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Today I was reading Jim Hagerman's interview about his Trumpet phonostage and learn that he uses LCLCRCRC filters for B+ in his design. I certainly do not question Jim’s decision; in fact I never heard this phonostage, but I would like to comment, collaborate and perhaps to learn about the subject.

I do not know a lot about the Trumpet but looks like it has 4 stages of 12AX/12AU7 (~.5mA each), that makes the total plate current extremely low. Approximately 4-5 years ago when I built from scratch my beloved 2x843PT (that essentially has also “virtually nothing current” in B+) I went over the ceremony of discovering how to power the thing. The filaments were unavoidably LCLCRC but when I tried to put input choke on the 843PT’s anode I had quite poor results (sound). Being kind of religiously-input-choke-guy for whatever that has draw more then 10mA-15mA, I found that for ultra low current it did not worked. I mean it worked but it did not sound well. I remember the I got the first choke of stupidly-high inductance as well and I drew 30mA through the filter using bleeding resistor but regardless what I did the phonocorrector did not sound OK. To my surprise, the default 843P’s voltage doubler with CRC works absolutely the best and it was how I finished it up.

Did anyone have success to power ultra low current with LC and get correct sound (bass for instance)? Why my bleeder did not help to Sound if the limitation was presumably only with the critical inductance for the given current? I have my interest to ask because I’m now drastically modifying my analog and if any better scenarios to power the low currents do exist then I would like to learn about them.

Rgs,
Romy the Cat

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