Usefulness of buffer
I have a question.
I realized some pedals don't have buffers.
One of the biggest purpose of buffer is to provide large input impedence and isolate the circuit inside.
However wouldn't taking buffer out and putting a large resistor achieve same result?
I heard that it has something to do with noise and curret gain.
Wouldn't taking out buffer results in more "transparent" sound?
Well.. I don't think a buffer would make a noticeable difference.. but still..
I realized some pedals don't have buffers.
One of the biggest purpose of buffer is to provide large input impedence and isolate the circuit inside.
However wouldn't taking buffer out and putting a large resistor achieve same result?
I heard that it has something to do with noise and curret gain.
Wouldn't taking out buffer results in more "transparent" sound?
Well.. I don't think a buffer would make a noticeable difference.. but still..
How would a large resistor do the same thing? If you mean a large parallel resistor, then the resistor might as well not be there, the circuit will still suck treble if it is so inclined.shicky wrote:One of the biggest purpose of buffer is to provide large input impedence and isolate the circuit inside.
However wouldn't taking buffer out and putting a large resistor achieve same result?
If you mean a large *series* resistor, it does indeed give large input impedance and isolation of the circuit inside. But it also cuts the signal down hugely, in the ratio of the resistor and the circuit it's feeding. The bigger the series resistor, the smaller the signal that gets through.
And, by the way, the more thermal noise the series resistor generates.
I get a little nuts when people hear things on the internet, like the factoids drifted in on the wind like pollen.shicky wrote:I heard that it has something to do with noise and curret gain.
It's got a lot to do with noise. And a resistor has no current gain. Buffers do. So a buffer can take the input voltage, multiply its current, and not load down the signal source.
How, exactly?shicky wrote: Wouldn't taking out buffer results in more "transparent" sound?
And while we're at it, can you define exactly what "transparent" means?
Well designed buffers are inaudible in terms of noise and distortion. They are VERY audible in terms of keeping treble from being sucked out by loading.shicky wrote: Well.. I don't think a buffer would make a noticeable difference.. but still..
Sorry for being unclear. For an opamp based overdrive with soft clipping, you can put large parallel resistor before clipping stage. Timmy circuit for example. But now I think of it, it would affect the gain of the clipping stage... Sorry for asking a stupid question.How would a large resistor do the same thing? If you mean a large parallel resistor, then the resistor might as well not be there, the circuit will still suck treble if it is so inclined.
Well, of course resistor can't have current gain.It's got a lot to do with noise. And a resistor has no current gain. Buffers do. So a buffer can take the input voltage, multiply its current, and not load down the signal source.
I am an electrical engineer student but a noob
Ya, I know that its kind of vague term.. or wrong term.And while we're at it, can you define exactly what "transparent" means?
I used it to describe something that is not muddy. (losing treble perhaps)
In fact, some electronic components for audio applications are advertised or known as "transparent".
When I was playing with circuits, I noticed that buffer does matter.Well designed buffers are inaudible in terms of noise and distortion. They are VERY audible in terms of keeping treble from being sucked out by loading.
I just wanted to know some disadvantages of having a buffer.
In fact, transistor buffers output is only about 30% of an input signal and opamp buffer output is about 96% of the input.
( depending on the type of transistors and opamps )
By having 10 or so buffers on the signal path, it might alter the signal.
Well, I am not really a tone-freak so I wouldn't know for sure.
Thank you for clearing things out by the way.
Information
Where is this resistor in the Timmy schem ? I see only a 510k to Vref biassing resistor.you can put large parallel resistor before clipping stage. Timmy circuit for example.
S'OK. We were all there.shicky wrote:Well, of course resistor can't have current gain.
I am an electrical engineer student but a noob
OK, I'll accept that. That particular term sets me off. People who wouldn't know a phone jack from a pillbox get really picky about how transparent one heavy metal distortion compared to another.Ya, I know that its kind of vague term.. or wrong term.
I used it to describe something that is not muddy. (losing treble perhaps)
In fact, some electronic components for audio applications are advertised or known as "transparent".
You pass.
(a) Cost (b) smallish added noise (c )removing artifacts you might have liked, like a buffer before a fuzz face is not always good because it's a sound you didn't expect.I just wanted to know some disadvantages of having a buffer.
You do need to go look that one up again. Transistor emitter followers can have voltage gains of 0.96 to 0.99 depending. Opamp buffer gain depends on frequency, but at low audio, gains of 0.999... for followers are common. I'm particularly worried about who told you transistor followers only "followed" to 30%. Whomever it was either had a set of special conditions they didn't tell you, or did not themselves know. Even the perennial follower loser, the triode, is about 85-90% depending on tube.In fact, transistor buffers output is only about 30% of an input signal and opamp buffer output is about 96% of the input.
That is a real, valid concern. Noise build up is the major problem with opamp buffers. If you're using JFET source followers or tube cathode followers, you may get a build up of lowered gain, as 0.9*0.9*0.9*0.9... gets small after a while.By having 10 or so buffers on the signal path, it might alter the signal.
What what your profs tell you. Some of them really do know. The others? Sigh...