I’ve built an attenuator that will work for both 6.35mm and 3.5mm jacks, or rather I am trying to build this. My goal is to be able to take a signal going into let’s say a 6.35mm jack, adjust level, and then be able to use either a 6.35 or 3.5 jack output. However, it’s not working as I expected and I don’t know why. The pots are B100k.
What is happening is that when I plug audio into a jack and try to adjust the level the pot doesn’t have any effect on the sound until you turn the knob almost to full volume. Then the level goes from 0 to full loudness in a 16th of a turn. When I checked on my multimeter it shows that the signal starts at 0 when the pot knob is all the way down (turned to the left) and increases linearly as you keep turning the knob to the right or up. That’s what I expected to have happen, but when I plug audio in that is not what happens.
Why doesn’t the audio input work in that when the pot is all the way to the left there is no sound and when the knob is all the way to the right it is at full volume?
Don’t know what you have the output plugged into but it sounds like it might be something with a low input impedance. For instance if it’s 10k then the output voltage would rise to only about half the input voltage as you turn the pot from 0 to 90% full range, and then you’d get the remaining half as you go from 90% to 100%. If it’s plugged into something with a 100k input impedance it’ll be much closer to linear, and a suitably designed buffered multiple for instance will have a practically infinite impedance and then you’d see near perfect linearity.
If you need to go into something with a low input impedance then you need to use a correspondingly small valued pot, but then the attenuator has low input impedance and might similarly affect whatever’s plugged into its inputs. If that’s a problem (and you can’t put a buffer between modules) then you’d need an active attenuator.
No, an attenuator can be used on either CV or audio signals. For example there are some filters that behave badly if the input signal is too hot and an attenuator can be used to address that. Or you can use one to reduce the level of a signal you’re going to send to an external device that expects line level.
This was initially why I wanted to make this because I didn’t want to push levels that were too hot into another device or to my headphones. Then I realized that since I also have Eurorack modules that being able to go between devices was also helpful so I added 3.5 jacks on the ins and outs.
Don’t know what you have the output plugged into but it sounds like it might be something with a low input impedance.
I have had the output plugged into my headphones just so that I could test it. I chose the 100k pots based off of the MFOS link you had sent me a while ago. What size pots did you choose for yours? Just curious.
It does sound like an active attenuator is probably more what I’m going for…I think.
That’s it then — headphones generally have very low input impedance. They’re not at all what a passive attenuator module is designed to drive. If you need to use headphones with your modular there are Eurorack output modules that provide headphone outputs, for instance the EricaSynths DIY Output II, which is discontinued but has recently gone open source. (Or of course there are mixers and sound interfaces that you could send your attenuated signal into and which provide a headphone jack.)
Look closely, they’re oriented differently on the two sides. On the left side the bevel is upper right, on the right side it’s upper left. The wiring is correct.
Thanks for solving the problem and explaining it to me. I’ve been looking at getting either the Make Noise XOH or Befaco’s Output II module for a while. It sounds like either of these will solve the problem (or either of the ones that you suggested) that I’m having in terms of using headphones to check signal levels. I just wasn’t 100% sure that I built it correctly and was second guessing my work.
