Low-distortion Audio-range Oscillator - Page 187 - diyAudio
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Old 20th March 2013, 12:03 PM   #1861
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Quote:
Originally Posted by RNMarsh View Post
BTW - what opamp is being used in your 4402 oscillator? Have you tried changing it, if it is still a 318?
318's in mine, but I have no complaints:

Click the image to open in full size.
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Old 20th March 2013, 02:09 PM   #1862
davada is offline davada  Canada
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Quote:
Originally Posted by PChi View Post
Thanks for posting the picture of the PCB. I can appreciate the effort involved in the design. I am interested in how the frequency range switching is achieved. I can see what looks like pads for the connections in the middle of the PCB so would like to see pictures of the assembled board.

The range switching for the time being is a manual jump.
The switching will be done with relays controlled by a MCU and a small USB app.
I used Mdac's for tuning.
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Old 20th March 2013, 04:18 PM   #1863
mlloyd1 is offline mlloyd1  United States
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dick:

these improvements came from strictly dropping in a new op amp?
no changes to psu decoupling or anything else?

mlloyd1

Never mind - i see some of your comments later on some things I was curious about

btw, thanks to ALL you guys for sharing this stuff. great learning; just wish i had more time to play ...


Quote:
Originally Posted by RNMarsh View Post
Did I mention the THd of the KH-4402B with 2-opamp upgrades and a couple tuning adjustments is a really nice .0001% at 10Hz and .00013% at 1Khz and at 10Khz is .00015% THD+N. at 1volt into high Z. ?

If you just need a nice, clean oscillator that is flexible in output and frequencies.... it does very well.

[With the oscillator opamp changed out (LT1486 was used). No instabilities or weirdness with the opamp change.]

Thx-RNMarsh

Last edited by mlloyd1; 20th March 2013 at 04:32 PM.
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Old 20th March 2013, 04:43 PM   #1864
PChi is offline PChi  United Kingdom
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Quote:
Originally Posted by davada View Post
The range switching for the time being is a manual jump.
The switching will be done with relays controlled by a MCU and a small USB app.
I used Mdac's for tuning.
Thanks for the information.
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Old 20th March 2013, 07:45 PM   #1865
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by jackinnj View Post
318's in mine, but I have no complaints:

Click the image to open in full size.
Seems exceptional for a 318 opamp. I'd look into how the instrument you are using which came up with that THD+N number. Never-the-Less, the numbers were better when replaced with a quieter and lower thd LT1468. My goal is to be as low as it is possible to be ... not just good enough stock. In some cases, I can tune for a single freq to be 10X better. add another zero. But measuring this accurately has been a side trip and challenge.
So what hardware/software are you using?

Thx-RNMarsh

Last edited by RNMarsh; 20th March 2013 at 07:53 PM.
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Old 20th March 2013, 08:13 PM   #1866
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Quote:
Originally Posted by RNMarsh View Post
Seems exceptional for a 318 opamp. I'd look into how the instrument you are using which came up with that THD+N number.
I took the measurement after having spent about an hour adjusting the 4402B -- and I also found that the optimal output voltage was between 2 and 4 volts. Importantly, I took it on a Saturday morning when there was no bother from air conditioning etc. I used RG-59 cables that were only 6 inches long too.

The measurement was taken with an Audio Precision SYS-2722.
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Old 20th March 2013, 09:11 PM   #1867
RNMarsh is offline RNMarsh  United States
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the A-P page says it does around -115dB THD+N with a 22Khz BW.
You are close to the limit of the A-P.

BTW--- I do my THD+N tests/comparisons with a 100KHz BW.

Thanks- RNMarsh
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Old 20th March 2013, 09:17 PM   #1868
RNMarsh is offline RNMarsh  United States
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davada -- I am really looking forward to a new design as I have tried several existing sources and tried to upgrade/modify them. A new and flexible oscillator source of the same general level as Viktors or the ShibaSoku (Ag16 -- which i cannot find), would be a great addition. So, I'm done with the mods... until I find schematic of AD725D. I now have a base line from what is commercially available to compare against.

When I see my A-P again (its still in Thailand), I'll do similar to its oscillator to see how much more can be done to it. Such as drop in an AD797 (if my early Model One doesnt already use it?).

Thx-RNMarsh

Last edited by RNMarsh; 20th March 2013 at 09:20 PM.
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Old 20th March 2013, 10:29 PM   #1869
1audio is offline 1audio  United States
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A quick calculation indicated that -120 dB from 1V (120 dB THD+N) would require a source with an impedance below 300 Ohms and no internal noise sources. Another metric is that its around 700 nV RMS. A quick check would be the measure the noise level with the input of the instrument shorted to get its internal noise floor. Then figure at least 120 dB up from that for the signal level. Measure the noise with the target bandwidth.

Usually THD +N is measured in a narrower bandwidth because ultrasonic noise or 1/F noise tells little about the THD. In audible terms A weighting or even better CCIR/ARM will give better insight as to the relative intrusion of noise on the signal. Except for microphone and phono preamps the noise floor of audio systems is really a non issue today. Even Kool, CA has more ambient noise that a good line stage, amp and normal efficiency speakers. Here in the big city, forget even thinking about it.

THD however is deterministic and can be audible because it is deterministic and audible much lower level than random noise.
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Old 20th March 2013, 10:37 PM   #1870
1audio is offline 1audio  United States
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I believe the oscillator and output amp on the System One is mostly discrete. Opamps are used for servos etc.
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