Can Heat be used to add gain only to a synth that is naturally low volume?
What settings would you use personally to try to do this?
If this is not possible (adding pure gain only) what settings would you dial in to bring the volume up even if it beefed up the sound - but without audible distortion.
I am not against adding “character” or beef, but want to try keep it distortion-free, but definitely need to bring the volume up!!
Clean boost is the one to use. Should be possible to gain some with that. But it will color the sound. But most likely in a positive way. 
If you just want to add gain, use the clean boost circuit, then try the following settings in the AMP page.
Set drive to zero, fully wet, volume at max, then turn the wet level up until you’re happy.
If it’s still not enough at max wet level, add a little bit of drive and it should give you a nice boost without too much colouring.
Only problem is the Heat volume at max gives white noise/hiss.
Is it better to have the synth volume maxed out and the input sensitivity on Heat lower or the other way about?
I understand everything is a fine balance with the Heat but I wanted to get more experienced opinions.
Is it acceptable if it clips a little on the Heat?
It would be better if input sensitivity could be dialled in instead of 4 settings (low mid high max)
I like to have the input sensetivity low, because my synths are loud and the heat is very sensitive. I do agree with you though, it would be nice to have more control over the sensetivity.
I find the circuits work best when you’re not clipping the inputs, but still driving them pretty close to the limit. How quiet is your synth? Is it able to clip the input on the highest sensetivity?
Making something quiet louder, especially with something like the Heat, is likely to introduce a bit of noise or hiss, a noise gate might be useful here.
I had some problems with the AH input sensitivity to bring a very weak input signal to the recommended singal level for the Heat ( you need to set the input sensitivity before setting drive). Not sure how this affects the sound, though.
Edit: not sure what exactly the op meaned by gain. I thought they referred to drive, but maybe I am wrong.
Adding gain by its very nature will increase noise floor, you can get best results by ensuring your input is set correctly, and then using the envelope follower to reduce gain when no signal present, like in between notes.
I’d never thought about using the envelope follower that way, nice idea.
Yeah envelope follower is so useful for tons of things, I keep meaning to experiment with the CV ins to do something similar but never got around to it yet. Principle is the same, learn the CV input from an audio source then set the target parameter, it would mean splitting the audio into the AH audio in and the CV in though first.
Envelope followers are great, it’s a shame none of the other Elektron boxes have them.
MD too