Originally Posted by cfcubed
I've HE-500s myself & prefer my 2-channel b22 to CTH for them, O2 if something smaller is required (e.g. @ work). Same for when I'd owned LCD-2s. IMO & to my ears these orthos do not need warmness that tubes can impart, they benefit more from the drive of something like any b22. When I do sometimes miss the option to color/contour the sound w/tube swapping I swap in the CTH & use a tube w/sparkle like chrome plate Siemens (and it performs well & sounds quite nice).
Originally Posted by holland
Wow, CTH. This brings back memories, what a great little amp with some neat features like the self zeroing output diamond buffer.
Anyhow, I'm not Alex, but the CTH uses a class AB diamond buffer with approximately 20mA idle. It should peak out around 40mA before exiting class A. I am not sure what the voltage swing is, but for the HE-500 it shouldn't matter, it will be current limited.
I would guess the voltage swing should be about 13Vp-p, roughly 5Vrms. I'm guessing roughly 185mW rms. Heat in the small enclosure is a constant battle, I'm not sure it can sustain that. Note, no calculations done, and no measurements taken. I'm not really sure if it can hit that before it clips. Anyhow, for 38ohm you're likely looking at around 60mW of class A. That should land you around 105dB-ish before coming out of class A.
Depending on how much SPL headroom you actually need or want to target, should dictate your headphone amp requirements. I guess if you need 120dB peak out of your HE-500, then the popular DIY amps out there are EHHA and Beta22. The SOHA2 should land you around 112dB, in stock form. You can get more with a bigger heatsink.
Edit: keep in mind, it's all theoretical. One would need to bench the amp to see where it lands in terms of THD to determine what's acceptable or not.
To close this loop, I got my HE-500's yesterday. I'm quite happy with the HE-500's on the CTH but think it is current starved. The bass thumps and extends, don't get me wrong, and details in the mids and highs are wonderful, but bass can loose some slight details. IMO we are talking minor, but still. At reasonable to moderate loud volume levels I find it quite nice (volume control at 12pm). Saying that, I also ran the HE-500's from an old 20 watt speaker amp headphone out (Sanyo JA-220), and the speaker amp's power is able to drive the HE-500's to incredible detail from lows to highs. So, I also prefer the HE-500 with something with more power, but the CTH and HE-500 sounds great enough that if it was my only option, I don't think I'd worry too much about upgrading. It would be the last 10-20% type upgrade only.
Edited by civilmonkey - 7/11/13 at 11:19am