Driving K1000'sWow, an interesting thread. Something I think I can contribute a bit to.
First of all, I won't comment on cables - it's a subject I avoid like the plague.
But I do know what it takes to drive K1000's. I have tried a number of different amplifiers - both commercial and home-built - and can tell you what works and what doesn't. So here is a very long-winded discussion...
By far, the most important factor in making K1000's sound good is to drive them with a low impedance source. By this, I mean that the source impedance should be less than, say, 8 ohms. All amps designed to drive speakers meet this criteria, but few headphone amps do.
If you don't, the results are dramatic - at the extreme, the bass goes away completely. I think the K1000's are a little light in the bass anyway, so to me any loss is unacceptable.
If you don't believe this, try a simple experiment: hook up the K1000's to the 8 ohm speaker connections of any amp and listen, then insert a 100-120 ohm resistor in series. You'll have to turn up the volume to get the same level, but the loss of bass is dramatic.
I can hear the difference between a source impedance of 50 and 7 ohms easily, and I think I can hear a difference between 7 and 3. You may hear a difference between 3 and 1. The bottom line is that low is good.
There are many cases in electronics where you want the source impedance to match the load impedance - high-speed signals and RF, for example - but this is often not true in audio.
Part of the confusion here is understanding that source impedance is NOT the same as the rated load impedance. Almost all amplifiers designed to drive speaklers have rated load impedances of 8 ohms (and sometimes 4 or 16 ohms), but that is NOT their output impedance. Their output impedance varies between damn near 0 for many SS amps to 8 ohms or so for some tube amp circuits.
This also relates to the term "damping factor", which is a ratio of the load impedance to the source impedance. A high damping factor, at a given load impedance, means a lower source impedance.
With tube amps, the "impedance" of the secondary of the output transformer is rated at 8 ohms, but again, this is not the source impedance. For a 2A3 tube, for example, you usually use a 2.5k : 8 ohm transformer. But the tube's plate resistance - the source impedance driving the transformer - is about 800 ohms. This is reflected through the transformer to give a source impedance to the speaker of about 2.6 ohms.
Now, if you try and drive K1000's from the typical headphone amplifier, you get really poor results. Why? Mostly because the output impedance of headphone amps are usually 30-100 ohms, but also because the K1000's also need a lot of voltage, and power. They're about 1/10 as effecient as most headphones.
So, let's look at the numbers... If you assume you want to drive 1 watt into the AKG K1000's, you need about 11V RMS delivered into 120 ohms. To get 100dB SPL, you need about 400mW, which is about 7V RMS.
An amplifier designed to drive 15 watts into an 8 ohm load can deliver 11V RMS. If the amp has a very low output impedance, it will deliver vuirtually the same voltage into 120 ohms; a very low damping factor tube amp will deliver more voltage, around 22V RMS if it had a source impedance of 8 ohms (since it is more lightly loaded).
So, any amp designed to drive 8 ohm speakers at 15 watts or more can drive K1000's to 1 watt. To get 100dB SPL, you would need an amp that can do 6 watts into 8 ohms (for 400mW into K1000's).
A typical 2.5W 2A3 SET amp, with an output impedance of a couple of ohms, can deliver around 6V RMS (on an 8 ohm tap), probably enough but a little wimpy. Changing to a 16 ohm tap ups the voltage at the cost of a higher source impedance... louder, but less bass.
As for the solid state vs. tube, single-ended vs. push-pull, and class-A vs. class-AB debate... in theory, it shouldn't matter at all as far as the K1000's go. Of course, different amps will sound different, but no more so than if they were driving speakers.
But in reality, the issue that may make some amps sound good and others bad relates to the fact that most amps capable of driving K1000's are amps that were desigend to drive 8 ohm speakers. They weren't designed to drive, nor tested with, 120 ohm loads. Some can do it well, others fail miserably.
I'm guessing that this is why AKG recommends class-A amps; in general they are less likely to act up into a high impedance load. Some amps - especially class-AB amps with lots of negative feedback - do really nasty things with a high impedance load. They can oscillate, or they can have really high distortion.
Others will do fine. The Crown amp mentioned in a post above is known to be well-behaved into virtually any load - one of Crown's claims to fame - and that may explain why one of the posters found it worked well. (I have a D60 that's been running my TV sound for about 20 years - maybe I should try it!)
Most class A tube amps, both single-ended and push-pull, do OK with higher loads. Distortion is actually lower, but there are possible problems related to the ouput transformer. Class AB tube amps, which almost always have negative feedback, are more likely to misbehave.
One thing you can do to help these potential problems in any amp is to load the amp with a resistor in parallel with the K1000's. Use something between 10 and 50 ohms - enough to present the amp with something closer to it's designed load without dissipating too much power. I'd almost guarantee this will improve things if you're using a class AB amp with lots of feedback. (In fact, if you look at schematics for many classic amps with headphone jacks, they switch in a shunt resistor when you are using headphones).
So, you're in the market for an amp to drive K1000's. What should you buy?
Personally, I think tubes complement the slightly harsh sound of the K1000's. In general I tend to favor class-A circuits with no feedback, which also tend to work well with the K1000's high impedance load.
If you want to do SET with a K1000, I would recommend a 300B as the best power/output impedance choice. About the best sounding driver for the K1000, in my opinion, but expensive. A 2A3 will work, but it's a tad on the wimpy side - probably OK if you don't listen really loud.
A push-pull class-A tube amp might be a less expensive option that would still sound fine, and should do OK into the 120 ohm K1000 load.
As for solid-state amps and clas AB push-pull tube amps, I don't have much direct experience to guess which amps will be well-behaved and which won't. But if you put a shunt resistor in, most should at least do OK.
One SS amp that I would expect would work great is a class-A SE amp like one of Nelson Pass' MOSFET amplifiers. Anybody got one to try?
Well, hope this long explanation is helpful to somebody...