Why Not Wye?
As You know every gear usually has limiting / decoupling resistors on their op-amp outputs before the RCA's or XLR's, but one thing is puzzling me. Suppose I want to make a mono summer like Rane... If I go the Rane route with 4580's op-amps and 50-100 ohm resistors typical on many gear and +-15V rails and do the maths I get a current of 15/100=150 mA. Let's suppose I even short the outputs to ground. I think the chips can't handle this current. What am I missing here ?
I'm asking this because sometimes I need to connect a tablet or laptop to a PA speaker. Sometimes I also use mixers connected to a single speaker. As music is usually recorded in stereo I want to feed both channels. I know on a mixer I can use two mono channels for that and use only one output.
I just want to make an all-around adapter for mono mixing but I'm afraid I will need several with different resistors. I've been using 1K for the time being in order not to go the high impedance route compromising cable length.
What's the purpose of the third resistor to ground on Rane notes since they don't explain ?
.. and Yes I'm aware of DI's and active converter boxes.
Thank you.
As You know every gear usually has limiting / decoupling resistors on their op-amp outputs before the RCA's or XLR's, but one thing is puzzling me. Suppose I want to make a mono summer like Rane... If I go the Rane route with 4580's op-amps and 50-100 ohm resistors typical on many gear and +-15V rails and do the maths I get a current of 15/100=150 mA. Let's suppose I even short the outputs to ground. I think the chips can't handle this current. What am I missing here ?
I'm asking this because sometimes I need to connect a tablet or laptop to a PA speaker. Sometimes I also use mixers connected to a single speaker. As music is usually recorded in stereo I want to feed both channels. I know on a mixer I can use two mono channels for that and use only one output.
I just want to make an all-around adapter for mono mixing but I'm afraid I will need several with different resistors. I've been using 1K for the time being in order not to go the high impedance route compromising cable length.
What's the purpose of the third resistor to ground on Rane notes since they don't explain ?
.. and Yes I'm aware of DI's and active converter boxes.
Thank you.
I think it boils down to the individual output impedance specs, which can vary quite a bit. Not so much in the pro gear perhaps, but definitely in the "semi-pro" area, however that's defined these days.
Your example of the Rane 50-100 ohm output could be problematic for exactly the reason you (and they) describe. But there's lots of examples out there (mostly single-ended outs) that are more in the 500-1K output impedance range, which should be fine with a simple Y cord.
I'm hoping someone more knowledgeable can chime in with an answer about the 3rd resistor. It forms a voltage divider, so I'm guessing its purpose is to "nail down" the output impedance of the summing network a bit.
Your example of the Rane 50-100 ohm output could be problematic for exactly the reason you (and they) describe. But there's lots of examples out there (mostly single-ended outs) that are more in the 500-1K output impedance range, which should be fine with a simple Y cord.
I'm hoping someone more knowledgeable can chime in with an answer about the 3rd resistor. It forms a voltage divider, so I'm guessing its purpose is to "nail down" the output impedance of the summing network a bit.
Better math would be:
Chip #1 output impedance in series with Wye resistor.
in parallel with:
Chip #2 output impedance in series with Wye resistor.
both into the load impedance
The voltage will be the difference between the #1 and #2 signals which will seldom be 1 Volt.
The other resistor is so the circuit can be used with TRS oe XLR connectors.
Chip #1 output impedance in series with Wye resistor.
in parallel with:
Chip #2 output impedance in series with Wye resistor.
both into the load impedance
The voltage will be the difference between the #1 and #2 signals which will seldom be 1 Volt.
The other resistor is so the circuit can be used with TRS oe XLR connectors.
The voltage difference between left and right of a stereo signal is likely to be low, but not guaranteed to be, that’s why I always use at least 2k. I believe that the third resistor is to hold the signal around zero volts in the case of a capacitor coupled output. Shouldn’t really be necessary though and I never fit it
Brian
Brian
Most opamps are rated for continuous short-circuit - the output is current limited by design.
Yes I didn't think about that aspect, and it's written on most datasheets.
So I presume the resistors are there for dealing with capacitive loads and not for overcurrent protection. That's why there are thousands of wrong adapters being sold, because there is no hazard...
Thanks for Your feedback.
So I presume the resistors are there for dealing with capacitive loads and not for overcurrent protection. That's why there are thousands of wrong adapters being sold, because there is no hazard...
Thanks for Your feedback.
Yes they are, but will not sound nice at current limit.
Assuming a worst case of one output at 15V and the other at -15V, no output resistors in the source device and my method above of using 2k resistor or higher, I = V/R = 30/4000 = 7.5mA
Using the paper's recommended 470 ohm resistors:
I = V/R = 30/(2 * 470) = 30/940 = 31.9mA
These are peak currents from the output with the highest voltage to the output with the lowest
Either should be fine
Brian
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