Question about volume, detail and a Class A/B amplifier
Apr 1, 2015 11:56:16 GMT -5
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Post by KeithL on Apr 1, 2015 11:56:16 GMT -5
Exactly, there seems to be a whole lot of "audiophile mystique" about gain stages, and output stages, and such things - and those things are really not nearly as complicated as a lot of audiophiles seem to think.
When you look at a preamp like our XSP-1, it can be a pretty complicated device, and we have the schematics to prove it. However, the vast majority of that complexity is because of the extra features it has - like input selectors, and tone controls, and level controls, and firmware, and displays, and the phono preamp, and even things like the nice cabinet and the buttons.... If you look at the design of a "basic line stage", which doesn't have all of those extra features, it's really VERY simple. I'm not kidding or exaggerating.... the actual part of the circuitry that takes the line level signal and boosts it by 15 or 20 dB consists of a few dozen parts that will fit on a PCB about an inch square. It's all the other stuff, like the controls, and the cabinetry, and the power supply to run the fancy bits, that add all the size, complexity, and cost. (Of course, companies who sell super-expensive "line-stage" preamps with no features would obviously like you to imagine that there's some sort of magic involved that justifies what they charge. The parts cost $10; it's the magical knowhow of how to connect them together that you're paying the other $19,995 for. )
With a device like the Oppo, the output of the DAC chip itself is not designed to drive an interconnect cable, or another component, directly. Therefore, it requires some sort of "buffer" or "line stage". If I set the gain of that line stage to 0 dB, then it's usually referred to as "a buffer"; if I set the gain to 20 dB instead, then we might refer to it as a "preamp". Basically, though, the difference is in what values I pick for the four fifty-cent resistors that set the gain. (It's not like delivering 20 dB of gain, without altering or degrading the signal in any audible way, is all that hard... it really isn't. If you didn't want all the features, and didn't need to worry about input and output connectors, and selector switches, and good quality volume controls, and cases for shielding, and all you wanted was 20 dB of audio gain, you could make a perfectly lovely sounding "line stage" that would fit in a matchbox.... and sell it for $20 at a nice profit. (Make no mistake, it's not at all difficult to screw it up badly enough that it will in fact sound bad; however, any competent engineer should know enough to avoid doing that.)
Tube preamps are a slightly different story for two main reasons. First, tubes are intended to change the sound. (Say what you like, but very few people would buy tube preamps if they sounded exactly like solid state ones; and there is no technical superiority to using tubes.) Second, in design terms, tubes are somewhat more "needy" than solid state components. By that I mean that you need to take a little more care when designing with tubes if you want to get good performance from them. Tubes have basic power supply requirements that are more expensive to meet than solid state components, and are more sensitive to things like how they're wired and how good their power supply is, so you need to spend a bit more time and effort on the stuff that goes with them.
Either way, in principle, and not counting the changes you deliberately make with things like tone trims, a preamp should NOT alter the sound in any way (the original, and still popular, quote is "a straight wire with gain"). In some specific situations, due to the particular output and input characteristics of the components involved, and even of the interconnects that go between them, adding a preamp in-between may make a slight difference in sound. However, in most cases, you should NOT expect it to do so.
If you use the balanced outputs you get common mode rejection.
If you use the RC jacks you don't so you will lose some of your S/N ratio. I doubt you will notice it, but there is that.
Because 32bits is so much wider than any music sources dynamic range, there is no impact on the sound possible with the digital volume.
So I believe the only thing left that could possibly impact the sound is impedance matching. OPPO claims that anything between 10kohm and 100kohm will work with 47kohm being ideal. They implied it had more of an impact on how much volume (0-100) you needed to select reach a certain listening volume level than over the sound quality.
I won't discount the possibility of a 33kohm vs. a 47ohm impedance having some impact on the sound quality.
Any amplifier with a 47 or 50kohm impedance should sound identical to a properly matched preamplifier that had no impact on the sound.
That said, if you like the feel of an analog knob, it like any other subjective thing will feed into how you perceive what you are listening to. It is very nebulous, and without someone else touching all the equipment in a blind A/B testing at identical volume levels it would be hard to do an objective comparison.
The kicker is that I don't believe I would hear a difference if I hooked up a preamplifier and that alone would impact my perception as well. Psychologically I would be much more likely to not notice a difference even if there were one because it would conflict with my current opinion.
When you look at a preamp like our XSP-1, it can be a pretty complicated device, and we have the schematics to prove it. However, the vast majority of that complexity is because of the extra features it has - like input selectors, and tone controls, and level controls, and firmware, and displays, and the phono preamp, and even things like the nice cabinet and the buttons.... If you look at the design of a "basic line stage", which doesn't have all of those extra features, it's really VERY simple. I'm not kidding or exaggerating.... the actual part of the circuitry that takes the line level signal and boosts it by 15 or 20 dB consists of a few dozen parts that will fit on a PCB about an inch square. It's all the other stuff, like the controls, and the cabinetry, and the power supply to run the fancy bits, that add all the size, complexity, and cost. (Of course, companies who sell super-expensive "line-stage" preamps with no features would obviously like you to imagine that there's some sort of magic involved that justifies what they charge. The parts cost $10; it's the magical knowhow of how to connect them together that you're paying the other $19,995 for. )
With a device like the Oppo, the output of the DAC chip itself is not designed to drive an interconnect cable, or another component, directly. Therefore, it requires some sort of "buffer" or "line stage". If I set the gain of that line stage to 0 dB, then it's usually referred to as "a buffer"; if I set the gain to 20 dB instead, then we might refer to it as a "preamp". Basically, though, the difference is in what values I pick for the four fifty-cent resistors that set the gain. (It's not like delivering 20 dB of gain, without altering or degrading the signal in any audible way, is all that hard... it really isn't. If you didn't want all the features, and didn't need to worry about input and output connectors, and selector switches, and good quality volume controls, and cases for shielding, and all you wanted was 20 dB of audio gain, you could make a perfectly lovely sounding "line stage" that would fit in a matchbox.... and sell it for $20 at a nice profit. (Make no mistake, it's not at all difficult to screw it up badly enough that it will in fact sound bad; however, any competent engineer should know enough to avoid doing that.)
Tube preamps are a slightly different story for two main reasons. First, tubes are intended to change the sound. (Say what you like, but very few people would buy tube preamps if they sounded exactly like solid state ones; and there is no technical superiority to using tubes.) Second, in design terms, tubes are somewhat more "needy" than solid state components. By that I mean that you need to take a little more care when designing with tubes if you want to get good performance from them. Tubes have basic power supply requirements that are more expensive to meet than solid state components, and are more sensitive to things like how they're wired and how good their power supply is, so you need to spend a bit more time and effort on the stuff that goes with them.
Either way, in principle, and not counting the changes you deliberately make with things like tone trims, a preamp should NOT alter the sound in any way (the original, and still popular, quote is "a straight wire with gain"). In some specific situations, due to the particular output and input characteristics of the components involved, and even of the interconnects that go between them, adding a preamp in-between may make a slight difference in sound. However, in most cases, you should NOT expect it to do so.
The OPPO's DAC's are taking the digital signal and creating an analog ~ 2V signal no matter what you do with it.
If you use the balanced outputs you get common mode rejection.
If you use the RC jacks you don't so you will lose some of your S/N ratio. I doubt you will notice it, but there is that.
Because 32bits is so much wider than any music sources dynamic range, there is no impact on the sound possible with the digital volume.
So I believe the only thing left that could possibly impact the sound is impedance matching. OPPO claims that anything between 10kohm and 100kohm will work with 47kohm being ideal. They implied it had more of an impact on how much volume (0-100) you needed to select reach a certain listening volume level than over the sound quality.
I won't discount the possibility of a 33kohm vs. a 47ohm impedance having some impact on the sound quality.
Any amplifier with a 47 or 50kohm impedance should sound identical to a properly matched preamplifier that had no impact on the sound.
That said, if you like the feel of an analog knob, it like any other subjective thing will feed into how you perceive what you are listening to. It is very nebulous, and without someone else touching all the equipment in a blind A/B testing at identical volume levels it would be hard to do an objective comparison.
The kicker is that I don't believe I would hear a difference if I hooked up a preamplifier and that alone would impact my perception as well. Psychologically I would be much more likely to not notice a difference even if there were one because it would conflict with my current opinion.
