What does a resistor do to a audiosignal (W/Ohm)?

[ForHerDeadEyes]

I've tried asking this on other forums as well as searching, but can't get info on it.. I know people here build stuff that is way out of my league (I even failed at making the simple fuzzbox posted here, but I'll give it another go)

I mostly ask because I'll be adding a resistor(s) to a headphone output that sends too much signal/electricity..
I got the advice to add a resistor of around 10 - 33 Ohms to the output, but nothing on the wattage.. and also nothing on what the wattage nor the Ohm does with the signal, I'm sure it affects the frequencies / acting as a lowcut/highcut..

The resistors I've got now is two 5W 39 ohm, and ten 1W 39 ohm..
Just want the "best" possible signal out of it..
I got the 5W and 39 Ohm, just to be on the safeside, since the output is a bit strong..
What would it do to the signal if I put one on the input as well?

Thanks!

 

[jangoux]

It will attenuate the signal, and if you put it form the 'hot' lead to ground, it will change the input impedance. Well, it is more than that, but to I think this way it is less complicated to understand ehhe

 

[ForHerDeadEyes]

It will attenuate the signal, and if you put it form the 'hot' lead to ground, it will change the input impedance. Well, it is more than that, but to I think this way it is less complicated to understand ehhe

Thanks for the quick reply!
To simulate headhpones being plugged, I'm supposed to put the resistor between hot and ground, like you described..
Since it's 5w and 39 ohm, I'm guessing it won't cut all that much frequency.. :S
Though the recommendation was 10 - 33 Ohm..

 

[JakeAC5253]

Pretty much what jangoux said. In the general sense, it is as simple as attenuating a signal and nothing more, but when talking a more specific purpose, the effects of using a certain value over another can be extremely complicated and situational.

For your own usage, I assume that you are using these resistors in parallel rather than in series. For a parallel resistor at line level, you are safe in using standard quarter watt resistors, half watt on the safe side, that's what I would use. Line level means you are not pushing any wattage, so using a lower wattage component may just cause some harmonic distortion that will vary from part to part. Higher wattage components in this case will just make it perform its job of attenuating signal without causing harmonic distortion better. HOWEVER. Since we are talking about using a parallel shunt resistor to drag down the impedance of a line level signal, we will be affecting the net impedance seen by the output and input circuits on either side of this attenuation pad. This will result in an audible tone change, a high pass filter will be put into place and you will lose some low end response.

 

[ForHerDeadEyes]

Pretty much what jangoux said. In the general sense, it is as simple as attenuating a signal and nothing more, but when talking a more specific purpose, the effects of using a certain value over another can be extremely complicated and situational.

For your own usage, I assume that you are using these resistors in parallel rather than in series. For a parallel resistor at line level, you are safe in using standard quarter watt resistors, half watt on the safe side, that's what I would use. Line level means you are not pushing any wattage, so using a lower wattage component may just cause some harmonic distortion that will vary from part to part. Higher wattage components in this case will just make it perform its job of attenuating signal without causing harmonic distortion better. HOWEVER. Since we are talking about using a parallel shunt resistor to drag down the impedance of a line level signal, we will be affecting the net impedance seen by the output and input circuits on either side of this attenuation pad. This will result in an audible tone change, a high pass filter will be put into place and you will lose some low end response.

I think I'm getting it.. thanks for further explaining..
So if I'd put it on the line-out I'd be making a "highpass filter"..
The main use is on a headphone-output from a guitar-amp..
I have two amps that don't have a line-out..
The first of them works fine with headphones out to line-in..
The second one not so much, almost had gear fail on me.. but.. when I used some resistors it worked..
So, I guess I could use one of the 5 W 39 Ohm (to be on the safe side) to connect hot and ground, seeing as I could crank the volume up.. I still have the 1 W ones..
I thought about making a loadbox, not buy one (since it's a 15 W amp), but it seems a bit more complicated to make it line-out, and it has the HP-output..

 

[JakeAC5253]

Sure, try it. You aren't going to harm anything by doing this, but depending on what you connect the output to, it may make your amp sound like a TS9 If this mod gives you the signal level that you want, but too bright a tone, just use a capacitor in the same place that you put the resistor. Maybe between 1µF and 4.7µF depending on the sound.

 

[ForHerDeadEyes]

Sure, try it. You aren't going to harm anything by doing this, but depending on what you connect the output to, it may make your amp sound like a TS9 If this mod gives you the signal level that you want, but too bright a tone, just use a capacitor in the same place that you put the resistor. Maybe between 1µF and 4.7µF depending on the sound.

Awesome!
I'm connecting the output to line-in on my M-audio 1010LT.. without resistors I could've fried the card.. hopefully the 5 W will do the trick..
The other amp doesn't cause any problem and the tone is actually not that bad..