Hi,
I plan to build a passive summing mixer with 8 inputs and 2 outputs.
I follow this diagram :
All inputs resistors are 6.8k ohms
To calculate the summing resistor I use the New York Dave formula (I/N)*R/((I/N)-R, where I is the input impedance, R the desired output impedance, and N the number of channels.
So, here, the summing resistor is 165 ohms
How to calculate the output summing resistors needed if I want to add a second output to this diagram ? Each output need to be at 150 ohm for the mic pre amp that after.
Thanks
I plan to build a passive summing mixer with 8 inputs and 2 outputs.
I follow this diagram :
All inputs resistors are 6.8k ohms
To calculate the summing resistor I use the New York Dave formula (I/N)*R/((I/N)-R, where I is the input impedance, R the desired output impedance, and N the number of channels.
So, here, the summing resistor is 165 ohms
How to calculate the output summing resistors needed if I want to add a second output to this diagram ? Each output need to be at 150 ohm for the mic pre amp that after.
Thanks
may i guess....?
the outputs are paralleled, so double the 165 ohms res to 330ohms , one for each output.
the outputs are paralleled, so double the 165 ohms res to 330ohms , one for each output.
You are overthinking this.
1) Just use the 165r (it is pointless two use two 330 on the same network) and attach two "bridging" mike preamps. (Nearly all mike preamps bridge.)
2) Split the OUTput of one preamp. It is made for that. This avoids some difficulties about paralleling two low-hiss inputs.
1) Just use the 165r (it is pointless two use two 330 on the same network) and attach two "bridging" mike preamps. (Nearly all mike preamps bridge.)
2) Split the OUTput of one preamp. It is made for that. This avoids some difficulties about paralleling two low-hiss inputs.
in fact I want a second output to be able to compare with and without the pre amp color.
I imagine the setup like this. Maybe it's useless.
How can I compare that the simplest way ?
To be clear, it's my first project, i'm a pure newbie.
I imagine the setup like this. Maybe it's useless.
How can I compare that the simplest way ?
To be clear, it's my first project, i'm a pure newbie.
Last edited:
I might be missing something but won't there be a huge insertion loss with 6k8 series resistors and 165R shunts? I would leave the 165R resistors out completely.
Here is the problem. Do you really need an output impedance of 150 ohms? That will be unrealistic with a passive summing box.
Last edited:
> won't there be a huge insertion loss
Any many-input passive mixer *must* have a large loss from one input to output.
Obviously it wants an amplifier.
The most convenient amplifier in the mix-down phase is the mike preamp we used back in the tracking phase.
Such preamps have way too much gain. Transistor 'rock' amps may turn-down to 10dB, but we really love the old 'swing era' tube preamps which are often fixed 35dB gain.
And yes, the transformer inputs on these jobs are somewhat sensitive to source resistance. 60r to 600r is a good zone. It also tends to give a loading resistor which leads to about 30dB-40dB of loss, 'fixing' our excess gain problem.
The 1.7k inherent to an eight input 2*6.8k mix network leaves the preamp transformer nearly undamped, possible loss of bass and generally a treble peak.
Any many-input passive mixer *must* have a large loss from one input to output.
Obviously it wants an amplifier.
The most convenient amplifier in the mix-down phase is the mike preamp we used back in the tracking phase.
Such preamps have way too much gain. Transistor 'rock' amps may turn-down to 10dB, but we really love the old 'swing era' tube preamps which are often fixed 35dB gain.
And yes, the transformer inputs on these jobs are somewhat sensitive to source resistance. 60r to 600r is a good zone. It also tends to give a loading resistor which leads to about 30dB-40dB of loss, 'fixing' our excess gain problem.
The 1.7k inherent to an eight input 2*6.8k mix network leaves the preamp transformer nearly undamped, possible loss of bass and generally a treble peak.
Thanks PRR for all this clarification.
I need some more clarification:
Is it really necessary to know exactly the sound card impedance 8 outputs?
ie: i know my Mic PreAmp input is 1.3K so I apply the DNY formula to find the best shunt, but how to chose the input resistor value, I put 6.8k as the original diagram, but is the best choice ?
Thanks
I need some more clarification:
Is it really necessary to know exactly the sound card impedance 8 outputs?
ie: i know my Mic PreAmp input is 1.3K so I apply the DNY formula to find the best shunt, but how to chose the input resistor value, I put 6.8k as the original diagram, but is the best choice ?
Thanks
> is there a way to correct or improve that inside the summing diagram ?
That's what the 165 ohm resistor is for.
NYDave was utility audio technician and historian in the military. He knew his stuff. Just do what he tells you to do.
That's what the 165 ohm resistor is for.
NYDave was utility audio technician and historian in the military. He knew his stuff. Just do what he tells you to do.