Re the sub-thread about the Ref3 sounding dull and bland, and whether or not that can be attributed to impedance mismatches between preamp and power amp, I agree with Tvad, at least in the context of his XA60.5's.
A balanced output impedance that, per John Atkinson's measurements, is 635 ohms in the treble and mid-range, and rises to 1437 ohms at 20Hz, will not have any audibly significant consequences working into a 30K balanced input impedance. Especially given that the 30K is "constant across the audio band."
Putting it quantitatively, the effect of the rise to 1437 ohms will be an attenuation at 20Hz of less than 0.2db relative to the impedance-related attenuation at mid and high frequencies. The attenuation at higher bass frequencies, relative to mid and high frequencies, would rapidly fall off to considerably less than 0.2db.
That is simply not audible, and even if it were audible it would not correlate with a subjective perception of dullness and blandness (which would relate to effects at much higher frequencies than 20Hz).
The 635 ohm output impedance at high frequencies might be marginally significant, however, if cable capacitance is extremely high. A long length of very high capacitance cable (say 25 feet at 100 pf/foot) would produce a very slight but perhaps audible amount of upper treble rolloff. That would have nothing to do with the power amplifier, though.
Mapman, your LS16 preamp appears to have an output impedance which is considerably lower even than the REF3's. And your Bel Canto's appear to have little similarity to your prior Musical Fidelity amp beyond the fact that they are both solid state. I would not attribute any of the sonic differences you perceived between the two amps to their differing input impedances. To the extent that those sonic differences relate to interface characteristics (as opposed to the undoubtedly considerable internal differences), their output characteristics (damping factor, current and power capability) are probably much more significant.
Pubul57, re your question about why solid state amps are often not designed to have higher input impedances, I can't offer too much in the way of specifics. But a general answer would be that transistors are inherently low impedance devices that require significant current drive, compared to tubes which are inherently high impedance devices that are voltage driven and require minimal input current. It is certainly possible to design a solid state amplifier with very high input impedance, but the choices of device types and circuit topologies would figure to be significantly limited by that constraint. And in most situations a 30K or 50K input impedance is good enough.
Tvad, thanks for the nice words.
Best regards,
-- Al
A balanced output impedance that, per John Atkinson's measurements, is 635 ohms in the treble and mid-range, and rises to 1437 ohms at 20Hz, will not have any audibly significant consequences working into a 30K balanced input impedance. Especially given that the 30K is "constant across the audio band."
Putting it quantitatively, the effect of the rise to 1437 ohms will be an attenuation at 20Hz of less than 0.2db relative to the impedance-related attenuation at mid and high frequencies. The attenuation at higher bass frequencies, relative to mid and high frequencies, would rapidly fall off to considerably less than 0.2db.
That is simply not audible, and even if it were audible it would not correlate with a subjective perception of dullness and blandness (which would relate to effects at much higher frequencies than 20Hz).
The 635 ohm output impedance at high frequencies might be marginally significant, however, if cable capacitance is extremely high. A long length of very high capacitance cable (say 25 feet at 100 pf/foot) would produce a very slight but perhaps audible amount of upper treble rolloff. That would have nothing to do with the power amplifier, though.
Mapman, your LS16 preamp appears to have an output impedance which is considerably lower even than the REF3's. And your Bel Canto's appear to have little similarity to your prior Musical Fidelity amp beyond the fact that they are both solid state. I would not attribute any of the sonic differences you perceived between the two amps to their differing input impedances. To the extent that those sonic differences relate to interface characteristics (as opposed to the undoubtedly considerable internal differences), their output characteristics (damping factor, current and power capability) are probably much more significant.
Pubul57, re your question about why solid state amps are often not designed to have higher input impedances, I can't offer too much in the way of specifics. But a general answer would be that transistors are inherently low impedance devices that require significant current drive, compared to tubes which are inherently high impedance devices that are voltage driven and require minimal input current. It is certainly possible to design a solid state amplifier with very high input impedance, but the choices of device types and circuit topologies would figure to be significantly limited by that constraint. And in most situations a 30K or 50K input impedance is good enough.
Tvad, thanks for the nice words.
Best regards,
-- Al