Adding a blend to a Promethium (HM-2)

[Mir9]

I modded my real HM-2. The schematic at the Peperspedals link shows it wired right in between the flip flop switching (Q4 & Q10). The Promethium also has the in and out buffers, so it should work the same.

You can see where "send", "return" and "output" are wired, when using the Tagboard layout he recommends.
http://tagboardeffects.blogspot.com/2012/01/mini-blend-jfet.html
Attached is a schematic of the blending circuit, though Peppers used different values.


On the Promethium:
"send" between Q1 and C2 to the blend board, which then goes to blend pot #1
"return" from volume #2 to blend pot #3 (notice " disconnect here")
"output" from blend pot #2. I'm not sure if YOU need that 1uf (C32 on the Boss schem) as you're using true bypass.

 

[Danbieranowski]

I modded my real HM-2. The schematic at the Peperspedals link shows it wired right in between the flip flop switching (Q4 & Q10). The Promethium also has the in and out buffers, so it should work the same.

You can see where "send", "return" and "output" are wired, when using the Tagboard layout he recommends.
http://tagboardeffects.blogspot.com/2012/01/mini-blend-jfet.html (he made the 10nf, 100nf on his)

On the Promethium:
"send" would be between Q1 and C2
"return" would be from volume #2 to the blend circuit (notice " disconnect here"
"output" would connect back. I'm not sure if YOU need that 1uf (C32 on the Boss schem) as you're using true bypass.

You're a golden god! I'll try this out.

 

[Mir9]

I hope it helps. I edited my post to describe the pot connections.
An interesting use I'm finding for the blend is to place the HM-2 after another distortion pedal and blend in a little bit of "chainsaw" for all new tones.

 

[Danbieranowski]

I hope it helps. I edited my post to describe the pot connections.
An interesting use I'm finding for the blend is to place the HM-2 after another distortion pedal and blend in a little bit of "chainsaw" for all new tones.

Thank you for doing that for us!

 

[Danbieranowski]

On the Promethium:
"send" between Q1 and C2 to the blend board, which then goes to blend pot #1
"return" from volume #2 to blend pot #3 (notice " disconnect here")
"output" from blend pot #2. I'm not sure if YOU need that 1uf (C32 on the Boss schem) as you're using true bypass.

Do I need to do anything where it says "disconnect here". I saw in his original post that he actually cut through the PCB trace there.

 

[Mir9]

Do I need to do anything where it says "disconnect here". I saw in his original post that he actually cut through the PCB trace there.

On the Promethium, it would splice between the connection of Vol#2 and C21. With this mod, Vol#2 now goes to Blend#3 and Blend#2 goes to where Vol#2 used to be.

Here's a clip of me strumming a chord while I move the blend pot from clean to full.

https://soundcloud.com/user-562468024%2Fhm2-blend-20210227

 

[ANGRY_SWEDE]

Hey all,

I've tried a few different things with this, and all have failed for one reason or another.

I just want to add a blend to a Promethium.

If I use the Promethium board alone (no blend mod), it sounds and works great.

I've tried the GuitarPCB Buff n' Blend, but it oscillates. No oscillation if I don't run it through the send and return of the Buff N Blend, so it's definitely the BNB causing the issue.

I've tried a Mini-Mixer (little parallel mixer), with the idea of giving him one volume knob that's his clean signal, and one volume knob that's the HM-2 so he can mix to taste. The problem that I have with this is:
A) I get a little bit of volume or tone loss with the Mini-Mixer (found here: http://www.generalguitargadgets.com/effects-projects/boosters/mini-mixer/).
B) I can't think of a way to wire it up where, when switched off, the pedal is just standard true-bypass, but when on, I can feed the clean input signal to one pot of the Mini-Mixer, and feed the output signal of the circuit to another pot of the Mini-Mixer.

I'm not sure what else I'm not thinking of here, but I feel like there's a glaringly obvious way to do this, and I just need a sanity check from the PedalPCB folks. Any help would be appreciated!

GuitarPCB BnB is bad for high gain applications, especially if you are running the Promethium into a dirty channel. Mask Audio make a blender that may work. I do know from experience the Pepers Pedals blender works perfect for such an application.

 

[Feral Feline]

Check out JMK's Paralyzer as another option.

 

[Danbieranowski]

Check out JMK's Paralyzer as another option.

I was hoping for the JMK Panner or Paralyzer but both are sold out and he told me he doesn’t know when he will get them in stock unfortunately.

 

[Feral Feline]

I was hoping for the JMK Panner or Paralyzer but both are sold out and he told me he doesn’t know when he will get them in stock unfortunately.

I'll have a snoop for vero/perf layout of it then.

 

[Danbieranowski]

I'll have a snoop for vero/perf layout of it then.

I made one of these today. Haven’t finished it or tested it but I’m hopeful.

Splitter Blend Simpler by Flo | Online stripboard layout editor!

diy-layout.com

 

[mdc]

GuitarPCB BnB is bad for high gain applications, especially if you are running the Promethium into a dirty channel. Mask Audio make a blender that may work. I do know from experience the Pepers Pedals blender works perfect for such an application.

Trust this human their name is Angry Swede.

 

[mdc]

I made one of these today. Haven’t finished it or tested it but I’m hopeful.

Splitter Blend Simpler by Flo | Online stripboard layout editor!

diy-layout.com

If you're still having issues it might be worth trying a blender with a phase inversion option?

 

[Danbieranowski]

If you're still having issues it might be worth trying a blender with a phase inversion option?

View attachment 13168

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.

 

[Feral Feline]

Hmm guessing there isn't such a JMK layout as it hasn't popped up in a search.
Given that the schematic is in JMK's build doc, I'm surprised it hasn't been done yet.


So I made 3 perf layouts, none verified, with two options for the Panner orienting the pot either on the back of the board or off to the side.

If anybody verifies any of the three, please let me know... Critiques of the layouts welcomed as well.


[DELETED due to error]


If anyone wants the schematic numbering instead of the values, I can upload that as well.


FIXed:

 

[Danbieranowski]

Hmm guessing there isn't such a JMK layout as it hasn't popped up in a search.
Given that the schematic is in JMK's build doc, I'm surprised it hasn't been done yet.


So I made 3 perf layouts, none verified, with two options for the Panner orienting the pot either on the back of the board or off to the side.

If anybody verifies any of the three, please let me know... Critiques of the layouts welcomed as well.


View attachment 13186


If anyone wants the schematic numbering instead of the values, I can upload that as well.

If I have the time and can find my perf I’ll build one tomorrow and test.

 

[Danbieranowski]

Hmm guessing there isn't such a JMK layout as it hasn't popped up in a search.
Given that the schematic is in JMK's build doc, I'm surprised it hasn't been done yet.


So I made 3 perf layouts, none verified, with two options for the Panner orienting the pot either on the back of the board or off to the side.

If anybody verifies any of the three, please let me know... Critiques of the layouts welcomed as well.


View attachment 13186


If anyone wants the schematic numbering instead of the values, I can upload that as well.

For the record I’ve never built anything on perf before so it’ll be an adventure. I’ll build the top left Panner. It seems like the best way to do this is print this and then print the reverse image to take care of the soldered traces on the bottom. Is that normal SOP for perf builds?

 

[Feral Feline]

For the record I’ve never built anything on perf before so it’ll be an adventure. I’ll build the top left Panner. It seems like the best way to do this is print this and then print the reverse image to take care of the soldered traces on the bottom. Is that normal SOP for perf builds?

There's no right or wrong way, only the way that works for you.

I'll sometimes NOT cut leads off components and use the lead to continue the "trace", then go over it with solder as well — depending on the space constraints, whether or not I'm shifting something over for a larger component than indicated on the layout etc.



Upper left layout, just flip the above image in your graphics program.


@Danbieranowski — Hang on a tick, I found an error in the layout, pin 3 isn't connected... fixing it now.

PS: Schematic numbering so you can cross-check more easily.

 

[Bobbyd67]

Maybe you can look how Dunwich did it on their version of the HM-2

OSH Park ~ Shared Projects by dunwichamps

oshpark.com

There's a schematic in the project document... Or you could just order the oshpark board xD

It uses a extra tl072, my guess is everything connected to ic3 is the blend circuit

 

[Danbieranowski]

Maybe you can look how Dunwich did it on their version of the HM-2

OSH Park ~ Shared Projects by dunwichamps

oshpark.com

There's a schematic in the project document... Or you could just order the oshpark board xD

It uses a extra tl072, my guess is everything connected to ic3 is the blend circuit

I have a few of those sitting on my desk just gotta get to it.