I do enjoy the clean, chill vocal of my K702 a lot, so switching to another headphone isn't my current consideration.
I haven't tried out much amps and that's why I might be overestimating the effect of amps on the voice.
I'm just looking for an qualified amp with warmer vocal comparing to product at the same price, not trying to convert my K702 into a bass monster like HE-500.
Bass Monster vs no bass aren't your only options when I mentioned using the amp as an equalizer.
And neither am I saying that there are absolutely no differences between amps.
What I am saying is that the primary goal of the amplifier is precisely to
not modify the sound, ie,
amplify the sound without adding (audible) noise and distortion. This is why it's called an
amplifier instead of something like a
warmifying boombasticator sugar enfuser. Basically, all the amp does in changing the sound primarily is to get to a higher output level without distorting or clippingand without adding noise; the secondary job is just putting that final polish in the sound so that for example that last bit of sharpness in the sound won't be there or at least not make a headphone that has some peaks in the response that an amp could otherwise exacerbate.
Basically, don't expect the amp to drastically change the sound, and that goes beyond just turning it into a "bass monster."
Think of it in other terms. If the amp's effect on the sound is like a whetstone, using it like an EQ is like putting a knife on a 320grit stone at a different angle than the edge it has to reprofile it; ideally it should just be like an 8000grit to smooth out any remaining microscopic jagged bits of metal still left on the edge. because if you stop at 1000grit, the knife might be sharp, but the edge is still kind of rough that even a pull cut won't have it go through paper (let alone tomatoes or raw fish) smoothly.
And even if you don't expect it to be like an EQ as described here, the thing is you still have to be aware that what you're asking for is either going to be as excessive, or possiblyitually inaudible to you and worse, by your standards, disproportionate to what you'd spend to get that little bit of improvement. I can tell you that if you really wanted that improvement in the vocals to try a Violectric V200, or maybe a Meier Jazz FF, or heck, a WooAudio WA6se with the upgraded tubes, but even if you can easily hear the difference, would you consider the cost worth it? You have to be aware of that.
I believe that this is me making a mistake on using vocabulary, LOL.
At first, I was one step away from ordering a Valhalla directly from Schiit before I read some user reviews.
From the reviews I read, products from Schiit including Valhalla, Lyr do run at higher temperature even comparing to other amps which leads to slight distortion. (I'm not sure about the distortion since I own neither Valhalla nor Lyr.
I'm not sure I understand how THD and temperature are related. AFAIK either the tube is too cold to work properly or it's too hot you're going to break it.
Maybe you misunderstand what they meant about Class A/B topology where if the headphone or speaker needs enough power the amp switches over to Class B operation. So listening to an HE400S hooked up to a Lyr3 for example will at moderate levels very likely have it stay in Class A operation, but switch to a harder to drive headphone either by lower sensitivity or very low impedance and high current requirements, and the Lyr3 will run in Class B to remain stable.
I do appreciate your reply a lot. I looked for the Heed CanAmp and found less information. Is there any other amp recommended to fit my headphone?
If you're looking to warm up the vocals, very likely not without risks with OTL amps.
If you just expect it to be more of not exacerbating the treble as much as what you're using now, maybe try the Meier Jazz FF.
If you can spend more, maybe the Violectric V200 or Burson Soloist.