Hey,
I am beginner DIY audio enthusiast.
I found that all my audio stuff from factor have some output protection capacitors. And I realize that, they affecting sound so much.
It's always better to remove them.
Without them sound goes more vivid, natural and have a lot of space, even bass goes deeper and it's more precise.
Main question is. This is some kind of protection needed to achive RoHs or CE standard for selling on global market?
I know danger there is still possibility to damage something when accidently create shortcut in audio. But sound is so much better.
I don't doubt that sound is better without the capacitors, but capacitors in the signal line are protecting against DC voltage, which can burn out your headphones, your speakers, perhaps any device you choose to connect after those capacitors. Most tube amps start out with a positive bias voltage and if capacitors are not on the output, you could expose your equipment to hundreds of volts of DC - not a good thing - at all. OTL tube amps MUST be made this way. In fact, many are provided with a relay-delay circuit on the output connection, because despite the capacitors blocking DC on the output, those capacitors need time to charge when turning the amp on, otherwise, DC passes right through. This is bad and destructive enough that the few seconds it takes to charge the output capacitors is long enough to blow out speakers and headphones, if left plugged in.
Output transformer-coupled tube amplifiers need no capacitors on the output, but sometimes have inter-stage capacitors ahead of the transformer connection, where the capacitors do not have as much effect on the sound quality. Further, inter-stage capacitors can be made much smaller. Thus, much higher-quality film caps can be used, as opposed to the clunky, bad-sounding electrolytics required on the output of an OTL tube amp. This is because bass is filtered out by the RC circuit that's formed and if the capacitance or resistance is not large enough, that bass filtering occurs in the audible band. With output transformers, the inter-stage capacitors are seeing a resistance of 10,000 ohms or more at the transformers, a big difference from the 32 - 300 ohms typical for headphones (or 4-8 ohm speakers!).
In many high-voltage tube amps, capacitors also protect Human Safety in case of unpredictable failures that occur in the circuit.
At the inputs, capacitors are often placed to block DC from less-than-cleanly designed devices (see paragraph above for consequences without). This protects the device from DC damage if a cheap source with DC on the output is connected. Here in DIY, we rarely build anything with input capacitors - mostly because we know what we are connecting and usually have the tools to check if there is a DC offset on the device plugging in.
Output capacitors in non-tube amps are a different story. The fundamental reason they are used is that it's quite difficult to build an amplification circuit, without feedback, that has no DC offset. Sometimes you can make it work by very closely matching the parts to eliminate DC offset. This is often trial and error and is hugely labor intensive. You can get custom work this way, but probably no mfr will do it. The other is to use a servo device to zero the offset. These circuits are usually made with fast-responding opamps wired up to zero out the voltage. However, they can be expensive, unstable, and can also have an effect on sound quality. The standard fallback is feedback, which is actually how the servo works in the first place. Some people think feedback effects sound quality, too.
So ... there you are. It's not so easy to eliminate capacitors in the signal path
