boost function with the lead and ultra

What is your experience with the boost engaged and disengaged with the lead and ultra channels? I think that it adds fizziness to the sound, i haven't tried another booster with this amp like a tubescreamer yet.Anyone uses other boosters with the amp?

I've used it to compensate the input gain of a Tele when switching from a Les Paul. Functional, prefer the Seymour Duncan Booster, but it's another plug in.

I know it's been pointed out before but for people coming across this thread before seeing it elsewhere, we believe the GM36 boost is not just a clean boost. It is effectively an improved Tubescreamer in front of the valve stages.

I have seen the schematic for the TM18 and I would think the idea is pretty standard across the range. With the boost both in or out it is absolutely clean up to a point, then a single sided clipping action kicks in, then at another point the other side starts to clip too. You will get a very usable clean boost up to a point, then good assymetric overdrive and finally full on distortion.The input is restricted before the boost to just above 6V peak to peak. With boost off its gain is about 3X, with boost on it is increased to about 7X. And the two stages of clipping kick in at about 5.5V and 12.3V output from the boost stage.

It is an extremely clever and versatile system. You can play off the Tubescreamer type clipping distortion and the internal valve stage distortion perfectly. You just need to balance your input level with the guitar volume, the gain of the boost stage, in or out, and the internal gain to get a full range of overdrive/distortion tones. It is one of the things that makes the H&K so versatile.

I just started playing with an OCD and Xotic EP in front and A/B'd with the GM boost. What I found is that I get an overall warmer OD and pick squeals are wayyyyy easier to coax out with either of the two OD pedals than the GM boost. I wonder if there is a way to mod the GM boost to closer emulate those types of pedals...

FYI, I am mostly a metal player so I've been focused primarily on the Lead and Ultra channels with this experimentation.

I kind of figured you would play metal Toddler . Modding the GM is not impossible but very difficult unless you are used to hand working close packed PCBs. You also have the problem of not having the schematics. H&K are naturally very close with those. There is no doubt that you could reverse engineer them but it would take a lot of time and effort. I can't help thinking that the best thing is to stick with your current way of working and don't allow the GM's front end overdrive to get in and colour the sound. You're obviously happy with it as it stands, why go chasing something you don't know when what you do is good?

Looks like your Xotic EP Booster is a basic single FET amp with a BJT emitter follower. There is passive circuitry shaping the frequency response so it's not transparent. Seems it's also permanently in circuit, (that'll upset the Druids)! The OCD (Fulltone?) is a two opamp (cheap ones) design with a little passive shaping. The distortion machanism is a tad unusual using a couple of MOSFETS and a diode to clip the voltage peaks. Good to see them taking the pragmatic route and not wasting high cost high performance opamps where they can't make any difference. None of this is criticism at all, just observation.

Different way of working to the H&K, overall you have more options to select from!