Buffer - Component and Value Differences

[Slight Return]

Hey all.

I successfully made an onboard buffer for my guitar. It's switchable via DPDT switch, and I wired it so the buffer input and output goes between the Volume Pot and Jack on my guitar. I used vulcanized fiberboard and eyelets to make a small point-to-point wired board that mounts under the pickguard like a Clapton boost circuit. Very cool! I followed a simple wiring diagram based on this schematic:



However, I used what I had available: 1M resistors instead of 2.2M, and a ceramic disc cap instead of the recommended film cap. The op-amp and electrolytic cap should be fine.

I'm mostly using this buffer for use with Direct-In recording thru my Focusrite 2i2 interface. I find that the buffer immediately cleans up my signal to near crystal-clarity. So it is working. Without the buffer, my clean sound is quite dull and sounds like a ton of high end has been chopped off. I do find it makes a difference playing through my amp as well, but the most drastic and obvious difference is going into my interface for direct-in recording.

That being said: Would changing the resistor values to 2.2M each change anything compared to using 1M resistors? I've seen a couple schematics using different resistor values and I don't understand why. Also, is there any benefit or difference to using a film capacitor of the same value compared to a ceramic disc capacitor? Might the cap value have to be adjusted if the resistor values are changed?

Thanks guys.

[samhay]

> Would changing the resistor values to 2.2M each change anything compared to using 1M resistors?

Yes, they would increase the input impedance from 500k to 1.1M.
For a 'modern' circuit that is not supposed to colour the sound, we often aim for 1M input impedance. However, 500k is not very different to this (you have to think orders of magnitude), so it's debatable as to whether you could hear the difference.

>Also, is there any benefit or difference to using a film capacitor of the same value compared to a ceramic disc capacitor? Might the cap value have to be adjusted if the resistor values are changed?

Leave the cap sniffing to the audophiles. Yes, it will make a difference, but it is unlikely to be significant.
The corner frequency of the high pass filter is 0.1 u vs. 500k (1M || 1M) = 3 Hz. With 2.2M bias resistors, this is ~1.5 Hz. Again, I don't think you can hear the difference.

Ultimately, it is good to appreciate the theory, but at the end of the day, if it sounds good, it is good (not my quote).

[ElectricDruid]

+1 agree with everything samhay said. Your version doesn't change anything critically.

[Slight Return]

Thanks guys! Sounds like I should be good to go. I've got a lot to learn with Direct In recording but it's nice to know I don't need to worry about the buffer part anymore.

And it only cost me around 10 bucks to make it, too. Very cool.

[Slight Return]

Actually, I've got one more question:

I always get a loud pop when I flick the switch to engage the buffer. I have one pedal that does this also, so it isn't the first time I've heard it.

Is this some kind of cap discharge or something? And is there any way to set it up so the buffer turns on and off silently? Or does the "pop" when turning the buffer on via DPDT just come with the territory?

Thanks!

[ElectricDruid]

There are various possible causes:

http://www.muzique.com/lab/pop.htm
http://www.geofex.com/Article_Folders/box_pop.htm

Probably the first thing to try is a 10M to ground from the outside end of the input and output capacitors. That might not be the cause, but then again, you might be lucky.

[antonis]

To be a little bit more lucky than Tom wished, wire your DPDT switch for IN & OUT grounded when buffer by-passed..