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Old 5th September 2012, 05:20 AM   #1421
BudP is offline BudP  United States
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Hmmmm I appear to need to provide an updated data sheet. Much better low level 20 Hz performance than I originally showed. I apologize.

Bud
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Old 5th September 2012, 06:54 AM   #1422
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally Posted by BudP View Post
Hmmmm I appear to need to provide an updated data sheet. Much better low level 20 Hz performance than I originally showed. I apologize.

Bud
looks good enough for me

feel free to send some , for proper disposal

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Old 5th September 2012, 11:59 PM   #1423
lhquam is offline lhquam  United States
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I am still stumped by Nelson Pass post #435. Both my prototype build and simulations show increased THD at both frequency extremes, but most at high frequencies. In the simulations, the interwinding capacitances are a major contributor to the high frequency 2nd order harmonic. Below are THD vs Frequency sweeps for open-loop, Gain=10 and Gain=5, and my circuit schematic.

If Nelson's results are significantly different from these, then his circuit has some tricks that I haven't figured out.


Quote:
Originally Posted by Nelson Pass View Post
I don't think you do understand. The capacitance of the transformer would
only influence the distortion at higher frequencies, not at lower, but when
we look at the open loop (or closed loop) distortion of the F6 prototype
we don't see an increase in distortion at the frequency extremes.

Remember that the quadfilar windings have symmetric capacitance, so all
windings exhibit the same conditions with respect to that.

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File Type: jpg F6-Rs-0R47-open-loop-fsweep.jpg (122.2 KB, 411 views)
File Type: jpg F6-Rs-0R47-Gain-10-fsweep.jpg (123.2 KB, 370 views)
File Type: jpg F6-Rs-0R47-Gain-5-fsweep.jpg (123.0 KB, 346 views)
File Type: jpg F6-20120830-order-sch2.jpg (97.8 KB, 371 views)
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Old 6th September 2012, 12:22 AM   #1424
kasey197 is offline kasey197
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lhquam, i have it set up like your first chart right now, with Rs=0.47R and no feedback (battery biased for convenience). At 1khz i get THD at 0.017% (1 watt) so not far from yours. I'll check the THD at 10 and 20khz tonight and let you know what I find.

Separately, did you ever manage to measure the output impedance ? For the first case you have (open loop, Rs=0.46R) I'm getting approx 30 R.....

Last edited by kasey197; 6th September 2012 at 12:23 AM. Reason: added 1 W for clarity
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Old 6th September 2012, 03:58 AM   #1425
lhquam is offline lhquam  United States
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Here is a circuit that has flat open-loop THD vs Frequency like Nelson posted.

The circuit cancels most of the 2nd harmonic distortion due to the transformer interwinding capacitances. The output power supplies float together. Out+ and Out- have resistors to ground in a manner similar to that in the circlotron, except that the Out+ resistor is split to provide the feedback attenuator.

The only unfinished part of this design is a way of deriving the V2+ and V2- voltages for the input JFETs from the floating V1+ and V1- supplies.

Here is the schematic and open-loop THD, H2, H3 vs Freq plot for this circuit from Spice. (H2 and H3 are the 2nd and 3rd harmonics).

This looks very good! I need to bench test it.
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File Type: jpg F6Bunbal-in-1-open-loop-sch.jpg (95.5 KB, 200 views)
File Type: jpg F6Bunbal-in-1-open-loop-fsweep.jpg (124.5 KB, 162 views)
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Old 6th September 2012, 10:49 AM   #1426
buzzforb is offline buzzforb  United States
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This seems to be a departure from the design being a circlotron. Having you tested the working version vs the sims? Perhaps the frequency roll off is a simulation issue. The specs of the Jensen do not seem to indicate a problem when it comes to either end of the frequency. You should have plenty of drive current, so that should not be an issue. Perhaps lighten up on feedback, although Melson seems to suggest his doesn't change much. Shoot for gain of 12-15dB
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Old 6th September 2012, 12:17 PM   #1427
generg is offline generg  Germany
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here is the distortion spec of the M2, but of course there are differences in construction, but Nelson says the distortion is mainly due to the xformer......
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Old 6th September 2012, 12:49 PM   #1428
Zen Mod is offline Zen Mod  Serbia
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me likee

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Old 6th September 2012, 01:03 PM   #1429
lhquam is offline lhquam  United States
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This schematic shows a circlotron resulting from a swapping of the position of lower power supply relative to the bottom FET in the schematic of post #1425 and some rearrangement in the drawing. Major difference is that the power supplies float relative to each other as well as ground and the it is difficult (or impossible) to derive the V2- voltage for the input stage.
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Old 6th September 2012, 01:29 PM   #1430
bobodioulasso is offline bobodioulasso  Europe
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Nice, but Papa's schematic is clearly not a circlotron.
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