Quote:
The decision to use a ~30uf cap actually makes sense in a round-about sort of way.
Lets start: as caps get bigger (more capacitance) they generally sound worse. Its doubly true when your using "who cares how it works as long as it survives voltage and measures right" parts.
Now that that's out there, since we are talking about measurements & calculations before sound, simple cathode followers (like the darkvoice) absolutely suck for driving low impedance loads. I happen to like the way they sound most of the time, but if we only care about the distortion measurements simple cathode followers dont work with low impedance headphones. In real life you can tell something is different at a quick listen, but I dont think its bad. Mneh.
So for the last part crunch the numbers where the amp works better - with a 300ohm headphone & 33uf you do have a -3db point of ~16hz, which is on the slightly high side compared to the standard 20hz. OTOH When you consider that VERY little music actually goes below 50hz (and that sub-50hz is reallllly hard to hear on headphones even if the amp was flat to DC) you do still have a bit of breathing room. With 600ohm or 2Kohm headphones the -3db frequency is low enough to be meaningless. In a practical world the choice to save a few bucks and use a slightly small part represents a very reasonable compromise for an amp like the DV.
I appreciate your point, nikongod, about the relevance to design of making cost-efficient tradeoffs. That is almost surely the reason the DV designers made the choice of 30uf caps rather than ones with a greater value.
As I suggested in my comment about the 30uf caps, there's by no means a consensus as to whether or not a 3db down corner at frequencies where music happens is sufficient. For example, here's a blurb from the V-cap site:
"The real reason we don't select 20 Hz [for the corner frequency] is because near the the -3db point, there may be some phase anomalies introduced into the signal, and therefore we want to operate with a buffer from this ragged edge. We recommend using a -3db point of 1/10th of your desired low frequency response. For Human beings with audio systems manufactured on Earth, that would be 1/10th of 20 Hz, or 2 Hz."
Of course the V-cap people aren't audiophile gods to whom we must defer, but it's worth considering that inputting the value of 30uf for a 300ohm headphone into their calculator yields a value of 176Hz for what they refer to as "optimal low frequency response."
The salient question, I think, is this: if the 30uf caps aren't the cause of the DV336's poor low frequency response with high impedance phones like the HD600s, then what is? Evidence that the cause may be the caps (and I'm not arguing that it is, as I'm unsure what it is) is a number of head-fiers who have mentioned the poor low frequency response and stated that the most significant sound-altering mod they've made to the 336 is changing out the caps for larger ones.