Posted by Tnuctipun [ 64.12.116.14 ] on January 22, 2005 at 21:21:51:

In Reply to: Re: C1, 4.7uF cap posted by manualblock on January 22, 2005 at 20:58:37:

it is indeed the output coupling cap. Since the impedance of a cap is 1/j-omega-C, we want the cap as large as is sonicaly reasonable. Forget about j and root negative 1. It is the real part of this we will look at.

At 20 cps, omega is 2*Pi*20 radians per second and C is 7.5 * 10^-6.
this yeilds 1061.03295 Ohms. At 40 cps, it is half that, and at 80 cps, half of that. This is close enough to the 10:1 ratio of input impedance to output impedance which keeps us from rolling off too early, even with a 10kOhm SS amp. For a 100kOhm Valve amp and several tens of pF of cabling capacitance, we're still good.
regards,
Douglas

Replies:

• How's this cap? - colinhester 15:24:07 01/24/05 (1)
  • That is a *FINE* cap... - Tnuctipun 16:29:49 01/24/05 (0)
• Re: C1, 7.5 uF/440VAC - manualblock 07:59:36 01/23/05 (0)