Scott Dorsey wrote:
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.
They vary widely. They may be under 20 pF/foot. I think the 60 pF/ft
ones ayou are talking about are down the page quite a bit:
( units are in meters at the link )
http://www.shootoutguitarcables.com/...nce-chart.html
That's not a specific, lab-grade set of measurements, just an idea of
the range available.
It also depends very much on what input you're driving.
The ones I use are probably about 30pF per foot for 10 feet
and they are fine. I cannot readily tell the difference between a 3ft
and a 10 ft cable, even if plugged into a cheap 1 Mohm DI box.
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.
Yeah, I don't think that's commonplace. From 500 to 2k is critical on
electric guitar - people would notice this immediately.
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
--
Les Cargill