Should I buffer my output?

[ninjaaron]

Hey, I tried to ask at HCFX and TGP, but nobody had much to say.

I'm proto-typing a 'dual drive' pedal (like a Jekyl and Hyde, except with a JFET OD on one side and original design for the other side that is more or less a Tube Reamer with the possibility of adding diodes to ground for additional raunch).

Anyway, the question is whether its worth the effort to add an output buffer and have low impedance output, or should it just go out strait up?

[MikeH]

Hey, I tried to ask at HCFX and TGP, but nobody had much to say.

Well, duh. 

It all depends on the needs of the user; If it's just you and you already have plenty of buffering in you chain, then there's really no need.  If it's for someone else who could possibly be running it as the only effect in their chain... a buffer is highly suggested.  From what I understand, output impedance isn't nearly as important as input impedance.  You shouldn't have to worry about lowering your output impedance unless for some reason it is abnormally high (most aren't, or rather, don't need to be).

[ninjaaron]

It all depends on the needs of the user; If it's just you and you already have plenty of buffering in you chain, then there's really no need.  If it's for someone else who could possibly be running it as the only effect in their chain... a buffer is highly suggested.  From what I understand, output impedance isn't nearly as important as input impedance.  You shouldn't have to worry about lowering your output impedance unless for some reason it is abnormally high (most aren't, or rather, don't need to be).

Well, see, I want to have the possibility to run an 25k volume pedal after the effect, and they both use 100k volume pots, so I'm thinking the volume pedal will load the signal. That's my real concern.

[ninjaaron]

Hey, I tried to ask at HCFX and TGP, but nobody had much to say.

Well, duh. 

Funnily enough, I did get a lot more feedback at HCFX than I have here so far. 

[solderman]

If you build true by pass you probably donut need that since your effect probably acts as a buffer with lo ipm. when its not by passed.

//Solderman

[ninjaaron]

If you build true by pass you probably donut need that since your effect probably acts as a buffer with lo ipm. when its not by passed.

//Solderman

doesn't going thought the volume pot add impedance to the circuit. I was under the impression that it did, but I guess I could be wrong.

[earthtonesaudio]

The potentiometer style volume control as used in most pedals does add series output resistance (except when up to full volume).  The more resistance in series with the pedal's output, the lower cutoff you get with the lowpass filter formed by cable capacitance (and whatever capacitance the next input in the chain has).

You can make the output volume control smaller, but that will load the circuit output more.  This is where the output impedance of the last active device comes into play.  If it's a JFET drain, the output impedance is set by the drain resistor, and is usually high, so a small volume pot will load the output down and rob gain.  If it's an op-amp output pin, the output impedance is very low and will drive much smaller resistance values without changing the rest of the circuit.

From your description it sounds like you have a couple circuits with moderate to high output impedances.  This means you should use large value volume pots for each, and add a buffer afterward, or go straight into a buffer and then stick a small value volume pot at the very end.  I'd recommend the first method, as it retains all the buffer's benefits and gives you more flexibility when designing the output of each section.

[ninjaaron]

yeah, that's what I was thinking. Thanks.

[solderman]

If you build true by pass you probably donut need that since your effect probably acts as a buffer with lo ipm. when its not by passed.

//Solderman

doesn't going thought the volume pot add impedance to the circuit. I was under the impression that it did, but I guess I could be wrong.

OK,  I tought that you ment that you allready had an out put buffer in each circuit..

//Solderman