Adding a buffer

[Saturated]

Hi,
I have a question about adding a buffer. I apologise if this has been covered before. I got the attached schematic from Arons site, hope he doesn't mind me posting it. On the website it states that it can be added to the output of any circuit. This is great for me because me and tb wiring don't mix. My questions are,
1.) does this mean I can put this on the output of a build, just use a simple on/off foot switch and still have the led/dc/battery setup without using a 3pdt?
2.) my knowledge of opamps is limited but this is designed as a unity gain amplifier? So wouldn't that mean that it will take the signal from the output of a circuit and amplify it by 0?
3.) what happens in bypass mode? It seems like it should be something that runs paralell to the circuit so when the effect is off, it hooks from the input to the output and the result is unity.



I guess I'm looking for an easy way to add a buffer and wire a build as bufferred bypass.

[ElectricDruid]

1.) does this mean I can put this on the output of a build, just use a simple on/off foot switch and still have the led/dc/battery setup without using a 3pdt?

Whether you put this on the input or the output of a circuit is up to you, and it doesn't determine how you wire up the bypass.

2.) my knowledge of opamps is limited but this is designed as a unity gain amplifier? So wouldn't that mean that it will take the signal from the output of a circuit and amplify it by 0?

No, "unity" = x1. You could say it has a gain of 0dB if you like, but it's the same thing.

3.) what happens in bypass mode? It seems like it should be something that runs paralell to the circuit so when the effect is off, it hooks from the input to the output and the result is unity.

That'll depend where you deploy this circuit, and you haven't shown any bypass wiring, so we can't say. But yes - you're going to to need some path for the bypassed signal.

I guess I'm looking for an easy way to add a buffer and wire a build as bufferred bypass.

Ok, so stick the buffer on the front of your pedal, take the bypassed signal from the buffer output, take the effected signal from the output of the effect, and switch between them using a DPDT, with one half doing the switching and the other half doing that LED+resistor you mentioned. Rather like this image from AMZ:



That six-legged thing at the bottom is a DPDT switch, with the contacts shown in red in the bypassed position. You'd be replacing the Q1 transistor buffer with the op-amp buffer you've shown, but otherwise it's the same. This also shows an output buffer after the effect, which you may or may not need (that'd depend on your circuit).

[Saturated]

Thanks Electric Druid,
This makes a bit more sense now.
Can I ask, what exactly in my circuit would determine if I need a buffer on input AND output? I mean, other than plugging in to 20ft cables, how would I know?

[ElectricDruid]

In general, we want a low impedance output with a decent ability to drive stuff that follows it. If the last stage in our pedal is a Marshall tone stack, for example, we might find that it's fussy about what its output gets plugged into, because the impedance of the following pedal will act in parallel with the tone stack. In a case like that, you'd definitely want an output buffer.

In that example, it's pretty likely that someone would have designed one in already, because you'd get volume loss from the tone stack anyway - but if it follows a gain stage like an overdrive, they might not have bothered since there'd be enough level to be able to afford to lose some.

[Saturated]

Thanks again. Is there any harm in adding one of these buffers to the output of every circuit I build? I mean, just in case it needs it? It doesn't exactly change the sound dramatically, right? And it's only about 4 components to add.

[ElectricDruid]

No, there's no harm, it shouldn't change the sound at all. But it will be pointless in some/many cases. Have a look at the circuit and see if the output has a buffer already, at least. It might be a transistor buffer like in that AMZ circuit above, or it might be an op-amp buffer like you posted.

[antonis]

>No, there's no harm, it shouldn't change the sound at all<

Hope no Fuzz Face reads you, Tom...

[ElectricDruid]

Fuzz Face is a barely-designed-at-all circuit. If it wasn't a historical classic, no-one would stand for such misbehaviour from a pedal!

If I designed one now that was as sensitive and fussy, I'd be ridiculed, and rightly so. Imagine if half the people who built Flangelicious said it sounded rubbish and I told them that's because they've got the wrong guitar?!? 

[antonis]

I presume a "purist", like Sir Mike, would totally agree with you..

[Saturated]

So...can I assume that s fuzz face doesn't like a buffer?

[anotherjim]

So...can I assume that s fuzz face doesn't like a buffer?

Fuzz Face & many other early (*) fuzzes and wha-wha's's and the good old Rangemaster treble booster don't work as known and loved with a buffer in front. The reason is the passive guitar driving them - it has an inductive pickup, capactive tone control and variable resistances that become part of a complete circuit with the effect pedals input circuitry. These all interact in what usually happens to be a very useful way. Fitting a buffer in between breaks the interaction with the guitar - it's a completely different circuit.
This is the conundrum of the pedal world. It is possible to make pedals with buffered electronic bypass control that work very well such as the Tube Screamer- until you want one of those interactive pedals to go after the buffered pedal in your side chain.
May be the reason you hear so much of "so and so swears by this pedal, but I tried one and it sucked".

(*) There are more recent designs of simple fuzz distortions that deliberately have low input impedance to load treble off the signal from the guitar, otherwise the fuzz will be too harsh. Again, you don't want a buffer in front.

[ElectricDruid]

In the ideal world, all pedals would sound the same no matter what order you put them in or what was in front of them. Now, the thing is...that's not actually that hard to achieve. People would be shocked by this kind of behaviour from modern studio equipment, for example. It's just that many classic pedals don't do it, because technology ain't what it used to be (thankfully) and also partly because people love to believe in magic, and having something that's all interactive and weird with stuff around it is considerably more "magical" than something that's well-designed and reliable. Unfortunate, but that's human psychology - no-one said we were rational!