Which buffer do you like?

[culturejam]

Is there a good location to view example applications of op-amps? It seems like a surprising number of big-name manufacturers used an example design in this fashion.

Here's one: https://www.sparkfun.com/datasheets/Components/General/LM358.pdf

Starts on page 11. "Klon buffer" is on page 13. There are a buttload of applicaiton circuits in that PDF (more than the usual op amp datasheet).

I've heard that both the Cornish and "opamp-in-the-klon" buffers are straight up Text Book buffers. Would love to find the old British data sheet or electronics mag that Cornish sourced-nicked-borrowed his design from.

There's only so many ways to make a buffer, and all of them come from textbooks and application notes on data sheets. The basic building blocks are spelled out by the semiconductor manufacturers so that people will know what they can do and want to buy them. No shame in reading the damn manual, you know. 

And to be fair to Bill F, I don't ever recall him saying that the Klon buffer was some kind of special sub-circuit that he invented. It's the Klon-worshipers that made that leap of faith.

As for Cornish, it looks to me like a simple BJT buffer (off the datasheet) but with the input impedance adjusted downward and some RC filtering going on at the output. Definitely not a "clean" buffer that seeks reproduce the input precisely. And that's probably why some people like it. The filtering/impedance adjust part is that makes it sound different, and I kinda doubt he copied that out of a textbook, since most books try to avoid signal degradation. Schematic is attached, and *yes* I did "steal" it from FSB. 

Same goes for overdrive and fuzz. You don't find that kind of thing in an electronics book or datasheet because the general idea with amplification is that it *doesn't* distort/clip the input signal.

[culturejam]

One more thing on Cornish...

When the G2 was traced, the schematic showed that the bypass setup is buffered all the time. And when the effect is on, there is also a fixed buffer on the effect circuit. So you have an input buffer with some filtering going into an input buffer with some filtering...going into a fancy Muff. Profit!!

[jimilee]

I mentioned the 2 buffers because they seem to be the ones people reference and use the most. I don't know that much about buffets as far as differences between them but I do understand what they do. I just didn't know if there was one that would be better matched for bass because of the frequencies.


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[culturejam]

I just didn't know if there was one that would be better matched for bass because of the frequencies.

Higher headroom is better for bass. At least as far as I understand things. So I would think an op amp buffer running at 18v would be optimal, but that's just a guess on my part.

[jubal81]

I just didn't know if there was one that would be better matched for bass because of the frequencies.

Higher headroom is better for bass. At least as far as I understand things. So I would think an op amp buffer running at 18v would be optimal, but that's just a guess on my part.

I was thinking that. If it's a standalone pedal, then there's plenty of room for that. Split supply and ground bias would squeeze a little more noise out of the system, too.

[jubal81]

I mentioned the 2 buffers because they seem to be the ones people reference and use the most. I don't know that much about buffets as far as differences between them but I do understand what they do. I just didn't know if there was one that would be better matched for bass because of the frequencies.


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R-C values on that workup more than plenty low to get all the bassy goodness.

[culturejam]

Yeah, actually running at +/-9V might be better than +18v with virtual ground. Would allow the use of more types of op amps and not have them running right at the upper limit of the positive rail max.

[thesameage]

I'd love that osh park layout to add to a compressor>fatpants pedal I'm building for bass.

[juansolo]

Is there a good location to view example applications of op-amps? It seems like a surprising number of big-name manufacturers used an example design in this fashion.

Here's one: https://www.sparkfun.com/datasheets/Components/General/LM358.pdf

Starts on page 11. "Klon buffer" is on page 13. There are a buttload of applicaiton circuits in that PDF (more than the usual op amp datasheet).

I've heard that both the Cornish and "opamp-in-the-klon" buffers are straight up Text Book buffers. Would love to find the old British data sheet or electronics mag that Cornish sourced-nicked-borrowed his design from.

There's only so many ways to make a buffer, and all of them come from textbooks and application notes on data sheets. The basic building blocks are spelled out by the semiconductor manufacturers so that people will know what they can do and want to buy them. No shame in reading the damn manual, you know. 

And to be fair to Bill F, I don't ever recall him saying that the Klon buffer was some kind of special sub-circuit that he invented. It's the Klon-worshipers that made that leap of faith.

As for Cornish, it looks to me like a simple BJT buffer (off the datasheet) but with the input impedance adjusted downward and some RC filtering going on at the output. Definitely not a "clean" buffer that seeks reproduce the input precisely. And that's probably why some people like it. The filtering/impedance adjust part is that makes it sound different, and I kinda doubt he copied that out of a textbook, since most books try to avoid signal degradation. Schematic is attached, and *yes* I did "steal" it from FSB. 

Same goes for overdrive and fuzz. You don't find that kind of thing in an electronics book or datasheet because the general idea with amplification is that it *doesn't* distort/clip the input signal.

We decided to make a CSOD with a buffer on to get around it's problems of operating like an old fuzz (doesn't like wah's/they don't like it, etc). Tried the Klon and it coloured the sound of the CSOD too much. Used the G2 buffer in the end and tweaked a few parts here and there (imp and filtering funnily enough) to get it to the point where it sounded right next to an unbuffered CSOD. It's a lot more handy in that sort of circumstance. Also the Klon one only seems to do bright, which isn't always what you want.

[samhay]

As for Cornish, it looks to me like a simple BJT buffer (off the datasheet) but with the input impedance adjusted downward and some RC filtering going on at the output. Definitely not a "clean" buffer that seeks reproduce the input precisely. And that's probably why some people like it. The filtering/impedance adjust part is that makes it sound different, and I kinda doubt he copied that out of a textbook, since most books try to avoid signal degradation...

Nope. The cap from the emitter to the bias resistor (C3) is there for bootstrapping and increases the input impedance. With a BJT with mid-high gain, you can get >1 M input impedance, which is as good as essentially all op-amp designs commonly used. The filtering is designed to be flat too.
It's a good design, and I very much doubt I could tell the difference between it and an op-amp buffer in a blind listening test...
Which leads me to my answer to the OP - use whatever you have handy as you probably can't tell the difference.

[sturgeo]

maybe like this?

credits to azilts/coldcraft

I like the adjustable output impedance, I keep meaning to breadboard an opamp buffer with switchable (via relay) impedance for the input section of a looper i'm working on... slowly. Any more details on the circuit?

[lars]

I find that this buffer adds incredible shine and sparkle...

[culturejam]

Nope. The cap from the emitter to the bias resistor (C3) is there for bootstrapping and increases the input impedance.

I was actually thinking of the interplay between C4, R7, R8, and R39 when I said "filtering at the output". But now that I look at it again, you're right. It's almost exactly flat.

So yeah, I guess the Cornish buffer really doesn't do much of anything other than act as a buffer. Which makes me wonder why he used so many parts to do what an op amp can do with half the parts?  Maybe it's part of the mystique of "Class A discrete buffer" that he talks about in marketing literature. Here's an interesting thread on the topic: http://www.diystompboxes.com/smfforum/index.php?topic=33241.0

[jubal81]

Nope. The cap from the emitter to the bias resistor (C3) is there for bootstrapping and increases the input impedance.

I was actually thinking of the interplay between C4, R7, R8, and R39 when I said "filtering at the output". But now that I look at it again, you're right. It's almost exactly flat.

So yeah, I guess the Cornish buffer really doesn't do much of anything other than act as a buffer. Which makes me wonder why he used so many parts to do what an op amp can do with half the parts?  Maybe it's part of the mystique of "Class A discrete buffer" that he talks about in marketing literature. Here's an interesting thread on the topic: http://www.diystompboxes.com/smfforum/index.php?topic=33241.0

If you're building at quantities, the cornish buffer is a lot cheaper, too.
Mouser pricing at quantity:
BC549: 4 cents
Resistors: 10 cents
Caps: 15 cents
Total: 28 cents


And these are parts he's already buying anyway, which makes a big difference.

[jubal81]

K, here's the updated version: