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

Here is another question that almost from the DIY-Audio universe.
 
Dima is finishing Zaratustra II amplifiers. It will be quite interesting beast and I’m slowing begin to think about the power supplies – it will be my responsibility. The Zaratustra II will be up to 175W of pure class “A”, without an ability to switch into class “B”. I said “up to” because it will have quite a few interring innovations that make taking about the Zaratustra II power…  hmmmm...complicated.

Anyhow, sine the output stage sucks constant high current and since I would like it... to sound good we are planning to go for Input choke, with my usual LCRbigC filter. So, I am hunting for the choke.

The output stage will be operating between 3A and 5A. At 3A the critical inductance should be around 30mH and at 5A it should be around 18mH. I usually use triple of critical inductance. Trying few different chooks during the construction of Melquiades (where I was buying them and listening them) I learned that it is very hard to beat the pane-vanilla Hammond chokes. They are silent in Input choke application and they sound better then any other chokes I tried. For high currents I usually order a custom “Ripley” version where a choke submerges twice into Ripley Epoxy - it make it dead silent.

So, the Hammond has two 100mH chokes:

195T5  -  5A  -  .64R - 14Pouns - $69

and

195T10  - 10A - .42R - 35Pound - $260

Both of them can do the job, but I’m a little concern that the first choke might be too small if I drive though it 5A. Also, those chokes run this max current they… kind of vibrate… The 10A is 7x8 inches… it is big. In addition, I’m conserved the with lover current it should give up lower inductance, would it be?

It will take for Hammond 2 month to” Ripleynize” my choke and I need to make decisions if it will be 195T5 or 195T10.  I personally inclined to go for 10A version as if for whatever reasons the filter will, not work as I expects then I could always drive it in necessary operation by shunting the PS and driving more current via the filter. The alternative version would be use of two 5A chokes, combining them in series or parallel connection, depends of what I need…

Any bright ideas?
The caT

Well, I also would like to have a spare ability to care current but 10A is 35 pounds monster and… it has just 100mH. I would prefer to have extra inductance then exacta current. The current wise is juts the thickness of the wire as I understand…I prefer the chokes gets hotter then they stop to “regulate”….

Yes, I know about the swinging chokes and I was searching for someone who would do 7A total, 200mA as 1.5A but it was not successful. There were places that wiling to do it but I never dealt with their chokes and I was afraid to order form then. The problem that they clams that no one among their customaries use their chokes right after rectifies and therefore they might have no idea how to build chokes that will be working within high ripples environment and to be silent at the same time. I have an unfortunate collection of the chokes that I made when I built Milq, the chokes that do wonderful job filtering with leading cap but they all too noisy with input choke.

Ironically the Hummonds, being the cheapest turned out to be the most silent, particularly the Ripleyed-epoxyed. What I inclined to do is to put two 5A, 100H chokes (still – 28 pounds of stupid metal ballast!!!), one on play and one on minis and they shunt them with a cap. This way each shoulder will buffered with choke… that “might” even prevent me form making a start delay for charging the 550.000uF caps.