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In the Forum: Analog Playback
In the Thread: The last phonocorrector: “End of Life" Phonostage

Post Subject: Caps and chokesPosted by N-set on: 8/31/2011

Oh, Romy, I meant the air caps in the corrector loop of course!!!
Adjusting PS caps I leave to AA morons and alike.

Believe me or not I did go very serious about the proper choke input operation.
What I meant is that I have to get hold of a scope to check if it all works as it should.
The input chokes were already changed once (once too low voltage rating,
another time too low inductance for a given voltage/current).
The heater/bias input choke is for example 300mH (!), dictated by the tranny
output voltage/heater current (and the Hammond range). Then the LC tanks are additionally damped
with series resistors to bring the Q's down. I'll post the schematics.

I'd strongly desagree that the L-input on B+ is questionable. First of all the choke is dictated
by both the input voltage and the current draw. It's perfectly fine to make a 2mA choke input
supply--the choke will have to have a big inductance, which is easy with low mA's.
Second there are VR's and a serious bleeding resistor down the chain so a small current
drawn by the signal part itself is not an issue. I very much like this implementation of yours. I believe
it helps a lot to stabilize the supply.
Third, and probably most important, L-input is inherently less noisy (provided min current is
met). With such a delicate preamp, the current spikes
emitted by the cap input filter (they depend on the cap size, not the current draw, and could easily go into ampere's range
if the cap is big enough...which would be the case to filter well) could do a lot of harm: may spread all over
the place and trigger ringing here and there. I'd not even consider a C-input.

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