Output capacitor: subjective and objective views?

[Gordy]

Capacitors are used at the outputs of some pre and power amplifier designs to block DC offset. Some people have the opinion that these capacitors can be subjectively detected and that they ‘do not sound good’. I would like to ask for your opinion on the subject…

> Preamplifier:

Have you changed a circuit to replace an output capacitor with a DC servo, and if so what was the subjective difference?

Have you made objective distortion measurements with and without the capacitor… any difference?


> Power amplifier:

Large value electrolytic capacitors are placed at the output of single ended transistor amplifiers that use single supply voltages…

Have you heard amplifier designs with electrolytic output coupling capacitors (your own designs or commercial)... what was your opinion of the performance with these capacitors in the circuit?

[bob91343]

I don't believe there is any audible difference. That said, the main reason for using such a circuit is for economy. It only requires a single power supply, mainly.

The capacitor itself is important but most modern units are just fine. There needs to be feedback around the capacitor, not from its input.

[bobodioulasso]

I don't believe there is any audible difference

So do i, provided , in case of an electrolytic, that some consequent dc voltage is present across the cap.
Which is the case of a single supply output stage.

[Mooly]

I use a DC servo on my power amp... which is single ended, DC coupled running on split supplies.
http://focus.ti.com/lit/an/sboa092a/sboa092a.pdf

I have built several AC oupled amps over the years and never had cause to suspect the coupling cap was doing anything to the sonics.

Caps in preamps are transparent if the design is right. I have no issues at all with using them.

Built a Radford HD250, that was single ended.

[Bigun]

my recent experiences are here (and quoted below)

TGM2 amplifier

Output Capacitor: just for interest, and although not needed, I thought I'd listen to the amplifier through an output capacitor. I found that the bass was noticeably worse off through a 220uF Nichicon MUSE. But through a 2,200uF Nichicon MUSE the bass was fine. I also tried a 10,000uF Nichicon HE cap. Overall I was hard pressed to hear a difference between the use of the two larger capacitors but I could hear a very subtle difference between cap and no cap. The output without a capacitor seemed to have just a tad more 'space' around the upper mids. That's about all I know how to explain what I heard. I concluded that I could be happy with an amplifier that used an output cap.

[PMA]

Even input non-polarized coupling capacitors are audible, you can hear a difference between polyester (mylar) and polypropylene, of course depending on resolution of the whole system.

[EBM_dude]

Capacitors do funky stuff with the signal's phase. I *think* I can hear the difference between 4700µF caps and no caps on my TDA2030A amp.

[Telstar]

I hate passive components across the signal. I have speakers without crossovers and although i havent done proper tests, i'm sure that the effect of the ouput capacitor can be heard.

If it has to be used, bigger is usually better.

[bobodioulasso]

When looking at the output currents, the output cap of an amp is in the signal path the same way the supply caps are in the signal path in a symetrical supply.
Provided the output cap is big enough, it has no influence.

[Bigun]

Originally Posted by bobodioulasso

When looking at the output currents, the output cap of an amp is in the signal path the same way the supply caps are in the signal path in a symetrical supply.
Provided the output cap is big enough, it has no influence.

I agree that even without a dc coupling cap on the output you still have capacitors in the signal path because of the PSU. However, doesn't mean that it's good for sound. There are many reports (look at the Class A web site dedicated to JLH) of people improving the sound by swapping out the PSU caps with higher quality units.