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Old 28th May 2010, 02:47 PM   #1
trv is offline trv  Israel
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Default Buffer for long cable capacitance

Hi all,

As I understand the guitar cable line is like a capacitor, as long as the cable is, the high cable capacitance is, that's why long cable results high freq loss (capacitor in parallel to signal), solution for this is the buffer.

Buffer has low output resistance, how does it prevent the high freq loss?

What is the considerations and triad off for selecting buffer's input & output resistor ?
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Old 28th May 2010, 03:20 PM   #2
PMA is offline PMA  Europe
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Audio Buffer in english

No problem to drive 100m or more.
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Old 28th May 2010, 03:30 PM   #3
pilli is offline pilli  France
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Quote:
Originally Posted by trv View Post
Buffer has low output resistance, how does it prevent the high freq loss?

If the buffer is "before" the cable
(that is between the pickup+pots and the cable)
then the buffer output resistance (which is low) defines the RC
instead of the pickup + potentiometers output R.

The corner frequency of the filter is 1 / (2 * pi * RC)
so the smaller the RC, the further up your corner frequency.

The buffer also has a high input resistance, thereby "isolating" the pickup.



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Old 28th May 2010, 03:33 PM   #4
PMA is offline PMA  Europe
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In case you match series and terminating impedance to cable characteristic impedance, then you avoid capacitive loading rule and you can send signal to several hundred meters without problem.
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Old 28th May 2010, 04:18 PM   #5
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Put the buffer with 75R output resistor at the transmitting end of cable. Use 75R cable (like coax). Insert 75R resistor across signal and ground at the receiving end of cable or on input of amplifier/mixer/what ever. Works every time
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Old 28th May 2010, 05:05 PM   #6
trv is offline trv  Israel
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So why most of guitar effects has about 10k to 100k resistor at the output buffer?
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Old 28th May 2010, 05:47 PM   #7
trv is offline trv  Israel
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correction:
the 10k to 100k resistor is in parallel and not in serial
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Old 28th May 2010, 06:10 PM   #8
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In both cases. Maybe because they didn't take long leads into considerations................
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Old 28th May 2010, 06:27 PM   #9
trv is offline trv  Israel
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Talking about impedance matching, guitar pickup resistance is about 10k.
Why in many guitar effects there is a big resistor (100k to 1M) in parallel in the input of the entry buffer?
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Old 28th May 2010, 06:35 PM   #10
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I'm in no where into "live" gear, but mostly the reason to high input impedance is to provide as high load as possible for the equipment connected to it (to minimize Current need at the output). Two different worlds.....
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