Nwavguy designed O2 with versatility in mind. Indeed, with the Dual Gain Switch that he implemented, it is. It provides enough juice for power-hungry orthodynamic phones with its default 6x gain, and can also operate at a lower, 2.5x gain. Indeed, if you want, you can do some DIY and lower the gain further to 1x (but then you will lose the 6x gain). Well, we all like versatility, don't we? With the help of a head-fier, I have here at hand a one-of-a-kind, custom-made O2: O2 with Triple Gain Switch. As you can see, we added a switch inside the enclosure. Now, when the switch is towards the front of the amp, the in position is 1x gain. When it's toward the back, the in position is 6x gain. And whenever it's an out position, it's 2.5x gain! And for cable believers, note that we used silver plated copper Teflon wire, so SQ is not affected! For more information about this design, see here: http://www.head-fi.org/t/622658/how-to-o2-with-triple-gain-switch-1x-2-5x-and-6-5x It comes with an AC Adapter (the one recommended by Nwavguy), JDS Labs silver front panel and a Black knob (not the silver knob in the picture). Condition: Used – Good with some signs of usage. Prices include CONUS shipping. International buyers please add $12 to cover additional shipping fee. Accepts PayPal personal or buyer adds 4% (Amazon payment is free BTW). Thanks for looking! --Rick "Fine print" - I can declare a lower value for custom declaration purpose, but only if the buyer bears the risk of insurance covering only the declared value. - I bear the risk of having my gear damaged when it is being inspected at the buyer's country customs. Because of this, I demand international buyers to send payment using PayPal Gift. - All products are tested before shipping. But if the buyer finds a problem and reports to me within seven days, I will issue a refund upon a third-party inspection. The third party will be any Headphoneus Supremus of the buyer's choice (has to be CONUS based). The Headphoneus Supremus will get the product from buyer and tests to see if there is any problem. If there is, the product will be shipped back to me, and I will issue a full refund and reimburse shipping. But if the Headphoneus Supremus determines that there is no problem, the product will be shipped back to the buyer, who will bear all the shipping charges, and will not receive any refund. Because the Headphoneus Supremus is chosen and contacted by the buyer, I will not be responsible if the product get stolen, lost, or damaged in the process.