Buffer build for pedalboard use...

[pott]

I'd like a permanent buffer for my board, to put in a tiny plastic or metal case and plug the guitar into before the signal chain. What would a good, proved buffer be for that use? Thanks!

[David]

GGG (General Guitar Gadgets) has a JFET buffer and an op-amp buffer incorporating circuits specified in Jack Orman's "Basic Buffers" article on AMZ.  I can vouch for the op-amp buffer.

[stumper1]

I+1 for the GGG op-amp buffer.

[CGDARK]

An op amp buffer is much better or you can build a booster so you can add a little gain if needed.

CG

[Pushtone]

I did the same with the GGG IC buffer.

It's an easy fit in a 1590A or this little 2" x 2" box. Sorry forget the number but its on the Hammond site.




The knob is a 1M pot and 250k resistor to ground that acts to change the loading on the pickups.
But it only works that way when the buffer immediately follows the guitar.

Got the idea from the Radial Dragster and it works really well to un-brighten (is that a word?) the signal.
Some folks complain about too much treble when a buffer follows the guitar.
The Dragster can dial in any amount of tone suck to solve that treble issue.

[pott]

Thanks guys! I'll do that IC buffer as all the components are available here. I'll TRY to find an enclosure. Thanks for the help!

[Satch12879]

If you're going to make it in one of those silly-small enclosures with minimum features, invest in a very good opamp, perhaps one of the JFET input Burr-Browns by TI tailored for audio.  Be careful and avoid BiPolar opamps as their input impedances are often too small for passive instrument applications.

Also, a paralleled opamp scheme in Jack Orman's AMZ Super Buffer and in this Jensen Transformers Application Note using a dual opamp is a good idea to maximize drive on the output.

Just a remark, I do not understand the point of the Drag feature that Radial is marketing.  The whole point of using a buffer is that you get NO TO MINIMAL SIGNAL LOSS and hence you hear your instrument or whatever you're feeding into the buffer as it was intended.  If I get the Drag control, it introduces a variable resistance and hence decreasing the input impedance and KILLING THE SIGNAL!

Why? You've got a full level signal, just fix it with equalisation OR dial out all of the extra treble you had to compensate for in the first place because of excessive loading, cable capacitance, etc..

::shakes head::

[PerroGrande]

I agree with the previous post:  If you're going with an Op-Amp buffer, the ones designed specifically for audio are good choices.  The OPA-132/134 series is quite good.  The TL-07x is also a good choice, as is the NE-5532/5534.

The purpose of a buffer is to provide a high impedance input (i.e. one that doesn't draw much current from the source -- your guitar -- thus avoiding "sucking tone") and a low impedance output (one "stiff" enough to drive the next stage, even through a long cable.)  Many people who have connected their guitars to devices with relatively low input impedance *will* experience a brighter, more treble-rich tone when a buffer is introduced.  For the first time, they are really hearing the output from their pickups without tone-loss.

[Processaurus]

If you're going to make it in one of those silly-small enclosures with minimum features, invest in a very good opamp, perhaps one of the JFET input Burr-Browns by TI tailored for audio.  Be careful and avoid BiPolar opamps as their input impedances are often too small for passive instrument applications.

Also, a paralleled opamp scheme in Jack Orman's AMZ Super Buffer and in this Jensen Transformers Application Note using a dual opamp is a good idea to maximize drive on the output.

Just a remark, I do not understand the point of the Drag feature that Radial is marketing.  The whole point of using a buffer is that you get NO TO MINIMAL SIGNAL LOSS and hence you hear your instrument or whatever you're feeding into the buffer as it was intended.  If I get the Drag control, it introduces a variable resistance and hence decreasing the input impedance and KILLING THE SIGNAL!

Why? You've got a full level signal, just fix it with equalisation OR dial out all of the extra treble you had to compensate for in the first place because of excessive loading, cable capacitance, etc..

::shakes head::

Loading down your pickups is a wacky way to EQ a guitar, I agree, but it may be the exact sound someone wants, and buffering it will help  them consistently get a specific sound.  Whatever load you have after the buffer, the guitar sound won't change.  Also noise and crosstalk in badly designed/wired pedals can be minimized (like if you hear the effect a little in bypass, or the click of an LFO), especially things like true bypass loopers, with high gain effects in the loop.  A buffer before the loop can save you from oscillations from the output capacitively feeding back a little to the input.

[David]

Satch:

I must respectfully disagree with you.  First, the 5534 and 5532 op-amps are designed specifically for audio use -- AND they are bipolar.  They are excellent for this purpose.  As proof, I built the GGG op-amp buffer with a 5534.  There are no impedance issues.

[trevize]

my ggg ic buffer works well with tl071. ne5534 took away all the strat's single coil brightness.

[slacker]

I must respectfully disagree with you.  First, the 5534 and 5532 op-amps are designed specifically for audio use

NE5532s can have input impedances lower than 100k so they aren't ideal for using as buffers for a guitar signal. Technically JFET input opamps like TL07Xs are better as these have input impedances of 100M or more, which is so high you can ignore it.
Doesn't mean you can't build a decent buffer with an NE5532 though, but it's not the best thing to use. I can't really see any point using fancy opamps either, TL07Xs are quiet and do the job fine.

[pott]

Well the TL072 is already my favorite opamp for TS style circuits so I doubt I'll try any others, especially as I know absolutely nothing about them, neither about buffer technology 

Thanks for the help though guys! I'll do that GGG buffer at some point

[Pushtone]

Loading down your pickups is a wacky way to EQ a guitar,

Is not there a benefit with the Dragster in that it is not active and in no way adds noise to the signal?

We often talk about eliminating unnecessary active components to keep noise down in a circuit.
If all I want is to tame the amount of high frequency "revealed" by a buffer then the Dragster can accomplish this quite nicely without active circuitry.
Add an active EQ pedal may be like shooting at ducks with a compression phaser rifle.

Yes its counter intuitive and I turned my nose up at it when I first encountered it but the bottom line....
It works when used as directed.


Speaking about counter intuitive learning....
I saw a Discovery channel piece about fire fighters learning that they should spray the hot smoke to prevent a flash-over.
Until recently, they have been taught to spray the fire, not the smoke.
It was presented as "counter-intuitive" learning.

[Gus]

You could try the beginner project the NPN boost.

[oldrocker]

I put a Strato Blaster in this bypass all effects box.  I uses relays instead of DPDT's.

[PerroGrande]

Good point on the 5532 op amp.  I included it in my list as being specifically designed for audio -- which it is.  It does not, however, have a particularly high input impedance as op amps go.  One with an FET input stage is probably a better choice for this particular application.

[the_random_hero]

Good point on the 5532 op amp.  I included it in my list as being specifically designed for audio -- which it is.  It does not, however, have a particularly high input impedance as op amps go.  One with an FET input stage is probably a better choice for this particular application.

If you're non-inverting, doesn't the input impedance greatly go up when the op-amp is used as a buffer?

[shredgd]

pott,

if you want to get a very sparkling tone from your guitar (beware: harshness is next door!), then go on and build a JFET or Op-Amp buffer as suggested. But if you like the tone you get from your guitar straight to the amp via one cable and nothing more, I really suggest you to build a simple bipolar transistor buffer.

Why? Well, I did a lot of experiments in the past. I needed a buffer because my signal chain had become longer in the past few years because of the added diy (true bypass) pedals, so I experienced a loss of treble content in my signal. So I started to build those JFET and Op-Amp buffers, because they had the highest impedence, etc. However, none satisfied me, because they altered my tone too much: they gave me even too much treble/presence. Most people say: that's the real tone of your pickups, the one you never heard before bacause of the capacitance of your cable, etc. But I don't care, I like the tone I get from my guitar when plugged to an amp via one 5 meters cable as it is. Also, most overdrive/distortion pedals and most of today's amplifiers give an excess of treble, so feeding them with a treble-strong guitar signal isn't recommendable, in my opinion. Therefore, as I realized I liked the buffered sound I got from a Boss pedal, I decided to go for the same technology used in 99% of Boss analog pedals: bipolar buffers! Now I'm very happy with my pedalboard buffer! It keeps the treble content of my guitar signal without adding any extra presence.

I built the buffer shown at: http://www.muzique.com/lab/buffers.htm It is the fourth buffer from top, the one next to "An alternate configuration is shown...". I did some minor variations, based on experience and on readings:
- I used a 560k resistor for R1 in mine, to have an extra 50k of input impedence
- I used a 3.3k resistor for R2, to have a stronger signal
- I paralleled the 10u electrolytic output cap with a 100n film cap, to preserve the signal from alterations due to the electrolytic cap
- as I made my buffer switchable, I added a 100k resistor from output to ground to prevent pops

It seems I'm the only one (or nearly) to think it this way, but the fact big companies keep using this kind of buffer in their pedals has a meaning to me.

Hope this helps,

Giulio

[bipedal]

Jumping in on this thread...

Giulio -- I'm interested in your comments about the bipolar transistor buffer.  I now have 5-ish pedals on regular duty on my pedal board, so it's probably about time to get a buffer in there, but as a Strat & Tele guy I was worried about the possibility of things getting too crispy and bright.  Your approach might be the answer for me.

What transistor did you use for your buffer?  (I've got a few extra 2N3904's from a recent Tube Screamer build -- might one of those be applicable?)

- Jay