Originally posted by michaelab
On the subject of the Corda HA-1 I've not heard it (or any other headphone amp for that matter) but I was thinking of getting one at one point and checked out some reviews on the headphone forums and it seems like the HA-1 didn't get very good reviews (by the people on the forum).
Michael.
Really? The Corda HA-1 is VERY highly spoken of on
www.headfi.org
However, as I have mentioned Mike, I didnt find it ANY better than my speaker amp. Although Rory heard it and *thought* it was much better, I failed to see how or why he came to this conclusion.
Maybe it isn't a significant enough upgrade over a stock headphone out of a reasonable integrated, hence why there may have been less than glowing reviews?? (I thought it was fairly well reviewed though - the Prehead is at any rate, as is the HA-2 as far as i can gather). Paul's experience with the HA-1 ilustrates this to some extent. I know from my experience that there is very little difference between the XCansV2 and the headphone socket of a NADC370. So if somebody was to buy this product soley on the basis of improving their existing stock headphone socket, they may be disappointed
There are a number of reasons why a dedicated amplifier *should* be better than the headphone jack of an integrated amplifier.
First of all, the quality of the headphone circuitry of integrated amplifiers varies greatly. For example, I have rarely heard particularly great things about the quality of Arcam jacks for example, most people saying they suffer noise, and also very poor sound quality. On the other hand, NAD and Rotel are very well known for having very high quality headphone circuitry in their amps. So in the case of an amp with poor headphone circuitry then this is one potential area where a headphone amp can offer improvements.
The second reason is that a headphone amplifier will offer an output impedance of close to 0 ohms. Generally, the headphone jack on integrated equipment will not offer such a low output impedance. If the output impedance is too high, it can affect the sound negatively. As a rule of thumb, the lower the output impedance, the "cleaner" the output will be, the higher it is, the "warmer" it will sound. Many amps offer a couple of jacks, one with a higher impedance and one with the low impedance, and which the user chooses will be a matter of taste. Integrated amps nearly always have a slightly higher output impedance.
Another thing that output impedance can affect is the frequency response. If the output impedance is higher, then it can exagerrate the frequency in a certain area. Lets take a look at this graph.... (hope this works)
http://www.headphone.com/graphCompa...0020110931&buttonSelection=Compare+Headphones
As you can see here, the Grado SR-325 has a very flat impedance response through the frequencies. The Grado should therefore should not be affected by bumps in the frequency range due to increased impedance of the output. The Beyer DT931 on the other hand, has a very severe increase in impedance in the bass. This not only means that the cans will have a bump in the frequency response in the bass when fed with increased output impedance (actually DEFINITELY NOT a bad thing in the case of this particular can), but the high impedance means that it can draw a lot of current from the amplifier.
So is it as simple as looking at impedance response? Not always. For example, a low impedance phone can in many respects be driven better by a dedicated amplifier than a high impedance one. For reasons I cannot quite explain, if the output impedance of the headphone jack is higher than the impedance of the headphones, it *CAN* (but not always) mess the sound up. Therefore, higher impedance cans, which take more current, can sound better out of integrated amps than low impedance phones, which on paper, should not take a lot of power and their impedance is a lot closer to that of speakers, which in theory should make them easier for integrateds.
As much as I've had many cans, I have not had enough to conclusively prove whether high impedance phones are better for integrated than low impedance phones, the only way to know it to experiment.
For example, I have had 3 low impedance cans in my collection - Grado SR-80s, Sennheiser HD497s and AKG K271s. The K271s (55 ohm) were dreadfully closed in. Not so out of the Corda. The SR-80's (32 ohm) were too bright (but check out their frequency response). The Sennheisers sounded just fine. So I feel it may be the exception rather than the rule. The Corda actually struggled to drive some of the more demanding headphones in my collection - did it really have the current capability I ask myself, or did it naturally just sound a bit lean? Probably the latter....
So, a good headphone amplifier like the Prehead should be noticably better than the lower cost amplifiers, and also those on low cost integrated amps, but I think the differences between GOOD low cost headphone amps and integrateds and the higher end stuff such as the pre-heads are smaller than many headphone fanatics would have you believe, and that good low cost solutions, as with many things in audio, are already into the laws of dimishing returns. Sure there will be improvements, but only you can decide whether the dramatic increase in cost is worth the relatively small potential increase in performance. All these things are, of course, subjective. I had thought about going for a Pre-head myself, but given my disappointment with the Corda, I will be sticking with my Rotel for some time yet (until I get a very substantial payrise at least).
If you think I am just saying this, then I'd like to refer you to this thread on the HA-2, which is VERY, VERY close to the performance of the Prehead, where this dude, is left somewhat disappointed with his HA-2. Keep this in mind - an amplifier is just that, an amplifier, it increases the strength of a signal - in theory it should not change the sound, and a good solid state solution should not colour it. If you want colouration, go valves (I am thinking RKV Audiovalve amplifier for you

)
Here is that thread....
http://www4.head-fi.org/forums/showthread.php?s=&threadid=30717&highlight=HA2