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Old 29th March 2012, 01:48 PM   #101
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Default More juicy sauce for ya all!

As per my friend's results

"All simulations were run with IRF610/9610, 5.7x gain and 10K ohm load.

Note that real-world performance will never be as good as the simulation, but my experience with this is that it's a good approximation of reality.

Click the image to open in full size.
Amplitude (green) and phase (red) response. This is with a 1V input sweep from 0.1Hz to 100MHz. Note the output amplitude response is flat at 5.7V output (signifying the gain of 5.7) and begins to fall at >1MHz. It reaches the -3dB point (0.707x) at around 15MHz. The phase response is flat until after 100KHz where it gradually starts to deviate from 0 degree.

Click the image to open in full size.
This is the amp swinging almost 80Vpp (28Vrms) 1KHz sine wave.

Click the image to open in full size.
This is the amp swinging about 34Vpp 100KHz square wave.

Click the image to open in full size.
Same as above, but with X axis expanded to show the square wave rising edge with greater resolution. The edge rises smoothly and produced only a very mild overshoot.

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This is the amp swinging about 60Vpp 100KHz square wave. Something weird happens here, as the rising and falling edges become much slower and rounded. This shouldn't be an issue in actual use, as this circuit will never be swinging this much voltage when driving a power amp. The power amp would have gone into severe clipping at a much lower level.

Click the image to open in full size.
This is the output impedance of the amp. It's a constant 196 ohms (mostly contributed by the two 100 ohm output resistors), up until over 1MHz where it starts to rise, reaching a peak of about 238 ohms and then falling again beyond that.

Click the image to open in full size.
Harmonic distortion spectrum with a 1KHz sine wave fundamental, at 5.7V output. Note that the 2nd harmonic is 1.208uV in amplitude which makes it 0.000021%. There are no other significant even harmonics present, only odd harmonics, at 3KHz, 5KHz, 7KHz, 9KHz, etc. All those are even lower than the 2nd harmonic. The numbers look amazing, but this is one where real life
is probably much worse, because devices won't be as perfectly matched. Nevertheless these are excellent results."

Enjoy!
Do
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Old 29th March 2012, 02:46 PM   #102
Wolfsin is offline Wolfsin  United States
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Default Yesssssss

Quote:
Originally Posted by pinnocchio View Post
swinging about 60Vpp 100KHz square wave. Something weird happens here, as the rising and falling edges become much slower and rounded. This shouldn't be an issue in actual use . . . when driving a power amp.
But I plan to drive headphones so no problem?

If I had a copy of that model I would use it for sensitivity analysis. From day one most of my questions have surrounded the issue of matching. How close is close enough!
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Old 29th March 2012, 03:40 PM   #103
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Quote:
Originally Posted by Wolfsin View Post
But I plan to drive headphones so no problem?

If I had a copy of that model I would use it for sensitivity analysis. From day one most of my questions have surrounded the issue of matching. How close is close enough!
BTW, this was by feeding it directly 24Vdc, bypassing the 30Vdc to 24Vdc regulator.

According to my friend, with a really good reg, you can safely bypass this regulator but not the 15V for the opamp...

The model is ran through PSpice on Orcad. Do you have the software? If yes, I can ask him again.

Ciao!
Do
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Old 29th March 2012, 04:46 PM   #104
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Default Yes, & Yessssssssss

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PSpice on Orcad. Do you have the software? If yes, I can ask him again.
Yes, and please do.

I would create component models for each of the active components typically matched (jfets, and mosfets), by first cloning and renaming the matched part, running again to assure no errors and then altering the values on which matching is usually performed. We know higher IDSS is better but is 3% match good enough?

The combination of this and socketed actives would keep my workstation humming and RightMark analyzing for quite a while. There is some chance we could sharpen John's prescriptive.

Quote:
Originally Posted by john curl View Post
It requires a good same device match, but the complementary match is more forgiving.
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Old 29th March 2012, 08:32 PM   #105
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Quote:
Originally Posted by Wolfsin View Post
Yes, and please do.

I would create component models for each of the active components typically matched (jfets, and mosfets), by first cloning and renaming the matched part, running again to assure no errors and then altering the values on which matching is usually performed. We know higher IDSS is better but is 3% match good enough?

The combination of this and socketed actives would keep my workstation humming and RightMark analyzing for quite a while. There is some chance we could sharpen John's prescriptive.
Just sent a request for the model. I don't know what the answer will be. Will keep you updated.

Thanks
Do
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Old 30th March 2012, 03:57 PM   #106
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I don't think we're getting the model. He never actually tried to export a model and there are many files involved and located in different folders...

We'll see what happens. Anyways, he was very kind to spend some time and run the simulations for us.

Do
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Old 30th March 2012, 04:37 PM   #107
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That makes sense, and yes, building and running was very generous. I looked again at the schematic and it is clear that the servo and cap multipliers can be left out for simulation purposes. What remains is not all that complex so it will not be hard to build the small part that is germaine to my needs. Please thank your friend for his help.
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Old 2nd April 2012, 02:57 PM   #108
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Wolfsin, you might be disappointed in driving headphones, unless you use LOTS of second stage idle current and run heavy Class A. This circuit is sensitive to loading, and very low Z loading throws away the open loop gain of the circuit. This is why this circuit is called a TRANSCONDUCTANCE AMPLIFIER.
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Old 2nd April 2012, 04:02 PM   #109
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Good to hear from you again and thanks for the warning. I have found the challenge of understanding what you designed more fun than building it. It is likely that the balanced output of these will feed dual Aragon 2004s bridged across magneplanars.

Splitting the thread allowed more of the power issues to be handled here. I hope to edit the original thread and return to it as the main focus. This one would be ancillary reading since the most interesting issues are those surrounding the JC-80.
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Old 4th April 2012, 02:49 PM   #110
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Wolfsin found an article that explains several aspects of Transconductance Amplifiers

http://www.ece.gatech.edu/academic/c.../Diff_Pair.pdf

The discussion of matching and the graph showing the non-zero offset explained many of his unanswered questions. Simulations without the servo would likely not be very useful.
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