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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

Correct way to split line level inside dual headphone amp
Correct way to split line level inside dual headphone amp
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Old 5th September 2014, 09:51 AM   #1
Seggelke is offline Seggelke
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Default Correct way to split line level inside dual headphone amp

I am building a dual headphone amp (two separate amps sharing the same unbalanced input)

Is the best way to do this to use resistors, or will it be fine to just split the signal?
Input impedance on the headphone amp is 10kΩ

I also intend to make a balanced version that will split the balanced input between one or two headphone amps and a balanced line level output

Last edited by Seggelke; 5th September 2014 at 11:02 AM.
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Old 5th September 2014, 06:18 PM   #2
bentsnake is offline bentsnake
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You could use Figure 2, but reverse the input and output. Now you have a splitter instead of a summer: Why Not Wye?

However, a passive (resistor) setup might be called a bit shadetree. You're actually talking about a "distribution amplifier." One common way to do this is to use a buffer for the input, then the buffer's output feeds as many output ICs as you like. Well...as many as you like within some kind of reason.

Don't be intimidated by the page title, just scroll down to Figure 18a: Designing An Opamp Headphone Amplifier | HeadWize

And/or, Google for:

headphone distribution amplifier circuits

Lots of people share your idea.
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Old 6th September 2014, 01:47 PM   #3
bentsnake is offline bentsnake
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<< I also intend to make a balanced version that will split the balanced input between one or two headphone amps and a balanced line level output >>

I'm not sure what you mean by splitting the balanced input. Just in case:

Be aware that balanced lines (XLR connectors) have nothing to do with audio directly. Their sole function is to minimize noise pickup by connecting cables.

To do this, the single audio signal is sent to two different IC amps, one of which is non-inverting, the other inverting.

The non-inverting output is the original audio signal, sent down the line from the HOT terminal of an XLR connector.

The inverting output is 180-degrees out of phase with the original, it's sent down the line from the COLD terminal.

At the receiving end the inverted signal is again put through an inverting amplifier. It's now in phase with the original and the two are combined, again producing a single audio signal.

All of which means that if you split a balanced line you'll find that one side of the split is in phase with the original, but the other side of the split will be out of phase. This might not matter to your purpose, but I thought I'd mention.
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Old 6th September 2014, 03:12 PM   #4
Seggelke is offline Seggelke
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Quote:
Originally Posted by bentsnake View Post
.
<< I also intend to make a balanced version that will split the balanced input between one or two headphone amps and a balanced line level output >>

I'm not sure what you mean by splitting the balanced input. Just in case:

Be aware that balanced lines (XLR connectors) have nothing to do with audio directly. Their sole function is to minimize noise pickup by connecting cables.

To do this, the single audio signal is sent to two different IC amps, one of which is non-inverting, the other inverting.

The non-inverting output is the original audio signal, sent down the line from the HOT terminal of an XLR connector.

The inverting output is 180-degrees out of phase with the original, it's sent down the line from the COLD terminal.

At the receiving end the inverted signal is again put through an inverting amplifier. It's now in phase with the original and the two are combined, again producing a single audio signal.

All of which means that if you split a balanced line you'll find that one side of the split is in phase with the original, but the other side of the split will be out of phase. This might not matter to your purpose, but I thought I'd mention.
.
Thanks, this much I know.

What I mean is splitting off the signal to two headphone amps and one balanced line out.
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Old 6th September 2014, 03:13 PM   #5
udok is offline udok  Austria
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Quote:
Originally Posted by Seggelke View Post
I am building a dual headphone amp (two separate amps sharing the same unbalanced input)

Is the best way to do this to use resistors, or will it be fine to just split the signal?
Input impedance on the headphone amp is 10kΩ

I also intend to make a balanced version that will split the balanced input between one or two headphone amps and a balanced line level output
Just feed the input to the two parallel headphone amps. Input impedance will be 5k if each amp has 10 k input impedance, which is ok.
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Old 7th September 2014, 02:20 PM   #6
Speedskater is offline Speedskater  United States
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Balanced interconnects are a lot trickier than that. By the time it gets to the receive end all you have is the Hot & Cold conductors. The reference to common (aka ground) is lost. So you can't just use the Hot output for one signal and the Cold output for the other.
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Old 7th September 2014, 02:25 PM   #7
Speedskater is offline Speedskater  United States
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Rod Elliott edited the great balanced circuit paper:

"Design of High-Performance Balanced Audio Interfaces"
Bill Whitlock - Jensen Transformers, Inc. (Edited By Rod Elliott)
Balanced Interfaces

*************************************
The Doug Self Balanced Line Technology paper:
Balanced Line Technology

***************************************
The Rane "Why not Wye" paper:
Why Not Wye?
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