Interconnect Inductance vs. Capacitance

Regarding the 500K input impedance, a common-cathode tube input stage can indeed have high input impedance levels. If you measure the resistance between the grid and the cathode of a tube, it is in the order of several mega ohms or higher. To lower it to 500K, one would need to put grid resistors to get that level.

Another concept to clarify is that it is the output impedance of the preamp that can cause the roll-off highs, instead of the input impedance of the power amp. This is because the capacitance of the ICs and the preamp output impedance form a low pass filter.

Regarding the experiments with two capacitors, the smaller value ones are actually the higher end model. The smaller ones are Mundorf Silver/Gold & Oil, and the larger ones are Mundorf M Caps.

TRL told me that they had experimented various capacitance levels of the same brand and same model of capacitors. Their findings were similar to mine. If you look at the Dude preamp, you will be amazed by the size of the output coupling caps.

Just out of curiousity, do you think that anyone selling cables has IC designs that would exhibit enough capacitance to grossly affect high end frequency response? Isn't this more an issue for the designer than the consumer?

Just out of curiousity, do you think that anyone selling cables has IC designs that would exhibit enough capacitance to grossly affect high end frequency response? Isn't this more an issue for the designer than the consumer?

No, as far as I am aware no one sells interconnects with capacitance high enough to "grossly" affect high end frequency response. But under extreme circumstances (high component output impedance, long cable length, high cable capacitance per unit length), it could become marginally significant. So in that sense it is potentially a system-level issue, that the consumer should be aware of.

Thanks for your very comprehensive and well done earlier post, btw.

Regards,
-- Al

Thanks all for the great comments. I understand that the capacitance and the inductance are not the whole picture for most high-end audio gears. Like what I said earlier, I have a preamp that uses a 100K attenuator at the output and I need 10 ft of ICs between preamp and power amp.

Let me use an example to illustrate my point. Take Cardas Golden Cross ICs as an example. According to its website, the capacitance is 25.5 pF/ft. For 10 ft ICs, it yields 255pF.

Since the preamp attenuator has 100K max resistance, let's assume 50K ohm output impedance. With these two numbers, let's compute the 3dB roll-off freq, Fc.

Fc = 1/(2*Pi*R*C) = 12.5 KHz

As you can see, the highs are significantly rolled in this configuration! Hope it all makes more sense now.

Can you please chart the numbers you used, my calculations are different then yours. I used 1/2*3.14*100 or 50*255), neither one of the impdencance vlaues match your solution. I got 20017.5

Using the same forumula, and for my system, I have 14 foot cables, but a low 14pf per foot for a total 196Pf, Neotech UPOCC cables, preamp has 100ohm output impedance and the amps are 210 kOhm input impedance.

The numbers read: 1/(2*3.14*100*196)= 30772

I think my math is off some, Thanks.
Audioquest4life