Adding a blend to a Promethium (HM-2)

[Mir9]

I built one of the new Dunwich boards. Like the Pepper's blend, the clean is split off at the beginning and remains unity volume. Since normal use of the HM-2 is maxing out those tone controls, you won't get an even clean blend. The distorted half will overpower the clean, but it works just fine for me.
I use it as a boost into an already distorted amp and blending some clean in with the Dunwich added some much needed clarity.

 

[Danbieranowski]

I built one of the new Dunwich boards. Like the Pepper's blend, the clean is split off at the beginning and remains unity volume. Since normal use of the HM-2 is maxing out those tone controls, you won't get an even clean blend. The distorted half will overpower the clean, but it works just fine for me.
I use it as a boost into an already distorted amp and blending some clean in with the Dunwich added some much needed clarity.

Just out of weirdo curiosity, would it be possible to insert a clean boost somewhere in that clean circuit? Maybe that's something someone can do to create a unique version of this.

 

[Feral Feline]

Just out of weirdo curiosity, would it be possible to insert a clean boost somewhere in that clean circuit? Maybe that's something someone can do to create a unique version of this.

In the schematic floating around the net of the Dunwich HM-2, IC3A is the clean blend op-amp if I'm not mistaken. It's right below the blend pot.

R32 is the feedback resistor for that op-amp, it's 10k, if you stuck a 50k or 100k pot in series with it, that would give you a "clean-signal" gain boost. At least, that's where I'd start experimenting.

 

[Danbieranowski]

In the schematic floating around the net of the Dunwich HM-2, IC3A is the clean blend op-amp if I'm not mistaken. It's right below the blend pot.

R32 is the feedback resistor for that op-amp, it's 10k, if you stuck a 50k or 100k pot in series with it, that would give you a "clean-signal" gain boost. At least, that's where I'd start experimenting.

Maybe I’ll just throw a trimmer in there!

 

[ANGRY_SWEDE]

This is one of the ones I'm looking at. Waiting to test something else, but this is a definite option as well. Thanks for dropping it in here, as I think it's good for anyone interested.

I built a stand-alone Mask Audio Electronics MAE blender, and it works 100% with an HM-2 into a dirty channel. Zero high freq squealing. That was my test before dedicating it to a pedal.

 

[Danbieranowski]

I built a stand-alone Mask Audio Electronics MAE blender, and it works 100% with an HM-2 into a dirty channel. Zero high freq squealing. That was my test before dedicating it to a pedal.

I just bought a handful of those and I'm waiting for them to arrive. Thank you tons!

 

[ANGRY_SWEDE]

I just bought a handful of those and I'm waiting for them to arrive. Thank you tons!

It has a dual footprint for the Q's [2n5457] so you can use either SMD or through-hole.

 

[Kroars]

Great thread!

 

[Slurp]

I just bought a handful of those and I'm waiting for them to arrive. Thank you tons!

Hi there, did you ever end up getting one of these methods to work?

I did some mods to an HM2 and increased the overall output volume by a little bit, but my mask audio blend is whistling

I just encapsulated the fx in and fx out with the send / return, no luck so far

 

[Danbieranowski]

Hi there, did you ever end up getting one of these methods to work?

I did some mods to an HM2 and increased the overall output volume by a little bit, but my mask audio blend is whistling

I just encapsulated the fx in and fx out with the send / return, no luck so far

I have not built one that didn’t whistle with a blend yet. Without a blend, yes. But not with. Gonna try the Dunwich next.

 

[Slurp]

I have not built one that didn’t whistle with a blend yet. Without a blend, yes. But not with. Gonna try the Dunwich next

Ahhhh not the answer I was hoping to hear haha. I just finished building an FZ2 and couldn't get a blend to work with it either. Was hoping the HM2 might be more manageable since I've seen so many clones pull it off. I'll also give the dunwich opamp version a go and report back

One thing that is throwing me off though is the difference in the output section... So basically I will need to bypass everything after IC 1.1 in the promethium and implement a little custom board using an extra TL072 for the blend, output buffer, and new 100k Volume pot. Going to be a mess

 

[Feral Feline]

Looking forward to seeing the Dunwich ones built by you guys...

 

[Slurp]

I have not built one that didn’t whistle with a blend yet. Without a blend, yes. But not with. Gonna try the Dunwich next.

Looking forward to seeing the Dunwich ones built by you guys...

Ugh, it worked perfect with single coils, then when I switched to a guitar with humbuckers it was just as bad as anything else with the feedback at 50% volume. This is crazy, my build is actually really similar to the dunwich mods so I am very surprised that this one isn't working.

Plus this one seems to have a ton of bleed compared to the other blends? I kinda want to look into the actual circuit design considerations at this point, because this is honestly my 5th blend knob that I've attempted with a high gain pedal that has failed

I etched a little 805 smd PCB with the following schematic, and made these connections using the PedalPCB suggested 3PDT true bypass wiring:
- IN to center node of 3PDT
- 4V5 to left side of R21 (the side closer to IC2)
- TO_IC1.1_OUT to the (+) node of C20 (I removed C20)
- OUT to top right node of 3PDT (left Promethium PCB FX output floating)
- 9V and GND to power supply / gnd of course

 

[Danbieranowski]

Ugh, it worked perfect with single coils, then when I switched to a guitar with humbuckers it was just as bad as anything else with the feedback at 50% volume. This is crazy, my build is actually really similar to the dunwich mods so I am very surprised that this one isn't working.

Plus this one seems to have a ton of bleed compared to the other blends? I kinda want to look into the actual circuit design considerations at this point, because this is honestly my 5th blend knob that I've attempted with a high gain pedal that has failed

I etched a little 805 smd PCB with the following schematic, and made these connections using the PedalPCB suggested 3PDT true bypass wiring:
- IN to center node of 3PDT
- 4V5 to left side of R21 (the side closer to IC2)
- TO_IC1.1_OUT to the (+) node of C20 (I removed C20)
- OUT to top right node of 3PDT (left Promethium PCB FX output floating)
- 9V and GND to power supply / gnd of course

View attachment 14851

Yeah it’s incredibly frustrating!!!

 

[fractal33]

Sorry for reviving a somewhat old thread, but I thought I'd put my 2 cents in here since I've been lurking for a while and I've also been trying to figure out how to add a blend control to a Promethium.

I built a Split 'n Blend(which is identical to the mask audio blend schematic) on perfboard using two 2N5457's for the buffers. I had zero bleed or phase issues and it seems to work very well overall. The intense noise and feedback that seems to turn into oscillation at dimed settings is present, but it is actually far worse on my original unmodified made-in-Japan HM-2.

I wish I had a better point of reference for what the Promethium sounded like dimed without the blend control, but I don't usually run the distortion on max to begin with, as the chainsaw tone most people seek lies mainly in the maxed EQ. Unless I'm missing something here, the blend is functioning exactly as it should, and overall the Promethium even with the Split n' Blend is far less noisy on dimed settings than its original Boss counterpart - sans blend control.

I believe this was posted here earlier, but this is the layout I used:
http://effectslayouts.blogspot.com/2015/12/split-n-blend.html

I wired the Split 'n Blend to the Promethium and 3PDT as follows:

• SNB IN to 3PDT board IN
• SNB Send to promethium PCB IN
• Promethium PCB OUT(return) to Blend lug 3
• SNB blend 1(or OUT on mask audio's blend) to Blend lug 1
• 3PDT board OUT to Blend lug 2

 

[fractal33]

Small update... I realized after toying around with it for a while there was actually some bleed going on, so after playing operation for a while and disconnecting the ins and outs from the Promethium PCB to the blend control and 3PDT entirely, I noticed on dimed settings there was STILL a small amount of signal coming from the pedal output into the amp that was being processed by the engaged pedal! How is this possible?

Just to recap, I had no input or output connected to the Promethium board or the blend board. The only connections on the 3PDT breakout board were from input and output jack tips, 3PDT ground->promethium ground, 3PDT switch->promethium switch. I'm thoroughly baffled how that is even possible. I checked for bridged connections with a multimeter and couldn't find anything abnormal. Could this be some type of crossover from the 3PDT ground or switch out? Or is this some electrical phenomenon that I'm completely unaware of?(definitely possible)

 

[Feral Feline]

Another case of a possessed PCB.

You must call a high priest of your preferred denomination, but must be one that does exorcisms, because failing the exorcism ... you will have to put a hot soldering iron tip through the main IC right through the board to the other side. That will make it bleed out completely once and for all.

After it's pierced through its "heart", build a funeral pyre and burn the whole thing, lest it resurrect itself. The capacitors can sometimes give off a flare when they pop from the heat while releasing the demons, so stand well back. The colours of the flames are pretty, though, so it's well worth watching and besides, you need to watch to ensure all is burnt completely.

 

[Danbieranowski]

Small update... I realized after toying around with it for a while there was actually some bleed going on, so after playing operation for a while and disconnecting the ins and outs from the Promethium PCB to the blend control and 3PDT entirely, I noticed on dimed settings there was STILL a small amount of signal coming from the pedal output into the amp that was being processed by the engaged pedal! How is this possible?

Just to recap, I had no input or output connected to the Promethium board or the blend board. The only connections on the 3PDT breakout board were from input and output jack tips, 3PDT ground->promethium ground, 3PDT switch->promethium switch. I'm thoroughly baffled how that is even possible. I checked for bridged connections with a multimeter and couldn't find anything abnormal. Could this be some type of crossover from the 3PDT ground or switch out? Or is this some electrical phenomenon that I'm completely unaware of?(definitely possible)

It's because we live in a hell of our own making, my friend.

 

[fractal33]

Yeah I'm at a loss here... Good news is it gave me a chance to A/B with and without the Split 'n Blend, and there was no difference in feedback or added oscillation. In fact, the SNB is working exactly how it should and this "bleed" is apparently not bleed from the blend at all. It goes away if I dial the settings back a little, but somewhere there is some input signal getting through to the mainboard even with the IN and OUT from the promethium PCB disconnected. Gonna go listen to Bleed by Meshuggah for a while and get that soldering iron nice and hot to prepare for the exorcism.

 

[benny_profane]

Small update... I realized after toying around with it for a while there was actually some bleed going on, so after playing operation for a while and disconnecting the ins and outs from the Promethium PCB to the blend control and 3PDT entirely, I noticed on dimed settings there was STILL a small amount of signal coming from the pedal output into the amp that was being processed by the engaged pedal! How is this possible?

Just to recap, I had no input or output connected to the Promethium board or the blend board. The only connections on the 3PDT breakout board were from input and output jack tips, 3PDT ground->promethium ground, 3PDT switch->promethium switch. I'm thoroughly baffled how that is even possible. I checked for bridged connections with a multimeter and couldn't find anything abnormal. Could this be some type of crossover from the 3PDT ground or switch out? Or is this some electrical phenomenon that I'm completely unaware of?(definitely possible)

How do you have power connected to each circuit and what are you doing with the grounding of each circuit?