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(101) Comments for: [3rd round] AN67 Ultra-low THD 10kHz sine oscillator PCB Group buy. Page Tools Search this Page
Old 5th September 2012, 09:58 PM   #91
cobretti is offline cobretti  United States
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Quote:
Originally Posted by Stefan0815 View Post
Just a post for those ones, who like pic's.
And for me who like to show what he has builded up
What are those PSUs? Any schematics?
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Old 5th September 2012, 10:32 PM   #92
brickj is offline brickj  United Kingdom
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I had a little more luck this evening, managing to get the oscillator to work pretty well, though not reliably.

Rather than solely using the high impedance scope input, I added a 100k load. This seemed to calm things down and, with careful adjustment of the gain and amplitude controls, I was able to get a respectable 10kHz sine wave; clean, 5V pp, reasonable THD.

However, if I cycled the power with the gain control anywhere near the required level to start oscillation, I would have a 1MHz parasitic on top of the 10KHz wave. This could only be avoided by powering the oscillator with the gain control set materially less (multiple turns) than the level required to start oscillation. The higher the amplitude setting, the harder it was to start the oscillator without the 1MHz signal.

In summary, the only time I've had reasonable success is: 100k load; amplitude set to mid; gain turned down; slowly increase gain until oscillation, and once stable; increase amplitude to 5v pp. This would work fine, but power cycle would result in 1MHz parasitic and you would have to turn off and repeat this whole process.

This is still half in the case and using SSR01/2 regulators.

Nice build, btw!
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Old 22nd October 2012, 12:27 AM   #93
klewis is offline klewis  United States
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Quote:
Originally Posted by brickj View Post
I had a little more luck this evening, managing to get the oscillator to work pretty well, though not reliably.

Rather than solely using the high impedance scope input, I added a 100k load. This seemed to calm things down and, with careful adjustment of the gain and amplitude controls, I was able to get a respectable 10kHz sine wave; clean, 5V pp, reasonable THD.

However, if I cycled the power with the gain control anywhere near the required level to start oscillation, I would have a 1MHz parasitic on top of the 10KHz wave. This could only be avoided by powering the oscillator with the gain control set materially less (multiple turns) than the level required to start oscillation. The higher the amplitude setting, the harder it was to start the oscillator without the 1MHz signal.

In summary, the only time I've had reasonable success is: 100k load; amplitude set to mid; gain turned down; slowly increase gain until oscillation, and once stable; increase amplitude to 5v pp. This would work fine, but power cycle would result in 1MHz parasitic and you would have to turn off and repeat this whole process.

This is still half in the case and using SSR01/2 regulators.

Nice build, btw!
I just got mine finished, up and running. I found that the gain control only needed to be about +1/2 turn cw, maybe 3/4 for it to run consistently. The amplitude is at +6 cw and 1.5Vrms output. The 2nd harmonic trim is centered. I didn't find an easy way to measure the trimmers as the voltage in the psu caps throws the measurements off and they don't seem to bleed down. I had to turn the trimmers all the way until I heard their clutch click, then 12.5 turns to get them centered. I'm using a lab bench supply- and old HP 6205B and the onboard cap multiplyer. I presume that if you are using ssr1/2 regulators you are bypassing the cap multiplyer. I seem to recall reading that the Jung style regulators don't like bypass caps.

I was able to measure -126db 2nd Harmonic with Vout = 1.5Vrms. Pretty darn good. Didn't have much luck adjusting the 2nd H trim. Used Dick's Twin-T to null the fundamental to -47db.

Ken
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File Type: png an67_full_scale.png (40.5 KB, 49 views)
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Old 22nd October 2012, 12:31 AM   #94
klewis is offline klewis  United States
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Frex,

Thank you so much the oscillator works great. It took a few hours to get the hang of tuning it, but, now it works quite consistently.

I have a question for you. I'm getting a frequency of 10,040 hz and would like it closer to 10,000 hz. Your note says adjust R59 and R60 to get closer to 10k. Should I use larger or smaller values? Is there some ratio in need to adhere to?

Thanks again.

Ken

zoom in of the 2nd H attached
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Old 22nd October 2012, 02:39 PM   #95
Frex is offline Frex  France
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Hello Klewis,

You've done a good job !
If you want to decrease the oscillating frequency, you need to increase R59/R60.
The oscillating equation is writen in the design schematic.
Fo=1/ (2.pi.R.C)
Regards

FRex
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Old 22nd October 2012, 08:38 PM   #96
Stefan0815 is offline Stefan0815  Germany
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Sorry for my late answer Coretti.
The Powersupplys are from Funk Audio Berlin. They are quite sophisticaded and are "priceworthy" (around 80€). Mr. Funk is a very nice little bit nerdish engenier for special studio applications. I met him a few weeks ago in his outstanding laboratory and it was a nice talk.

Here are the measurements of those powersupplys:
http://www.funk-tonstudiotechnik.de/PWS-04a_V2-1-Messschriebe-2012.pdf
You must keep in mind, that they are "lowdrop" and do not dissapate a lot of heat.
He has also even better switched Powersupplys in his programm:
http://www.funk-tonstudiotechnik.de/...-2-spaltig.pdf

For me there was no chance to build up my own regulators with the same money/time investment.

Last edited by Stefan0815; 22nd October 2012 at 08:52 PM.
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Old 27th October 2012, 11:02 PM   #97
cobretti is offline cobretti  United States
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Quote:
Originally Posted by klewis View Post
I just got mine finished, up and running. I found that the gain control only needed to be about +1/2 turn cw, maybe 3/4 for it to run consistently. The amplitude is at +6 cw and 1.5Vrms output. The 2nd harmonic trim is centered. I didn't find an easy way to measure the trimmers as the voltage in the psu caps throws the measurements off and they don't seem to bleed down. I had to turn the trimmers all the way until I heard their clutch click, then 12.5 turns to get them centered. I'm using a lab bench supply- and old HP 6205B and the onboard cap multiplyer. I presume that if you are using ssr1/2 regulators you are bypassing the cap multiplyer. I seem to recall reading that the Jung style regulators don't like bypass caps.

I was able to measure -126db 2nd Harmonic with Vout = 1.5Vrms. Pretty darn good. Didn't have much luck adjusting the 2nd H trim. Used Dick's Twin-T to null the fundamental to -47db.

Ken
What did you use to measure THD? Is this 0.0076% THD the best your oscillator can do, or is it the limit of measurement method?
I have got much better THD than yours.
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Old 28th October 2012, 04:24 AM   #98
klewis is offline klewis  United States
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Quote:
Originally Posted by cobretti View Post
What did you use to measure THD? Is this 0.0076% THD the best your oscillator can do, or is it the limit of measurement method?
I have got much better THD than yours.
That result is from my HP8903a. It's the best the 8903 can do, not the oscillator. To get the actual distortion, I would need to calculate it from the measured harmonics, of which only the 2nd is visible. Even the 2nd might be an artifact from the active twin-t filter I used to null the fundamental.
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Old 11th March 2013, 08:16 PM   #99
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by cobretti View Post
What did you use to measure THD? Is this 0.0076% THD the best your oscillator can do, or is it the limit of measurement method?
I have got much better THD than yours.
I agree.... for a few pp-billion, it must be a lot better. What thd numbers did you get and what did you use to measure it?

Thx-RNMarsh
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Old 12th March 2013, 12:33 AM   #100
klewis is offline klewis  United States
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Quote:
Originally Posted by klewis View Post
That result is from my HP8903a. It's the best the 8903 can do, not the oscillator. To get the actual distortion, I would need to calculate it from the measured harmonics, of which only the 2nd is visible. Even the 2nd might be an artifact from the active twin-t filter I used to null the fundamental.
I just hand calculated the THD using the -126 db for the second and -134db for all others - as the actual harmonics are lost in the noise floor of -134. I get 0.00007% THD. An Hp3562 was used for the fft. As I mentioned Dick Moore's active twin T was used to null the fundamental by approx. 50db to get the harmonics to show within the range of the 3562 (range approx. 80 to 85 db). I also have a KH4402, the noise floor on the AN67 looks to be about 8 to 10 db lower than the KH4402.

Ken

Last edited by klewis; 12th March 2013 at 12:43 AM.
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