You are buying one of the now-famous O2 (Objective2) headphone amplifiers designed by a US electrical engineer "NwAvGuy" and described on his blog at blogspot.com! The O2 headphone amplifier puts "CMOY" headphone amplifiers to shame as NwAvGuy shows on his blog. His stated goal is to "bust several audio myths" by showing from actual measurements that a very good headphone amplifier can be produced for a relatively low cost.
O2 Details on NwAvGuy blog
O2 Summary on NwAvGuy blog
O2 discussion thread on DIY Audio
He has designed all the parameters of the O2 with a $10,000 "dscope" professional audio analyzer and posted those results on his blog. The measurement graphs show extremely flat frequency response from 20Hz to 20kHz and extremely low levels of noise floor, total harmonic distortion, intermodulation distortion, plus parameters such as square wave response and many others.
The O2 headphone amplifier is capable of 70mA+ per channel and up to nearly a 10V peak voltage swing, plus battery charging, while running on the included 16VAC 400mA ac adapter, or 6V peak while running on batteries, insuring this headphone amplifier can handle both high and low impedance headphones. With a larger 16VAC 1000mA adapter (not included) the O2 is capable of over 120mA+ per channel. You won't find this with a CMOY! The O2 headphone amplifier runs either off wall power with the included AC adapter or off batteries with the two included 250mAh NiMH rechargeable cells. The O2 recharges the batteries when the AC adapter is plugged in along with powering the amplifier!
The O2 headphone amplifier has a "gain" switch on the front that allows selection between 2.5x and 6.5x gains, which allows the O2 to work with a wide variety of input audio source levels. One of the design points of the amplifier is making it two-stage for the lowest distortion. The first stage provides voltage gain using a NJM2068 op amp while the second stage provides current gain (unity voltage gain) using paralleled NJM4556 op amps. Each chip here does what it is designed to do best. The NJM2068 is a low noise, low distortion, audio-specific (bandwidth and frequency compensation) op amp. The NJM4556 is a low noise, high current, audio buffer op amp. A typical CMOY will have just one op amp wired for both voltage and current gain. NwAvGuy did extensive measurements of various popular "audio" op amps in one posting and found nothing beat the NJM chips for high performance for the lowest cost when tested with the dScope and a high-end Agilent digital oscilloscope.
Op Amp Measurements on NwAvGuy blog
The O2 is designed as a do-it-yourself amplifier build project with NwAvGuy giving specifications for the circuit design, PC board layout, and Bill Of Materials for all the parts but not actually selling the amplifier himself. You are buying a completed and tested O2 headphone amplifier consisting of a high quality PC board with all parts soldered and the completed unit tested and "burned in" for 24 hours powering headphones. Also included is a 16VAC 400mA AC wall transformer, a WAU16-400 unit listed by the designer in the Bill Of Materials (BOM).
The amplifier includes the black B2-080 metal case, which includes blank front and back panels and cover screws. Note that THIS AMPLIFIER DOES NOT COME WITH A FRONT PANEL. You will need to buy the front panel separately if you wish. A pre-drilled and etched front panel can be purchased from Front Panel Express. An information sheet will be included with the amplifier on where to find these parts and information on the internet. NwAvGuy also provides the measurements to drill the panel the comes with the case yourself. You will also need to drill a hole in the metal case at a location of your choosing to attach a ground wire, as NwAvGuy describes in the "details" post about the O2.
The parts used in the O2 you are buying all were purchased directly from Mouser Electronics in the US (except the batteries and case which Mouser does not carry), from the Mouser part numbers given by NwAvGuy in his blog for the O2's BOM. This particular O2 build includes several of the "upgrades" listed by NwAvGuy in the BOM including
* The super-quiet "DD" versions of the NJM2068 and NJM4556 amplifier chips
* The gold plated Tyco IC sockets
* The low noise ACTG versions of the voltage regulators
* Has the Bourns "pro audio" volume control option on the BOM.
* The compact and relatively light weight 16VAC 400mA AC adapter option on the BOM.
* The solder used is very high quality 62/36/2 "eutectic" silver-bearing rosin core solder. Eutectic solder does not develop grains on cooling like cheaper 60/40 tin/lead solder. The 2% silver in the solder prevents leaching of precious metals plated on device leads and produces greater joint strength. The rosin flux in the solder is electrically inert, unlike "no-clean" solders used commercially that have to be washed or will short. A temperature controlled soldering station was used for all the soldering work. The board was cleaned after soldering with a quality flux remover.
The amplifier comes with 2 of the blue Tenergy NiMH 8.4V (9V type) rechargable batteries, as shown on NwAvGuy's blog. This O2 is built with a blue "input" jack and a green "output" jack - the same color green as is used on PC sound cards for output jacks. The amplifier has the default specified gain switch settings of 2.5x on low and 6.5x on high. NwAvGuy describes how to change resistors on the board to change those gain settings in his blog article, but that would require unsoldering and soldering resistors. NwAvGuy has posted that the default gain settings here cover the vast majority of sound sources. The amplifier comes with the specified plastic knobs and caps from Mouser for the volume control and push buttons. Also included is an input audio connection cable with 3.5mm plugs on either end as shown in the photos. An adapter cable is included to convert one end of the 3.5mm / 3.5mm cable to RCA plugs for sources with RCA line out jacks rather than 3.5mm.
United States destinations only for this sale. Sorry but I will not ship to any international locations. For the 48 continental US states FREE FedEx ground shipping is included in the sale price, with a $10 additional surcharge added for Alaska, Hawaii or Puerto Rico. FedEx ground usually delivers within 4-5 business days. If you want express shipping just message me via eBay before you purchase for a quote on the express shipping to your zip code. Full tracking is included and a tracking number will be sent after the sale. The shipment will also be fully insured against shipping loss. A SIGNATURE WILL BE REQUIRED UPON RECEIPT. You can make arrangements with FedEx to hold it at their local office for signature and pickup if nobody is home during the day to sign.
The unit comes with a 30 day warranty on construction defects. In the event of a warranty claim you will be required to pay the cost of returning the unit for service, but it will be sent back prepaid. The O2 headphone amplifier is fully tested prior to shipment and will be sent in an anti-static bag with anti-static packing. The amplifier can be returned for a full refund within 3 business days after receipt, if the amplifier is received in the original condition, with the AC power adapter, and is shipped back in the anti-static packaging. The buyer is responsible for the cost of return shipping.
Shipment will be within 2 business days from receiving cleared payment via paypal in US dollars.
Important! Only use the included AC adapter with the O2 headpone amplifier. It uses an adapter that outputs AC, rather than DC like many electronic items use. A DC adapter will not work correctly with the O2.
Don't pass up your chance to own one of the best headphone amplifiers out there right now!