The reason why you like the sound of CCS loads over that of transformers can be seen in the load line. The CCS presents a perfect horizontal load line. The transformer presents the tube with a slanted elliptical load line.
You shouldn’t have hum issues with 46s as drivers especially if they are push pull drivers. I’ve always been able to get away with center tapped transformers and no hum pots. The push pull action cancels the hum.
That cap from the OPT center tap to B+ is letting hash from the power supply in the signal path. A cathode cap to ground usually prevents this. Every amp is different, so all the above my not apply to you. YMMV.
Rgs, JLH
Andy,
Please excuse this late contribution to your thread that is now out of context. However, if you might still consider the Karna Amplifier, you should read Lynn comments here: http://www.diyaudio.com/forums/showthread.php?t=134804. He comments on his design and proposes an improvement by eliminating one of the interstage transformers.
Two birds, one stone.
Looney
Please excuse this late contribution to your thread that is now out of context. However, if you might still consider the Karna Amplifier, you should read Lynn comments here: http://www.diyaudio.com/forums/showthread.php?t=134804. He comments on his design and proposes an improvement by eliminating one of the interstage transformers.
Two birds, one stone.
Looney
thanks JLH and Loony Tunes - I've been looking at the Karna thread.
That cap from the OPT center tap to B+ is letting hash from the power supply in the signal path.>> writes JLH. The cap was from cathode of 807s to OPT centre tap. See Lynn Olsen below. I didn't find it improved the sound of the 807s, but Lynn talks here of the driver stage.
<<I'd also add 20~40 uF of capacitance between the virtual cathodes of the driver stage and the B+ of the driver stage and replace the negative-supply current source with a simple resistor to ground; what you have now is differential drive, and this has substantially higher 3rd-order harmonic content (2 to 3 times) and far less peak current drive capability than Class A PP (which is what the bypass cap gives you). This one change alone might improve the frequency response and distortion substantially. (I'd also do it for the input stage as well; the improvement might actually be greater, but the driver stage MUST be Class A PP, not differential. I've tried differential, and the performance is substantially poorer in every respect - more distortion, less available current, higher Zout, and sounds worse, too.)
That cap from the OPT center tap to B+ is letting hash from the power supply in the signal path.>> writes JLH. The cap was from cathode of 807s to OPT centre tap. See Lynn Olsen below. I didn't find it improved the sound of the 807s, but Lynn talks here of the driver stage.
<<I'd also add 20~40 uF of capacitance between the virtual cathodes of the driver stage and the B+ of the driver stage and replace the negative-supply current source with a simple resistor to ground; what you have now is differential drive, and this has substantially higher 3rd-order harmonic content (2 to 3 times) and far less peak current drive capability than Class A PP (which is what the bypass cap gives you). This one change alone might improve the frequency response and distortion substantially. (I'd also do it for the input stage as well; the improvement might actually be greater, but the driver stage MUST be Class A PP, not differential. I've tried differential, and the performance is substantially poorer in every respect - more distortion, less available current, higher Zout, and sounds worse, too.)
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