Marginal (although not always illicit; sometimes just marginally spec-ed) capacitors have long been an issue including in consumer electronics.

As an example, the Mac Plus power supply was notorious [well, at least if you were repairing them] for failing. Some people put out instructions for upgrading it by replacing a subset of components including IIRC certain capacitors.

I've also read accounts of people improving the output e.g. of cheaper CD and DVD players, by replacing certain components particularly in the post DAC circuitry, again including capacitors, with better quality/rating components. I've never experienced this first hand, so I can only pass on second hand anecdote.

This is indeed true. Some (all?) amp designs place resistors and capacitors in the signal path. This distorts the sound. For one channel, that would be fine, since the distortion is usually just a phase shift that you won't notice. (Play a song. Then play a song but start it 1ms after you were planning to start it. It will sound fine both times :)

The problems start to show up with stereo, though, where you have two channels to deal with. When you use low-quality components, the phase shift can be significantly different between the two channels. (Components have a, say 10% value tolerance. If one channel is +10% and the other is -10%, you have a problem.)

This difference destroys the phase information between the two stereo channels, resulting in poor "imaging".

When you replace the 10% tolerance components with 1% tolerance components, you lose the phase distortion, presumably increasing sound quality.

(I am not an EE, but I have built a lot of headphone amps. The sad part is how people with $1000 amplifiers often have worse components than an amp built from $30 worth of parts. Ah, the free market...)

> (I am not an EE, but I have built a lot of headphone amps. The sad part is how people with $1000 amplifiers often have worse components than an amp built from $30 worth of parts. Ah, the free market...)

Don't forget your monster cables. (Or what where they called?)

Also, I now have a sudden urge to build another headphone amplifier... :)

Glad to be of service. Hmm... and since you seem to know your way around them, do you take orders?

(Another startup born on HN! ;-)

I did for a while. I am not sure I am knowledgeable enough to do a good job anymore, however.

If you are ever in Chicago, we can have beer and I will teach you how to build an amp :)

Far north suburbs. I've been a recluse, lately, but maybe when things pick up for me, I'll see you at one of the HN meetings. (Didn't realize until now that you're in the neighborhood.)