Headphone mixer design

[yosh]

Hello, I'm working on a design for a headphone distribution and mixing system.

There will be a distribution box which will contain INA134 balanced to unbalanced chips and a power supply. From the INA134 chips 1 stereo and 8 mono signals will continue unbalanced along with DC power down a 15 conductor cable with DB15 connectors to each of the personal cue mixers.

I've drawn up a schematic for the mixers with inspiration from a few things I found on the web. The ACN I found here http://www.all-electric.com/schematic/simp_mix.htm, and the headphone amp schematic I found here http://sound.whsites.net/project30c.htm.

I wonder if anyone with more knowledge than I might check this out and give feedback about any errors or possible issues this design might face? Thanks in advance!

 

[Nick Franklin]

Sorry not directly applicable to your design but if you are after a more ready made solution, JLM Audio's headphone amp kit can do the mixer thing REALLY easily. You could put together a headphone mixer system so easily with these which might save you some time and effort!

 

[yosh]

Sorry not directly applicable to your design but if you are after a more ready made solution, JLM Audio's headphone amp kit can do the mixer thing REALLY easily. You could put together a headphone mixer system so easily with these which might save you some time and effort!

I had not seen these. It does look like it'll help me do what I'm trying to achieve. Thanks for pointing me in this direction!

 

[abbey road d enfer]

Hello, I'm working on a design for a headphone distribution and mixing system.

There will be a distribution box which will contain INA134 balanced to unbalanced chips and a power supply. From the INA134 chips 1 stereo and 8 mono signals will continue unbalanced along with DC power down a 15 conductor cable with DB15 connectors to each of the personal cue mixers.

I've drawn up a schematic for the mixers with inspiration from a few things I found on the web. The ACN I found here http://www.all-electric.com/schematic/simp_mix.htm, and the headphone amp schematic I found here http://sound.whsites.net/project30c.htm.

I wonder if anyone with more knowledge than I might check this out and give feedback about any errors or possible issues this design might face? Thanks in advance!

That would work somewhat. However, I need to warn you about the noise issues you may be facing. In order to minimize noise, you need to make sure the operating level is high enough. You are loosing about 10dB in the balance/pan pot circuit. I would do it differently, with separate L and R level pots, and decrease the gain of the power amp, but the LM1875 needs to operate with minimum 20dB gain, so you could decrease the gain of the phase-inverter that follows the ACN. Anyway, the LM1875's current draw may be an issue, with risks of noise and oscillations. Unfortunately, there are not many alternatives within the constraints.
You may need to boost the distributed signals in order to improve the S/N ratio.

 

[yosh]

That would work somewhat. However, I need to warn you about the noise issues you may be facing. In order to minimize noise, you need to make sure the operating level is high enough. You are loosing about 10dB in the balance/pan pot circuit. I would do it differently, with separate L and R level pots, and decrease the gain of the power amp, but the LM1875 needs to operate with minimum 20dB gain, so you could decrease the gain of the phase-inverter that follows the ACN. Anyway, the LM1875's current draw may be an issue, with risks of noise and oscillations. Unfortunately, there are not many alternatives within the constraints.
You may need to boost the distributed signals in order to improve the S/N ratio.

Thank you for your feedback! Just to clarify, when you talk about possibly needing to boost the distributed signals, are you talking about buffers in the signal path before the level and pan/balance circuits? Thanks again!

 

[abbey road d enfer]

Thank you for your feedback! Just to clarify, when you talk about possibly needing to boost the distributed signals, are you talking about buffers in the signal path before the level and pan/balance circuits? Thanks again!

What I mean is that the signal should be boosted before being sent through the wires.