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大家都知道，经典的Les Paul在拾音器中间档位，当你用一支音量钮关闭一个拾音器的时候，两个拾音器的音量全部关闭了，许多朋友不喜欢这个特点，所以提出了独立音量控制的改造方式：
采用这种电路改造可以实现中间档位，两支音量旋钮分别控制两个拾音器音量的功能，看上去很美是吧？你在感叹Gibson出厂的时候为啥不用这种电路？工程师真是一帮保守的老顽固是吧？But！这种改造方式会带来以下问题：
当你在琴颈档位，将琴颈拾音器的音量关闭到0，而琴桥拾音器音量开到10的时候，你扔能听到一丝琴桥拾音器的输出信号存留在总输出中，当你把琴桥拾音器的音量也关闭到0的时候，才能实现完全静音……而且，当你关闭吉他音量以后会发现噪音比不关音量的时候还要大……
国外网友提到过同样的问题：
http://www.mylespaul.com/forums/tonefreaks/129435-wiring-problem-switch-bleed-w-independent-volumes.html
关于这个问题产生的原因，Lyle Caldwell大师进行过详细的论证：
Here's why I dislike the "independent volume" circuit:
In a "regular" volume pot circuit in a Les Paul, here's what happens.
For all this, assume a 500K audio taper pot.
When the volume is on "10" there are 0-5 ohms between the output of the pickup and the wiper of the pot (signal sent to the switch) and about 500K ohms between the wiper and ground.
With the volume on "5" there are about 450K ohms between the output of the pickup and the wiper (signal) and about 50K ohms between the wiper and ground.
With the volume on "0" there are 500K ohms between the output of the pickup and the wiper (signal) and 0-5 ohms between the wiper and ground. So at "0" there is a huge amount of signal attenuation and the signal is essentially "grounded out" so the amp input is silenced.
With "independent volume" wiring:
When the volume is on "10" there are 0-5 ohms between the output of the pickup (wiper of the pot) and the signal sent to the switch (lug 1) and there are 500K ohms between the signal and ground. Keep an eye on this number.
When the volume is on "5" there are about 450K ohms between the output of the pickup (wiper of the pot) and the signal sent to theswitch (lug 1) and there are STILL 500K ohms between the signal and ground. See, this number hasn't changed.
When the volume is on "0" there are about 500K ohms between the output of the pickup (wiper of the pot) and the signal sent to theswitch (lug 1) and there are STILL 500K ohms between the signal and ground. The wiper is only 0-5 ohms from ground, so there is very little if any signal from the pickup heard, but...
The input of the amplifier is still 500K from ground (a little bit less, as this 500K is in parallel with the typically 1M resistance to ground in the amp's input circuit). But the amp input is still about 500K away from ground yet has no signal going through it. The circuit now behaves almost like a cable plugged into the amp but not into a guitar - it acts as a noise antenna. Not quite as bad as an unplugged cable, but not great.
This explanation is a little oversimplified, as I don't have time today to explain how pickups behave as inductors, and there are some other variables at play, but the core concept here is correct and applicable.
原帖链接：http://www.mylespaul.com/forums/tonefreaks/122705-more-grounding-misconceptions-3.html#post2485445
结论：Gibson原厂的工程师不是老顽固，更不是傻子，不采用“独立音量控制”电路是有道理的！如果你不能接受“独立音量控制电路”带来的这种Bug的话，老老实实用原厂的电路吧！ |
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发表于 2012-1-22 20:25:04
