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Old 3rd October 2012, 02:52 PM   #2211
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If the parasitic capacitance is a major issue as you suspect, then you could use two separate transformers for the two halves to prove the point either way, esp as you have two of the jensens already... Just my 2 cents ...
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Old 3rd October 2012, 03:20 PM   #2212
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If two transformers are used in the way shown in the F6 Conceptual Schematic, there is still a problem. The AC voltages between the secondaries and the primaries are different. The top trafo has (Gain-1)*Vin AC voltage. The bottom trafo was -Vin AC voltage. If the Gain is chosen to be one, then the interwinding currents will cancel, otherwise they will not.

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If the parasitic capacitance is a major issue as you suspect, then you could use two separate transformers for the two halves to prove the point either way, esp as you have two of the jensens already... Just my 2 cents ...
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Old 3rd October 2012, 06:17 PM   #2213
lhquam is offline lhquam  United States
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The sweet spot?

If the "spare" transformer winding is connected to a resistor divider generating (approx) Vout*(Gain-1)/Gain as shown in the schematic below, the interwinding parasitic currents are nulled.

I used a potentiometer to adjust the resistor divider ratio and generated the following harmonic distortion sweeps with slightly different adjustments of the Zen amount pot.

If you want to add more 2nd harmonic, use the Zen amount pot to increase it.
Attached Images
File Type: jpg F6-txmod-2-cleaned-sch.jpg (68.7 KB, 380 views)
File Type: jpg F6-PCB2-Rs0R12-Gain-5-Txmod2.jpg (152.9 KB, 374 views)
File Type: jpg F6-PCB2-Rs0R12-Gain-5-Txmod2c.jpg (156.8 KB, 354 views)
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Old 3rd October 2012, 06:42 PM   #2214
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I like that mid pic

regarding parasitic cap. of winding - moi thinks that we are splitting da hair

can you hear difference ?
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Old 3rd October 2012, 07:44 PM   #2215
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Zen, consider the 3.5k to 90k multiplication factor provided by the core, to any irregularity in the B Field transform from antenna to antenna up through 3.5 kHz. Then consider that it is physically impossible to wind quadfiller and keep all wires where they should lay. You can get a bifillar winding to couple perfectly, or very nearly so. You cannot say the same for four wires, wound into a narrow winding well, guided by either delicate fingers or uncontrollable mechanical traverse. The graphs shown will sound different, if for no other reason than where the differences are in the FR.

Contemplate the differences heard between two drivers, one with an uncorrected initial 4 ms response and one with a 4 ms response corrected with manic spots.
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Old 3rd October 2012, 07:59 PM   #2216
lhquam is offline lhquam  United States
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In post #2213 I forgot to mention that the graphs were NOT from simulations, but actual measurements.
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Old 3rd October 2012, 09:22 PM   #2217
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I can confirm by experiment today that the Zen Pot is a fine way to trim distortion level and spectra even in the case of feedback with Mufollowers like SIT2 (NFB) and J2 (FB)

the link again... L'Amp: A simple SIT Amp

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Old 3rd October 2012, 09:45 PM   #2218
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You are overlooking another location for trimming the cancellation, which is
resistance across the secondary coils. Typical values would be on the order
of 200 ohms or more.

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Old 3rd October 2012, 10:02 PM   #2219
generg is offline generg  Germany
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Mostly I have no overlook.... especially in the case of F6.

Still fixed on J2 and Mikes SIT amp I confess.

Thanks for the hint......
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Old 3rd October 2012, 11:14 PM   #2220
lhquam is offline lhquam  United States
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I briefly experimented with that in the early days of my Teaser-6 build, but other parameters were too far from the "sweet spot" at the time to detect an improvement. I will experiment with it again.

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You are overlooking another location for trimming the cancellation, which is
resistance across the secondary coils. Typical values would be on the order
of 200 ohms or more.

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