Buffer position in an fx loop

[i2k]

Hi all,

I'm going to build a 3 channel parallel fx loop for bass. I have some questions about the splitter part where 1 input is splitted into 3 fx send out. Some schematic put 1 buffer after the input then split the output of that buffer into several fx sends like this http://objsql.sourceforge.net/media/looper_4.png. While the other splits the signal after input then put a buffer before each fx sends, like ROG's splitter blend here http://runoffgroove.com/splitter-blend.html ?

Questions :

Which one is more correct ?

On the 1st schematic if the phase reverser is in-active, does is function as normal buffer ?

[blackieNYC]

yes it does function as a normal buffer. You can move the polarity reverser/buffer forward, and make these buffers to go out to the sends. Your returns would then be just before the 10u caps.  I did mine that way, but didn't try the other.  The ROG is also very good, but you do need a mixer.  I like the first one, for your purposes.

[i2k]

yes it does function as a normal buffer. You can move the polarity reverser/buffer forward, and make these buffers to go out to the sends. Your returns would then be just before the 10u caps.  I did mine that way, but didn't try the other.  The ROG is also very good, but you do need a mixer.  I like the first one, for your purposes.

Hi & Thanks Blackie.
If the polarity reversers are moved forward before the sends, do I still need the first buffer (the one just after the input) ? So I can use the remaining opamp to create dual supply without have to add MAX1044.

Another thing that I dont understand on the ROG splitter blend is: why there's a JFET buffer before the polarity reverser if the polarity reverser itself can function as buffer ?

So I plan to make something like this :

input --> split into 3 buffer with phase reverser --> send  ---> return --> summer + mixer

Is that correct ?

[blackieNYC]

Can the output of the previous pedal, or the guitar, drive your three signal paths?  I would think an initial buffer there before the split would be best.

[Quackzed]

I would think an initial buffer there before the split would be best.

+1, you want to be sure you can drive the splitter without signal loss.

[i2k]

Can the output of the previous pedal, or the guitar, drive your three signal paths?  I would think an initial buffer there before the split would be best.

There will be compressor before the input, so it should be able to drive the split without initial buffer ?

[idy]

I think the JFET buffer before the polarity reversing opamp is there because Opamps set up as inverters have a lower input impedence, and one idea of mixer/splitters is to avoid loading a signal. Without it you might find a change in the tone of a weak guitar pickup when you switch the polarity.

[i2k]

I think the JFET buffer before the polarity reversing opamp is there because Opamps set up as inverters have a lower input impedence, and one idea of mixer/splitters is to avoid loading a signal. Without it you might find a change in the tone of a weak guitar pickup when you switch the polarity.

Got it & thanks a lot

I found Keeley Parallel Mixer schematic and will use it as base to a looper with 3 send / return loop.

[blackieNYC]

That's good.  Consider whether or not you need volume pots on each return.

[i2k]

That's good.  Consider whether or not you need volume pots on each return.

I don't plan to put any volume pot on the returns as all effects that will be connected to the returns has level control. The only vol control will be at the output.

[i2k]

Dear all,

I extend Keeley's Parallel Mixer design by adding one loop with phase inverter. So SW1 & SW2 are the phase inverter switch and switches after returns are mute switch. All coupling caps are 1 uf as I have bunch of WIMA's 1 uf, so why dont use it ?

The dual supply power will come from separate board using NE555 which converts +9V into +/- 9V.

Keeley Parallel Mixer is here : http://www.robertkeeley.com/manuals/Keeley_Parallel_Mixer.pdf

I also plan to have parallel/series switching for loop 1 & 2. But it will be done by outboard wiring.

Could you please kindly check this schematic below ? Thanks in advance

[slacker]

Looks good to me, I would maybe make R14 220k like in the Keeley schematic, this gives you option of some boost or just lets you compensate for any volume loss you might get mixing certain things.

[i2k]

Looks good to me, I would maybe make R14 220k like in the Keeley schematic, this gives you option of some boost or just lets you compensate for any volume loss you might get mixing certain things.

Thank you, I'll consider to put a trimpot on that position.