is capacitance capacitance?

[Mick Bailey]

With regard to the original question; any complex circuit can be simplified for the purpose of analysis. How the simplified model then holds up in real life is another matter.

Whilst adding capacitance to one end to make up the measurable capacitance gives the same reading, in reality your cable has distributed capacitance. This means that there are an infinite number of parallel capacitors, and an infinite number of series resistances, as well as an infinite number of inductors. When you measure a cable at the end you're seeing the total of all of these.

Distributed capacitance acts differently than just adding a capacitor at one end, but is probably not detectable to the ear at audio frequencies. At RF it shows up in how intermodulation frequencies get attenuated along a transmission line.

[daz]

Well, so much for this idea. Once again i have run into something so puzzling i can't begin to understand what could be going on. I took a patch cable and unscrewed the shield at one end to get to the conductors. Plug it into the look with a pot's center lug soldered to the hot lug of the plug and a cap from one of the outside lugs to ground of the plug. Turn the pot either way and no effect whatsoever. Tried a different pot, still nothing. Removed the .022uf i used and put a friggin .1uf. Nothing. Then i took the pot off and soldered the cap directly from the plug's hot lug to it's ground. NOTHING ! And yes, it's a series loop because if i put a pedal in it and turn the pedal's volume to zero the amp is silent. What in god's name could possibly be happening here !?

[g1]

What amp is this? Or can you provide loop schematic if this is a build.

[Jazz P Bass]

I believe it is the newer Fender Mustang 'modeling' amp.

[Dave H]

What in god's name could possibly be happening here !?

It's the effects loop isn't it? It's not high impedance like a guitar. Perhaps it has a low enough output impedance to be able to drive the capacitor without audible attenuation of guitar frequencies?

[daz]

I believe it is the newer Fender Mustang 'modeling' amp.

Yes.

[daz]

It's the effects loop isn't it? It's not high impedance like a guitar. Perhaps it has a low enough output impedance to be able to drive the capacitor without audible attenuation of guitar frequencies?

yes, a series loop. But i fail to see any way sending the signal to ground, especially via a .1uf anywhere wouldn't pretty much kill all the high end and mids. I mean, closing the hot to ground with a screwdriver tip totally killed all signal, and sending the signal thru a cap that is large enough to pass most guitar frequecies should do almost the same.

[Jazz P Bass]

Yes.

Mustang I, II, III, IV or V?

[Dave H]

yes, a series loop. But i fail to see any way sending the signal to ground, especially via a .1uf anywhere wouldn't pretty much kill all the high end and mids. I mean, closing the hot to ground with a screwdriver tip totally killed all signal, and sending the signal thru a cap that is large enough to pass most guitar frequecies should do almost the same.

A screwdriver is a dead short at all frequencies. A capacitor is frequency dependent. A 0.1u capacitor has an impedance of 500 ohms at 3kHz. If the effects loop has an op-amp for its output it can easily drive 500 ohms.

[eschertron]

A screwdriver is a dead short at all frequencies. A capacitor is frequency dependent. A 0.1u capacitor has an impedance of 500 ohms at 3kHz. If the effects loop has an op-amp for its output it can easily drive 500 ohms.

+1.

A 0.1uF cap feeding a guitar channel input (high impedance, ~1M Ohm) has a knee freq of 1/[2piRC] or ~1.6Hz and rolls off everything above that. If we assume the FX return has an impedance of 1k Ohm (for argument's sake), then the cap starts rolling off freq above 1.6kHz or so. "should be" audible, but maybe not so much for an already band-limited signal. And the knee freq is higher for a lower circuit impedance. To force the issue, put a resistor in series with the audio, and the cap to ground. Classic LPF.

[J M Fahey]

+1.

A 0.1uF cap feeding a guitar channel input (high impedance, ~1M Ohm) has a knee freq of 1/[2piRC] or ~1.6Hz and rolls off everything above that. If we assume the FX return has an impedance of 1k Ohm (for argument's sake), then the cap starts rolling off freq above 1.6kHz or so. "should be" audible, but maybe not so much for an already band-limited signal. And the knee freq is higher for a lower circuit impedance. To force the issue, put a resistor in series with the audio, and the cap to ground. Classic LPF.

You mean it rolls off everything below crossover frequency.

[daz]

Mustang I, II, III, IV or V?

III. 100w mono output. the IV and V are stereo.

[Jazz P Bass]

What version?
V2.1 supposedly addressed a few loop oddities.
http://support.fender.com/software/f...rmware_2.0.zip

[daz]

What version?
V2.1 supposedly addressed a few loop oddities.
http://support.fender.com/software/f...rmware_2.0.zip

I was 2.1 when new but i immediately updated it to 2.2.

[g1]

Did you try a series resistor yet like eschertron suggested?