I want to update the ROG SplitterBlend

[Elijah-Baley]

Hello, I'm building the ROG Splitter Blend, because I wanted to build something different.
I built the perfboard and drilled the box. But before to finish it I watched a video of the Wetter Box here: https://shop.thegigrig.com/wetter-box/
It's a kind of Splitter Blend but with other things. Maybe I'll finish my pedal just like the stock Splitter Blend, but I would like to know if I can do something more.

This is the ROG Splitter Blend page: http://www.runoffgroove.com/splitter-blend.html

And here the schematic:



The Wetter Box has these extra features:

1. Blend in an effect in parallel with your direct signal
Well, I think I did it. I used a patchcord to jumper one of the loop. Probably I can do it using normal switched jacks to jumper the loop. Like a normal loop efffect in the amps.

2. Do [the blending] in real time with an expression pedal
I think this is easy. We can use a switched TRS jack in the pedal to disconnect the potentiometer. A stereo cable carries the three signals to the jack of an expression pedal. Of course the expression pedal should be arrange to do that It need a 25k pot and a stereo jack correctly wired.

3. Independent gain controls on each loop
This could be a bit complicated, lookinag at the schematic. I guess we can act in the last stages of the two loops to control the gain, but the stages are different each others.

4. True stereo signal path using TRS cables
I should understand better what it means. Maybe it's enough use a TRS input jack. The Tip and the Ring are connected if the cable is mono. Splitted if the cable is stereo.

5. Two separate modes of operation, BLEND (crossfade from loop A to loop B) or MIX (add loop B to Loop A)
The Blend is the Splitter Blend function. How we can do the Mix. The loop A have to be fixed at 100%, the Loop B is set from 0% to 100% by the pot.

6. Internal voltage doubling compatible with guitar level or amp fx loop level
It's just a charge pump. RIght?

7. Internally isolated power
Like normally our diy pedals are?

8. True Bypass or Buffered Spillover bypass
Ok. A switch to true bypass od buffered bypass.

9. Control the bypass state remotely with any latching switch
What? Just an external latching switch to replace the pedal footswitch?

10. 100% analog signal path
Well, of course.

11. TheGigRig OptoKick footswitch
Ok, it's the switching system.

So, what we can do? The main parts is the MIX function and the two gain controls.

[MikeA]

Your list of functions sounded familiar, then I remembered I used to own a Pigtronix Keymaster (no longer made) that did most of that.   I believe there's a schematic that can be located through the magic of Google, if you want to see someone else's solution to the same design issues.  Might be more fun not to look, though....  

[Elijah-Baley]

I couldn't resist, I searched the Pigtronix Keymaster, I didn't remember it. I have to say it's different from the Splitter Blend, and more complex than the Wetter Box.
With Pigtronix Keymaster you can bypass individually loop A and loop B, you can put them in series or in parallel, you can use an expression pedal. It works at 18v, none charge pump in there. It has two boost control, but one in front, and another in the output. I find it a bit weird. It has XLR input and output. It doesn't have any phase switch, maybe because the input stage?
A big pedal, but I'm not sure, I guess we will go out of topic if we start to analyze too much that pedal.

Let's try to stay on the ROG's one, but thanks to talk me about it.

[MikeA]

Yeah, Pigtronix would do a mod to add a phase switch if you wanted.  I think it was conceived as a re-amp interface, thus the balanced TRS and XLR ins/outs. 

[Elijah-Baley]

I read that the crossfade of the Pigtronix Keymaster is not really 100%, but loop B sounds even with the pot at max to the loop A, or whatever.
It should be a nice machine, but now I definitely want to stay on the ROG Splitter Blend.

Getting on focus on the extra features, the expression pedal mod I think it's exaclty as I though: a TRS jack is used to replace the three signals on the pot. And the cable have to be stereo.
I found a list of expression pedals with the pot description:
Bespeco VM18L - 20k
Boss FV-500 - 10k linear (expression pot)
Boss EV-5 - 10k linear
Boss EV-7 - 10k linear ("extra range" pot adds up to 50k ohms)
Boss FV-50L - 50k linear
Ernie Ball VP jr. (active) - 25k log
Ernie Ball VP jr. (passive) - 250k log
Korg EXP-2 - 50k linear
Kurzweil CC-1 - 20k linear
Line6 EX-1 - 10k linear
Mission EP-L6 - 10k linear
Moog EP-2 - 50k linear (reducable)
M-Audio EX-P - 10k linear
Pigtronix EP-1 - 20k
Proel Volume Pedal - 100k linear
Roland RV-5 - 10k linear
TC Electronic X1 - 25k log

I think a linear pot is the right choice. I'm wondering what happens if the pot is 10k, 50k or 250k. Probably the wiring of the pot should be modify.

How can we pass from crossfade effect to the mode with the loop A 100% mix just the loop B?
And some idea to add two effective gain controls?
I have some doubts about the stereo input. I think I'll need a very different approch of the input stage, at least to make something like the Pigtronix Keymaster.

[GGBB]

How can we pass from crossfade effect to the mode with the loop A 100% mix just the loop B?

The general idea would be to have a fixed resistance that can be bypassed on one side of the pot. The value should be close the same as the pot:

[Elijah-Baley]

Ok, thanks. I have to try that trick. I will use a 24k.

[Marcos - Munky]

For the expression pedal, you may have some issues doing it that way. While it does sonds simple enough, you may have some noise issues by using an external expression pedal to act as the mix pot, because you'll have basically long wires carrying the signal from one point to another and those wires may be near an interference source. Even a shielded cable going straight from guitar to amp can pick some noises based on what is near the cable and how much gain have the amp.

Take a look at this article: https://tech.thetonegod.com/rockncontrol/rock.html

[Elijah-Baley]

Ok, thanks. This could be mess up a bit the expression pedal option.
The option of a expression pedal that we can match with the Splitter Blend could be a bit complicated, and I don't know how many expression pedals like that we can buy ready to use for the purpose.
And, I'm not sure, but with that approch the expression pedal will work, of course, but I assume it doesn't work exactly like the pot on the pedal. Maybe it's not a real issue.

It's just know something more about how it could work, but I still didn't find any useful information about the original expression pedal of the Wetter Box, except it needs a stereo jack. I just noticed that it has two input. Why?

I forget to say that the current draw of the GigRig Wetter Box is 185mA, it's pretty high.
And I miss something. It has two ouput: Left and Right. So I need to know more about the stereo option.

[Elijah-Baley]

Ok, I found this: https://www.youtube.com/watch?v=lAIPF52Bh0Y
Here's a expression pedal, it's is a cheap one, and normal I guess, expression pedal. And it works fine.

I tried the 24k resistor to blend just one loop, and it worked.

In my tests sometime I noticed that the volume is not constant. When the pot is at half the volume is lower than when it's setted clockwise or anticlockwise. This is a annoying when you set the Blend, and in case the use of the expression pedal.

[idy]

You need a different taper for the pot.... look for balance pot.

[GGBB]

In my tests sometime I noticed that the volume is not constant. When the pot is at half the volume is lower than when it's setted clockwise or anticlockwise. This is a annoying when you set the Blend, and in case the use of the expression pedal.

As idy suggested - a balance/blend dual pot might work better for taper. But it might not solve the volume difference between 50/50 blend and 100% either side. For that you can try adding some resistance on both ends of the pot from the op-amp outputs so that you are never at zero-resistance between the output on the wiper and the op-amp output. Not sure what value - try a 1k to start. You might want to also try dropping the 25k pot to 10k.

[CodeMonk]

In my tests sometime I noticed that the volume is not constant. When the pot is at half the volume is lower than when it's setted clockwise or anticlockwise. This is a annoying when you set the Blend, and in case the use of the expression pedal.

As idy suggested - a balance/blend dual pot might work better for taper. But it might not solve the volume difference between 50/50 blend and 100% either side. For that you can try adding some resistance on both ends of the pot from the op-amp outputs so that you are never at zero-resistance between the output on the wiper and the op-amp output. Not sure what value - try a 1k to start. You might want to also try dropping the 25k pot to 10k.

It was a few years ago, but I have fiddled around with this ROG circuit.
I've tried several different pot values and 25k seems to be the optimum value.
With your common CTS or Alpha pots, you aren't likely to see a 0/100 - 100/0 percentage. Maybe around 2/98 - 98/2 reading, but either side won't likely be equal to the other. You're never really at zero resistance on either end.
Maybe instead of a resistor at either end to even things out, try a trimmer at each end?

If you want to get 0/100 - 100/0, look into some Bourns pots. That single pot alone may cost more than the rest of the components combined though.

The option of a dual gang pot might be good, but as you stated, but the 50/50 and 100 and either end may be an issue, unless both wafers are totally identical.
Again, a higher end pot like a Bourns may be better at achieving that.

[Elijah-Baley]

I started to think about a blend/balance pot since I noticed that kind of volume issue. I think that turning the linear alpha pot tape work like that:

0% - 100% -> 25% - 75% -> 50% - 50% -> 75% - 25% -> 100% - 0%

So at 50/50 blend we lose volume from both the loops because both are at 50%.

A blend/balance pot, MN tape, I think will have this progression:

0% - 100% -> 50% - 100% -> 100% - 100% -> 100% - 50% -> 100% - 0%

With at least a loop always at 100% I thought we can't lose volume. Is a balance pot better in any case than a regular linear pot? Probably I can menage the same thing using two pots for the two loops, useful, but a bit less easy to use.
Anyway, that kind of pot it's easy to find with 250k or 500k value, I should order a 25k MN pot from China with a cheap one, I guess. Or pay it a lot (including a Bourn).
But if this will not solve the volume issue a normal pot 25k it's good enough, probably. Of course I don't know the Wetter Box schematic, but if it works fine with that expression pedal i saw in the video i linked in my previuos post, that probably will have something between 10k and 50k pot inside, I still didn't found it, I'll keep to search.

Do you hear something wrong in the tape of the pot of the Wetter Box tape or while the expression pedal is used?

[CodeMonk]

I started to think about a blend/balance pot since I noticed that kind of volume issue. I think that turning the linear alpha pot tape work like that:

0% - 100% -> 25% - 75% -> 50% - 50% -> 75% - 25% -> 100% - 0%

So at 50/50 blend we lose volume from both the loops because both are at 50%.
...

It doesn't really work that way.
Given equal volume coming from each side, overall volume won't change due to pot rotation.
As the signal from one side decreases, the other side increases.

Consider the Big Muff tone control:


The tone control pot in the big muff when rotated doesn't alter the volume an appreciable amount.
And it performs the same function as a balance pot of the ROG splitter/blender.

Here's a little test you can do...
You need:
Battery
Pot (value doesn't matter)
Ohmmeter
Battery snap with wires would be good

Attach one of the battery terminals to tab 2 of the pot. Which battery terminal doesn't matter.
Set pot to 0.
Measure voltage between the other battery terminal and pot tab 1. Then terminal and pot tab 3.
Add voltages together.

Now set the pot to any number of positions you want and do voltage measurements as above.
Regardless of where the pot is at, the resulting voltages will be the same (within a few percent anyway).
Like this "0% - 100% -> 25% - 75% -> 50% - 50% -> 75% - 25% -> 100% - 0%", each pair adds up to 100.

Oh, and, I've built a few of these, or included it in other circuits.

[Elijah-Baley]

Thanks, I'll try that test to understan better,

Anyway, I don't know if it counts, but if I bypass the two pedals I have in the loops, blending two clean sound, I notice the loss volume when the pot is at half.
Another thing I can say, when I tried the resistor trick like GGBB suggest to let one loop (the red loop) at 100%, it does exactly the same issue.
To make it clear: I have a delay in the green loop and a distortion in the red loop. When the pot is all at one side I got 100% distortion and no (clean) delay, when the pot is all in the other side I have 100% delay, but the distortion is not at 100%, because turning the pot it lose something and it sounds a bit tamed, I lose a bit of volume. It's like when I have the pot at half in the stock mode.

[CodeMonk]

I never had any problems with volume drop out of the ones I have built.

My current project uses it.
And my board is etched and I've drilled about half of it.
Hopefully sometime this week, I'll be able to finish that and build it.
Its the standard circuit you have in the OP.
But that's only about 25% of the total circuit.

When you said you bypassed the pedals, blending two clean sounds, are you just patching the send and return for each channel?

And when you have the distortion side at 100%, the volume is ok, but if you have the delay at 100%, there is a volume drop?
If that's the case, then swap the channels (delay in red, distortion in green) and see if the volume lose follows the delay.
That may narrow down where the issue lies.

Oh, and if you are doing wiring the Send > Return direct, try swapping those too.
The Green side has a lot more parts in it. Perhaps something there is bad?

I'll see if I can duplicate your results, hopefully by this weekend.

[Elijah-Baley]

I bypassed the pedal in the loops through their footswitches, but I tried patchcords between the loops jack, too.
When the distortion pedal (or the delay) is at 100% it's hard to say if the volume loses something because the volume pot on the distortion pedal helps to set the volume, and because I'm testing the board without the footswitch, even if, indeed, I tried to connect it to an AB Box for this reason. I'd say I don't have that kind of volume issue, anyway.

I feel that the signal with the pot at 50/50 is not at 100% in none of the two channels, but rather at 50% for both. In the mix mode (the one with the resistor, I'll call it like that) one side should be always at 100%, else it has no much sense. Instead, when I mix the delay I hear the distortion a bit tamed, not a volume drop, but it's sound like the signal is a bit low, I'd say at 50%. It's hard to explain, but it's like if this mod change the tape of the pot like if it halved the pot of the stock mode. So at this point I can do the mod using the pot from 8 o'clock to noon to use at "100%" one loop, or from noon to 5 o'clock to use at "100%" the other one loop.
I think if the two loops are not really at 100% the mod is useless and the setting, though it sounds nice, is annoying because the signal loss and because you can't never get the right sound of the pedals just if the pot is at one of the two extreme.

Seeing the espression pedal used int the Wetter Box video I'm sure that a regular linear pot will be ok, but maybe there's some arrangement in the schematic we can use to get 100% of both loops with the pot at half.
The guy of GigRig say that, in the Mix Mode, one loop stay at 100%, so it's not possible that it loses signal. Again, else it's will be pointless.
I even thought that the two gain pots, that I didn't see used in none video, does this kind of adjustment. But I'm not so sure. Maybe that is jsut to set the volume directly on this pedal without touch the pedals in the loops, it could be even longer pedal chains in the loops, if we want.

[GGBB]

I feel that the signal with the pot at 50/50 is not at 100% in none of the two channels, but rather at 50% for both. In the mix mode (the one with the resistor, I'll call it like that) one side should be always at 100%, else it has no much sense. Instead, when I mix the delay I hear the distortion a bit tamed, not a volume drop, but it's sound like the signal is a bit low, I'd say at 50%. It's hard to explain, but it's like if this mod change the tape of the pot like if it halved the pot of the stock mode. So at this point I can do the mod using the pot from 8 o'clock to noon to use at "100%" one loop, or from noon to 5 o'clock to use at "100%" the other one loop.
I think if the two loops are not really at 100% the mod is useless and the setting, though it sounds nice, is annoying because the signal loss and because you can't never get the right sound of the pedals just if the pot is at one of the two extreme.

A balance/blend dual-pot should help that - not sure if it will make it perfect but it should help a fair bit.

[Elijah-Baley]

If there's no other way to make the two loop in parallel at 100%, yes, I think the balance pot is the better thing I could try.

I can't imagine how we can't do it the 100% - 100% using a regular pot.

I found a pack with three 25k balance pot from China at very low price, no Bourn and maybe no Alpha, none brand mentioned. I don't know how much I can trust on it, but at least I can use the better of the three, and in case I'll have two in stock. This is my first Splitter Blend, it's a kind of prototype, if it works it's just fine. If I have to build a better one I'll buy a Bourn 25k balance.