I have a 10V audio source that I want to bring it to line level 1V. That’s pretty easy: I just need to use a voltage attenuator 10:1 like image below. I used resistor values of 1k ohm (R1) and 100 ohm (R2) and it worked great! BUT I have a question: what if I had used 100k and 10k ohm resistors? The ratio is still 10:1 but I think it would not produce a good result (I have no idea why I think so).
Would you please tell if I am right? If so... should I use 100 ohm (R1) and 10 ohm (R2) resistors instead of 1k ohm and 100 ohm that I am currently using? Would it be a good idea? I just want to bring this 10V speaker level to line level and so far using 1k/100 ohm worked fine (no noise, no humming...)... but I am wondering if I am doing it right... should I try different resistor values (keeping the same ratio, of course)?
Would you please tell if I am right? If so... should I use 100 ohm (R1) and 10 ohm (R2) resistors instead of 1k ohm and 100 ohm that I am currently using? Would it be a good idea? I just want to bring this 10V speaker level to line level and so far using 1k/100 ohm worked fine (no noise, no humming...)... but I am wondering if I am doing it right... should I try different resistor values (keeping the same ratio, of course)?
With a 10 to 1 resistance ratio, you attenuate 11 times. That's assuming 0 source and infinite load impedance, otherwise it becomes more than 11 times.
The resistances have to be large enough not to load your 10 V output too much, small enough to drive the load and small enough not to produce too much thermal noise.
For example, 0.09 ohm and 0.01 ohm would probably overload your signal source.
900 kohm and 100 kohm would result in much more than 10 times attenuation when the circuit you drive has a 10 kohm input impedance. Besides, it would be unsuitable to drive cables, as the slightest cable capacitance would cause treble loss.
There is still a large range that should work well. The values you now have seem perfectly reasonable.
The resistances have to be large enough not to load your 10 V output too much, small enough to drive the load and small enough not to produce too much thermal noise.
For example, 0.09 ohm and 0.01 ohm would probably overload your signal source.
900 kohm and 100 kohm would result in much more than 10 times attenuation when the circuit you drive has a 10 kohm input impedance. Besides, it would be unsuitable to drive cables, as the slightest cable capacitance would cause treble loss.
There is still a large range that should work well. The values you now have seem perfectly reasonable.
@MarcelvdG thank you so much! Now I understand it much better!!! Just one final question: if I place a resistor between R2 and - (voltage source) of value like 10ohm to prevent any shortcircuit in the future, do you think it would affect the Vout?
R1 limits the short circuit current. Nothing else matters. Short the output voltage and current is determined by R1 alone.
If you are using 1k now and have 10 volts available (and lets call that 10 volts rms and so 14.14 volts peak) then you limit the current to I=V/R which is 14.14/1000 which is 14.14 milliamps.
I would agree with @MarcelvdG to stick to 1k and 100 ohm. Do not make the 1k any lower. You can alter the 100 ohm as much as you want.
If you are using 1k now and have 10 volts available (and lets call that 10 volts rms and so 14.14 volts peak) then you limit the current to I=V/R which is 14.14/1000 which is 14.14 milliamps.
I would agree with @MarcelvdG to stick to 1k and 100 ohm. Do not make the 1k any lower. You can alter the 100 ohm as much as you want.
@Mooly everything you said made lots of sense! Thank you so much!
One more thing: I took a look at the specification of line output, and it says it should produce a load between 100 and 600 ohm. In my case, if I use a potentiometer of 1k with a 100ohm (R2), what would be the resulting load when the potentiometer is at 1k ohm and when the potentiometer is at 0 ohm? I think the load value will be exactly the potentiometer value, right? So I should add a 100ohm resistor in series with it to make sure I never get below 100 ohm?
One more thing: I took a look at the specification of line output, and it says it should produce a load between 100 and 600 ohm. In my case, if I use a potentiometer of 1k with a 100ohm (R2), what would be the resulting load when the potentiometer is at 1k ohm and when the potentiometer is at 0 ohm? I think the load value will be exactly the potentiometer value, right? So I should add a 100ohm resistor in series with it to make sure I never get below 100 ohm?
I don't quite follow that tbh 🙂
A line level output is a 'voltage source' and should be unaffected by loading although there will be a minimum load value specified somewhere. I would need to see the context of where that phrase comes from. 600 ohm is typical minimum value, 100 ohm would be classed as very low impedance to load a line level stage with.
If you are just wanting to derive an adjustable line level signal from a speaker feed then a 10k resistor for R1 and a 1k or 2k pot for R2 would be fine. 2k would give you a bit more level if you needed it.
Remember that a "voltage divider" is never just the two resistors you see. There's always a source and always a load.
If you use "100k and 10k", and then feed a 10k load, you get half of what you expect.
"Line level" was historically 600r (500r, 150r) in LONG line broadcast audio (derived from similar not-simple custom in telephony), 100k in much tube audio, 10k in most transistor audio (though ubiquitous chips usually drive 2k or less well).
If you use "100k and 10k", and then feed a 10k load, you get half of what you expect.
"Line level" was historically 600r (500r, 150r) in LONG line broadcast audio (derived from similar not-simple custom in telephony), 100k in much tube audio, 10k in most transistor audio (though ubiquitous chips usually drive 2k or less well).
Does it not say that the line output should have an output impedance between 100 and 600 ohms? That is something different than 'producing a load' whatever that is.
Jan
Jan, in post #1 there is mention of:
So it reads as if this is a low impedance speaker feed that needs bringing down, perhaps to feed a sub or something like that. I couldn't get the context of the 100/600 ohm bit 🙂
So it reads as if this is a low impedance speaker feed that needs bringing down, perhaps to feed a sub or something like that. I couldn't get the context of the 100/600 ohm bit 🙂