[stellarelephant]

1. Forums

There's a new DIY Altoids tin amp in town, and it's Class A!  For those of you who don't regularly check the DIY forum, here's a link:
http://www.head-fi.org/t/833106/new-diy-altoids-tin-amp-the-class-a-wintergreen-handwarmer-by-xrk971#post_13199563
 
Pretty exciting, as I'm only aware of one commercial option for portable class A, the Aune B1.  I think this new design (currently in the final stages of PCB development) is a remarkable achievement, and I'll be building this amp.  Can't wait to hear it.
 

 
I don't want to be cross-posting, so if you want to follow developments on this amp, please go to the thread I linked to.

 

[Jimster480]

This looks pretty awesome! I've never seen an amp in an altoids container lol

 

[stellarelephant]

The CMOY amps made by JDS and many others are almost always in a mint tin. Those are based on op-amps though. This one uses a JFET and MOSFET transistor for gain, and the resulting sound has been described as realistic and tube-like. The Group buy for this amp PCB is now live over at DIYA!
http://www.diyaudio.com/forums/group-buys/302859-xrk971-pocket-class-headamp-gb.html

 

[Jimster480]

The CMOY amps made by JDS and many others are almost always in a mint tin. Those are based on op-amps though. This one uses a JFET and MOSFET transistor for gain, and the resulting sound has been described as realistic and tube-like. The Group buy for this amp PCB is now live over at DIYA!
http://www.diyaudio.com/forums/group-buys/302859-xrk971-pocket-class-headamp-gb.html

But I Thought that tubes change the sound depending on the tube.

 

[stellarelephant]

That's true in a sense. But the best tube gear is transparent, not colored. This amp has very flat frequency response and low distortion with a mostly 2nd order harmonic distortion profile. This makes it sound (according to the designer) like a very high-end tube amp. This is due to the single ended (SE) Class A circuit, which Nelson Pass says gives the most realistic and engaging sound of any circuit type.

 

[proid]

That's true in a sense. But the best tube gear is transparent, not colored. This amp has very flat frequency response and low distortion with a mostly 2nd order harmonic distortion profile. This makes it sound (according to the designer) like a very high-end tube amp. This is due to the single ended (SE) Class A circuit, which Nelson Pass says gives the most realistic and engaging sound of any circuit type.

 
Lol, which "very high-end tube amp" did the designer use to make this statement?

 

[stellarelephant]

The designer actually made comparisons to other SE Class A desktop solid-state amps, not tube gear. Really the whole "tube sound" thing is kinda vague, if not a misnomer. According to Pass, it's the circuit topology that determines the harmonic distortion profile and overall sound of an amp, rather than whether tubes vs transistors are used in that circuit. The "tube sound" that these guys refer to would probably be better named the "SE Class A sound" even though that doesn't exactly roll off the tongue. This sound signature is commonly associated with tubes because so many tube amps are in fact SE Class A designs. I'm no expert, but this guy is... https://passlabs.com/press/single-ended-class

 

[spacecowboyz]

Will this mint tin work with 16Ohm IEMs or is the impedence too low ?
Any hiss with IEMs ?

 

[ahmadfaizadnan]

I can see that you have t90 in the picture. How well do they pair?

 

[xrk971]

Folks have used them with 16ohm IEM's that have high sensitivity and they a reported to sound very good. I would recommend 30ohms or higher but you may find that 16ohms works fine for you. The amp is dead quiet, absolutely no hiss on even the most sensitive IEMs.

A new review of thisamp by Headfonics.com just came out today.

http://headfonics.com/2017/06/the-class-a-nhb-pocket-amp-by-xrk-audio/

 

[xrk971]

I just ran an LTSpice sim for Andromeda's 13.8ohm 115dB. With dual 1000uF oscons and 100uF silmic, the THD at 109dB is 0.05% with 96% of it at H2 and balance is H3 and nothing else. Even at threshold of pain 121dB, THD is well below 1%. Freq response -0.2dB point is 15Hz so should handle high sensitivity low impedance IEM's just fine.

 

[Jimster480]

What does the output impedance come out to be?