IC or Transistor buffer?

[nero1985]

Hi guys, I couldn't find any threads about this so here it is.

I wanna build a buffer for my pedalboard, for the input to be exact, I have parts to build either an IC or a JFET buffer, i have TL072s, J201s,2N5457N,2N5458 and so on, the question tho is which one works best at the input and why?

Whats the reason to choose one over the other one? does it matter that I play les pauls with humbuckers rather than single coils? could that play a role in choosing the right one?

Thanks!

[antonis]

IC needs less items but has more pins to solder...


Both kinds of buffer have high enough input and low enough output impedance so you can't notice any difference in signal loss...
(the loss with a 50k coil resistance and a 5M input resistance is 1% - less than the one with a long guitar cable...)

As for frequencies that are involved in guitar pedals there isn't any reason for taking in mind parasitic capacitances and Miller effect in gain stage (which is anywise 1)..

[mth5044]

I can't really hear a difference, but AMZ reports that "many believe they are somewhat colder sounding and more sterile than the transistor versions".

http://www.muzique.com/lab/buffers.htm

[Groovenut]

If you're justbuffering the pedal board, I dont think you'll hear a difference between BJT, JFET or Opamp buffers. The only real advantage, drive wise, to the opamp buffer is that it (in general) can drive longer cable runs while maintaining signal integrity. I like BJT for standard gtr input to pedal buffers, JFET if there's a piezo, or similar, involved and opamp for long runs. JMO

[Gus]

Did you type "buffer" into search at this forum? 

[highwater]

Best option: build both (use sockets so you can swap jfets/opamps), and rig-up a switch between the two so you can decide which you like more. Keep the other as a spare after you've made your decision.

Most practical option: build whichever is easier, based on your strengths/weaknesses in soldering/layout. An opamp buffer will have less parts to keep track-of, a jfet buffer doesn't implicitly have four pins right next to each-other (twice).

Laziest option: build whichever you first find a layout for.



Unless what comes after the buffer is especially sensitive to noise, or the signal going through the buffer gets "close" to the supply voltage, the tonal difference is simply mojo... I'm not one to deny mojo, but it's a definitely a matter of personal taste at that point. You're asking about an *input* buffer, which will never have to deal with a signal hotter than what the bare pickup(s) could put out... with super-duper-hot pickups you might have enough output to distort/clip the first few cycles of a note, but even that difference will likely be lost in most situations. An *output* buffer for a pedal (or pedalboard) with gain might-well be worth careful consideration, but an input buffer rarely needs to do more than simply exist.

[anchovie]

I can't really hear a difference, but AMZ reports that "many believe they are somewhat colder sounding and more sterile than the transistor versions".

http://www.muzique.com/lab/buffers.htm

BWAHAHAHAHA!

"I wish I'd never got this buffer, it doesn't colour my sound at all."

[Gus]

What matters the most is the interaction with the passive guitar or bass, cable capacitance and the input of the buffer.
A thread
http://www.diystompboxes.com/smfforum/index.php?topic=107397.0 look at reply 10

Also the interaction changes as you turn down the volume control the sim is at max guitar volume and the tone is full treble.  I did not show this in this sim.  You might find the thread with the change that happens with a search.

The guitar volume control is a tone control.

R5 is a simple input resistance that changes from 10K to about 10 meg note most of the change stops at 470K(red) and above. Also note 510k is close to 470K what buffers use that?

So model your guitar and run some sims

[shredgd]

Hi guys,

even though this makes user "anchovie" laugh, there IS a perceivable difference between IC, bipolar and FET buffers in terms of tone. I did a lot of experiments about this in the past and I came to the conclusion that I liked simple bipolar buffers best, and that's what my two pedalboards have at the beginning of the signal chain.
In a direct guitar-cable-amp and guitar-cable-buffer-cable-amp comparison, using low capacitance cables and repeating the test many times, even in different days, and with different guitars, I could clearly notice with no doubt that with IC and FET based buffers the tone gets harsher than the standard guitar-cable-amp. And what I want from a buffer is to keep my tone faithful to that, not to add any treble or other frequencies. Some say "ok, but actually the tone you are hearing when using just a guitar-cable-amp setup already suffers from the loading effect of your cable, even if it is a low capacitance cable, and what you're hearing is the IC/FET "bringing back" frequencies, etc". I (and I think most of us) don't care about this theoretical explanation, because what we like, what we're used to, what guitar and amp builders use when fine tuning their products is: guitar-cable-amp. That's the tone I want to be faithfully kept by a buffer (if I have to put something between my guitar and my amp, otherwise I won't use any buffer).

Being that said, if I have to use an IC, one way to make it sound right is to add a 120-150pF cap in the feedback loop. For example, that's what I did for the two MXR microamp (an "IC buffer capable of boosting keeping the same flat frequency response") I built and which I use for a pure volume boost for solos at the end of the signal chain and for a gain boost before an overdrive. Using the original schematic, with just a 47pF cap, engaging the pedal meant having a treble/presence boost which in my opinion doesn't make sense, especially for a solo.
Now, I don't know if a similar cap to ground, as it was suggested, might achieve the same result, but that's my experience.

Giulio

PS: I'm even thinking of adding such a cap in my Mesa boogie Triaxis, which has a TL072 with no feedback loop cap at the end of the preamp circuit and which I believe is the reason why I always have to keep the presence to 0.0 in all my patches. But that's another story...

[GibsonGM]

^^^  But, then how can you know what your 'normal' tone is?? The device may just be reproducing what it hears...the increased fidelity in the reproduction of highs may make you think you're hearing 'harsh' or otherwise nasty tones!  With no buffer, you might be experiencing a LPF effect somewhere (amp input...etc) that is altered by the buffer's high(er) input Z!   So, the pF value cap is just an attempt to return to the 'lo fi' you had before, which is of course perfectly fine...

Like it was said, probably trying both types of buffer would be a good idea - they are very low in parts count, a 1/2 hour experiment on a Friday night      

One advantage of using an IC is that if you use a dual (or more....) opamp you have another amp stage there for use elsewhere in the circuit...a BJT or FET would only give you the one stage in the same real estate.   But for discrete "I just want a buffer", my choice is FET or BJT...

[allesz]

Never tried FET buffer, but tried both BJT and IC buffers.

I prefer BJT because they seem more natural sounding to me; ICs are too hifi sounding and the resulting sound is a little too bright....
maybe are the bjts that sucks away some treble and the ICs are simply more faithfull to the original input signal, maybe too much.

Some people swear about fet buffers...

The idea of trying both (on breadboard for example) is a good one btw.

[karbomusic]

maybe are the bjts that sucks away some treble and the ICs are simply more faithfull to the original input signal, maybe too much.

That's simply an adjustment of the input impedance not the IC itself IMHO.

[R.G.]

IC buffers, in the form of carefully designed opamp circuits, can reproduce audio signals vastly more faithfully to the original than single- or few-transistors buffers of either the BJT or FET varieties can. It's a simple matter of measurement, and is repeatable by disinterested third parties.

However, musicians are almost never interested in "more faithful", only in vaguely and individually-vaguely defined "better". As we well know, "better" means nothing unless you define how you measure it, and if the only measurement is the human ear, well, everybody has two ears, and they're all different. (Yes, even in the same person, and even from time to time.)

In general, musicians are suckers for a little even-harmonic distortion. Single transistor buffers of the BJT or FET kind provide this. Compared to the warmer, butter-poured-over-it sound from these, opamps which are actually more faithful to the input signal sound "sterile". Just like anything tasted after eating a lollipop tastes less sweet than it might otherwise. This is why there is the never-ending argument about tubes, transistors, FETS, and opamps. And there can never be an end to it, because all of the people arguing actually have the opinion they state; it does sound better to them - at that moment, in their ears, and with their set of preconceptions and biases.

Remember: there are only two ways to decide "better" and "best", one of which is only inside one person's head. The other involves writing down what "better" and "best"mean, and making measurements that are repeatable and can be done by independent and disinterested parties. Anything else is like saying which girl or guy is "best" at the dance.

[shredgd]

We are saying the exact same thing!
Luckily, we're not comparing two different pickups, amps, overdrives or whatever here. So there is not any subjective "best". For once in a while, we have a precise and definite "target tone", which is our standard guitar-cable-amp tone. It doesn't matter which guitar, cable and amp we are using, or how beautiful or ugly our tone is, because buffering is not a matter of "I like this more than that" but instead of "this sounds like the original tone (guitar-cable-amp), while that doesn't".
My suggestion is just to save some people time (as people ask that) and avoid them the time-waste of building three different buffers and keeping each one week around their feet, alternating the buffer with the direct (and reference) guitar-cable-amp tone.

PS: I also recently discovered a famous boutique pedals builder uses a BJT in his buffer pedal, and his thoughts (he explains on his site) are exactly the same as mine. Two people getting the same conclusions independently are better than one...

[Ice-9]

Remember: there are only two ways to decide "better" and "best", one of which is only inside one person's head. The other involves writing down what "better" and "best"mean, and making measurements that are repeatable and can be done by independent and disinterested parties. Anything else is like saying which girl or guy is "best" at the dance.

So you still go to the dance R.G. 

[Joe]

I normally would just use a basic transistor buffer unless there were an extra opamp stage available, in which case I would choose the latter. (And if opamps are already involved, I doubt this would matter...)

[ashcat_lt]

Hi guys,
...
Giulio

I know you "don't care", but did you put any effort into matching the input impedance of the buffer to what your guitar would actually see at the input of the amp?  Many buffers kind of "default" at 1M, while almost no actual amplifier sit there.  This will make a difference somewhere between imperceptible and subtle-but-noticeable.

On another note:  A typical opamp buffer has straight wire from the output to the inverting input.  A cap parallel to that straight wire does exactly nothing.  Putting the cap in place of the straight wire causes DC gain to go infinite, and slams the opamp into one rail or another.  Exactly what is the recommendation here?

[shredgd]

Ashcat, I used my Triaxis for those experiments. The Triaxis has an input impedance of 1M, the same as the IC and FET buffers I tried. If Mesa is lying about that value, then yours is a clever suggestion to experiments with input resistors in buffers.

Yes, the cap is in parallel. My experience refers to the microamp circuit, which does have a resistor in the feedback loop of the opamp, even though gain can go down to 1 when the gain pot (which is connected from the feedback loop to ground) is at min (=resistance to max).

[ashcat_lt]

The microamp has nearly 10M Input-Z.  Changes tend to get real subtle above 500K or so, but I am willing to believe you might hear a difference between 1M and 10M, especially if there's any distortion down the line which would tend to magnify those differences.

Unless that gain pot is "no load" modded, it doesn't actually get down to unity.  It gets pretty close, but you've already got us niggling over fractions of a db.    The parallel cap doesn't make much difference at that point.  I personally don't see that as the right answer, though.  The "problem" is that L times R is "wrong".  You can't change L, but you can change R.  Or you can try to apply another filter down the line to try to compensate, but is that really the same thing? 

(A quick side note that most guitars have a knob on them which sits parallel to the load and is quite effective at varying that impedance.)

Consider for a moment that input of many modern solid state amps looks very much like that little opamp booster.  It can't possibly be true that just putting it in a box with a power amp changes the way the circuit interacts with the pickups, can it?  So what else is different?  That one biasing resistor is bigger in the microamp.

[Gus]

You need to control the input resistance and high pass filter to make a fair comparison.

If you look at the link in my first post note how the high end response changes with resistive loading changes

Next are you using a rail to rail opamp?

How do you have the JFET biased and what is the drain current and drain resistor?

How do you have the BJT biased and what is the collector current and collector resistor? 

I have posted in the past about moving the emitter away from 1/2 supply for more equal drive

Are you using a resistive source or emitter or a constant current source or emitter?

Sweeping comments make no sense