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

Post Subject: Schematics IIPosted by N-set on: 9/1/2011

Here is the signal box:

The design is double mono past the VR's. Including the bias.
The coupling caps are Arcotronics KP172 from RS-Online, quite prised by Thorsten Loesch. THey are sitting on
sorbothane pads. The air caps are: 1) 365pF some +/- standard US radio type with alu blades
2) 150pF is Jackson low power from mainlinegroup.co.uk, type C803B150 with silver-plated brass blades (15GBP/pcs,
super nice people). They also have a 350pF with silver-plated brass blades: C9-5070-2 but for a whooping 64GBP!!!
The input/output RCA (why the fuck are we bound to that misery 1000yrs old design???) are the copper Vampire.
The CCS heating is done around LT317A. The 2R resistors before the 470u Elna's are the "intelligent bypass",
damping possible interactions of the Elna's with the big 3x10mF Nichicon block. The bias voltage is taken directly from
one of the Elna's at the V2 socket.

I've decided to split PSU/Signal in the given way with the ballast 5k and 2R resistors in the Signal box rather than PSU
to form a voltage divider for the noise picked by the umbilical: the noise source located in the umbilcal sees at the PSU end
a short path to ground, while from the Signal signe a divider with a series R and shunting C/VR to ground. So the nett noise voltage
at the shunting element (C or VR) is effectively divided. Makes sense?

The overkill Caddock MP820 as the VR ballast is a result of an unexpectedly poor preformance of a new production
4.7k 12W Mills in this place. With merely 2W or so it was sweating like a dog. Truly unexpected from 12W Mills.
MP820 was what RS-online had and I could buy without the shipping costs.

I contemplate 2 intellectual cosmetic changes in PS: 1) a Romy-style VR bypass (the first 100uF cap is close to the V3 tube
rather to the VR's) with two additional 47uF caps connected directly between the VR sockets (GND) and the tube-end of 12.1k Mills'.
In this way the roles are divided: the 47u +12K filetr the VR noise, while 100uF takes care of the signal.
2) A common mode filter in the heating located either before or right after the 30.000uF block.
I even have the ferrite-core choke ready

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