Not much info about the SAP-4S on the web, this was a purchase I made mostly based on curiosity; there's only a single review about it in English that seemed pretty positive so I went for it.
Packaging is a nice little white box with relevant logos. When opened you're greeted by various neat accessories like a flat usb charging cable, protective leather case, silicon band, and well made 1/8" interconnect. The amp is very solid, well built and feels pretty hefty in the hand for such a small device.
In terms of sound, it seems to do a pretty good job of keeping things neutral and not coloring the the sound of my headphones or IEMs, for the most part; It's not quite O2 neutral, but on the slightly warmer side of neutral. I do notice a very small amount of bass being added by the amp, either that or it's pulling the treble back ever so slightly.
Most of the specs can be found on the various listings of the SAP-4S on ebay, etc. Power output is 100mW into 32ohms, which is close to the 130mW per channel into 32ohms rating that Maxim Integrated has listed for their MAX9722 chip that's used in the amp.
I didn't notice any listings mentioning output impedance, so I tried measuring it myself. Using a 60hz sine wave file, DMM, y-splitter, and 32ohm load (Senn. HD428), the SAP-4S measured at ~0.15Ω, pretty nice, and good news for my Sony XBA-3, which sounds abit too treble happy straight out of my phone (Samsung Galaxy S Vibrant) with a ~8.2Ω output impedance
![size]](http://files.head-fi.org/images/smilies/redface.gif[size=13px][/size])
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Other things to note:
Hiss+noise - I've tried the SAP-4S with various IEMs, including Sony XBA3ip, Vsonic GR07(mk1), Brainwavz B2, Altec Lansing IM616, Earsonics SM1, Sony MH1C, and of those i've only heard noticeable hiss coming from the GR07 and B2. For the others, hiss was not a problem.
The amp does pick up some noise from my phone, while the wi-fi is on and also when I am receiving calls.
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--Quick update - June 12, 2013 - For fun I tried running some of my less efficient headphones (FA-011, Superlux HD330, T50RP) out of the Sap 4s just to see if it was capable enough...I was able to get good volume out of them but they seemed to lack some authority in the lows, and less cohesive presentation compared to when driven out of my desktop amps.
--Also an update on hiss+noise, I had an opportunity to listen with the amp in a good, quiet environment and noticed the hiss is present with most of the IEMs I had mentioned previously, some more than others. In an environment where the noise level is roughly 45db-50db or higher, the hiss probably won't be noticeable at all for most IEMs except the most sensitive. If one was in, say a quiet library or something similar though, hiss might be a problem for the most discerning listeners. For that im going to have to dock a little bit off the ratings.
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edit - Also one thing I forgot to add, opened the amp to check out the internals, and it's mostly pretty straightforward. Pics of internals can be found here - http://www.sp01.jp/26_1628.html
Something to note is the PCB is thin, about the thickness of a pringles chip.
_____________________________________
Other output impedances i've measured, for reference:
edit2 - SGS output impedance changed, I did it wrong the first time
Packaging is a nice little white box with relevant logos. When opened you're greeted by various neat accessories like a flat usb charging cable, protective leather case, silicon band, and well made 1/8" interconnect. The amp is very solid, well built and feels pretty hefty in the hand for such a small device.
In terms of sound, it seems to do a pretty good job of keeping things neutral and not coloring the the sound of my headphones or IEMs, for the most part; It's not quite O2 neutral, but on the slightly warmer side of neutral. I do notice a very small amount of bass being added by the amp, either that or it's pulling the treble back ever so slightly.
Most of the specs can be found on the various listings of the SAP-4S on ebay, etc. Power output is 100mW into 32ohms, which is close to the 130mW per channel into 32ohms rating that Maxim Integrated has listed for their MAX9722 chip that's used in the amp.
I didn't notice any listings mentioning output impedance, so I tried measuring it myself. Using a 60hz sine wave file, DMM, y-splitter, and 32ohm load (Senn. HD428), the SAP-4S measured at ~0.15Ω, pretty nice, and good news for my Sony XBA-3, which sounds abit too treble happy straight out of my phone (Samsung Galaxy S Vibrant) with a ~8.2Ω output impedance
Other things to note:
Hiss+noise - I've tried the SAP-4S with various IEMs, including Sony XBA3ip, Vsonic GR07(mk1), Brainwavz B2, Altec Lansing IM616, Earsonics SM1, Sony MH1C, and of those i've only heard noticeable hiss coming from the GR07 and B2. For the others, hiss was not a problem.
The amp does pick up some noise from my phone, while the wi-fi is on and also when I am receiving calls.
_________________________________________________
--Quick update - June 12, 2013 - For fun I tried running some of my less efficient headphones (FA-011, Superlux HD330, T50RP) out of the Sap 4s just to see if it was capable enough...I was able to get good volume out of them but they seemed to lack some authority in the lows, and less cohesive presentation compared to when driven out of my desktop amps.
--Also an update on hiss+noise, I had an opportunity to listen with the amp in a good, quiet environment and noticed the hiss is present with most of the IEMs I had mentioned previously, some more than others. In an environment where the noise level is roughly 45db-50db or higher, the hiss probably won't be noticeable at all for most IEMs except the most sensitive. If one was in, say a quiet library or something similar though, hiss might be a problem for the most discerning listeners. For that im going to have to dock a little bit off the ratings.
_________________________________________________
edit - Also one thing I forgot to add, opened the amp to check out the internals, and it's mostly pretty straightforward. Pics of internals can be found here - http://www.sp01.jp/26_1628.html
Something to note is the PCB is thin, about the thickness of a pringles chip.
_____________________________________
Other output impedances i've measured, for reference:
60Hz sine wave, 32-ohm load (Senn HD428)
Project Starlight, "LowR" - ~1.5Ω Project Starlight, "HighR" - ~71.6Ω
HLLY RMK-5 - ~67.2Ω
O2 - ~1Ω
60hz sine wave, 150-ohm load (Superlux HD330)
HLLY RMK-5 - ~82.4Ω
Project Starlight, "LowR" - ~1.5Ω Project Starlight, "HighR" - ~71.6Ω
HLLY RMK-5 - ~67.2Ω
O2 - ~1Ω
60hz sine wave, 150-ohm load (Superlux HD330)
HLLY RMK-5 - ~82.4Ω
edit2 - SGS output impedance changed, I did it wrong the first time
iPod - 103.5 x 61.8 x 10.5 mm
SAP-4S - 83 x 58.3 x 9.5mm