directdriver,
Nice schematic!
Very interesting!
But it is only part of the signal path.
I see that there are 4, perhaps* 5 low frequency poles:
The two 4.7k, two 100 Ohm, and Jensen input transformer secondary inductance (the negative feedback "Sees" that low frequency pole).
The RC coupling from the dual JFET / Triode cascode to the next dual triode stage.
The next dual triode stage's RC coupling to the missing [output tubes? Hopefully, there are no additional stages besides the output tubes].
The Output transformer's primary inductance.
. . . And, perhaps*, the low frequency pole of individual self bias resistors and individual bypass caps of the missing [output tubes].
Global Negative Feedback?
GNF Covers a multitude of sins, and creates some sins of its own.
"All Generalizations Have Exceptions"
Nice schematic!
Very interesting!
But it is only part of the signal path.
I see that there are 4, perhaps* 5 low frequency poles:
The two 4.7k, two 100 Ohm, and Jensen input transformer secondary inductance (the negative feedback "Sees" that low frequency pole).
The RC coupling from the dual JFET / Triode cascode to the next dual triode stage.
The next dual triode stage's RC coupling to the missing [output tubes? Hopefully, there are no additional stages besides the output tubes].
The Output transformer's primary inductance.
. . . And, perhaps*, the low frequency pole of individual self bias resistors and individual bypass caps of the missing [output tubes].
Global Negative Feedback?
GNF Covers a multitude of sins, and creates some sins of its own.
"All Generalizations Have Exceptions"
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Its a rocky road to perfection. I personally like the sound of transformers. My preamp uses a SE output transformer and the sec is therefore balanced output. It sounds great and the background is absolutely silent. Not relying on signal ground for grounding between amps. This is why audio transformers will never die. Hail the transformer.
I've been following Lynn's Karna from the beginning and also zigzagflux and his PP amp. I finally got where I want with an all DHT config and this thread has some interesting measurement techniques I want to try.
Most of the regular DHTs were plentiful when I started 20 odd years ago but now, unobtanium so went with Lundahl 1676 input, 2P29L choke loaded DC coupled to 4P1L, Lundahl 1671 IT to GM70 fixed bias Sowter O/P. Thanks Lynn for the inspiration; it's been a long journey but finally a very rewarding listen.
I also have zigzagflux style line stage; Lundahl 1544a 12B4 differential to Lundahl 1689 for 0 gain overall.
My Site
Most of the regular DHTs were plentiful when I started 20 odd years ago but now, unobtanium so went with Lundahl 1676 input, 2P29L choke loaded DC coupled to 4P1L, Lundahl 1671 IT to GM70 fixed bias Sowter O/P. Thanks Lynn for the inspiration; it's been a long journey but finally a very rewarding listen.
I also have zigzagflux style line stage; Lundahl 1544a 12B4 differential to Lundahl 1689 for 0 gain overall.
My Site