Low-distortion Audio-range Oscillator - Page 52 - diyAudio
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Old 27th September 2012, 03:59 PM   #511
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Like this one. It's supposed to be super duper, and it's great he's labeled all of the modules, but I still can't follow it very well. I can see it follows the basic SVF oscillator pattern, but it's so complex that I get lost. The rectifier seems excessively complex to me, for example.
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Old 27th September 2012, 05:10 PM   #512
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Quote:
It's so complex that I get lost.
Well, designing a high-performance variable-frequency oscillator is so difficult that it's just not possible to end up with a trivial schematic. GK's design is still pretty easy--check out the AP System One! Not wanting to offend, but if you have no chance to follow even Victor's simple (yet smart!) design, then designing one yourself is likely just out of reach for the moment being...

What are the specs you need? Can't you meet them with a second-hand oscillator?

Samuel
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Old 27th September 2012, 05:37 PM   #513
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Originally Posted by Samuel Groner View Post
Well, designing a high-performance variable-frequency oscillator is so difficult that it's just not possible to end up with a trivial schematic. GK's design is still pretty easy--check out the AP System One! Not wanting to offend, but if you have no chance to follow even Victor's simple (yet smart!) design, then designing one yourself is likely just out of reach for the moment being...

What are the specs you need? Can't you meet them with a second-hand oscillator?

Samuel
I was hoping to improve on my Kenwood 204D, and have two unbalanced and two balanced outputs.
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Old 27th September 2012, 05:38 PM   #514
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Originally Posted by dirkwright View Post
Thanks. It's not working for me either.

I've found a few good sites about really good state variable oscillators. This one stands out:
An Audio T.H.D. Analyser
He provides all the details, including Gerber files, for his project. I don't think I'll use it though. I've found another that seems to be good but is much more simple. Unfortunately I lost the URL, but printed out the schematic. From the above link it seems that the best op amp for these things is a low bandwidth type like the NE5534.
Hi Dirkwright,

Thanks for bringing this link to my attention; I had been unaware if it. It looks like Glen has done a very nice job of updating my THD analyzer from 1981, using modern parts and using relays to replace those damned rotary switches I had in mine. I have often thought of updating mine by using relays for frequency selection as well. It does take a good number of them, epecially if you cover 11 spot frequencies per decade, but it is worth it, especially in terms of assembly labor. I don't think that Glen provided a link to my article. It can be found at CordellAudio.com - Home under the instrumentation tab.

Cheers,
Bob
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Old 27th September 2012, 05:50 PM   #515
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Originally Posted by EssB View Post
I knew I'd seen the all inverter config before:
Low distortion oscillator tests measurement circuits | TMW
I finally got around to looking at this one! It looks very easy to build. Thanks.
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Old 27th September 2012, 06:23 PM   #516
DDB is offline DDB  United States
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Quote:
Originally Posted by EssB Click the image to open in full size.
I knew I'd seen the all inverter config before:
Low distortion oscillator tests measurement circuits | TMW


dirkwright: I finally got around to looking at this one! It looks very easy to build. Thanks.
The Janascard oscillator is a single frequency inverting Wien bridge circuit much like Victor's. As such it has very limited lock in range with tight AGC and per the author in a message to me will be difficult to convert to wide frequency use.

Cordell's circuit has been implemented by Dick Moore on his site: IG-18 #2, the BIG-18 and works very well as a wide range oscillator as documented by Dick. Dick states he will provide pcb layouts and that board works well.

The board can be incorporated in your box along with PS, switching or relays etc if you like. This is a good way to start rather than all the thrashing around trying to convert single freq circuits to wide band.
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Old 27th September 2012, 06:29 PM   #517
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Here's an equation which describes the VTL LDR behavior --r2 is very high as the errors of a few percent are offsetting. I plugged the datasheet from the VTL5C9 into Eureqa and went to the deli for a sandwich:

Click the image to open in full size.

The lines are quite compressed at the low R end, so the errors exceed 10% as the current approaches 40mA.

Edit == Yes, there are too many parens!

Last edited by jackinnj; 27th September 2012 at 06:43 PM.
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Old 27th September 2012, 07:03 PM   #518
EssB is offline EssB  United Kingdom
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Thanks for that Jackinnj, I have an automatic parenthesis filter anyway.
That eqn. makes sense, gives R=145 .. infinity for I=0.04 .. 0.
I'll stick it in the model later tonight.
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Old 27th September 2012, 07:13 PM   #519
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Originally Posted by DDB View Post
The Janascard oscillator is a single frequency inverting Wien bridge circuit much like Victor's. As such it has very limited lock in range with tight AGC and per the author in a message to me will be difficult to convert to wide frequency use.

Cordell's circuit has been implemented by Dick Moore on his site: IG-18 #2, the BIG-18 and works very well as a wide range oscillator as documented by Dick. Dick states he will provide pcb layouts and that board works well.

The board can be incorporated in your box along with PS, switching or relays etc if you like. This is a good way to start rather than all the thrashing around trying to convert single freq circuits to wide band.
OK, thank you. I'm crest fallen... sigh.

I don't understand why the Janascard oscillator can't be used over a wide frequency range, but that's ok, there are plenty of things I don't understand. Is it because the AGC has limited bandwidth?

I've been to Mr. Moore's pages before and I can't find a schematic for his wide range oscillator. I can layout a PCB board myself.

Last edited by dirkwright; 27th September 2012 at 07:15 PM.
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Old 27th September 2012, 08:22 PM   #520
davada is offline davada  Canada
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Thanks David, that looks like a different model - I'll give it a go.
Okay well good. Let me know how it goes.

David.
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