27v Split n' Boost

[MAO]

by request from GrooveChampion:

"Can we get this but with 1 channel, a fixed resistor to set the blend at 50/50 and a dry volume that can actually boost the signal?"

Inspired by BYOC 27v boost with Craig Anderton's Spluffer, Phase Switcher and a non-inverting "mixer".

I haven't built it, but this combination should give a huge amount of headroom and 20dB of non-colored boost for the "dry" signal via the Dry Boost control. The Effect signal should be at unity if my math is correct.  

The Phase Switch would be set for the loudest/fullest sound.

Be sure the electrolytic caps are rated at least 50v just to be extra safe since there is a 27v swing powering the circuit.  

Also, There are two additional/optional ground connections available. I would suggest wiring up the "Effect Return" jack with the normally closed tip connection wired to ground. (labeled "Jack SW Ground" on the layout). This will ground out the "Effect" channel when nothing is plugged into that jack, then the Split n' Boost can then be used as just a clean boost. The other ground connection can be used to ground the enclosure to one of the jacks.

You can sub electrolytics for the 2u2 MLCC caps, the (+) sides are towards the IC.

Hope it works :0)

[GrooveChampion]

THAT'S AWESOME MAN! THANKS!

But its friggin gigantic....Now I feel bad for asking.

[MAO]

No apologies needed, I misunderstood. Thought you were looking for a utility pedal. Im now assuming you wanted something to add to an effect in the same enclosure?

It was fun to design anyway, I may build it tomorrow :0)

[GrooveChampion]

It is a fantastic design indeed, but I do need something small that can fit inside a pedal with another circuit. I think the phase switch is overkill and I will simply figure out if the pedal is phase inverting or not.

The aim is to get something that works like the blend on the MXR Bass Fuzz where you have seperate volumes for dry and wet signals.

[MAO]

Gotcha,

Assuming the effect will have it's own volume control, for the smallest, simplest design I think you would just need an 8 pin dip IC that would handle the buffering, split and the volume boost for the clean channel, and a jfet for combining the Effect and Clean outputs.

Or 3 jfets would also work. 1 buffer, 1 boost, 1 mixer. Don't think that would save on size though.

And if your tapping off the effect's 9v supply, the amount of clean boost will be somewhat limited before clipping. If you have lower output pickups such as vintage humbuckers, single coils, etc, then no problem. Otherwise, you would want to power the booster with 18v or 27v via a charge pump for more headroom...which would add another IC.

I think it's doable with 1 8-pin IC, 1 jfet, 4 or 5 resistors and a couple caps will work, but again I made a few assumptions such as the effect already having a volume control, you'd be tapping off it's existing 9v power supply and vintage output pickups.

Let me know

 

[GrooveChampion]

That's the deal, I have an active soapbar bass and an Ibanez with high gain humbuckers. So I guess a charge pump is nessacery.

[MAO]

Maybe keeping the charge pump and boost as separate boards is the way to go.

More options to stuff them in that way, but additional wiring...always a catch 22.

Any idea how large the daughter board(s) can be?

[GrooveChampion]

Well I'd say the size of the Mini Jfet Blender.

[MAO]

ouch! No way I can do that small...not even close. Sorry

Maybe someone with SMD layout skills can pull that off.

[GrooveChampion]

Welp, crap. So can we go without the charge pump and call it a day? Just an opamp and a Jfet?

Key word is "Compact". I dont think some distortion on the dry signal will hurt, besides it will most likely be only if the volume of the dry is turned way up high, which is not what this is meant for.

[MAO]

All right, give this one a try.

This is the smallest, bare bones version I could come up with that may actually do the trick.

Again, assuming you will be tapping off a clean 9v supply from the effect as there is no DC filtering included other than for the Vb. Also, it would be good if the effect has it's own volume control in case you want to mix in a lower clean signal.  

To save space, hopefully you can lay down the bottom 10u, and tuck it below the IC. The 10u near the top can be replaced with a MLCC, probably anything above 1u will be fine.

The 2u2 MLCCs can be a smaller value if you don't have any, but I'd probably keep them at or above 1u. Or you can use electrolytics with the + side towards the IC, but no room to lay them down so MLCC will keep the size down.  

Either use 1/8 watt resistors for the light blue 100k and 1k, or bend one of the legs back underneath for 1/4 watt resistors, or just stand them up a bit.
 
The jfet can be just about anything with a DGS pinout.

D4 is optional. If you omit it, don't make the cut underneath it.

Opamp is TL072 or similar.  Try a 5532 if you already have one.  
 
The max available gain for the strait signal is 11x (20dB). If you need more boost for the clean signal, lower the value of the 10k resistor, start with 6k8. If you don't need 20dB, increase the 10k up to 20k or 22k, or you can lower the pot value to 50k.

Good luck!

[GrooveChampion]

I fucking love you.

[MAO]

Thanks Groove,

Here's how to do it with a DSG jfet (2n5457, J201 etc).

D4 can be replaced with a jumper.

[GrooveChampion]

Dude stop I am gonna fucking cry. You are making me blush.



Seriously, I cant thank you enough for this, gonna try it out with a Russian Muff right away.

[GrooveChampion]

I just built the DSG version with a 2n5952(I flipped it)....it doesnt work, no signal what so ever...I used it with a Woolly Mammoth

[MAO]

I'll build one asap and get back to you

[GrooveChampion]

I am so sorry for the hassle

[GrooveChampion]

Any updates dude?

[MAO]

Yes, sorry, mine also has issues.

Only passed signal with the drive knob turned all the way down, and even then noisy and distorted on both the dry and the effect send sides.

It also seems the drive control is interacting with both sides.

Sorry, not sure what the solution is at the moment but it seems the circuit design itself is flawed.

Was going to try powering with 18v to see if a higher supply voltage makes any difference, will get back to it asap.

Sorry for what seems to be a bad design...

[MAO]

Ok, solved part of it.

Replace the 1k resistor with a capacitor. 10nf, 22nf or 100nf etc. The dry side should then work properly.

The effect's return signal is being squashed, have to crank the effect volume all the way up to hear something...and even then it doesn't sound very good.

Must not have implemented the jfet mixer properly. Thought it could be done with just the one jfet. Still thinking about this part of it...