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Pre-amp Master Volume with Subwoofer Control

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What I would consider doing is to "move the controls" or the ones you care about. i.e. replace the integral control with a panel mounted one and hide it in a "rack case".

Input and output Z of the audio inputs in consumer stuff is generally misunderstood. Commercial audio uses 600 ohms in/out and balanced differential signally with twisted pair cables. The 600 matches the characteristic impedance of the wire. The "right way".

In consumer audio, the output has to be much less than the input Z. 100 ohms vs 10K in the above example. The 100 helps to eliminate ground loops., but there is a slight voltage divider effect with the 100 and 10K..

So, your suggestion would be to replace and relocate the "output level" pot with a comparable valued log pot panel mounted the way I was planning on mounting my 10k pot? Unfortunately, I don't think that would have any impact on the sub-woofer output.

With regards the input and output level difference, are you saying that the input impedance being 20k ohm versus 100 ohm output impedance is necessary for eliminating ground loops? I'm not familiar with voltage divider effects, so I'm not clear on what your final statement impacts.
 
I'll respond better later. On phone. The active xover also has a sub level. That could be moved externally too.
An amp has a spec called damping factor. 100 is good. This means that the amp has a characteristic impeadance 100X less than the load 100/8.
 
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Ok, the 10K input is likely seen by an OP-amp inside the unit which could have a 1e16 ohm input Z, This effectively makes the 10K 10K

The output Z of 100 ohms could be done in one of two ways:
1) Where feedback is taken after the resistor.
2) Where feedback is taken before the resistor.

#1 basically current limits the output where #2 adds a 100 ohm series resistance. So in #2, the output sees 10,100 ohms

You can go here: **broken link removed** and make R1=100 and R2=10K with 1 V in and you'll see the output doesn't change by much. The best would be R1=0.

In a 600 ohm system, the currents are higher. This **broken link removed** is the way it's supposed to be done and is done that way in professional systems.
 
A quick discussion. **broken link removed** This has 100K inputs and 100 ohms outputs and Ac coupled.

It "no way" matches the quality in my pre-amp of the 80's. It can be direct-coupled from input to output and has a 0-100 kHz bandwidth. To increase the ability to handle transients, gain is distributed through three linked inter-stage attennuators.
 
A crossover that is 12dB per octave has 180 degrees phase shift at the crossover frequency if the highs and lows are in phase so they cancel causing a notch. If one set of speakers has its phase reversed then they add +3db at the crossover frequency. A Linkwitz-Riley alignment prevents the +3dB.
A 3rd-order crossover is 18dB per octave and does not cancel or add.

The Soundstorm SSLSX310 is 12dB per octave and its spec's say only its length and width, nothing about its alignment or if it avoids cancelling or adding at the crossover frequency. They do not know anything about specifications for sound products.

Here is a simulation of a 12dB per octave active crossover with a Butterworth alignment and the highs and lows in phase showing the notch (solid line)and the phase shifts (dotted line). They are mixed with a passive mixer which causes the -6dB at extreme frequencies.
 

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A modern amplifier has an excellent "damping factor" that controls the speaker properly by damping its resonances. Without good damping then a speaker rings at resonance and sounds like a bongo drum and makes male voices sound boomy if the speaker is good and causes female voices to sound funny if the speaker has poor low frequency response. Some speakers have a resonance in the upper midrange that makes a shriek sound when not damped.

The excellent damping is created by the extremely low output impedance of a modern amplifier, 0.04 ohms or much less.
An L-pad inserts a resistance in series with a speaker and an amplifier that ruins the damping and was used with old vacuum tube amplifiers that had a high output impedance and poor damping.
 
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