The best buffer... or at least my favorite!

[DavidRavenMoon]

Electrolytic caps don't lose high frequencies. But I prefer tantalum over aluminum cans.

Type "equivalent series resistance" on google 

You're new at this. That's obvious because you're stumbling your way through circuit snippets from other people's circuits. I've been doing this since the 70's, thanks. 

I put my first buffer in my '73 Rick bass in 1977.

ESR isn't going to do crap in a circuit like this. Plus, did you find out what the ESR is at the frequency range for a guitar on those brand caps? Bet you didn't. Plus putting two caps in parallel would decrease the ESR. Parallel resistance is the difference of the two values. The resistance is lower. But now you also increased your cap value.

ESR is a problem with filter caps.

So use a tantalum cap.

You don't seem to understand how impedance works in regards to passive guitars.

If you are right about saying the above buffer circuit has 150k input impedance, then nobody in this thread/forum does, only you do. You lucky boy! 

How many buffers that didn't come out if a pedal have you tried? You pretty much answered that in your original question. Not many.

Why would a bi-polar transistor sound different from a JFET buffer (such as the Alembic Stratobladter, which is a textbook buffer stage.

JFETS (as well as JFET based op amps) have a higher input impedance. 

Look at something like an EMG pickup. The older series have an output impedance of 150k. This is pretty high for an op amp based circuit. 10k is more typical. But this makes the pickup see larger load, since it's a higher impedance source. And this makes them not sound like a passive pickup through a high z buffer, like the Stratoblaster.

The Redeemer buffer also has an input impedance of about 150K. The thing you notice about that is it keeps your guitar sounding passive. I have some blind test sound clips of a passive bass, then through an EMG BTC preamp, a JFET buffer, and the Redeemer. The very high input z of the JFET (about 10M) gives the guitar a glassy top end. The other two don't. And the reason is they have a lower input impedance. So they aren't isolating the guitar as much, while still having a low output impedance for driving loads like your cables and pedals, etc.

So try experimenting with different input impedance.  You will find one that keeps your guitar sounding like it's straight into the amp (which is what the Redeemer is said to do).


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[shredgd]

I respect your experience, but I invite you to respect my experiments.

Did I try various types of buffer? Yes, I did! Did I play with different values of input impedance? Yes, I did!
If you read the thread from the beginning, you wouldn't have to write all those examples of different input impedance buffers. Input impedance means a lot, of course it is the major determinant of the behavior of the buffer. BUT I swear it, if you set a JFET buffer with a 1M input impedance or even 500k (or even less: I experimented with a pot to ground), it will still sound different from a bipolar buffer (set to have the same input impedance, of course), and different from your standard guitar-cable-amp tone (when set to the same input impedance of the amp, i.e. 1M, or again, even less). Don't ask me why, but JFETs have a kind of "scooped" tone to them.
Please, do the A/B test (as soon as I'll be able to record high quality clips, I will do it again and let you hear the results).

Buffers DO have a tone, even if spice simulations and electronic books might orient to a plain 1:1 response. This is because components have their inner electrical properties which make them different from a pure ideal and theoretical electronic component, and because of e different frequencies into play.
That's why you prefer tantalum to electrolytics by the way! 

[bool]

You will uncover the part of the "secret" why a bjt buffer sounds different to a jfet one when you simulate the bjt circuit and look at the Iin (input current) curve which directly translates to dynamic and mildly assymetric input impedance ....

And things get even more interesting when you factor in the frequency-dependant load-to-bjt-base impedance reflecting.

IOW, a bjt buffer isn't a "buffer" like a opamp (or a fet-based) one, but is more of a small "tone machine". (just look what ppl say about the "cornish buffer").

(I buffered my first bass somewhere around '83 or '84, heh)

[shredgd]

I recently gave the Cornish buffer a try, as someone suggested bootstrapping to raise a bipolar buffer impedance.
I first used a BC549B transistor as indicated, but that sounded a bit overly rich in presence compared to the straight guitar-low impedance cable-amp tone, and a bit "stiff" under the pick.
Today I tried a PN2222A (my undefeated favorite) and I must say the sound is pretty exactly the same as the straight to the amp sound, tone wise. This is probably due to the lower gain of this transistor (hFE circa 200), which means lower input impedance compared to the BC549B; the latter probably raises input impedance over 1Mohm, that's why I hear more presence than the straight to the amp tone.
However, headroom with the Cornish buffer is much lower than my optimized buffer (see above) and I don't like this added compression at all: could this be due to the bootstrapping approach?

In conclusion, the one in the schematic I posted is still my favorite buffer: oomph, headroom, sweet midrange. And the PN2222A is still my favorite transistor! Give it a try!

Giulio

[bool]

I suppose PN2222 isn't that far tone-wise from a metal-can 2N2222 which I have had (quite long ago).

If you seek a slightly thinner tone with slightly compressed mids, you can get there on the cheap with using BC547B or BC548B (the B suffix, seek the betas around 300-350).

[shredgd]

Actually I could compare the metal can 2N2222 and the PN2222A and I would say they are two completely different beasts: the 2N2222 sounded muffled, as if there was some extra input capacitance. The PN2222A doesn't have a thin sound or compressed mids at all

Giulio

[bool]

Really? That's good to know. The PN was supposed to be the same die as the 2N in plastic package..

Compressed mids aren't really a bad thing when you need to record takes that stack up nicely otoh.

[pruttelherrie]

Hahahaha shredgd you're full of sh*t.
Please compare the datasheets. It's actually the same datasheet. It's attached to the last post of this thread: http://www.electro-tech-online.com/threads/is-the-pn2222-transistor-the-same-as-a-2n2222-transistor.19161/

I'd like you to do a DOUBLE BLIND test of the buffers you've built and tried, and especially the identical buffers with 2N2222 and PN2222A in it.

50% chance you'll guess right

[shredgd]

Mmm... unless the metal-can one was damaged (but I bought it new last month from a known German electronics store) the difference was really clear. Actually the metal-can one was unusable as a buffer, I must say, too much treble cut.
I will soon record clips of the transistor shootout in my buffer, and my buffer vs. the Cornish one, and post it here.
Meanwhile, as we say in Rome, "full of sh*t" your sister... 

[pruttelherrie]

Mmm... unless the metal-can one was damaged (but I bought it new last month from a known German electronics store) the difference was really clear. Actually the metal-can one was unusable as a buffer, I must say, too much treble cut.

Hmm, that _is_ weird. I've ordered from BZ, MD and T-T before, and never had problems with any of their stuff...

My guess is, that most of the behaviours described in this topic, should be attributed to other things than the transistors, even down to that one extra can of beer which f*cks up anyone's perception or state.

I will soon record clips of the transistor shootout in my buffer, and my buffer vs. the Cornish one, and post it here.

Please do! Preferably "blind"!

Meanwhile, as we say in Rome, "full of sh*t" your sister... 

Fair enough
Even though here in the Low Lands it's mostly our mothers!

[bool]

If you're that kind of guy (girl?), you can deduct "behaviors" from devices' datasheets. Some of the mistery is right there in the graphs that correlate device Hfe vs. Ic. (In short; because the Ic changes with the signal, everything else that's affected by changes in Ic also changes).

In short, and simplified, the actual device nonlinearities will effect everything that's plugged after the buffer - and before the buffer because modulated Hfe means that actual buffers' input impedance also changes with the signal.

If the buffer has it the magic "mojo" (just the right nonlinearities), your rig will sound "better" ... and vice versa.

If you seek total linearity, use a FET opamp.

If you seek the mojo, use a BJT. (I mean the one that "plays" with you, not against you).

[pruttelherrie]

With "behaviours described in this topic" I mean things like "I swapped trannies and suddenly all highs were gone!" or "buffer B sounds much more scooped to me than buffer A!"

There's no mystery in the graphs. It's what it says on the can. From the signal you know what the collector current will be. From the switching speed (ns range) you can tell that the actual frequency of your signal will not change the hFE/Ic graph (there's no frequency dependency at audio frequencies). So from there you know exactly how the transfer will be. From the hFE/Ic graph you can see, that up to 10mA of collector current, the hFE increases up to 200% of the value at 0mA. Depending on the design (the stage) this calculates into a gain. Then you know how your signal will be compressed or expanded (=> the transfer function of your buffer)

Anyway, much more useful:
* build an A/B box
* socket your transistors
* play with both buffers back and forth
* switch transistors
* repeat playing
* see if the results are the same
* report

Now you know if the difference was in the transistors or in your builds.

Also: have a few beers, repeat the above. Or do the test the first thing in the morning, when the ears are still fresh. Or repeat at rehearsal volume. Or....

There's so many things that influence the sound that we experience, but nooooo, it has to be the transistors, who have identical datasheets!

Great designs remove tolerances from the equations. Great designs remove the outside world from the equations. That's why al these 80's japanese designs always sound the same and are not influenced by either the guitar or the amp.

[DavidRavenMoon]

Since most audio semiconductors are all very similar tone wise, i.e. they just amplify the signal, the big difference in buffers in the context of a passive guitar or bass is the input impedance. The higher it is, the brighter your tone. If you don't want that brightening, go with a lower input impedance.

1M and up will be very bright, while 150k will sound more like the passive guitar unbuffered, but then the low output impedance of the buffer will drive the rest of the signal chain, and all buffers isolate your guitar from further signal degradation.


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[shredgd]

Pruttelherrie, I don't drink and I usually do all my tests with "fresh ears". I also use sockets for transistors and do back and forth comparisons. As you can read in my previous posts, I paid much attention to my tests (read about the head position above, please), and for most of my conclusions I did the same observations even in different days.
I know they were not blind tests, but I didn't "want" the PN2222A to be a winner (I don't even know why I had a couple in my drawer; I didn't even know they were called with the P and not a 2, I thought they were 2N2222 so I even wrote wrong in my opening  post, which I don't know why I cannot modify anymore). On the contrary, I was previously convinced that the higher the HFE the better, because of the closeness to unity gain. I didn't "want" to discover the need of that resistor to ground after the output cap. I didn't "want" to discover I prefer the PN2222A over the 2N3904 (both relatively low gain), I didn't even expected to hear differences, it just happened, but I continued hearing those exact differences and I continued favoring the first. So, yes, I could do a blind test now and still tell you what I prefer. And no, I won't build an A/B box to compare two transistors because tolerances exist, and I just want to hear one different component if I have to judge its role in the circuit.
Lastly, before I manage to do some recordings, you are invited to build a buffer and swap transistors/components values... and then come back here and say "man, I have to tell you, I was wrong, I can definitely hear differences, too!" 

[bool]

A different wording: in case of a simple buffer, input signal is going to dynamically modulate a BJT's transfer curve (unless it's loaded with a canonical ideal CCS) and as a result of these factors the input impedance (reflected back to BJT's base) is going to be dynamically modulated as well (a bit simplified but hey).

You arent getting as much of these influences with a jfet or a mosfet buffer - or a fet opamp.

In short, the "right" bjt will play with you, the wrong bjt will play against you.

[shredgd]

So, finally, this is for the sceptical ones.

I recorded a couple of clips and converted them into a youtube video.
First of all, I realized I had something wrong with my cables when I first tested the metal can 2N2222: it indeed sounds as good and sweet as the PN2222A I have. Therefore I'm going to edit my previous posts where I wrote about not-stellar results with ii. Actually the metal can 2N2222 is the one featured in this video.

Please use a good pair of headphones/speakers to listen to the tones: we're talking about subtle differences, not Marshall vs Mesa Boogie

Notice that although the BC549B has more bass, probably due to its higher hFE of 370 (you hear it with the bridge pickup), the 2N2222 (hFE 255) has a much sweeter midrange, lively sound, more twang with the neck singlecoil and more attack. The BC549B gives a compressed note attack, which sounds dreadful in neck position.

Edit: fine, I cannot edit my previous post anymore, maybe because they received replies.

[bool]

Perhaps (perhaps not) you'd dig 2N5551 or a MPSA06. (both plastic)

But hey you've got a metal-can 2222 already; that's a lot of vintage cool and mojo there.

[shredgd]

Perhaps (perhaps not) you'd dig 2N5551 or a MPSA06. (both plastic)

But hey you've got a metal-can 2222 already; that's a lot of vintage cool and mojo there.

Ahahah, my other two pedalboards will still have the plastic PN2222A... the metal can transistors are messy with my ultra-compact layouts because they touch everywhere! 

[pee-j]

1M and up will be very bright, while 150k will sound more like the passive guitar unbuffered, but then the low output impedance of the buffer will drive the rest of the signal chain, and all buffers isolate your guitar from further signal degradation.

this is such an amazing concept! not to mention that it has been tried!!

thank you!

PS: if you read this, what buffer did you put in your '73 bass in '77?

[Steben]

So, finally, this is for the sceptical ones.

I recorded a couple of clips and converted them into a youtube video.
First of all, I realized I had something wrong with my cables when I first tested the metal can 2N2222: it indeed sounds as good and sweet as the PN2222A I have. Therefore I'm going to edit my previous posts where I wrote about not-stellar results with ii. Actually the metal can 2N2222 is the one featured in this video.

Please use a good pair of headphones/speakers to listen to the tones: we're talking about subtle differences, not Marshall vs Mesa Boogie

Notice that although the BC549B has more bass, probably due to its higher hFE of 370 (you hear it with the bridge pickup), the 2N2222 (hFE 255) has a much sweeter midrange, lively sound, more twang with the neck singlecoil and more attack. The BC549B gives a compressed note attack, which sounds dreadful in neck position.

Edit: fine, I cannot edit my previous post anymore, maybe because they received replies.

Aaaaaaaaaaaaand ..... no I have to repeat. Can't hear any difference. But I am over 20 so my ears are deteriorating.
What I'ld like to add is there IS a numerical difference: a different hFE. This means you should take that into account. That hFE changes a lot of things.
So better would be comparing a BC549 with a 2N2222 both with a hFE around 250...