Booster pedal with built in buffer

[fif_freakboy]

Hey guys,
  I'm pretty new at pedal building as I've only done some GGG pedals. I'm looking to build a booster pedal, most likely the mini-booster, but since I have only true-bypass pedals I'd like to incorporate an always-on buffer. How would I go about doing that properly?   Forgive me in advance if this has been on the forum before. Thanks for the help!

[MmmPedals]

You could do it in any pedal on a separate board. Hardwire the input to the buffer then go out from the buffer to the bypass switch.
If you do this you could use a DPDT and just one pole for the bypassing and the other for a led. It wont tone suck because of the buffer.

[fif_freakboy]

So take the input of the booster circuit and place the buffer circuit before it? Like (Input-buffer circuit-output)-input-booster circuit-output to switch?

[petemoore]

 I think you want a ''1rst thing buffer'', take your first pedal, the buffer board In/Out can be spliced between the *jack and before the bypass *switch [by cuttingsplicing the buffer into the signal path of the existing *wire].
  Depending on position of the switch mode, the input of the effect or the bypass output sees buffer.

[fif_freakboy]

If I understood that correctly that would allow the buffer to be in the signal when in bypass and the effect only to be on in "on". I only have about 22 feet of cable and 6 pedals with six inch connectors, do you think that a buffer of this type would make that much of a difference in signal loss or am I over working this?

[Ben N]

A couple of useful links for your pondering:
http://www.muzique.com/lab/tsbuff.htm
http://www.muzique.com/schem/mosfet.htm

The first one shows one way to set up a buffered bypass using a standard input buffer; the second has a diagram showing an easy way to wire up the Mosfet Boost to switch between boost and buffer modes. That might actually be the simplest/best solution.

[petemoore]

only have about 22 feet of cable and 6 pedals with six inch connectors, do you think that a buffer of this type would make that much of a difference in signal loss or am I over working this?
easy to tell, if you have commercial pedal with buffers.
  Also not too hard to wire up a buffer and see, except you almost want to have it on a bypass switch to hear with/without differences.
  Sometimes the difference pops out, sometimes it over-brightens a distorter [usually an easy work around, pull the buffer, tame the signal otherwise or whatever].
  In any case it'll let you know if you like it, if it matters is something that may crop up later when cables are under full moon, damp or otherwise loading the signal for some new reason.
  Another way to help get complete signal transfer assurance at any rate.

[fif_freakboy]

Thanks a lot for the help guys! I'll give those a look and order the pcb and parts and let you know how it goes when I get the time to build it

[oliphaunt]

Here is a buffer/booster I put together with some forum help.  Iit's a nice clean boost and basic IC buffer, you get both just by switching in/out a few parts.

http://www.diystompboxes.com/smfforum/index.php?topic=83783.0

[merlinb]

Here is a permanent buffer/boost pedal that I built recently.
http://s81.photobucket.com/albums/j207/merlinblencowe/Glass%20Blower/
Beware though! To my knowledge it is the most powerful booster pedal (to use a 9V battery) yet conceived
With a rail-to-rail opamp and a new battery I have had 20Vp-p output from it (for overdriving valve amps). Overdriving pedals though, to such levels, might let the magic smoke out. In which case use a regular opamp instead, which will limit the output voltage to no more than 12Vp-p.

[Gus]

You could use a fet input dual opamp.  First stage as a buffer, out to - in,   1meg to + input and the other side of the 1 meg to a 1/2 power supply voltage divider.

The other 1/2 could be setup as a noninverting variable gain stage booster.  Buffer connected to booster in series

One output from the output of the booster.  The other output from the booster.  Switch between them.  The buffer is always in circuit.  This is something like the glassblower link in the above post from merlimp.  It looks like merlimp is looking for some crossover distortion.

[Ben N]

Or this:

With a 3PDT, you could ditch the 4007, JFETs, 2N5089 and associated Cs ad Rs. A nice clean buffer that switches to a clean boost with tone control.

[Krinor]

This may not be exactely what you're looking for, but here's a design I use all the time for a very clean and nice live sound. I use this buffer/booster for acoustic guitars with piezo's in them and also for a large celtic harp which has a guitar transducer in it among other things. This is just my private sketch so forgive me for the low quality... As you can see I like to use terminal strips. You'll probably want to change the input impedance. As you can see this buffer has a very high impedance - good for piezo pickups, but not for magnetic pickups. The buffer design is from Muzique.com. The booster is the EHX LPB2.

[merlinb]

  It looks like merlinb is looking for some crossover distortion.

Look again, the output is not taken from the emitters of the transistors! They are for rail bootstrapping, not signal amplification!

[Gus]

Yes I see how you are using the transistors to move the output power supply rails "up and down" and are using the stored charge in C7 and C6.  I was looking at the waveforms and saw crossover in some photos at the link.  Interesting guitar circuit.

  Question when the transistors start to conduct to move the rail voltage does the STEP of the transistor starting to conduct show up in the output of the opamp or does the opamp correct  it out?

[merlinb]

  Question when the transistors start to conduct to move the rail voltage does the STEP of the transistor starting to conduct show up in the output of the opamp or does the opamp correct  it out?

You can see from the output scope traces that there is no trace of cross over distortion in the output. Both rail pins move simultaneously, so overall there is no change in the voltage across the opamp anway, even if it didn't have great PSRR (which it does)

The scope shots of the crossover region show the signal at the emitters of the transistors, not the opamp. I took them as a reference for someone else who was troubleshooting a build.