Runoffgroove Splitter-Blend wet and dry

[FunkyGibbon]

Hi,

I would like to use a runoffgroove Splitter-Blend as a mixer for a certain very cheap echo modeller with a noise problem.

Splitter-Blend is here: http://www.runoffgroove.com/splitter-blend.html

I would like one side of the splitter for the echo, the other side clean/dry.

I would also like to have separate wet and dry controls instead of the blend knob.

Is the following diagram an appropriate way to modify the circuit to do this?





Thanks.

[MikeH]

This will work in term of having a "wet" side and a "dry" side.  Couple of things though:

1- I don't think your level controls will work as they are set up.  They need to look more like a volume control you see at the end of 90% of distortion pedals.  Roughly 100KA pot with lug3 connected to the circuit, 2 to the output, and 1 to ground.

2- Keep in mind that the "Dry" side level control will only reach unity gain at max (which sometimes isn't enough for "clean blending"); if you want more out of it (a la Maestro Brassmaster, ie) you'll have to either adjust the gain of U1B, or put some kind of gain boost in you dry path.

[Ben N]

Truth be told, you could probably do just fine with a simpler circuit using one dual opamp. Just an input buffer split to effect send and dry, and a virtual earth mixer with two inputs, the dry (hardwired) and the fx return.

But if you want to adapt the spitter-blend: You don't need U2B as a buffer anymore, but you do need a mixer. So:
Change both level pots to audio taper and wire them signal to ground, like a guitar volume control. Connect the wipers of both pots to the inverting input of U2B (pin 2). The "top" of the dry level pot should go directly to the output of U1B (pin 1). I don't think you need the 2k2 resistor there, but if anyone knows, chime in. Connect a 100k resistor for feedback from the output of U2B (pin 1) to the inverting input (pin 2). Remove the 1M resistor from pin 3, and connect it directly to Vref. Now take your output from pin 1 of U2B through a series coupling cap (2.2 to 10 uf) and a 1M resistor to ground, and wahlah!

[FunkyGibbon]

Great, thanks.

That makes sense - it looks a lot more like the Bass Paralooper now. Of course, I could also modify that for this purpose. It does sound quite bassy (i.e. suited to bass, but not guitar), but I'm pretty sure that's about the cap going to ground (C5) in the clean channel. If one removed that I think it would sound a lot brighter.

It's here: http://www.moosapotamus.net/THINGS/paraloop/paralooperSCH.gif

Back to the Splitter-Blend, do I not need electrolytic caps between the volume pots and where their wipers join together at the inverting input of U2B, to prevent interaction between the pots?

Here's the new Splitter-Blend




and here's what I think would be the Paralooper equivalent. Will the removal of C5 be enough for a clean guitar sound (should all those 1u caps be higher - 2.2u)?




Thanks.

[Ben N]

Yes, you should use the mixing caps. I don't see C5.

[FunkyGibbon]

Thanks re the caps.

Ah, yes, C5 was on the original Paralooper circuit (see the link above). I removed it. So, it's an imaginary C5.

[bozzbass]

did you build this reworked version of the splitter blend?

i'd like to have a go myself and am wondering how successfully it worked.

[FunkyGibbon]

Hi.

Have been really busy, so I still haven't finished that. The board need drilling and populating. Will let you know how it goes.

[FunkyGibbon]

I finally got around to trying this, using the ROG Splitter-Blend version.

It works, but only for a VERY narrow range of both the Wet and Dry pots. Outside of these ranges, there is a pop and then the signal simply switches off. The only exception is just at the edges of this range, where there is a faint, sputtery distortion sound.

The pots seem okay - I checked them and they give the appropriate values as I turn them.

I used a 2N5457 instead of the MPF102.

Any suggestions anyone? I really not sure where to start here, apart from checking that everything is connected correctly, and that the board matches the schematic, both of which I'm pretty sure about. These might be really obvious symptoms to somebody more experienced...

Thanks,

Christopher

[FunkyGibbon]

I swapped in an MPF102, and replaced the TL072s, just in case I'd damaged them (when I first fired it up I had forgotten to attach the standoffs to the boards, so they were shorting on the enclosure!). However, it's still the same, except that the Wet control now has a much wider range of use. The Dry control still makes the whole thing cut out either side of a very narrow band.

Could the mixing network be incorrect? Could there be a need for a series resistor after each 10u cap, to ensure the signal doesn't leak to ground through one of the pots?

I really don't know.

Thanks,

Christopher

[FunkyGibbon]

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