Audio - Split and adjust only one output

Thread Starter

andyhof

Joined Jun 22, 2011
13
Totally noob here, so please be patient ! But you guys have been helpful before so here goes:


I am looking at creating a splitter box for an unbalanced line level audio signal.

organ rotary signal (+) ~4dBu
audio ground (-)

I would like to split the 1 signal into two separate outputs.

One separate output would continue unchanged to organ speaker/amp.
I would like the 2nd output to be controlled to vary its output (decrease) before it reaches the speaker/amp.

So, in theory, I would like one input, two outs, with a volume pot on one output

I understand (or have been told) that this cannot be done passively.

Is there a simple circuit i can put together to accomplish this?

I'm open to learning and welcome any suggestions.

thanks
Andrew
 

Thread Starter

andyhof

Joined Jun 22, 2011
13
Dead easy I like

But since this is new to me..
I need the circuit spelled out

Should we continue off list in email so others don't get bored?
 

crutschow

Joined Mar 14, 2008
25,646
I see no particular reason for the buffer amp, unless the reduced output is driving a long cable.
Just run the signal directly to the non-altered output and use a pot for the second output (a 10kΩ or so pot should work).
 

Thread Starter

andyhof

Joined Jun 22, 2011
13
I see no particular reason for the buffer amp, unless the reduced output is driving a long cable.
Just run the signal directly to the non-altered output and use a pot for the second output (a 10kΩ or so pot should work).
So, if i make a "daisy chain" splitter, and use a pot for the second output, that simple?
 

AnalogKid

Joined Aug 1, 2013
8,686
It can be. Here is a seat of the pants method for thinking about the voltages and components.

If the audio source has a relatively low output impedance, and both amps have relatively high output impedances, then you can run the audio directly to amp #1, and through a simple volume control to amp #1. For example, if the source is an electronic circuit such as an opamp output stage with a 100 ohm series resistor to prevent damage from accidental short circuits as things are plugged and unplugged, then the output impedance is 100 ohms. If the input impedance to amp #1 is 100 K, then when it is connected the source voltage decreases 0.1%, trivial. If you also connect a 10K pot, then the source decreases 1%, barely noticeable. The worst case output impedance of a 10K pot is 5K, and amp #2 has that 100 K input impedance, so at 50% rotation (assuming a linear pot, which you would *not * use but it makes the math easier), the input to amp #2 will be 5% lower than the actual 50% audio voltage. But you don't care about that because it is an adjustable attenuator on purpose, so you turn it up a tiny bit to compensate.

A voltage follower buffer or two make the two outputs absolutely independent, but there is no reason (yet) to make that your starting point.

ak
 
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