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In Reply to: RE: I know, I know posted by 6AS7_6SN7 on November 05, 2009 at 00:32:36
The first Circlotron patent was by Cecil Hall. The second by Bongiorno and the the 3rd and 4th by Atma-Sphere. There was never an EV patent.
A lot of the distortion you are showing is likely coming from your driver circuit, not the output. If you tinker with the cathode resistor values of the driver (and use a bipolar power supply) you will see what I mean. CCS circuits will clear this up a lot. I would also explore what happens with different values of current limiting resistors in the output section.
The means for driving the power tubes is another area of weakness of this approach (which has been used by at least 3 manufacturers that I know of, only one of which is still in business). In practice, an amplifier like this will exhibit slow overload recovery, bias instability and/or weak bass, possibly both.
U.S. Patent 2,705,265, C. T. Hall, "Parallel Opposed Power Amplifiers" was filed on June 7, 1951 and granted on March 29, 1955.
Finnish Patent 27332, Tapio Köykkä, (original amplifier) was filed on September 2, 1952 and granted on November 10, 1954.
U.S. Patent 2,828,369, A. M. Wiggins, "High Fidelity Audio Amplifier" was filed on March 1, 1954 and granted on March 25, 1958.
Finnish Patent 29642, Tapio Köykkä, (improvements to the amplifier) was filed on September 30, 1955 and granted on April 10, 1958.
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Have Fun and Enjoy the Music
"Still Working the Problem"
And all this time I thought the Wiggins was just a variant. Thanks for the looky-look.
.
Have Fun and Enjoy the Music
"Still Working the Problem"
"The second by Bongiorno"
just curious... is that Bongiorno as in James Bongiorno of Great American Sound(and others) fame?
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Dear Ralph,
I have provisionally replaced common cathode resistor with current generators (ideal CCS) of the same value of the bias currents.
The overall result is negative, that is, no major change of output spectrum.
Then I have checked the spectrum at the output of the first stage and at the output of the second stage. Here I have seen the likely culprit.
There is an unexpected (and fixed) -55 dBc third harmonic at the output of the first stage in both cases (that is, with and without CCS).
The likely problem is that computer simulations with 'simple' tools (of the level of free LTSpice), due their inherent numerical errors, do not deliver reliable results below -50 dBc (0.3% distortion).
As a consequence, as it is not easy for me to unmask the effect of the third harmonic that is unexpectedly present at the output of the first stage, and that is likely due to numerical rounding errors, it is not possible to ascertain with LTSpice the prospected effect of your recommended modifications.
We can only trust your professional experience.
I have been told that other SPICE tools, whose license cost more than several thousand dollars, could deliver improved accuracy (down to 0.1% distortion or even better), but that kind of investigation is too expensive for me.
Best Regards
Luca Cellai
ecc230
I don't know how spice models CCS circuits, but I find that most CCS designs commonly seen in tube and transistor amps are inadequate designs. If you can, look through the ASOG archives at the bottom of this page- somewhere in there is a schematic of a more effective CCS. The results we have been getting out of it have been transformation.
I am a hobbist.
I got your message.
I will take your suggestions as new food for brain.
Best Regards
Luca Cellai
ecc230
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