HM2 / Promethium distortion mod - bypass distortion?

[daeg]

I think the crossover distortion is just a consequence of implementing the rudimentary noise gate with the diodes. With everything else destroying the sound wave, that’s not going to be the most present distortion artifact.

Also, this circuit has gain stages all over the place. Most likely trying to keep noise low (evidenced by the gate block too) while keeping the op amp stable. At least that’s my guess.

Smart man. A problem with that design is crossover distortion will increase and become more apparent as you turn the gain now (amplitude is lower, so more sine gets chopped off by the diode forward voltage + less harmonics mess to cover it up).

 

[daeg]

Smart man. A problem with that design is crossover distortion will increase and become more apparent as you turn the gain now (amplitude is lower, so more sine gets chopped off by the diode forward voltage + less harmonics mess to cover it up).

This is perhaps one of the many reasons the pedal is only used in 'full-speed-ahead' mode with the gain control dimed.

 

[benny_profane]

This is perhaps one of the many reasons the pedal is only used in 'full-speed-ahead' mode with the gain control dimed.

Oh that’s interesting, I hadn’t thought of that implication. Very good point. With the soft and hard clipping, how present is the crossover distortion at lower gain levels? The gate will cut anything lower than ~300mV and the threshold for hard clipping will be twice that. The soft clipping is a part of that crazy gain stage with the BJT in the feedback path...without doing the math I can’t easily see how that’s coming into play.

 

[Nostradoomus]

Listen to On The Turning Away by Pink Floyd, that would be an HM-2 on the solo...they sound awesome haha

 

[benny_profane]

Listen to On The Turning Away by Pink Floyd, that would be an HM-2 on the solo...they sound awesome haha

Oh I’m familiar with the pedal...just curious about how all the stages come together and what each adds.

 

[daeg]

The soft clipping is a part of that crazy gain stage with the BJT in the feedback path...without doing the math I can’t easily see how that’s coming into play.

It only has the appearance of a feedback path. If you look closer, you'll notice that the wiper of Dist pot is grounded. No Feedback.

Funny that this came up. PRR over at DIYSB corrected some of us in his typical terse way when we were discussing the 'Nature' pot of the in the BJF Honey Bee. When I first looked at that HM-2 schematic, I was thinking Q3 was to invert the signal and create NFB for the Dist pot, which is connected to the Non-Inverting OpAmp. I further speculated that maybe they used a Non-Inverting OpAmp because when it clips (meaning the diodes are turned on) the Gain doesn't go lower than 1 as it would with a Non-Inverting stage. That narrative went completely out the window once I realized there was no NFB.

 

[Devoureddeth]

Listen to On The Turning Away by Pink Floyd, that would be an HM-2 on the solo...they sound awesome haha

Such a bassy solo, probably the best sounding HM-2.

 

[Nostradoomus]

Such a bassy solo, probably the best sounding HM-2.

It’s such a great lead sound...love playing it with a harmonic energizer too

 

[yazooligan]

Would anybody be interested in some deluxe promethium mods? I will have to trace them out but it might be worth sharing.

Yes please.

 

[yazooligan]

I’ve never been that good with wire management. At least it’s not veroboard

This is such a great idea. It makes it a much more versatile pedal if you ask me. I'm about to do a Promethium build myself and I'd love to get your insight before attempting this same mod. Thanks!

 

[blueimpala]

Would anybody be interested in some deluxe promethium mods? I will have to trace them out but it might be worth sharing.

Double yes please. That would be awesome!

 

[mnemonic]

This is such a great idea. It makes it a much more versatile pedal if you ask me. I'm about to do a Promethium build myself and I'd love to get your insight before attempting this same mod. Thanks!

not to much to it really, if you want to do this same mod,I would just follow the schematic changes in post #7, but do it after C1 rather than before. Or if you do it before C1 like in the picture, just add a 47nf off the switch (Where it’s marked orange).

mine is technically a ‘bodge’ since I added a cap off R1 since I didn’t want to pull the board again to do it right. So technically I have two caps in series when in normal mode.

you can see in the pics where I had only soldered on one leg of C1 and c12 so I could add in the switch.

 

[yazooligan]

Is it a lone wolf audio THE FIRST AND BEST AND ONLY BOOTEEK HM2 CLONE? I hope so, fuck that guy haha

For the prices he’s asking I’d expect a little more visual flair to the enclosures. They’re kind of uninspired if you ask me. There’s a video of him at 2017 summer NAMM showing off a bunch of his pedals, but no actual playing, and it’s like, uh, you do want to sell those right? Might not hurt for people to hear them. Maybe he’s a pair of camo cargo shorts come to life...

 

[Nostradoomus]

Definitely. For a 400 dollar HM-2 clone you should at least drill the holes straight too, it’s baffling.

 

[benny_profane]

Is that the HM-2 derivative with all the weird add-ons that oscillate and are unusable? I remember seeing one of them that just made me think, “wow, this couldn’t be more poorly designed.”

 

[ANGRY_SWEDE]

Would anybody be interested in some deluxe promethium mods? I will have to trace them out but it might be worth sharing.

Yes, I would greatly appreciate this!