O1-DAC by Head-Direct

This is a brief intial review of the new O1-DAC headphone amplifier marketed by Head-Direct.

I exchanged several emails with Fang regarding the sound and build quality of the new amp/dac that they are now offering. I have had nothing but superb experiences with Head-Direct when purchasing my Yuin PK1 and PK2 earbuds.

Based upon the quality of the Yuins and the positive experiences that I have had previously with Head-Direct, I decided to order one of the new O1-DACs.

The amp arrived within a couple of days, very securely packaged. Upon opening the package, I found a rather large, quite heavy amplifier which appeared to be of quite high build quality. The amp measures about 6.25" long X 4.5" wide X 2.5" high.

Although too large to be considered a portable amp, the footprint is no larger than my Earmax Pro since the power supply is housed within the O1-DAC rather than using an outboard power supply such as found in the Earmax and many other headphone amplifiers. The lack of battery power also effectively rules out portable use.

The front panel of the amplifier is very clean, containing only a volume knob on the right, a blue LED pilot light in the center and a 1/4" stereo phone jack on the left side of the amp.

Located on the rear is a recessed 3-prong AC plug such as found on printers and as such is removable. Also on the rear of the amp is the On/Off switch, Aux, Optical, and Coax inputs. There is, however, no USB input to the DAC. Switching between sources is automatic, depending on which input is used.

Although at this time, I have only about 4 hours burn-in time on the amp, the sound is superb. I can best describe the sound signature of this amp as being one of the most neutral-sounding headphone amplifiers that it has been my pleasure to hear. Whatever goes in comes out exactly the same except with gain. Bass is deep, solid, and well-defined. Highs are clear and refined, with no evidence of sibilance.

The soundstage is wide and open, with performers and instruments remaining solidly in place. With no input, the background was totally black regardless of which phones I used.

The most noticeable thing one first discovers is the very wide dynamic range that is effortlessly presented. It is apparent that there is considerable horsepower under the hood of this amp!

Using my iRiver H-140 as a reference source playing 320 bitrate recordings and with my Sennheiser HD650s as the primary evaluation headphone, the O1-DAC volume control needed to be at about the 9:30 position compared to the 2-2:30 position on my Xin Reference for my normal listening levels.

The DAC optical input sounded the same as the aux input, clear, very detailed, and very neutral.

Considering that the price of this amp was only $299 including shipping, I feel that it is truly a bargain for those needing a dedicated desktop or workstation headphone amp of high quality and relatively small size.

The only nit that I can pick is that it does not have a USB input to the DAC. I certainly have nothing but praise for the sound, especially considering the pricepoint of this amp.

Below is a reply from Head-Direct to one of my inquiries for information regarding the performance of the amp:

"O1 and O1-DAC was designed by Mr. Jia, an EE PhD from Tsinghua University, the best engineer school in China. If you don't like it, return it in 30 days to get a 100% refund."

Below is a size comparison between the O1-DAC, iBasso D1 and the Xin Reference:

I have not opened the amp, as it takes a bit of work. I was told by Fang at Head-Direct that the boards are epoxy sealed. I am assuming that one cannot roll opamps, but I seriously doubt that I would want to change the sound of this amp.

I have compared it to my Earmax Pro, and it needs to make no apology to the Earmax.

I did compare the optical input of the O1-DAC to the Optical input of my Headroom Ultra Micro DAC and hear no discernable difference, at least with my iRiver source. That is pretty impressive to me as the Headroom DAC is twice the price of the O1-DAC!

To be very candid, I was not expecting this quality of sound from a $300 amp but I have found the Head-Direct folks to be very forthright in the information that they provide.

Although I haven't yet examined the inside, based on its weight I would assume that there is a transformer of considerable heft inside. It is much heavier than I expected for a solid-state amp. It has tighter, deeper bass than almost anything I have heard and delivered in a completely effortless fashion.

See my comments above regarding the comparison of other DAC. I have only compared it to the Headroom and iBasso optical inputs. As it lacks a USB input, I can't really evaluate it directly with the others, however it sounds just as good when feeding it the analog output of the iBasso or Headroom USB input.

If I could find any real sonic faults, I would certainly mention them. I have no connection with Head-Direct other than being a very satisfied customer.

You cannot use the DAC only, as you can with the D1. You can, however, use the amp only by going thru the RCA jack line inputs.

That is not what I stated. I compared the DAC of the O1-DAC with that of my D1 and Headroom Ultra Micro DAC, using the optical output of the iRiver.

Perhaps the subtleties of the differences between the DACs were more than my ears could discern, but they all sounded excellent.

I don't think there is a difference in the amp section, I believe that what was meant was that any amp will likely sound better with a digital input such as optical, coax, etc rather than with an analog input.