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Old 27th September 2012, 11:20 AM   #501
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Quote:
Originally Posted by EssB View Post
Looks like a Wien bridge to me, just configured a bit differently.

I'd agree with Richiem, Victor's design looks better.

I can never understand how a LDR + PI controller can work properly, seeing as the LDR is a PI control element in itself, or at least a leaky integrator. Everytime I've simulated one it's very difficult to get them to stabilise. By the time I got that AN43 design to work the distortion looked poor.

Does anybody have a spice model for the VTL5C10 ?
I only have Thomas Gootee's VTL5C2 model, the 5C10 is a low slope type.
I've given up on simulating an oscillator in spice. I'm just going to build them from now on. The parts for the LT oscillator should be arriving today. I had bought the VTL5C10 a few months ago so I might as well use them. I can't build something I don't have at least a basic understanding of so Victor's circuit is out for me right now.
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Old 27th September 2012, 11:23 AM   #502
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Series : C11 || C12 + R20 || R21 + R26 || R27
Parallel : (R28 + R29) || C16

The series part has R/2 and C*2 compared to the parallel in this design

Last edited by EssB; 27th September 2012 at 11:36 AM. Reason: rework
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Old 27th September 2012, 11:53 AM   #503
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Quote:
Originally Posted by EssB View Post
Series : C11 || C12 + R20 || R21 + R26 || R27
Parallel : (R28 + R29) || C16

The series part has R/2 and C*2 compared to the parallel in this design
Thanks.

I didn't know you could have a Wein bridge oscillator with unequal arms and have it function. I guess it's just the ratios that matter. There's a whole pile of other stuff in this design that I also don't understand if the actual bridge oscillator is around IC2a. I'm sorry I'm not smart enough to understand this circuit.

At any rate, I think it would be hard to make Victor's circuit a variable one unless the values in the bridge arms were changed.

Is there a way to use some of the ideas in Victor's circuit to modify the LT one?

Last edited by dirkwright; 27th September 2012 at 12:05 PM.
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Old 27th September 2012, 01:18 PM   #504
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Quote:
Is there a way to use some of the ideas in Victor's circuit to modify the LT one?
A variable frequency oscillator is a much more complicated design task than a fixed frequency one. A SVF topology is a much better choice here. Why don't you start your research by looking at variable frequency oscillators? The Tektronix SG505 or the design by Cordell is reasonably easy to understand and DIY.

Samuel
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Old 27th September 2012, 01:40 PM   #505
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Originally Posted by Samuel Groner View Post
A variable frequency oscillator is a much more complicated design task than a fixed frequency one. A SVF topology is a much better choice here. Why don't you start your research by looking at variable frequency oscillators? The Tektronix SG505 or the design by Cordell is reasonably easy to understand and DIY.

Samuel
Thanks. I have not been able to find the schematic for the SG505.

Mr. Cordell's article is something I am digesting right now.
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Old 27th September 2012, 02:06 PM   #506
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SG505 - TekWiki

Right now I'm getting a timeout error from this site, but I'm sure it will be back soon.

Samuel
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Old 27th September 2012, 02:46 PM   #507
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Quote:
Originally Posted by Samuel Groner View Post
SG505 - TekWiki

Right now I'm getting a timeout error from this site, but I'm sure it will be back soon.

Samuel
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.
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Old 27th September 2012, 02:53 PM   #508
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If you want to build something simple then that would do. It's not an SVF, it's an all pass phase shift oscillator. I think it was discussed in the first few pages of this thread. Don't expect it to be seriously low distortion or have very good amplitude staibility with frequency.

Your lost link is in post #10 of this thread.

Last edited by EssB; 27th September 2012 at 02:56 PM. Reason: add link info
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Old 27th September 2012, 03:05 PM   #509
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Quote:
Originally Posted by EssB View Post
If you want to build something simple then that would do. It's not an SVF, it's an all pass phase shift oscillator. I think it was discussed in the first few pages of this thread. Don't expect it to be seriously low distortion or have very good amplitude staibility with frequency.

Your lost link is in post #10 of this thread.
Oh, ok. It looked sort of like a SVF oscillator to me.

back to searching...
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Old 27th September 2012, 03:53 PM   #510
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What if I replaced the jfet amplitude control in this circuit with a VTL5C10? Would that improve the performance significantly? I get lost when circuits start to get really complex, like in the link I posted above.
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Last edited by dirkwright; 27th September 2012 at 03:55 PM.
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