Clean/Fx Loop Blend Control Board

[fractal33]

I was wondering if anyone would have any interest in the blend board I'm working on. It takes up more real estate than more simple counterparts, but it includes a phase switch for one of the sends, and if you use switched jacks you can turn the clean blend into a parallel FX loop. Not to mention it actually provides complete signal isolation at both sides of the pot even with an extremely high gain pedal which is something I have not been able to achieve with other builds.

I tested this on a breadboard and it worked exactly as intended and I'm almost done with the Pef layout in DIYLC. It uses a TL074, which might sound excessive, but the signal gets split and buffered by two channels, the third is an inverting buffer which you can switch for one of the signals via a SPDT, and finally the 4th is an output buffer used for when the signals are getting combined. The secret sauce really is the use of dual-gang pot wired like a guitar pickup blend pot. I stumbled upon this because I had one leftover from my Klone builds staring at me on my desk.

I'm not quite done with learning DipTrace yet, but I would love to get some of these fabbed in the near future. If anyone is interested in this or wants to help let me know. Not trying to turn a profit on these(as if I even could from something like this) I just don't want to finish learning Diptrace and end up with 100 blend boards all by myself.

 

[Mike52]

I'm interested in a similar thing. I am looking for a signal blender that splits the signal into three paths, each path with its own level control (blend) and then summed at the end into a single output signal. Path 1 would be an effects loop with a phase switch. Path 2 would be an effects loop with a phase switch. Path three would be the dry guitar signal. This is essentially the form factor of the Old Blood Nose Signal Blender.

I am not so interested in building one from scratch, since I am really ignorant when it comes to electrical engineering, but I was working on modding an existing design by Tonmann (and for sale at GuitarPCB). It mixes a wet signal with a dry signal but also uses a switching jack to insert another wet signal into the dry. I want three parallel signals that can each be adjusted to taste, but this only offers two signals although it vaugely suggests that there is a clean signal that gets through to the end even when the second wet effect is in the loop. I don't understand how this can happen.

Additionally, it includes a wet level for Path 1, a Dry Level and a Dry Gain, and I'm having a difficult time understanding the difference between the Dry Level and Dry Gain. It seems like the Paramix only lets you run one effect in parallel and another in series. And if the second effect is out of phase with the dry signal I'm not sure it can do anything about it. It's also got a momentary "kill" switch for one of the loops that I'm not sure adds much value to what I want to do.



I was thinking about removing P1 and jumpering a simple buffer from C4 to R10 and adding a mix pot at the end of that. This is a pretty ham-fisted approach, but like I said, I know nothing about this stuff.



This would be the buffer: I have a handful of them onhand. I also bought the PedalPCB simple buffer that may also work.

Anyway, I just bought 3 of these PCBs and plan to build one stock and play around with modding the other one. The application of a three-channel mixing circuit would be a clean signal on top of a modulated signal with some distortion or fuzz coloring the tails of it all. I'm very much interested in doing this on a PCB and not so much a vero board.

 

[Mike52]

It seems obvious that the best way to design what I want for a PCB would be to remove R5 and P1 and take the signal off of that stem to a second send jack that is wired to its own stomp switch and then just build a duplicate circuit from R15 to R9 with its own phase switch (SW1 at R6) and mixing pot. You could use IC1B for that return circuit and just plunk in a TL071 for the final buffering out or maybe a JFET of some kind (but this stuff is witchcraft to me, so no idea what to use). Then you'd eliminate the switching jack circuit between P2 and C3.

Unfortunately, that's not how this PCB is actually designed.

Thoughts?

(as I wrote this, I found this paper from the great Robert Keeley. Still reading it. Hmm, 18v, ok.)

 

[fractal33]

I'm interested in a similar thing. I am looking for a signal blender that splits the signal into three paths, each path with its own level control (blend) and then summed at the end into a single output signal. Path 1 would be an effects loop with a phase switch. Path 2 would be an effects loop with a phase switch. Path three would be the dry guitar signal. This is essentially the form factor of the Old Blood Nose Signal Blender.

I am not so interested in building one from scratch, since I am really ignorant when it comes to electrical engineering, but I was working on modding an existing design by Tonmann (and for sale at GuitarPCB). It mixes a wet signal with a dry signal but also uses a switching jack to insert another wet signal into the dry. I want three parallel signals that can each be adjusted to taste, but this only offers two signals although it vaugely suggests that there is a clean signal that gets through to the end even when the second wet effect is in the loop. I don't understand how this can happen.

Additionally, it includes a wet level for Path 1, a Dry Level and a Dry Gain, and I'm having a difficult time understanding the difference between the Dry Level and Dry Gain. It seems like the Paramix only lets you run one effect in parallel and another in series. And if the second effect is out of phase with the dry signal I'm not sure it can do anything about it. It's also got a momentary "kill" switch for one of the loops that I'm not sure adds much value to what I want to do.

I was thinking about removing P1 and jumpering a simple buffer from C4 to R10 and adding a mix pot at the end of that. This is a pretty ham-fisted approach, but like I said, I know nothing about this stuff.

Anyway, I just bought 3 of these PCBs and plan to build one stock and play around with modding the other one. The application of a three-channel mixing circuit would be a clean signal on top of a modulated signal with some distortion or fuzz coloring the tails of it all. I'm very much interested in doing this on a PCB and not so much a vero board.

Dry gain is actually boosting a signal, while dry level is simply attenuating it after the fact like a volume control. If you had an extremely loud pedal in the loop and wanted to mix in your clean signal, it would be desirable to boost the clean signal otherwise you would have to turn the level of the loop considerably to hear the clean.

You are correct that the clean signal with the inserts is in series and if you plugged something into them there would be no clean signal reaching the final output.

Ideally, I'd have another dual op-amp, split the signal at the non-inverting input of the first op Amp, replicate the return, get rid of the inserts, and connect where the other two signals meet before the output buffer.

Sorry how bad this looks, hopefully, you get the idea.

 

[djmiyta]

I was wondering if anyone would have any interest in the blend board I'm working on. It takes up more real estate than more simple counterparts, but it includes a phase switch for one of the sends, and if you use switched jacks you can turn the clean blend into a parallel FX loop. Not to mention it actually provides complete signal isolation at both sides of the pot even with an extremely high gain pedal which is something I have not been able to achieve with other builds.

I tested this on a breadboard and it worked exactly as intended and I'm almost done with the Pef layout in DIYLC. It uses a TL074, which might sound excessive, but the signal gets split and buffered by two channels, the third is an inverting buffer which you can switch for one of the signals via a SPDT, and finally the 4th is an output buffer used for when the signals are getting combined. The secret sauce really is the use of dual-gang pot wired like a guitar pickup blend pot. I stumbled upon this because I had one leftover from my Klone builds staring at me on my desk.

I'm not quite done with learning DipTrace yet, but I would love to get some of these fabbed in the near future. If anyone is interested in this or wants to help let me know. Not trying to turn a profit on these(as if I even could from something like this) I just don't want to finish learning Diptrace and end up with 100 blend boards all by myself.

This sounds awesome please let me know when

 

[Mike52]

Dry gain is actually boosting a signal, while dry level is simply attenuating it after the fact like a volume control. If you had an extremely loud pedal in the loop and wanted to mix in your clean signal, it would be desirable to boost the clean signal otherwise you would have to turn the level of the loop considerably to hear the clean.

You are correct that the clean signal with the inserts is in series and if you plugged something into them there would be no clean signal reaching the final output.

Ideally, I'd have another dual op-amp, split the signal at the non-inverting input of the first op Amp, replicate the return, get rid of the inserts, and connect where the other two signals meet before the output buffer.

Sorry how bad this looks, hopefully, you get the idea.

View attachment 19756

Interesting. Why would you split the second signal at the non-inverting. It seems like my idea would accomplish the same thing. (But again, I don't know circuits well enough to elaborate).

And I understand the difference between Dry Gain and Dry Level, but in this instance I just can't really see what is being accomplished by what he's doing there.

 

[fractal33]

Interesting. Why would you split the second signal at the non-inverting. It seems like my idea would accomplish the same thing. (But again, I don't know circuits well enough to elaborate).

And I understand the difference between Dry Gain and Dry Level, but in this instance I just can't really see what is being accomplished by what he's doing there.

Yeah it is a bit confusing but it seems to me that he probably wanted a way to boost the dry guitar signal and using an inverting opamp to do that has some advantages in this situation. The output buffer is inverting also so this flips the clean signal back to the original phase. I'm not an expert and there might be a reason why he put the dry level control where he did, but it would make more sense to me to be after the inserts in the original design so you could lower the level of the return insert.

 

[Mike52]

Yeah it is a bit confusing but it seems to me that he probably wanted a way to boost the dry guitar signal and using an inverting opamp to do that has some advantages in this situation. The output buffer is inverting also so this flips the clean signal back to the original phase. I'm not an expert and there might be a reason why he put the dry level control where he did, but it would make more sense to me to be after the inserts in the original design so you could lower the level of the return insert.

Yeah, makes sense. At the same time, Clean Gain sounds appealing here, but not necessarily something you'd reach for all the time. Maybe it could be done with an internal trim pot, set and forget sorta thing depending on the pedals you run through it. Then you are still looking at three main controls for the user to play with, along with two phase switches.

(Thinking out loud here, if you jumpered the second send/return channel wouldn't that give you a master gain for both the clean and first channel output?)

 

[fractal33]

Yeah, makes sense. At the same time, Clean Gain sounds appealing here, but not necessarily something you'd reach for all the time. Maybe it could be done with an internal trim pot, set and forget sorta thing depending on the pedals you run through it. Then you are still looking at three main controls for the user to play with, along with two phase switches.

Yeah I agree, but I suppose it depends on how many different toys you are going to be running this thing with. If it is the same pedals then a trimpot would make a lot more sense. I'm actually dealing with this issue right now because I'm building a massive pedal that blends clean/fx loop with an HM-2 style distortion and the clean signal needs a boost or it gets lost. What I've been doing is just running a boost in the loop like a Klone to bring the level up which is probably preferable sonically, but it would be nice to just have a quick and dirty clean boost onboard which is what he is doing here.

 

[Mike52]

Something about the power section doesn't look right. Should there be a capacitor between the TL074 power and TL072? Hmm.

Ps: lots of rookie mistakes. I just realized that i didn't include a switch and LED for the clean channel or a switch for the B effects.