Low-distortion Audio-range Oscillator - Page 21 - diyAudio
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Old 5th August 2012, 03:51 AM   #201
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Quote:
Originally Posted by DDB View Post
The seller also indicated he was comtemplating posting the schematic here or on his ebay ad.
Encourage him. I'm interested, but would like to know what I'm getting first! Also to know what the power supply requirements are to achieve the stated performance level.

Note he has added: "Improved version of this generator is on sale now . I can not change title. Typical performance of this generator now is app. - 136dB (0.15ppm) level of second harmonic, and unmeasurable (at this time) level of third harmonic (=<-140dB)."

Terry

Last edited by Terry McGee; 5th August 2012 at 04:06 AM.
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Old 5th August 2012, 04:30 AM   #202
1audio is offline 1audio  United States
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He did send me the schematic. It certainly has the potential to to meet those specs. The level detect is conventional, the circuit around the FET is novel.

At the price I have better things to do than build oscillators.
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Old 5th August 2012, 05:41 AM   #203
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OK, I've asked him ditto. And about the power supply requirements (ripple and regulation).

Terry
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Old 5th August 2012, 09:51 PM   #204
vicnic is offline vicnic  Latvia
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Hi to everyone.
I am author of this generator from ebay. Thanks to all, who trust and buy this. I designed this generator especially for best performance/cost ratio. Cause of many people ask me abut schematic, then now I post it to this forum:
Click the image to open in full size.
Symmetrized FET in AGC is the "heart" of this generator.
Improvement, which I made not long ago for better performance, is simple. I replaced all mean resistors in signal chain from 1206 Yageo cermet type to 0204 Vishay metal film. When I made 10kHz version, I observed some peculiarity in working, and in final I discovered, that resistors was not so good. And I was very impressed, when in 1kHz model distortions falls down after resistors replacement.
Excuse me, if there are some mistakes in my english.

Victor
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Old 5th August 2012, 10:11 PM   #205
vicnic is offline vicnic  Latvia
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P.S. About power supply. Cause of there are TL431 based shunt stabilizers on board, schematic is not very sensitive to supply ripple, but I recommend LM317HV regulator adjusted to 35V+/-0.5V as simple solution for this.

Victor.
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Old 6th August 2012, 06:55 AM   #206
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Thanks very much for that, Victor. I'm sure it's giving many of us a lot to think about!

Incidentally, I realise you probably optimise the timing for each fixed frequency to get the best results, but have you tried your FET control approach in a variable frequency oscillator? Can you achieve lower distortion and less "bounce" than say a thermistor-controlled system?

Terry
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Old 6th August 2012, 07:26 AM   #207
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Victor, thank you!
Now i just had to pull the trigger on the 1kHz version. I guess i'll take the 10kHz version too, in the feature...

Aargh, i need to finish my ADC rig.

Should i run it on batteries, or plain transformer regulated supply would suffice?
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Last edited by s3tup; 6th August 2012 at 07:29 AM.
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Old 6th August 2012, 07:45 PM   #208
vicnic is offline vicnic  Latvia
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Originally Posted by s3tup View Post
Victor, thank you!
Now i just had to pull the trigger on the 1kHz version. I guess i'll take the 10kHz version too, in the feature...

Aargh, i need to finish my ADC rig.

Should i run it on batteries, or plain transformer regulated supply would suffice?
Also thank you!
Plain transformer with simple regulated supply should be OK. I recommend transformer with windings in sections.
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Old 6th August 2012, 09:58 PM   #209
vicnic is offline vicnic  Latvia
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Quote:
Originally Posted by Terry McGee View Post
Thanks very much for that, Victor. I'm sure it's giving many of us a lot to think about!

Incidentally, I realise you probably optimise the timing for each fixed frequency to get the best results, but have you tried your FET control approach in a variable frequency oscillator? Can you achieve lower distortion and less "bounce" than say a thermistor-controlled system?

Terry
No one system is absolutely perfect, but if we have one target, we can optimize system for them. If we need to measure distortions, in my opinion, we not need do this in full frequency range, cause, that variable full range low distortions oscillator becomes very complicate and expensive. I think, we can measure distortions in some points with simple fixed frequency oscillators. Every AGC system also is not perfect. Thermistor make 3rd harmonic distortions, especially on low frequencies, have its own time constant, that we can not change and do not make good stability. I think, best simple solutin for AGC is optocoupler with photoresistor output, but it also have self nonlinear time constant and is not cheap.
Now FET controlled 1kHz oscillator have less than 0.3ppm distortions. I do not know at this time, which part of them makes measurable (app. - 136dB) 2nd harmonic, but once, may be I will find
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Old 8th August 2012, 11:45 AM   #210
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Originally Posted by vicnic View Post
No one system is absolutely perfect, but if we have one target, we can optimize system for them. If we need to measure distortions, in my opinion, we not need do this in full frequency range, cause, that variable full range low distortions oscillator becomes very complicate and expensive. I think, we can measure distortions in some points with simple fixed frequency oscillators.
Agreed, Victor. I'm looking forward to receiving one of your oscillators to be my primary distortion reference. I have a thermistor-style variable frequency oscillator and a function generator for other tests.

When I built my Noise and Distortion meter, I settled on three frequencies to avoid the complexity of full range tuning:

40Hz, being about the lowest musical notes likely to be encountered
400hz, being in the middle of the vocal and instrumental fundamentals range, and
4kHz, being about the top of the instrumental fundamentals range.

I didn't see much point in measuring harmonic distortion at 10kHz or so, as I was not going to hear even gross 2nd harmonic distortion at 20kHz, let alone 3rd at 30k. I'd be interested in comments on that strategy.

Terry
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