Good argument.

Posted by cheap-Jack (M) on March 29, 2007 at 07:50:01

In Reply to: Re: You may overlook something else ... posted by Tre' on March 28, 2007 at 16:00:44:

Hi.

RHD4 stated in "Input impedance & Miller Effect":-

"The total input capacitance also includes the capacitance from grid to cathode plus (A+1) times ANY stray capacitance from grid TO plate".

My interpretation is ANY stray capacitance from grid TO plate (not between grid and plate) also includes capacitance of the hook-up wires etc etc.

"Stray capacitance" is defined as "Undesirable capacitance btween circuit wires, btween wires & chassis, or between components and the chassis of the electronic equipment".

Correct me if I were incorrect.

The whole idea is to minimize any stray capacitance added to the grid circuit. Coaxial cable is a ready source of stray capacitance.
I would use only twisted pair withOUT any overall shield from the I/P jack to the triode grid. ALL my SS & tube phonostages never ever use any shielded signal cables.

Technically, the inter-conductor capacitance of a tightly twisted pair of wires of EQUAL size & IDENTICAL material is around 5pF, but the conductor-to-shield capacitance is in the order of some 40pF for EACH conductor, depending on the distance btween conductor & the shield.

For a coaxial cable, C=7.36xe/(log10 D/d) where e is the dielectric constant of the conductor insulation, D is the overall diameter of the insulation & d is the diameter of the conductor.

As Mark said it right, too much shielding capactance can only ruin the sound. This is the very reason I step away from any wire shielding.

For really EMI/RFI noisy environment, use a 100% metal chassis.

c-J

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Follow Ups Full Thread

Topic - Can anyone show me a Preamp Schematic with 30X gain using Mini Tube, the best/good ever build for your expereience ? - calico 18:14:05 03/26/07 (14)

Re: Can anyone show me a Preamp Schematic with 30X gain using Mini Tube, the best/good ever build for your expereience ? - danlaudionut 19:07:34 03/26/07 (13)

Shielded grounds - arend-jan 02:39:01 03/27/07 (0)

Dan, why on earth recommend a circuit that... - Allen Wright 01:03:03 03/27/07 (11)

Re: Dan, why on earth recommend a circuit that... - Tre' 08:03:51 03/27/07 (5)

You may overlook something else ... - cheap-Jack 14:00:14 03/28/07 (4)

Re: You may overlook something else ... - Tre' 16:00:44 03/28/07 (3)

Good argument. - cheap-Jack 07:50:01 03/29/07 (1)

Re: Good argument. - Tre' 08:51:56 03/29/07 (0)

And I'm gonna have to re-compute the values for ..... - Tre' 18:39:28 03/28/07 (0)

Re: Dan, why on earth recommend a circuit that... - danlaudionut 07:11:56 03/27/07 (4)

grid stop - Ralph 12:06:14 03/27/07 (3)

Re: grid stop - Tre' 13:03:42 03/27/07 (1)

That one... - Ralph 14:12:14 03/27/07 (0)

Re: grid stop - danlaudionut 12:44:15 03/27/07 (0)

Follow Ups

Good argument. - cheap-Jack 07:50:01 03/29/07 (1)

Re: Good argument. - Tre' 08:51:56 03/29/07 (0)

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