Composite amps -compensation ---> www.pdk101.com/Design_related/OPA/OPA_lowPower_HighGain_compensation.pdf
Thx-RNMarsh
Thx-RNMarsh
Hi,
What do you think about photo resistive optoisolators? Before some days, I thought, that these are one of the better things for VCRs. Now I have different opinion. Vactrol VTL5C7 measuring result (light diode current 6.5mA, voltage across photo resistor 40mV p-p, resistance app 200ohm, 10kohm resistor between 1kHz sine source and photo resistor):
http://content7-foto.inbox.lv/albums/e/elterra/VactrolMeasurment/VTL5C7dist2.jpg
Also I put them in different regimes and use another one, but results are very similar.
Victor.
What do you think about photo resistive optoisolators? Before some days, I thought, that these are one of the better things for VCRs. Now I have different opinion. Vactrol VTL5C7 measuring result (light diode current 6.5mA, voltage across photo resistor 40mV p-p, resistance app 200ohm, 10kohm resistor between 1kHz sine source and photo resistor):
http://content7-foto.inbox.lv/albums/e/elterra/VactrolMeasurment/VTL5C7dist2.jpg
Also I put them in different regimes and use another one, but results are very similar.
Victor.
If you look at the distortion vs. level you will see that it increases rapidly with voltage. For an oscillator that has a target distortion at -120 dB or lower the -80 dB you show at 40 mV needs to be attenuated by another 40 dB which really limits the amount of gain range possible. The Silonex LDR's are supposed to have less distortion. I will have some early next year and I'll see what I can find out about their distortion.
You are right, but as I previously wrote, FET in similar conditions shows more better results:
http://content8-foto.inbox.lv/albums/e/elterra/FETmeasurement/FET40mV.jpg
Hi vicnic,
Have you considered trying a thermal approach.
I know the LT part for RMS detection is no longer available and hard to get but a pair of RDTs in an insulated chamber might work. I doubt fast settling would be achievable.
Cheers,
Hi, David
I made some experiments around thermal in past, but not got good results. Almost one thing I remember - pain
. Thermal inertia, that I can not change.Victor
There is a positive temperature coefficient thermistor in an evacuated bulb that is very easily had in many values. Its called an incandescent light. The thermal inertia is essential to not add even order distortion as it changes with the waveform.
There are still issues of overall amplitude stability which my idea was to add a dc current to tweak the overall resistance to the target value that is controlled by a precision level detector.
There are still issues of overall amplitude stability which my idea was to add a dc current to tweak the overall resistance to the target value that is controlled by a precision level detector.
True RMS detectors are plentiful? I tried a Tellabs precision wirewound thermistor designed to compensate KT/q in log amps in a chamber. Settling was hopeless.
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I think he was referring to the now obsolete LT1088 == Linear's "thermopile on a chip". Jim Williams did an ap-note on True RMS and mentioned the device. Here's a link to the datasheet: http://cds.linear.com/docs/Datasheet/lt1088.pdf
Yes this is the one. I really disappointed this is out of production.
This thing can do 0 to infinity Hz.
Hi Scott,
What doesn't work with one oscillator type might work with another.
I have a multiplier along the lines of what Demian is suggesting. It doesn't work with a Bridged T but it works perfectly with a SVO. It doesn't work with a fast ALC because the tau of the lamp is too long. It doesn't respond fast enough. It is capable of stabilizing the SVO on it's own. All it really needs is an auto set level sort of thing. Some thing to just bring the level to a dc reference slowly but not so slow it is annoying.
Can you share some part numbers for these plentiful thermal RMS detectors?
Cheers,
For precision I would not recommend a thermal converter, unless you want to do down the vacuum thermocouple route Thermal Elements for Ballantine TVC. And that is way expensive. If the sine wave is clean enough (which it is in this case) peak detection will get you the most resolution easiest. Thermals are of course thermal. . . A good peak detector and a good voltage reference should get really good results. I would sense at the output terminals before the source Z setting resistor. Its more of a "leveling loop" like a microwave generator would have.
Hi Demian,
It's taking me so long to get this project together I may as well share the work I've done on my incandescent lamp multiplier. I keep getting distracted with other things like modding the 339a and such. I can't etch PCBs indoors because of the corrosive fumes attacking my furnace ducting. It was -32C, -25.6F outside yesterday so you can see etching outside is out.
I'll write up a short summery of the multiplier and follow up with a more detailed paper with graphs. All I ask is for others to let me publish the first working oscillator using this proven multiplier design but everyone is welcome to experiment with this.
This is a working physical model.
More to come.
Cheers,
Hi Rick,
Yes suppose I can but I don't like doing this for development boards.
It seems like such a waist of money if I make a mistake.
There is an outfit in Taiwan that will do cheap boards but I've never tried them
and they take forever to deliver parts. I waited two months for some LT parts.
Half the cost though.
Cheers,
Hi Dimitri,
That is certainly approaching my cost of producing PCB. At that price it doesn't seem worth it to make my own.
Do you have to use their software or can you send the gerbers from your own preferred CAD?
Or can they process from the output files of most popular packages?
I like expressPCB a lot. Its not real cheap but the boards are good quality and its easy to share the source files. And plenty quick. They arrive just as you thought of the other changes you want to make. I would not use them for leading edge stuff (you can't anyway. . .).
However Canada shipping may make it lots less attractive.
However Canada shipping may make it lots less attractive.