Accuphase Amplifiers: Damping Factor

[ticten777]

Hi All,

Accuphase is a brand that I have never owned but I get good vibes from them. I owned a Luxman 509X before. My question is: damping factors for pure class A amps tend to be on the low side and there seems to be a theoretical limit on how much global feedback you can use to improve damping factor for those amps (and indirectly I am assuming that bass performance improves in tautness and quality, I might be wrong). The reason is that excessive global feedback introduces distortion, and you need to strike a balance on how much is appropriate. Can anyone shed some light on this, in relation to your listening impressions? is it too good to be true that an amp like E-800 produces 50 watts pure Class A power with 1000 damping factor? Thanks!!!

 

[cloudhead]

Well, damping factor is also very much about reducing internal impedance in the amplifier, and Accuphase are improving their internal components with each iteration, swapping out higher impedance parts with lower impedance ones as they become available, which increases the damping factor with each new generation.

Just keep in mind that beyond ~300-400, increases in damping factor are not audible[1].

[1]: https://benchmarkmedia.com/blogs/application_notes/audio-myth-damping-factor-isnt-much-of-a-factor

 

[analogsa]

The reason is that excessive global feedback introduces distortion, and you need to strike a balance on how much is appropriate.

High NFB certainly does not generate more distortion, quite the opposite. Whether it sounds better is a different matter.

Personally, i prefer Df in the region of 50 but we all have different speakers and tastes. Whether Df above 100 is at all beneficial for bass is very debatable.

No idea which are the mysterious low Df Accuphase amps, they don't seem to go below 200, but i may be mistaken. Their class AB amps have bipolar outputs, while the class A are all mosfet. This may be one reason for the discrepancy in Df as bipolars have a higher transconductance. This assumes comparing amps with equal number of output devices and generally similar topologies. A bridged output will be inferior with respect to Df. It is also possible the class A amps have less Nfb, but i have not examined this.

Btw, Nfb and piling up parallel output devices is not the only way to obtain a high Df; positive current feedback is another.

 

[analogsa]

Well, damping factor is also very much about reducing internal impedance in the amplifier, and Accuphase are improving their internal components with each iteration, swapping out higher impedance parts with lower impedance ones as they become available, which increases the damping factor with each new generation.

This concerns their protection circuits which in more recent years have migrated from relays to solid state switches. Indeed, this brings a minor increase in Df. Many other manufacturers prefer not having a protection circuit in series with the output at all.

 

[ticten777]

Thanks for your replies!