Build Your Own Clone Message Board

Hey all, another CB question...
I made one of these a few months back, it worked of course-
and I threw it into a bin. Now several builds later, I've been reading up on buffer pedals,
and short of buying a kit for one on another website of gadgets, I remembered this abandoned baby.
I have several true bypass pedals that I run, none are buffered ie. Boss pedals, etc. and I need to run about 30' of cable from my pedalboard to my amp stash. I will use george L's for it's lower inpedence benefits, but I would like to add a buffer box in my chain to help keep the signal intact.
Can I appropriate the CB to do the job?
1) does it have the neccesary "high input" and "low output" impedences?
2)Does it have a fairly low noise floor?
(I would run it at zero gain, probably not even have a pot on the box)

I'd appreciate your comments.

Absolutely! The first half of the CB is a near-perfect buffer. All you need to do is remove R3 and the transistor, and take the output from where the middle lug of where the transistor was.

http://www.buildyourownclone.com/board/viewtopic.php?f=31&t=30938

Good to hear. What do you think of the suggestion that R2 and R3 get demoted to 10K apiece, instead of 2.2M,
if I'm using an AC adapter instead of batteries?

That could possibly squelch some noise but would severely decrease the input impedance. You could socket those two positions and try decreasing values if noise where an issue.

Morgan, thanks for your input, I will leave the values alone for now.
Would it be possible to hookup a LED to the circuit to let me know the CB is engaged?
a 3mm LED?

What CLR value would you recommend for a 3mm LED for wiring this circuit as a buffer pedal?

Anything from 1K to 4.7K or so will work fine.

Just gotta say, you forum guys are the best.
Thanks.

I just did this wih my confidence booster since it wasn't quite clean enough for my purposes and I already have a few other boosts on my board. Here's my question:

If I wire the output to a 3.5 mm mini jack, is the output impedance appropriate to plug into my macbook's mic jack? I'd like to be able to use guitar tones from Mainstage without dragging my whole audio interface around with me. I figure the confidence buffer could fit in an Altoids tin or something similar so I could carry it around with my laptop easily.

You likely want something with adjustable gain that boosts the signal for that. A MOSFET SHO style boost would probably work well enough. There are lots of layouts around for that.

Thanks for the suggestion. I'll add it to my queue of things to build and hang on to this buffer in case my board ever needs another one in addition to my Boss BF-2.

Line level for consumer audio is -10dBV or around 0.89V peak to peak. If we take a typical guitar signal to be 100mV pk to pk you need a gain of around 10 x at most.

Built to spec the transistor stage in the confidence boost provides a gain of almost 47 x. This can be reduced to 10 x by changing R4 in the CF to 180K and R5 to 1.8K. Modifying the transistor stage like this will give you the needed gain to drive a Macbook without over driving it and even with a 50K output pot the maximum output impedance will be around 12K which is low enough for most buffering applications.

If you connect a long length of co-axial cable directly to the output of most op-amps they will go unstable and oscillate at an inaudible frequency with unexpected consequences. This is because of the capacitance of the cable. This can be stopped by fitting a low value isolating resistor (470R would do) between the output of the op-amp and the output jack / cable connection.

Tark, I modded the CB to your suggestion and it works well. Not quite 100% clean, but I don't really care about that. This is more for convenience of being able to plug into the computer anywhere to jam, nothing really critical. I still have a bit of noise, more than I'd like, but I'll see if that goes away when I box it up.

if by 'noise' you mean low frequency hum, then yes building the circuit into a metal screening box which has a connection to the circuit ground / 0V is essential and that should get rid of the problem. If you mean high frequency hiss then no it won't make a difference.

If you still find you have more gain than you need then the resistors around the transistor can be adjusted for lower gain and I can work out the values you need for say 5 x gain.