In Line Potometer

silvrwolf

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Nov 30, 2006
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Downers Grove, IL
Hey, just a question what size pot. would I need to fully control the audio level between an aux send and an amplifier. The pot would be used as an input level control for the amplifier. The amplifier is a crown base 2 and the knobs for the input level of the amplifier are on the back and hard to get to during a show. I'm hopping to get a rackplate and mound a potometer for each channel of the amp to control it. This pot would not take the place of the factory one, it would just control the level before it got to the amps control. Oh ya, the signal leaving the board would be at line level.
Thanks
 

fosstech

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Jun 7, 2004
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Tacoma, WA USA
Why not just adjust the output level of the aux send? For proper gain structure, the amplifiers are usually stay at a certain level so the engineer at the board knows how much headroom he/she has. That's why the level controls on your PB2 are on the back. Level controls are also more complicated than just a pot inserted in the signal chain. Usually amplifiers are set turned all the way up, meaning zero attenuation. This means that a +4dBu output from the board will drive the amplifier to its maximum output before clipping. All amps are different, so make sure you check the spec sheet before you go assuming a +4dBu signal will drive your amplifier correctly.
 

Van

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Jul 27, 2006
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Portland, Or.
If'n I'm not crazy, and there are no assurances I'm not, and I'm rememberring my theory correctly a 120kohm audio taper potentiometer should do nicely. Obviously you'll need one for each signal or there are some "stereo" pots that are two ganged together. I'd go for two seperate however, as I like to make things as complicated as possible.
 
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silvrwolf

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Nov 30, 2006
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Downers Grove, IL
Why not just adjust the output level of the aux send? For proper gain structure, the amplifiers are usually stay at a certain level so the engineer at the board knows how much headroom he/she has. That's why the level controls on your PB2 are on the back. Level controls are also more complicated than just a pot inserted in the signal chain. Usually amplifiers are set turned all the way up, meaning zero attenuation. This means that a +4dBu output from the board will drive the amplifier to its maximum output before clipping. All amps are different, so make sure you check the spec sheet before you go assuming a +4dBu signal will drive your amplifier correctly.
Just in response to this, I know the way amps are run, but I have a different needs where I need to control my amps input gain during the show and due to my setup I couldn't do it with the aux control. If I could, I would control everything from the board but in some cases its not possible.
 

SHARYNF

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Sep 3, 2006
Probably the way you phrase the question and comments leads to the response. There is no way that a passive device in line is going to control the input gain on your amp, unless you went into the amp and actually altered the internal gain. Most modern amps don't allow for this, and as stated, just attenuate the input . So assuming you have no access to the amp input level control, the best you can do is attenuate the signal going to your amp. What this means is that you are probably going to increase the noise level in the system.

I'd probably go with http://www.adesignsaudio.com/atty.htm or
I've used this http://www.adesignsaudio.com/atty2d.htm with some carver amps that have NO input level control, does the job. Also Mackie's BIG KNOB monitor controller will work.

Sharyn
 

Chris15

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Jul 15, 2005
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Van, my gut reaction was a 10K logarithmic pot. But you might be better off with a 50 K or even 100K pot. Remember that the pot is acting as a voltage divider in this instance, so there is room to play with the actual value of the pot, because the ratios won't change.

And I'm going to have to disagree with Van. Dual gang pots are mandatory. This is because you are running a balanced signal through this and so changing the volume of one leg is not going to work as well as changing the volume of both legs. Unless the OP mean unbalanced when he referred to line level. If so, then you COULD get away with a single gang pot, but in the end, you might upgrade to balanced along the way and since a dual gang pot ain't that much more than a single gang one, just go for the dual gang.

When you get to wire the pot, you want to connect it as follows. Use shielded balanced cable for all connections. Hot line to one gang, cold line to the other, unless you want phase reversal. When looking at the pot with shaft sticking out and terminals at the bottom, connect shield to the left hand terminal on both gangs. Connect your output to the middle terminals (wiper) and your input to the right hand terminals.

Hope that helps.
 

TimmyP1955

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Oct 29, 2006
Location
Indianapolis
There's another way that may work well:

Put a 1k resistor in series with with each leg.

Put a 10K pot between the legs, on the amp side of the resistors.

When the pot is full, you'll have a little attenuation owing to the resistors. As you turn the pot down, it will blend the legs and thus attenuate the signal. (This is how it's done in a Leslie 122 amp.)
 

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