Very long winded noob post alert!
So, I built a Crack with Speedball. It (ironically) cracks and pops in the L channel, but that's another story for now. I no longer have HD650s that I paired with the Crack, however I have ended up with Massdrop Focal Elex and Sennheiser HD58X. It seem that, based on what I read on forums, both the Elex and HD58X "shouldn't" be paired with the Crack (or any OTL tube amp) due to their lower than ideal impedance values. The Crack, however, seems produce better sound to my ears than the Massdrop x Cavalli CTH, which ironically blew a tube the minute I plugged it in. Given my preference for the warm Crack-esque sound signature, I don't know if I should purchase what seems to be the more appropriate amp, the Bottlehead S.E.X. I'm trying to understand the science of electricity to aid in determining whether or not the S.E.X., or any other amp for that matter, will be a good fit or not (hehe). Read on...
When I plug in my Elex to the Crack, the sound is notably more bassy than other amps, and it's more bassy than the HD58X. I actually very much enjoy the sound of the Elex with the Crack, but it seems almost too "warm" and "loose". Clearly there's some science behind all of this, and I don't know how to make sense of it to extrapolate how this sound may change either of these headphones to different amps. Specifically, I want to know if I am fooling myself into believing that a SEX may sound similar to the Crack with the Focal Elex.
Headphones have what appears to be variable impedance depending upon the frequency. That variability is further variable across different headphones. Is that correct? My Focal Elex is listed as 80 Ohm impedance and Sensitivity of 104 dB SPL / 1 mW at 1 kHz. I see, for instance that Innerfidelity plots impedance vs frequency of the Focal Elear (same driver as Elex) where impedance is roughly 320 Ohms at 50-60Hz, but levels off to it's listed impedance of 80 Ohms above ~200 Hz. I can't find this info for the HD58X (150 Ohms) but can for HD650 which has a less variable,"softer" impedance curve between 300-500 Ohms across all frequencies.
Now I understand that delivering watts of power has certain voltage requirements, right? The voltage requirements increase as impedance of the headphones does, right? Does the voltage vary along with the impedance of the headphone across different frequencies? For instance, does an amp powering the Focal Elex playing a song that has a bass guitar playing 50Hz frequency on top of higher frequencies (cymbals, vocals, etc) deliver more voltage AND wattage during that time, then scale it back when its just the higher frequencies playing? How the heck does an amp with seemingly well defined impedance tolerances work when a headphone has such variable impedance? So when I read that an amp has a "headphone output" or "impedance" of "8-600 Ohms," what the heck does that mean for sound with headphones with different impedance and sensitivity?
Now enter the ever so confusing output transformer... Assuming that I am at least partially correct so far, is the fact that the Crack does not have an output transformer the reason for why I find the Elex to be bassy with the Crack? If I were to build a S.E.X. (which I read DOES have an output transformer and thus more compatible with something like the Elex?), how would the sound be different than it is with the Crack. What is happening differently with electricity??
Bottom line is this: I liked my Crack with the HD650, but I don't have them anymore and I generally like the Elex. The Crack is pretty much a goner and I don't really want to mess around with it any longer. If I build a SEX, is it truly like what Doc says about it being similar to the Crack but compatible with lower impedance cans? Can anyone give any info on how to choose an amp based on it's electrical specifications vs a headphones specs?
