More are available for a few more days!
"It's a superb sounding single ended (SE) Class A topology that has a predominantly a second harmonic distortion profile with just a tad bit third harmonic and not much else. The noise floor is about -125dB and dynamic range is about 96dB with THD measured to be about 0.029% at 1kHz and driving a 270ohm load at 700mV RMS. Note that most of that HD is H2 so the sound is very much like a nicest SE tube amps. Frequency response with a 47uF output coupling cap was measured at -1.5dB at 20Hz and 45kHz (probably limit of measurement as ADC sampling was 96kHz). The sims show that it can go beyond several MHz on the high end. Best part is that it fits in an Altoids tin and looks like a CMOY headamp - but it's no op amp. It relies on just two FETs. The ever popular BF862 JFET for the input and a ZVN4306 MOSFET for the output stage. The bias runs between 50mA and 60mA which allows it to last about 4 to 5 hours on a pair of 600mAhr Li-ion rechargeable 9v batteries. The amp dissipates about 2w so never gets hot but makes a nice hand warmer for your pocket in the winter. "
X posted the above summary of his amp today as part of this new thread:
The board being ordered will use both through-hole and SMT components in the circuit, and X says it will be easy to solder. (I hope he's right for my sake!)
Bonus! The components are affordable--about $20.. Here is the Mouser BOM::
Description Part No Qnty
n-channel power MOSFETs ZVN4306GTA 2
n junction JFET BF862 771-BF862-T/R 2
Panasonic OSCON 390uF 20v output caps 20SEPF390M 2
Output cap bypass WIMA 1uF MKS caps MKS2C041001F00KSSD 2
Input bypass Wima 2.2uF MKS caps MKS2B042201F00JSSD 2
Panasonic OSCON 100uF 25v rail caps 20SEP100MX 2
Switchcraft 3.5mm stereo jacks 35RAPC4BV4 2
Alps stereo pot with power switch RK0971221Z05 1
Plus you will need the following 0805 1% metal thin film SMT resistors (qnty):
33R(2), 47R(2), 270R(12), 1k(2), 15k(1), 47k(2), 100k(2), and qnty 4 x 100nF X7R 0812 MLCC bypass caps, and basic 3mm red or green LED.
In case you aren't excited yet...here are some listening impressions from the prototype:
"I have been listening to the Pocket Class A for an extended period now and have compared it to some world class head amps designed on this forum. I am happy to report that my listening impressions have not changed regarding how good it sounds. Being battery powered, it is utterly quiet and able to resolve some amazing low level detail when listening from a good DAC. My latest measuremts show an absolute flat noise floor devoid of 60Hz hum at -125dB and a dynamic range of 92dB - well matched to CD quality sound. I am using 47uF output caps at present so at 20Hz there is about a -2dB falloff but I plan on upgrading to a 390uF oscon output cap in the future. This should take the -3dB point to about 5Hz and give this amp the bass extension to meet any audio need. The one area where my "big amps" such as the Salas DCG3 and BF862 preamp with DAO buffer amp have an advantage is bass "slam" due to the fact that they have huge 18v to 20v dual rail multi-ampere power supplies. But for the rest of the music - this little amp surprises me all the time with how great it sounds. Natural, musical, easy on the ears, lively, not sterile, resolving, quiet when needed, expressive, accurate (due to flat response), most of all - enjoyable for hours on end. It beats all my other amps on noise. It is the quietest amp of all with only two transistors in a tight layout that doesn't pick up noise, and ultra quiet batteries to provide juice."
and to sum it up:
"Natural and very musical sound that is engaging, lively, never sterile."