mzy12
Active member
Thanks for clarifying, that makes sense
Understanding the Cornish style buffer (C-Buffer)
- Thread starter mzy12
- Start date
aquataur
New member
The principle of a bootstrapped device is actually quite simple to understand.
Cornish buffers are emitter followers, meaning they have a voltage gain close to one. On emitter followers, the signal is taken from the emitter and it is nearly a 1:1 copy of the input. A suitably large capacitor will convey any voltage change on the emitter back to the base, which is why both of them "see" the same voltage. No voltage change means no current change. No current change means infinite resistance.
Note: this is only valid for a signal change, not for static conditions.
What "AC" means in this therm is determined by the size of the bootstrapping capacitor obviously.
Cornish describes a scenario in his case against true bypass that probably will not affect 95% of us guys here.
That said, I am a long time promoter of buffering, but where necessary (and it is necessary in the scenario Cornish describes).
It is true that very many pedals have a too low impedance. Fuzz faces and derivatives are notorious for that, and should and can be fixed.
The purported "sterile tone" is just lack of understanding of the problem.
On the above linked page he writes:
Excuse me, but this is applied a bit thickly for my taste, to put it mildly (probably to highlight its superiority)
Provided he talks about the same circuit as we here,
The principle is proven working, which is why he uses it.
OP-amps principally work, but with today's flood of OPA's and their touted all-around superiority (and probably programmed obsolescence)
you have no time to gain experience on their overload recovery behavior, their headroom, their clipping mechanism and so on. We do not know how well the input is protected against spikes.
Note that the op-amp follower shown here somewhere will not work in the bare-bone configuration shown. It needs a bias, it has no RF protection etc. Very many schematics available do not provide any such protection.
With all this ado about keeping the signal pristine, one problem I never saw mentioned in this context is that the signal degrades, as soon as it leaves the guitar. Although a bit cumbersome in practise, the signal should be buffered right at the guitar, or tone will be degraded by the time it hits the first input. And this applies regardless of the subsequent device, even if it were a tube amp grid. The cable capacity has done its job.
Edit: The "C"-Buffer or the "K"-Buffer are highly regarded. They sound so good. This is entirely ridiculous. You will never hear any buffer. What you hear is the absence of the gremlins it just saved you from. Somebody even sells a K/C buffer.
Note that the cherished K-Buffer does not have any RF protection.
While the point Cornish brings up might be debatable, the double buffering appears a total overkill to me. What is not debatable is that many circuits and maybe a Muff too have a too low input impedance and do benefit from a buffered front-end, true bypass or not.
Hope this helps.
Cornish buffers are emitter followers, meaning they have a voltage gain close to one. On emitter followers, the signal is taken from the emitter and it is nearly a 1:1 copy of the input. A suitably large capacitor will convey any voltage change on the emitter back to the base, which is why both of them "see" the same voltage. No voltage change means no current change. No current change means infinite resistance.
Note: this is only valid for a signal change, not for static conditions.
What "AC" means in this therm is determined by the size of the bootstrapping capacitor obviously.
Cornish describes a scenario in his case against true bypass that probably will not affect 95% of us guys here.
That said, I am a long time promoter of buffering, but where necessary (and it is necessary in the scenario Cornish describes).
It is true that very many pedals have a too low impedance. Fuzz faces and derivatives are notorious for that, and should and can be fixed.
The purported "sterile tone" is just lack of understanding of the problem.
On the above linked page he writes:
Excuse me, but this is applied a bit thickly for my taste, to put it mildly (probably to highlight its superiority)
Provided he talks about the same circuit as we here,
- I do not see what is so extraordinary about it, although its components are certainly chosen with care for low noise and max. headroom.
- 1 Mohm is nothing extraordinary. 20pF is not needed, any length of cable will soon have several hundreds of pF.
- The highly efficient RF filter is a mere capacitor chosen big enough to roll off all RF frequencies (note that the small cap on the base will cancel out too...)
- Low output impedance... any old follower can do that. A few 100 Ohms are plenty low enough.
The principle is proven working, which is why he uses it.
OP-amps principally work, but with today's flood of OPA's and their touted all-around superiority (and probably programmed obsolescence)
you have no time to gain experience on their overload recovery behavior, their headroom, their clipping mechanism and so on. We do not know how well the input is protected against spikes.
Note that the op-amp follower shown here somewhere will not work in the bare-bone configuration shown. It needs a bias, it has no RF protection etc. Very many schematics available do not provide any such protection.
With all this ado about keeping the signal pristine, one problem I never saw mentioned in this context is that the signal degrades, as soon as it leaves the guitar. Although a bit cumbersome in practise, the signal should be buffered right at the guitar, or tone will be degraded by the time it hits the first input. And this applies regardless of the subsequent device, even if it were a tube amp grid. The cable capacity has done its job.
Edit: The "C"-Buffer or the "K"-Buffer are highly regarded. They sound so good. This is entirely ridiculous. You will never hear any buffer. What you hear is the absence of the gremlins it just saved you from. Somebody even sells a K/C buffer.
Note that the cherished K-Buffer does not have any RF protection.
While the point Cornish brings up might be debatable, the double buffering appears a total overkill to me. What is not debatable is that many circuits and maybe a Muff too have a too low input impedance and do benefit from a buffered front-end, true bypass or not.
Hope this helps.
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aquataur
New member
I just found this here from JHS pedals: Understanding Buffers
And this is closer to the truth IMHO.
That said, you may ask yourself: "from when on do I experience tone loss?"
From the moment the signal leaves your guitar. The lower your drive impedance is, the more it can drive without loss becoming apparent. (Note: there is always loss, but you can stop it from becoming apparent too early.)
This brings us back to the point I made earlier: the best insurance is to have a buffer either inside the guitar or immediately after it.
And if somebody claims this ruins your tone - you did not take the time to try to understand the problem. I have been going on at length about this on my web pages, and none of my fellow musicians ever felt my tone were ruined by buffering properly.
Thinking about the double Cornish buffer again... I should have mentioned that I refer to the circuit AIONFX has traced, which eventually peaked in their HALO deluxe kit. This schematic obviously is the result of a BMP pedal Cornish re-worked. Naturally, Pete did not comment his work, so the double buffering very likely has other reasons than achieving a ridiculously high input impedance. Maybe he incorporated a splitter or whatever. We cannot know, but two stacked high impedance buffers just make no sense for preserving signal quality even in the most stringent environments.
And this is closer to the truth IMHO.
That said, you may ask yourself: "from when on do I experience tone loss?"
From the moment the signal leaves your guitar. The lower your drive impedance is, the more it can drive without loss becoming apparent. (Note: there is always loss, but you can stop it from becoming apparent too early.)
This brings us back to the point I made earlier: the best insurance is to have a buffer either inside the guitar or immediately after it.
And if somebody claims this ruins your tone - you did not take the time to try to understand the problem. I have been going on at length about this on my web pages, and none of my fellow musicians ever felt my tone were ruined by buffering properly.
Thinking about the double Cornish buffer again... I should have mentioned that I refer to the circuit AIONFX has traced, which eventually peaked in their HALO deluxe kit. This schematic obviously is the result of a BMP pedal Cornish re-worked. Naturally, Pete did not comment his work, so the double buffering very likely has other reasons than achieving a ridiculously high input impedance. Maybe he incorporated a splitter or whatever. We cannot know, but two stacked high impedance buffers just make no sense for preserving signal quality even in the most stringent environments.
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