Is 600Ω a standard audio impedance?

Thread Starter

Wendy

Joined Mar 24, 2008
23,415
In that case, I'd agree with 2 x 1.2k in parallel, because that gains the greatest benefit of resistors in parallel decreasing error due to tolerance, and also good for stockholding!
This website
http://sim.okawa-denshi.jp/en/rercal.php
will calculate optimal resistors in parallel, potential dividers and loads of other stuff.
So you measure the resistance and adjust according, every tech worth a crap knows this. Of course, that is assuming the meter is worth a crap.
 

Ian0

Joined Aug 7, 2020
9,667
So, 10KΩ for audio input and 600Ω for outputs?
Yes - generally it's 10k to ground for a single ended input, and 2 x 10k to ground for a balanced line.
Outputs are more variable - anything between 47Ω and 330Ω, as long as they are matched on a balanced line output.
The matching of the two resistors on a balanced line input or output is far more important than their actual value.
300Ω in each signal of a balanced line would be a 600Ω output.
 

Deleted member 115935

Joined Dec 31, 1969
0
To take step back,
its al about power transfer / noise pick up / old system that can't change.

A telephone system of old , those that used metal conductors not this glass stuff, is fully differential, and matched impedance, so as to reduce line reflections,
The transmitter is 600 ohms, the line is 600 ohms, the receiver is a balance transformer, also 600 Ohms,

Traditional "Professional" audio systems, in particular mixers / microphones,
Microphones are fully differential , they have an output transformer, 600 ohms, twisted pair cables, 600 ohms, mixer input 600 ohm into a transformer.

In newer microphones, there is an amplifier,
these are "semi" differential, in that the cable screen is still not used as signal, but the signal pair are live / ground.
To fit into the existing system, these are designed to drive into 600 Ohms cable , 600 Ohms mixer inputs, and have "low" output impedance at the microphone,

The we have the prosumer market,
microphones tend to be just about any output impedance, typically low, and designed for low cost "coax", where screen is part of the signal, and input impedance of the mixer is high , 10 K being a popular nominal.


Then you have line inputs,
which basically follow the same , but at a higher voltage level, I think 0.7v into 600 Ohms .

So,
to question , is 600 Ohms a standard


Answer is

yes / Maybe / No

depending what system you working on .
 

Ian0

Joined Aug 7, 2020
9,667
To take step back,
its al about power transfer / noise pick up / old system that can't change.

A telephone system of old , those that used metal conductors not this glass stuff, is fully differential, and matched impedance, so as to reduce line reflections,
The transmitter is 600 ohms, the line is 600 ohms, the receiver is a balance transformer, also 600 Ohms,

Traditional "Professional" audio systems, in particular mixers / microphones,
Microphones are fully differential , they have an output transformer, 600 ohms, twisted pair cables, 600 ohms, mixer input 600 ohm into a transformer.

In newer microphones, there is an amplifier,
these are "semi" differential, in that the cable screen is still not used as signal, but the signal pair are live / ground.
To fit into the existing system, these are designed to drive into 600 Ohms cable , 600 Ohms mixer inputs, and have "low" output impedance at the microphone,

The we have the prosumer market,
microphones tend to be just about any output impedance, typically low, and designed for low cost "coax", where screen is part of the signal, and input impedance of the mixer is high , 10 K being a popular nominal.


Then you have line inputs,
which basically follow the same , but at a higher voltage level, I think 0.7v into 600 Ohms .

So,
to question , is 600 Ohms a standard


Answer is

yes / Maybe / No

depending what system you working on .
Mixer inputs are NOT 600Ω, and haven’t been for a number of decades, not since the transformer connected to the grid of a triode valve.
Neither is there a transformer on the input.
The distinction between microphones with or without an Amplifier is nothing to do with their age. Dynamic microphones do not have an amplifier, condenser microphones do.
Neither do dynamic microphones have a transformer. The 600Ω output impedance is the impedance of the capsule. There are often high-impedance versions of microphones which do have a transformer.
Proper professional microphones (both condensor and dynamic) have a differential balanced output. A few semi-professional ones have an output that is balanced but not differential. i.e. One side is connected to ground through a resistor the same value as the one on the signal side. The trouble with these is that pin 2 is “hot” in Europe and pin 3 is ” hot” in the USA, so if connected to an unbalanced input, there might be no signal.

Mixing desk inputs at 10k single ended or 20k balanced, and not transformer coupled.
Line level signals are 0.775V being 1mW into the (non existent) 600Ω input.

”prosumer” microphones are USB these days.
 

Deleted member 115935

Joined Dec 31, 1969
0
Mixer inputs are NOT 600Ω, and haven’t been for a number of decades, not since the transformer connected to the grid of a triode valve.
Neither is there a transformer on the input.
The distinction between microphones with or without an Amplifier is nothing to do with their age. Dynamic microphones do not have an amplifier, condenser microphones do.
Neither do dynamic microphones have a transformer. The 600Ω output impedance is the impedance of the capsule. There are often high-impedance versions of microphones which do have a transformer.
Proper professional microphones (both condensor and dynamic) have a differential balanced output. A few semi-professional ones have an output that is balanced but not differential. i.e. One side is connected to ground through a resistor the same value as the one on the signal side. The trouble with these is that pin 2 is “hot” in Europe and pin 3 is ” hot” in the USA, so if connected to an unbalanced input, there might be no signal.

Mixing desk inputs at 10k single ended or 20k balanced, and not transformer coupled.
Line level signals are 0.775V being 1mW into the (non existent) 600Ω input.

”prosumer” microphones are USB these days.
@Ian0

I think that is not in contrast with my summary

I use the word traditional as opposed to old fashioned,
I stated that balanced microphones are designed to work into a mixer at 600 Ohms

And Yes , we all know that USB interface, as well as Lightening et all microphones exist,
That's interesting , but I think low relevance to the original question.

But thank you for the information,
 

bogosort

Joined Sep 24, 2011
696
XLR connectors should be 600Ω
This is an odd thing to suggest. The presence of XLR connectors is a good indicator that the equipment in question is using impedance-balanced, differential I/O, likely at pro audio nominal levels (+4 dBu). But that has nothing to do with the actual value of the source/load impedance.

Almost all of my audio gear (and I have quite a bit) uses XLR interconnects and precisely zero of them present 600 Ω on either input or output. Pro audio abandoned the 600 Ω convention many decades ago.
 

bogosort

Joined Sep 24, 2011
696
So, 10KΩ for audio input and 600Ω for outputs?
No. If you want a rule of thumb, the convention is bridged loading, in which the load Z is at the very least 10x the source Z, but typically much larger. In your designs, the output should emulate a voltage source (very low source Z) as much as possible. The input Z should be high enough not to load-down whatever you expect to be driving it, e.g., an op-amp presenting a 50 Ω source.
 
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