Diff in audio capacitors

[dumbears]

What are the differences between a normal capacitor and an audio capacitor? I never hear of Panasonic FC or Rubycon ZA are audio capacitor, but still there're quite a number of people are using them in their amps.

 

[tomb]

Quote:

Originally Posted by dumbears /img/forum/go_quote.gif What are the differences between a normal capacitor and an audio capacitor? I never hear of Panasonic FC or Rubycon ZA are audio capacitor, but still there're quite a number of people are using them in their amps.

One sounds good (audio cap), the other one doesn't (normal cap). Performance has little bearing on it, apparently, because the Pana FC's are great - Pana FM's even better. Both sound bad in the direct signal path, however.

 

[kipman725]

it depends on where in the circuit the capacitor how much bearing it has on the sound. If the capacitor is just smoothing in a power supply then it will have no bearing on the sound (which is lucky as such capacitors are usually large value and expensive!). If the capacitor is in the signal path it's brand and type will have alot of bearing on the final sound. however most well designed amplifiers don't need a dc blocking capacitor on the output. For the ones performing other functions in the circuit I am less sure of.

 

[splaz]

Audio electrolytics also usually have a poor capacitive density, so they'll be a lot larger than a 'normal' electrolytic.

 

[Rescue Toaster]

Quote:

Originally Posted by kipman725 /img/forum/go_quote.gif If the capacitor is just smoothing in a power supply then it will have no bearing on the sound (which is lucky as such capacitors are usually large value and expensive!).

Remember that in all single-ended amps the power supply carries the full signal current, and in balanced amps the supply still carries all the distortion products. In the numerous 'active ground' headphone amps, it carries a weird combination of the signal & distortion products of both channels. How big of an impact this will have varies from amp to amp. Even regulation in the supply can fail to isolate the sound of the filter caps.

 

[amb]

Quote:

Originally Posted by Rescue Toaster /img/forum/go_quote.gif Remember that in all single-ended amps the power supply carries the full signal current, and in balanced amps the supply still carries all the distortion products. In the numerous 'active ground' headphone amps, it carries a weird combination of the signal & distortion products of both channels. How big of an impact this will have varies from amp to amp. Even regulation in the supply can fail to isolate the sound of the filter caps.

That assumes class B or class AB operation. For class A this is mostly a non-issue, and for amps with high PSRR, even less so.

 

[Rescue Toaster]

All amps that ground the headphone's ground (cmoy style opamps, diamond buffers without a ground channel, and the dynatoob for instance) pass full AC signal current through the supply, the bias current doesn't change anything. Likewise with distortion products in a balanced amp and the combined distortion & uncancelled L/R signal in an active ground amp.

As for how good the PSRR is... I know at least one case where a mediocre electrolytic was audible even though there was a cascoded CCS 'isolating' it.

 

[amb]

Quote:

Originally Posted by Rescue Toaster /img/forum/go_quote.gif All amps that ground the headphone's ground (cmoy style opamps, diamond buffers without a ground channel, and the dynatoob for instance) pass full AC signal current through the supply, the bias current doesn't change anything.

What you describe is signal ground pollution and is why I and a few other designers around here favor active "buffered" ground amps over passive ground.

Quote:

Likewise with distortion products in a balanced amp and the combined distortion & uncancelled L/R signal in an active ground amp.

If the active ground channel is also class A, the return current from the L and R sides, even the uncancelled L/R component, will simply be sourced and sunk by the ground channel's output stage without varying its total draw from the supply rails. That's the nature of class A, where the quiescent current through the output stage is much higher than the output current, and any excess current that is not needed for output will just continue to flow through the output stage. This is also true in balanced amps where class A really saves the day. Hence, there should be little disturance on the rails. High PSRR will just be icing on the cake, making the amp virtually immune to what little perturbations there may be on the power rails.

Quote:

As for how good the PSRR is... I know at least one case where a mediocre electrolytic was audible even though there was a cascoded CCS 'isolating' it.

Without scientific proof this is merely conjecture. If you could actually measure signal degradation in this scenario even with high PSRR, then I'll buy it.

 

[ericj]

Quote:

Originally Posted by amb /img/forum/go_quote.gif What you describe is signal ground pollution and is why I and a few other designers around here favor active "buffered" ground amps over passive ground.

fwiw, near as i can tell from the available literature, Onkyo's "WRAT" Wide Range Amplifier Technology is pretty much just an active-ground topology, possibly in conjunction with a non-feedback amplifier topology. Something like a three-channel Kumisa III. But while their cartoonish diagrams certainly indicate an active ground, the only clue to a non-feedback topology is a single use of the "NFB" acronym.

Just thought I'd throw that out, as evidence that this topology is not just crazy-talk, it's used in the consumer industry as well.

I am not golden-eared, but my Onkyo 7.1 receiver does an admirable job of driving my 4-ohm ADS L810's. Better than my old Sony at least.