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-   -   Cable capacitance? (http://www.talkbass.com/forum/f38/cable-capacitance-1042149/)

 friedtransistor 12-31-2013 09:41 AM

Cable capacitance?

I just decided to do an experiment. I hooked my cable to a 555 timer circuit, and then used capacitors to match the frequency of the cable's capacitance. My cable is about 495-500 pF, which means that a 1M resistor in series with it gives a lowpass response of about 320 Hz. Gives my guitar a jazzy tone with the resistor. Haven't tested it on my bass yet, my bass amp is out of order until I sort the mess of hair-thin traces Fender decided to coil all over the pcb for the grounding. Is there any way of getting around this high capacitance without usig a buffer? I mean, I can make a pretty mean little buffer/booster, but I'd rather not have the hassle of dealing with it. Would I need to solder resistors or caps into the plugs of the cable to counteract the cheapness? :b

 markanini 12-31-2013 10:00 AM

With an average pickup inductance of 3H the resonance is at 4100Hz.

 friedtransistor 12-31-2013 10:16 AM

Sorry, I didn't explain my calculations. Guitar->short low cap cable->1M resistor->long cable under test->amp. The capacitance to ground in the cable with the resistor in series acts as a simple 1 pole RC lowpass. 1/(6.28*0.000000000495*1,000,000)=~320Hz. Unless there is a better way of measuring capacitance other than using a 555 timer wih the cable as a cap, taking the output frequency, then using other caps instead of the cable untill I get the same output, then adding up the caps. I had to use a 470pF parallel to a 15pF to get the same oscillation.

 BlueTalon 12-31-2013 01:54 PM

You could go wireless, that would solve the capacitance issue.

 friedtransistor 12-31-2013 03:11 PM

And be way outside my realm of expenses. Idk, I've dealt with it this long, I probably just continue using it until it breaks, then move on to a low cap cable. Maybe I'll just make a buffer. Just need to order some parts, and since I got a power supply for christmas, order a dc jack. I'll have to wait, though, until I figure out what other project I want to make, so I can save on the cost of shipping. But I guess I need to tackle one thing at a time... *continues waxing guitar fretboard*

 dune2k 12-31-2013 03:58 PM

Do you hear a difference when you use a shorter cable (bass -> cable -> amp)?
If not don't make up a problem where there is none.

Also: Why did you put a 1M resistor in series with it? What's the idea behind it?

 friedtransistor 12-31-2013 04:39 PM

No, not really. I did hear a very slight difference, though, when my friend let me borrow his strat, but the difference is small enough that I had to record the two cables back-to-back to hear anything.
As for the 1M, I chose that value to see how much difference the cable really makes, as I have been experimenting lately with using 1M pots for volume controls. Also, it would be more noticeble than, say, a 100K resistor, which has a cutoff of around 3,200 Hz. Idk why it really matters to me, though. I mean, I built a delay with a 1 kHz cutoff, just because I thought it sounded good. Perhaps I should have kept my mouth shut and thought a little longer before posting a question that I have already answered without knowing it...

 khutch 12-31-2013 04:51 PM

You cannot cancel out the cable capacitance over a broad frequency range and to do it at all would require adding inductors, not resistors or capacitors. Loading resistors would make the capacitance inconsequential if they were low enough in value but then of course the tonal changes from the resistors would be worse than the capacitors were in the first place. If you need the long cable then a buffer is your best option. Even low cap cables will only be somewhat lower in capacitance, you can't make a shielded cable without any capacitance. Any active pedal could act as a buffer, if you use any pedals and if they are located before the cable and its capacitance. The only other thing you might use in place of a buffer is a signal transformer to lower the driving impedance of the bass. I'm not sure where you get one that works down to bass guitar frequencies.

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