinda large.

This Summer has been mostly manual labour. several trees to cut up, the firewood pile is getting huge. There will be lots of work for the log splitting machine in October.

My electronics this Summer has been construction of a half-wave dipole for FM. The width is obvious. All made with 1/2 inch copper pipe, so the spacing by the formula is about 3 inches to get 300 ohms.

Works OK part way up the tower so now gotta go all the way. Without falling off. Me, that is.

Cheers to all, John
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patrick-turner patrick-turner is offline
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Default Wien Bridge Oscilator, 1Hz to 1MHz.

patrick-turner;971790 Wrote:
It seems like I am the only ******* left alive on Planet Earth.


- show quoted text -

Has everyone died?

I have NOT.

Anyway, I have revised my page about the Wien Bridge oscillator with
re-done schematics including many new details.
See http://www.turneraudio.com.au/Wien-b...scillator.html

I will estimate its The Most Boring website page ever devised, unless
you'd like to make a half decent signal gene.

Of course, I have used a rotary two wafer make-before-break switch that
gives 12 F per decade evenly spaced around a dial at enough convenient F
to allow plotting most F reponses of any audio gear tested, unless a
high Q resonant filter is used, because the adjustablity of a pot of
variable C is not present.
For audio amp checking the unit is quite sufficient. Those wanting
infinitely varaible F should consider buying a dual gang reverse
direction log pot with value 15k. Lord Noze where you'd obtain one, and
one that gave you nicely spread out F around 315 degrees of rotation
with 1Hz at the max anti clockwise and 10Hz at max clockwise and 3.2Hz
at 1/2 rotation.
With a bigger box and slightly more range switch complexity you might
incorporate TWO 3 gang AM radio tuning caps with each gang 40 to 440pF
thus giving 132pF to 1,320pF which is fine for 100Hz to 1MHz, with fixed
R values. The two ranges 1Hz - 10Hz, 10Hz - 100Hz could use a pot with
fixed C and values are not difficult to implement. The variable tuning
gang as was made in 1950s is hard to beat for a WB oscillator but to get
down to 1Hz with max C = 1.320pF the R needs to be 120Meg ohms, an
impractical R value. But where you had 6 x 3gang C then C max = 3960pF,
and if your lowest range was 2Hz to 20Hz, then R need only be 20Megohms.

The minimum C = 396pF, and R need only be 200r for 2MHz. For stable
operation at such a high F you need low value R and C high enough so
stray C in devices does not make F adjustment too critical. The j-fet in
NFB network for Vo control should work up to 2MHz.

HeeLLLLOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO? anyone there? Ah, they all
musta died.

Think I'll go ride a bike, and even being attacked by magpies is just
fine.
Patrick Turner.



Still here Patrick & look in every day or two as I'm sure others do.
Today is my 81st so I will go out & do 50 km on the bike. Takes about
2h50m these daze. Twenty years ago could easily do 70 km in that time.
But August was good for 550 km anyway.

Lemme se now, your time is 2.83 Volts, and you have distance of 50 Ohms, so your average speed I = R / V = 50 / 2.83 = 17.67 Amps. It must be hilly where you are because I averaged 25.5 Amps for 91 Ohms on last Therzdi.

There's a guy of 78 in my cycling group and he does about 22kph av for about 75km, so he ain't far behind me at 26.2 usual average for the not too hilly terrain around here.

But be careful if you live to 240 years old. Maximum heart rate for many ppl is 220 - age, so if your'e 40, max HR = 180, and that's a very fine performance indeed.
But at 80, max HR = 140, also not bad, but when ya get to 240, HR max = 220 - 240 which is -20 beats a minute. I think if you cycle backwards you can avoid the problem of a negative HR.

No Magpies here, they are all in Western Canada. But we got their
relatives, Crows, Ravens, Jays & so on. The Redwing Blackbird chase in
their nesting season. Almost collided with a flying Wild Turkey a few
years ago. That would be a mess, they are kinda large.

The main threat to cycling on country roads are motorists. But the next worst thing to hit is a dopey kangaroo, can be same weight as a man, and their road sense is atrocious, so when I am decending on a mountain road at maybe 60kph, I have to keep a sharp look out for a roo which might just jump out of nowhere.

This Summer has been mostly manual labour. several trees to cut up, the
firewood pile is getting huge. There will be lots of work for the log
splitting machine in October.

Seems like you have a firewood obsession. I have an obsession with grass and hedge. Kylie and Samantha are helping out. Had row with Sam because she insisted she wear red hotpants while up the ladder with hedge clipper. Caused a couple of young blokes to crash their cars commin round the corner. I said, "Sam, safety regulations stipulate hi-viz gear, OK, so yol needta change red to grey pants and use a bright yello top...."

My electronics this Summer has been construction of a half-wave dipole
for FM. The width is obvious. All made with 1/2 inch copper pipe, so the
spacing by the formula is about 3 inches to get 300 ohms.

I have not moved up in frequency much yet, I'm still stuck below 1MHz most daze.

Works OK part way up the tower so now gotta go all the way. Without
falling off. Me, that is.

Yes, many an older man falls off a ladder or some other dang thing he shouldn't be up on.
But its a trouble many men face, they wanna do all this stuff, but they can't do it like they didded it when 25.

We seem to be getting October spring weather a month early.

Cheers to all, John

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