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Old 23rd February 2005, 03:39 PM   #1
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Default summing channels

I have been looking for a while on how to sum the left and right channels for use on a mono subwoofer and havent found the appropriate information.
I remember reading somewhere a long time ago about having to use a 10k? resistor somewhere in order to not"short" the right channel. It seems to sound fine to use the left and right connected together in parallel ie: just a y-adapter.
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Old 23rd February 2005, 03:54 PM   #2
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You do need a resistor in series with each channel. This will keep each channel from loading the other. A 1k will probably work fine. Most equipment makers put a series resistor on the output of line level products just as a safety measure, in case someone uses a 'Y' adapter. If your is working OK, thats probably the case.
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Old 23rd February 2005, 07:46 PM   #3
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Default resistors

So for building a sub amp I should do this for the inputs if i want to use both channels? Is the value of the resistor important or will change the sound signifigantly? The periods are just there as place holder for the diagram.
L+ ------\/\/\/\/\--------\
.....................................|-------------+amp input

Im just using a discman right now because of funds but eventually it will run off of normal CD/DVD source
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Old 23rd February 2005, 08:08 PM   #4
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Hi there, that looks good. The resistances define how much you'll load your source equipment. You'll notice an attenuate(quiet)output if the resistors are too big, but you'll have crossloading (as defined earlier) if they are too small.

For something like a discman, the output is designed to handle a lower resistance load because of headphones. In this case, 1K resistors are good.

In most audio equipment I use between 6.8K and 10K for my summation resistances; unless there's a special case like high voltage in tubes.

Hope this helps.
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Old 23rd February 2005, 08:09 PM   #5
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No, the value isnt real critical. It just provides isolation between the two channels. 1K is probably fine. Different values may cause a slight level difference, but thats all.
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Old 24th February 2005, 06:23 AM   #6
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I've been using a parallelled stereo amp running mono to drive a sub for over a year now.

It has an STK 4231-2 IC amp that's rated at 100W/ch at 8 ohms.

The Transformer measures 40/0/40 and is fairly big and heavy.

The inputs are connected together, and the outputs have a 0.1 ohm resistor at each output which connect together at the speaker.

This is running a single 12" 4 ohm speaker, at over 200W.

This sub gets slammed by this amp, but the bass sounds clear, controlled, and sounds good way down low, even at low volumes.

My original idea was to use a dual coil sub, but I couldn't find a good cheap one with dual 8 ohm coils, so paralleling 2 8ohm amps to make a mono 4 ohm amp worked better.
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