Don Pearce wrote:
On Mon, 5 Jun 2017 06:50:24 -0700 (PDT), wrote:
The tests have been done with a signal generator. The source should
have been a dummy circuit that simulates the complex impedance of a
pickup.
looks like the the 3rd plot did use an actual pickup as the source impedance
Something like, yes. The other plots though - appear to show rolloff
in bass and treble. I'd very much like to know how that is supposed to
happen.
Let's say we have a typical rubber cord at 60 pF/ft, and it's six feet long,
so we can view it as a 360 pF lumped-sum load.
Our load impedance is 1 megohm, let's assume the source impedance is 1 meg
also (and in reality it'll be worse than that and nonlinear too). So total
shunt resistance is 500K ohms.
So, best case 3dB corner comes out at 1/(2piRC), 1/ 6.3 * 5E5 * 36E-11
or 880 Hz.
So, in this case (and we're neglecting the series L of the cable), you can
view the cable+interfaces system as a first order low pass filter whose -6dB
point is at 880 Hz.
I'd call that a hell of a cable effect... and very different than what they
are describing.
I wouldn't expect to see _any_ bass rolloff, even with considerable cable
series resistance or series inductance. The fact that they are would indicate
to me that they're doing something odd.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."