simple output buffer

[sjaltenb]

hello,

I think I will use Jack Ormans JFET splitter for my input buffer on my board (split to tuner). But how would the simple Jfet buffer work as an output buffer for each effect? I am thinking this simple Jfet design would be best as it is quick, easy and cheap to build.

thoughts? I want the impedance of each buffer to be 1M throughout the entire board to be consistent.

any suggestions on the "best" transistors? Thanks!

[Ben N]

I guess it depends on the specific application, but a garden variety BJT would have a lower output impedance.

[Cliff Schecht]

A U310 is probably one of the lowest noise JFET's made at 1.2 dB (Mouser I believe still sells them). Or your garden variety J201, 2N5457, 2N5484, 5485 5486 etc.. will probably work fine, especially when you consider that a guitar signal isn't exactly hi-fi.

[R.G.]

Just offhand, there isn't much need for output buffers on effects. There are exceptions, like inductor wahs, a few others. But generally the output impedance of an effect is in the range of 10K or so, perhaps lower. You understand that I'm generalizing heavily here.  More importantly, I can't think of an effect with an inductive output impedance at audio frequencies, so the output impedance doesn't go up with frequency like a guitar's does. Maybe something else will come to mind, but i don't think many effects need an output buffer.

[Cliff Schecht]

Just offhand, there isn't much need for output buffers on effects. There are exceptions, like inductor wahs, a few others. But generally the output impedance of an effect is in the range of 10K or so, perhaps lower. You understand that I'm generalizing heavily here.  More importantly, I can't think of an effect with an inductive output impedance at audio frequencies, so the output impedance doesn't go up with frequency like a guitar's does. Maybe something else will come to mind, but i don't think many effects need an output buffer.

Agreed. Most effects will have some sort of output buffer circuitry, even if it's transistor based variant. If designed properly, pedal X should couple to pedal Y (or amp Y) properly in any condition. Considering that most effects feed into a very high impedance input (be it an effect or amplifier), a buffer usually isn't necessary.. Older transistor based circuits are really the only example I can think of where the input of one effect can get loaded down by the high output impedance of another.

I also hold grudges with people who die by true bypass effects, especially when the active bypass section is designed properly (ala Boss fet switching).

[sjaltenb]

thanks!

yes, i dont think I will be needing them either really, I just wanted to try one for experimentation.