Considerations when blending 2 circuits (Punkifier etc)

[nate433]

If you look at the schematic for the punkifier it has a Buffer -> Split into 2 circuits -> Combined through a W-Taper ->Output buffer -> Rest of the circuit

I'm obsessed using my OBNE Signal Blender. Plus the punkifier is a great underrated circuit. I would love to make a pedal where I combine 2 of my favorite gain pedals blended together like I use live. It would save me so much space going from 3 pedals to 1 haha.

So i had a few questions

1. Are there any considerations to keep in mind when doing this with other gain pedals? Impedance matching or something? Maybe normalizing the volumes so it doesn't jump up like crazy when you blend in the louder circuit? Phase issues? Or can you really just put whatever in between the buffers and you'll be fine?

2. Why is a W taper used? I assume one reason is it's at 50/50 at the mid point. Why is a liner taper not something you'd use?


Thanks!!

 

[manfesto]

1. Phase issues, primarily, but the OBNE Signal Blender has phase flip capability I believe?

2. Most likely because DOD had a bunch of W-taper pots; they're used in, like, a *lot* of DOD designs.

 

[manfesto]

(as for *why* DOD had a bunch of W-taper pots, basically, a W-taper pot spreads the middle-section of the dial out over more of the rotation of the pot, so if most of the useable range of a control is towards the middle instead of towards the ends, the W-taper will give you finer control of the useable range.

Whether or not that's the case in this particular circuit I dunno, but I doubt it's a big enough difference versus a B100K for DOD to have to buy and store a different pot just for this one pedal when they're buying like 4 x W100K pots for every, like, Milk Box they're building)

 

[nate433]

1. Phase issues, primarily, but the OBNE Signal Blender has phase flip capability I believe?

2. Most likely because DOD had a bunch of W-taper pots; they're used in, like, a *lot* of DOD designs.

1. Ya you're right you can flip the phase. So i'd either need to add the phase flip or just make sure the 2 pedals i pick don't invert the phase?

2. So beyond them just having a bunch of w-taper am I on the right page about the mid point being 50/50 you think? I know w-tapers aren't SUPER common compared to A or B. Off the top of my head I mainly think of them as what you use for TS style tone controls which according to ElectroSmash gives you more fine control in the middle section but you still get the extreme settings at either end.

 

[manfesto]

1. Ya you're right you can flip the phase. So i'd either need to add the phase flip or just make sure the 2 pedals i pick don't invert the phase?

2. So beyond them just having a bunch of w-taper am I on the right page about the mid point being 50/50 you think? I know w-tapers aren't SUPER common compared to A or B. Off the top of my head I mainly think of them as what you use for TS style tone controls which according to ElectroSmash gives you more fine control in the middle section but you still get the extreme settings at either end.

1. Yep! Although phase flipping isn’t just swapping a few wires and requires some active components to make it happen (not a lot, but still). I think GuitarPCB has a utility board or two with phase flipping, you can see how they implement it

2. Oh totes, both W and B taper will be 50/50 blend when the control is set to noon, which is the expected behavior for most users I’d assume.

 

[manfesto]

Oh here’s a nice small layout for a phase inverter if you need it

Inverting Phase Buffer

Got a request for a dual buffer that inverted the phase of the signal. Found this post from Parasit Studio and used it for the basis of this...

effectslayouts.blogspot.com

 

[nate433]

Yep! Although phase flipping isn’t just swapping a few wires and requires some active components to make it happen (not a lot, but still). I think GuitarPCB has a utility board or two with phase flipping, you can see how they implement it

Oh for sure. If only it was that easy. Also if anyone isn't aware there's a great list of pedals that invert phase. Not sure how often it's updated though.

https://www.thegearpage.net/board/index.php?threads/list-the-pedals-that-invert-phase.796444/

 

[jesuscrisp]

Oh here’s a nice small layout for a phase inverter if you need it

Inverting Phase Buffer

Got a request for a dual buffer that inverted the phase of the signal. Found this post from Parasit Studio and used it for the basis of this...

effectslayouts.blogspot.com

Or better, you can also aim for a unity gain or slightly boosting LPB-1 or SHO or use a leftover IC stage at the end of the phase-flipping circuit instead. The buffer in the link is a non-inverting buffer into an inverting one, which is sort of redundant.

For inverting/non-inverting you can keep in mind: each time the signal is going INTO the inverting input on an IC or coming OFF the collector/drain of a transistor, it flips phase once. Transistor buffers where the signal goes through the emitter or source, there is NO phase flipping, neither in non-inverting op amp stages (obviously).

What you might also want to consider is whether your circuit of choice reacts well to buffers in front. E.g. Fuzz Faces and other old-school fuzzes.

 

[manfesto]

Or better, you can also aim for a unity gain or slightly boosting LPB-1 or SHO or use a leftover IC stage at the end of the phase-flipping circuit instead. The buffer in the link is a non-inverting buffer into an inverting one, which is sort of redundant.

If OP's doing this with pre-existing PCBs or layouts instead of a fresh design, it's not super likely they'll have any unused IC stages (since it's bad practice, unused IC stages usually get repurposed for things like voltage buffers), and these days a single op-amp isn't really any cheaper than a dual so not sure it'd be worth it to replace one stage with a transistor stage and increase the size of the footprint