Simple IC Buffer: Build Report

[vanhansen]

Well, I finished another little project.  Gotta keep myself in to this by building something from time to time until our house is done and I can get more parts.

Anyway, since I have a few LM741's around, I decided to give it a try.  The op amp is the only part change I made.  Worked on first fire-up.  With that small of a part count, it should right?  Wrong!  Sometimes those really simple builds can bite you the most. Sometimes that's where I run in to trouble.  A circuit will work on the breadboard, work on perf on the test board, then when it's wired and boxed up, no workie.  BAH!! Stupid wiring mistakes.  :x  In any event, I either got lucky or know what I'm doing now because it worked first time even after I got it all wired up and boxed up.

I really like how this buffer doesn't color the tone very much, if any at all.  It's very subtle if there's any.  It definitely helps keep things nice and crisp when used with my pedalboard.  I even put a 1/8" headphone jack on the enclosure too so I can use it as a headphone amp. It's pretty darn quiet with the LM741.  There's some hiss with high gain but that's due to the high gain.  With low gain, you can't tell it's even on.

I'll post some pics later on.  I finished this up late last night and didn't get a chance to upload the pics and add the project page to my site.

Thanks to GGG (JD), Jack and Dirk for coming up with this one.  It's the little circuits like this that keep my enthusiasm up.

[Stevo]

Hey i am interested in building a buffer circuit.. I have AMZ circuit but it use 4 stages of two op amps could you post your buffer if you say you only use one I need the space since it is going to be in a small pedal....

[vanhansen]

It's just the Simple IC Buffer from General Guitar Gadgets.

http://www.generalguitargadgets.com/index.php?option=content&task=view&id=156&Itemid=190

[robotboy]

Can someone tell me the difference between a buffer and preamp?

[Mark F]

Can someone tell me the difference between a buffer and preamp?

I'm sure someone will chime in with a more detailed explanation but  in a nutshell, my understanding is : a buffer doesn't add gain just more drive and lowers output impedance. A preamp also adds gain. I hope that helps.

[Mark Hammer]

Can someone tell me the difference between a buffer and preamp?

Often nothing, but since you asked...

Something which has a high input impedance and a low-ish output impedance is described as being a "buffer" in that it allows a high output impedance device to be compatible with another device having a low input impedance.  It is a "buffer" in the same sense as "buffer zones" allow two parties which normally don't get along to peacefully coexist.

A preamp is anything that provides amplification (and current delivery) at levels lower than those required to power speakers.

Kinda bland, huh?

Here's the part where you got confused.  *ANY* preamp can also function as a buffer.  All it needs to do is have a high input impedance and low output impedance.  Usually, though, when people talk about buffers, what they tend to mean is a device that has little or no gain to it.  If you've ever seen an input stage in a schematic that used a noninverting op-amp with a straight wire link between the output and inverting input pin (check out the Tonemender at runoffgroove for an example), that counts as a buffer.

Buffers don't HAVE to use opamps, and they don't even HAVE to use semiconductors of any kind.  Transformer coupled direct boxes simply use a passive impedance-matching transformer as their "buffer".  Buffers can be based on transistors too.

Once gain enters the picture, people tend to stop talking about buffers and start talking about preamps.  The preamp may have a buffering action, but because its gain may be strategically set, folks talk about it as a preamp because its preamp aspects are of more interest to them.  Where buffers generally have but one stage (i.e., once the conversion is done, that's it, all buffering is accomplished), preamps can have several.  Some mic preamps that are intended to take puny voice mic signals and bring them up to close to line level so they can be fed to samplers and such can use several cascaded gain stages to achieve "preamplification" x1000.

Its a bit like lawns and yards.  They're both grass.  They're both on one side of your house and extend to the edge of your property, but we call the one in front a lawn and the one in back a yard.  preamp/buffer and lawn/yard are both fuzzy conceptual distinctions that generate warranted bewilderment in many.

[robotboy]

Can someone tell me the difference between a buffer and preamp?

I'm sure someone will chime in with a more detailed explanation but  in a nutshell, my understanding is : a buffer doesn't add gain just more drive and lowers output impedance. A preamp also adds gain. I hope that helps.

Hmm... can you tell me the distinction between gain and drive? As for impedance, I guess you'd use a buffer inbetween runs of long cable or after a low input impedance effect like a fuzz face? Does it lower noise? For some reason, I have a hard time understanding an effect that doesn't boost or color the sound  :wink:

[Mark F]

As I said, I'm sure someone will chime in with a more detailed explanation.   Again, Mr Hammer explains it like only he can. :wink: Thanks Mark now I have a better understanding of it also.

[robotboy]

Thank you for the clear and thorough explanation!

[bettycat]

Hi Erik, I´m glad you like it. I also think that this little circuit is a great help and everyone should have one.

[vanhansen]

I've got a few pictures up on my site now of this project.  Go to the link in my signature below and and go to the Projects link on the left.  Under there it is "Simple IC Buffer".

Or, just click here:  
http://www.erikhansen.net/diy/simpleicbuffer.htm

[vanhansen]

Last night I ran this buffer through my big rig (Marshall 100 watt amp) to see what it would do.  I tried it first at the end of my pedal chain between the guitar and amp.  As soon as I turned it on, it started picking up a local radio station, and very clearly too.  I attribute that to the fact that it's in a plastic enclosure.  It doesn't like the high gain before it apparently.  When I put it in the effects loop at the end of the pedals there (flanger, chorus, delay) there was no problem, no radio reception.  It behaved nicely and really brought back the punch that was being sucked away from the effects loop.  This one definitely has a spot in my rig.

[MartyMart]

I built the same thing recently for a friends pedal board, he had a lot of
pedals and too much "tone sucking" going on.
With this at the back end before the --- long cable run ---- to amp sounds
great, he was very pleased with it

Marty.

[Transmogrifox]

Can someone tell me the difference between a buffer and preamp?

I'm sure someone will chime in with a more detailed explanation but  in a nutshell, my understanding is : a buffer doesn't add gain just more drive and lowers output impedance. A preamp also adds gain. I hope that helps.

Hmm... can you tell me the distinction between gain and drive? As for impedance, I guess you'd use a buffer inbetween runs of long cable or after a low input impedance effect like a fuzz face? Does it lower noise? For some reason, I have a hard time understanding an effect that doesn't boost or color the sound  :wink:

Yes, actually, this can lower noise.  This depends on the input stage of the next amplifier--but generally the low output impedance works as a good place to "bleed off" input noise voltage that is generated by the next effect or amp in the signal chain.

The most noteworthy thing a buffer is used for is a "line driver" (one more confusing term to add into the mix).  When talking about RC time constants on a low pass filter, we have observed that the break frequency (3dB) is: 1/(2*pi*R*C).  Your guitar cable has some inherent capacitance.  With a large output resistance, "R" is large, and the low pass filter break frequency may be low enough to color your sound.  It would be like turning the tone knob to the "low" end.

With a buffer, the output impedance goes down, and the low pass break frequency climbs  far above the audio range so that there is no audible effect from the cable coloring your sound.  The buffer puts the "punch" back into  your amp by maintaining the signal's high frequency content.

[C Bradley]

A voltage follower is the ultimate buffer, according to my text books. Infinite input impedance, very low output impedance. Also, it's very simple to wire: two 1M resistors from 9V to ground, take your 4.5V from the junction and wire it to the non-inverting input, wire the output to the inverting input with a wire, use a cap from the input to the non-inverting input and another cap from the output to pin #6 on your LM741.