I have built a couple of NIGC's from BrianGT's kits and some speakers. But, I have no idea why I would need a buffer stage.
Help me understand this.
Help me understand this.
I am not familiar with this amp circuit but a buffer usually refers to impeadence matching. Perhaps the input inpeadence of this circuit is lower than what a typical pre-amp circuit outputs, and some type of emitter folower type circuit is needed to lower the impeadence. Other than this...😕 😕 😕
I agree with Cunningham. A buffer is also required to avoid capacitive loading of a source with high output impedance by the cable used to connect it to the power amp. Some of these 'special' cables have a relatively high capacitance per unit length so might exerbate the problem. (One good reason to avoid the 'special' cables. The other could be the outrageous price 😉 ).
With sources like CD players or SS preamps this very seldom is a problem. A buffer may be required with tube-output CD players or preamps, or when you are driving poweramps with relatively low input impedance (less than a few k or so).
It is my understanding that sometimes people use buffers to change the character of their sound system. That is of course a valid reason, but the buffer is not required for technical reasons in such a case.
Jan Didden
With sources like CD players or SS preamps this very seldom is a problem. A buffer may be required with tube-output CD players or preamps, or when you are driving poweramps with relatively low input impedance (less than a few k or so).
It is my understanding that sometimes people use buffers to change the character of their sound system. That is of course a valid reason, but the buffer is not required for technical reasons in such a case.
Jan Didden
A preamp is usually a voltage feedback amplifier, which is very sensative to capacitive loading. Square wave response will show very significant overshoot. I guess this is why cables make differences. A buffer does not have overall volatge feedback path, and usually has more graceful response to high capacitive loading. Inserting a buffer stage thus will usually make the response more close to what you want.
I guess you refer to some 'naked' VF opamps., driven by laboratory grade high-speed square-wave generators.
A competently designed preamp or source, IC or discrete, has no problems with anything but insanely large cables capacitances, and certainly no overshoot. I don't know of any musical instruments that give off square waves with very fast rise/fall times that cause ringing. Even if they exist, the source (analog or [filtered] CD) will not pass those fast edges anyway.
A buffer is totally superfluous here.
Jan Didden
A competently designed preamp or source, IC or discrete, has no problems with anything but insanely large cables capacitances, and certainly no overshoot. I don't know of any musical instruments that give off square waves with very fast rise/fall times that cause ringing. Even if they exist, the source (analog or [filtered] CD) will not pass those fast edges anyway.
A buffer is totally superfluous here.
Jan Didden
I think Jan is right that there is no square wave in music. Whereas I would think that the square wave response is a sign to indicate that the transient response has become worse, because the phase margin has decreased. If a preamp shows apparent overshoot for a square wave input, it is doubtful that it is in a good condition driving music signals. Inserting a buffer stage alleviates this doubt. And of course a buffer stage is not necessary if the pre amp is designed to drive capacitive load up to some possible value, say 2000pF.
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