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Old 4th September 2012, 01:36 PM   #1
disco is offline disco  Netherlands
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Default Recommendations on How To mono a pre amplifier?

Does an optimal method exist for producing a mono signal out of a 2-channel signal? I'd like to switch this option in and out on my pre amp without too much difference in audio level. So I was thinking of a relais and several resistors but this way it would raise output impedance (which is 1K5).

Bluntly shorting the hot wires on the output might be the simplest of simple solutions. Perhaps via two 1uF capacitors?

Shorting the inputs might upset the CD player, toasting the delicate BurrBrownies... hmmmm

OK, a summing amplifier goes a little too far )
On the other hand... how about connecting the cathodes together?
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Last edited by disco; 4th September 2012 at 01:38 PM.
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Old 4th September 2012, 02:04 PM   #2
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two 100-300 ohm resistors then short the outputs together.
i think the burrs shouldn't mind that, since they often drive 32ohm impedance's.

one 100-300 ohm resistor on each channel, then combining them after the resistor. i don't see any reason for that not to work. correct me if i am wrong
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Old 4th September 2012, 02:07 PM   #3
DF96 is offline DF96  England
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Many good preamps will already have resistors in series with the outputs, so no need to add extra ones.

PS this question comes up every few weeks - searching would find you the answer

Last edited by DF96; 4th September 2012 at 02:08 PM. Reason: add PS
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Old 4th September 2012, 05:00 PM   #4
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Quote:
Originally Posted by DF96 View Post
Many good preamps will already have resistors in series with the outputs, so no need to add extra ones.

PS this question comes up every few weeks - searching would find you the answer
Well, that might be so but the information is not accessible. Searching for 'mono' within Amplifiers leaves me with 101 pages of unrelevant information as there's no possibility to filter 'block', 'duo' etc. Ok?

So, your advise is to simply short the left and right output. Does this altered loading of the preceding CF have a sonical penalty or would this just be theoretical?
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Old 4th September 2012, 06:35 PM   #5
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My DIY amplifier has this facility, but not just mono-stero, I made a "stereo blend" control for the mid and higher frequencies. I used a 100K pot with a switch and a 2.2u capacitor. "OFF" position is stereo, then you blend the highs as much as you want.
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Old 5th September 2012, 04:02 AM   #6
disco is offline disco  Netherlands
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That's interesting Costis. Did I get it right?

Click the image to open in full size.
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Last edited by disco; 5th September 2012 at 04:30 AM.
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Old 5th September 2012, 04:27 AM   #7
disco is offline disco  Netherlands
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Quote:
Originally Posted by ruben alstad View Post
two 100-300 ohm resistors then short the outputs together.
i think the burrs shouldn't mind that, since they often drive 32ohm impedance's.

one 100-300 ohm resistor on each channel, then combining them after the resistor. i don't see any reason for that not to work. correct me if i am wrong
You are in favor of shorting the inputs of the pre amp (via resisters), if I'm reading you right Ruben?
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Old 5th September 2012, 09:46 AM   #8
DF96 is offline DF96  England
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He said outputs.
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Old 5th September 2012, 11:11 AM   #9
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Quote:
Originally Posted by disco View Post
You are in favor of shorting the inputs of the pre amp (via resisters), if I'm reading you right Ruben?
ground is common for both channels, so you can just combine both cannels after a 100-300ohm resistor on each channel.
dont bother about using pots ect because your load impedance is too low for it.
the reason to use the resistors is to avoid any harm to the pre amp from combining both channels.
so it is, 100-300 ohm resistor on each channel then after the resistors combine them, there you have mono.
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Old 6th September 2012, 06:20 AM   #10
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Here it is. L and right are connected to the outputs of the 2 channels (it's cathode followers). Shown in 3 positions for clarity. In my case, cathode follower resistors are 30K, pot is 100k. (so it does not disrupt much the AC conditions).

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