I need a little help with a utility box design: Buffered effects loop w/boosts

[pott]

Basically it would act as a pedalboard on/off switch for gigs.

The goal here is to have a bog standard effects loop, flanked by two buffers (in and out) which are always on. The tweak would be to make each of these buffers (say, each side of a TL072 or most dual opamps) 1) as transparent as possible and 2) with a variable boost.
Now I'm no electronics engineer, so I took existing buffer/boost designs, got the schematics online and as the pedal was designed by a very good friend of mine, great guy, and great electronician I won't state which it is and I'd appreciate if no one asked. This is just however a clean boost/buffer, no rocket science as far as I know.

Here's the input buffer:

And the output buffer/boost:


Now there's a filter at the very start of the input buffer... do I need this? I don't exactly get what it does. In said pedal those buffers are incredible. Really brings out a certain sparkle in my sound, but without changing it that much at all, in fact I couldn't tell the difference.

The output buffer also starts with a filter, but that used to come after a whole (switchable) drive circuit so I'm wondering if I could make do without it?
Also, can I just 'copy' the boost section of the output buffer and place it onto the input buffer and get the same results?
Finally, would sticking those two diagrams together make electronical sense and give me the results I need? Could I replace the opamp with a single TL072 or would that require a change of values? This pedal uses the LF347 but it's interchangeable with the TL074.

As I get it, R2 (input) and R11 (output) are the main elements of in/output impedance right?
Anyway... it'd be a three footswitches box with two knobs (the boosts levels). DPDTs for switching between boosts/neutral buffers, a 3PDT with LED for the middle effect loop and a DPDT for the output boost/buffer. This way I'd get a clean boost to stack with other pedals when the center loop is on, or simply two levels of additional gain/loudness when straight to the amplifier, the whole lot being buffered to make do for long cables.

[Andi]

I'd scrap a lot of that and use a simple op-amp follower as the buffer and a basic non-inverting op-amp circuit for the gain, with a 1M pot on the output to set the level.

Simple works well.

[pott]

... eh I have no idea what you mean sorry   

[Andi]

http://instruct1.cit.cornell.edu/courses/bionb440/datasheets/SingleSupply.pdf

Worth a look.

[slacker]

I built something similar to what you're talking about. It had a switchable Fx loop with switchable buffers/boosters before and after it.

There's a schematic  in my gallery.  It doesn't do exactly what you want because both the boosters are controlled by one switch but you could easily modify it so the boosters had separate switches.

Might give you some ideas anyway.

[R.G.]

The Adjusticator.

http://geofex.com/circuits/Adjusticator.gif

[pott]

Mhmm so I'd use the high impedance adjusticator first, figure out a way to have a switch to go from buffer to boost and then use a standard adjusticator last? Does it have a low enough output impedance?

[R.G.]

Mhmm so I'd use the high impedance adjusticator first, figure out a way to have a switch to go from buffer to boost and then use a standard adjusticator last?

One section of the Adjusticator mixer should do.

Does it have a low enough output impedance?

To do what? It won't drive quarter horse electric motors. But the LM833 will happily drive 600 ohm balanced lines to +8dbm if fed a proper power supply.

[pott]

Eerrr... I'm lost again... 

The reason why I posted those schems is that this pedal with that buffer I want to use sounds brilliant when bypassed, it does wonder for my sound. Now since that output buffer is also a switchable boost, I wanted to use two of these and have a loop in the middle where I would put the pedalboard, but that could also be used as an AB box or a multiple instruments box with adjustable levels for each...

When the drive section of said pedal is disconnected, the signal goes through schem 1 and then schem 2. There's nothing in the middle. What I'd like to do is achieve a similar effect to schematics two on the first part (input buffer), i.e transform it into a clean boost using a switch.

Thanks for all the help so far guys... I gotta be honest though I'm understanding very little. I'm reading up on this a bit but I've never had any sort of electronics lessons before and it's coming up very, very, very slow...

EDIT: ohhhh I just had a look at the mixer! So I could use one section of the mixer as my input and then that second schematic I posted and have exactly what I want?

As for impedance, well I just want to be able to get through long cables basically. I know those buffers I posted do and sound real good, hence why I wanted to use them as basis for this.

[sjaltenb]

R.G.--

not to hijack the thread, but I am working on an Adjusticator layout, and I believe you responded that this was correct in another thread ( i didnt want to start another thread just for this)- but for 2nd side of the opamp, you just T off a 2nd 100K resistor like this correct?

To look like this:



Sorry, im still learning Eagle..