I was the proud winner of the Head-Direct.com recent EF1 lottery give-away, and wanted to report on my findings with the amplifier.
The Head-Direct EF1 is a tube hybrid amp of their own design. It uses a dual channel opamp in the output stage and a 12AU7 type tube for the input stage. It uses the OPA275 opamp and the tube is reported to be a new production Chinese tube here on head-fi but the Head-Direct website says it is supplied with an RCA cleartop. Skylab had the chinese tube and he recommended the NOS RCA cleartop as well, so it may have been changed at that time. My tube doesn't have any markings and I don't have any spares for the EF1 right now. I do plan to try a cryo'd Mullard re-issue tube next week when my quad arrives for my Woo GES, and I have a pair of Amperex Bugle Boy 12AU7 coming too. I checked and found that we can use a 12AX7 in the EF1.
I really like the EF1 from the short amount of time I have spent with it (4 days of ear time since the 23rd when it arrived). I put over 80 hours on the tube (with 180 on the amp) at the time of the review, and have tried a selection of my favorite headphones and favorite music with it. I have to say Wow - this EF1 has crazy synergy with my APS V2 Denon D2000, like they were made for each other. It is also very good with my APS V3 cabled RS-1 and APS V3 Edition 9, although any synergy with my HD600 is not as remarkable. The remarkable thing is my Edition 9 are usually picky about amplification as they can sound boomy and dark with the wrong amp, but no such problem exists with the EF1. The EF1 with the HD600 is still very nice, but it doesn't knock my socks off like my more expensive amps, or like the EF1 with D2000.
In comparison with my Apogee mini-DAC headphone out, while the Apogee is technically very accurate and capable with these D2000, the EF1 conveys better emotion. The EF1 is also non-fatiguing, which the Apogee does to me with my D2000 sometimes. I have to say that the EF1 is a above that level of performance as far as listening fatigue, tonality and sound signature; and I liked that it is not too forward with my headphones. It has a relaxed smooth sound and is slightly warmer colored than my current SS amps (excluding the Single Power) with a seductive rich flavor. I previously compared it to like being a Mocha Latte (maybe with Kaluha) while the Grahm Slee NOVO was more like sparkling water (refreshing and clear and transparent with little taste of it's own). This does not mean to imply that the EF1 is dark or rolled off in the highs, which it is not; nor does it mean to imply that it is slow and thick sounding, because it is not. In rock music guitars are still crunchy, in jazz the saxophone is warm and breathy and reedy at the same time, hard strikes on piano keys don't drill into my head, and in electronic music like Infected Mushroom the attack is fast and punchy.
The EF1's soundstage isn't as wide or expansive as my single ended Woo WA6 Maxed w/PDPS and Sophia Princess rectifier ($1250) or my balanced Single Power Square Wave XL 2008 model with Blackgates (also $1250), but it sure is very enjoyable nevertheless. Instruments still have their place and position in the soundstage, it just doesn't have that same holographic 3D feeling that I sometimes get with the more expensive Woo WA6 or balanced Single Power amps.
At this point I prefer to listen to the EF1 above my Meier Headfive, Travagans Red/Green, or the headphone out of my Apogee mini-DAC which a few people have said is on about the same level as a Gilmore Lite. The only two amps in the house that I like more than the EF1 are the WA6 Maxed w/PDPS or Single Power Square Wave XL balanced at 3x the cost. The Dark Voice 336i is the odd duck out because of it's great synergy with the HD600, but it is not as enjoyable with the RS-1, Edition 9 or D2000 as they are with the EF1. I do have $120 worth of JAN CRC RCA 5692/6AS7G tubes in the Darkvoice as well, so it would be around the same price as the EF1 and typically sounds about as good as the Apogee head-phone out. But in this case the EF1 beats the 336i with three out of four of my top dynamic phones, and it's still close with the HD600 (which I am listening to now as I type this - and it is improving with more hours on the EF1 too). Right now the EF1 is still better with HD600 than the Apogee mini-DAC headphone out or my other lesser amps in the house. All four of those headphones have the APureSound cable on them, but the Denon D2000 and HD600 are both terminated with a 4-pin balanced neutrik plug and I use APureSound adapters to connect them to either single ended or balanced amps as needed. The RS-1 and Edition 9 are both single ended only.
As for the $400 loaner Grahm Slee beta NOVO that I recently reviewed, it is no longer here to directly compare amps. Nothing stood out as being particularly wrong with the NOVO while I had it, and it was also ranked similarly to the EF1 in comparison to my other amps. But the NOVO really benefited from an additional cost PSU to rise to the level that it did - which means it was no longer a $400 amp. The EF1 already seems to have a good PSU which is a large 15v 1.5A power brick that sits between the amp and the wall (about the same size as the power brick for my Single Power). The EF1 is being enjoyed here right now, and I don't believe I would give it up for the NOVO if someone wanted to trade amps with me.
The one complaint that I have is that there is a small amount of noise that can be heard with the volume all the way down, but it is quiet enough to be well below the music with full-size headphones, and was most noticeable with my Edition 9 but not hardly at all with my D2000. Skylab says, "According to Fang from Head-Direct, the reason for this is because they use an active volume control, which Fang says results a lot of sound quality benefit specifically from this design." The good news? With the Edition 9, I found that between 12 - 3 o'clock on the volume it was very quiet, so I used my Apogee mini-DAC as a preamp and controlled the volume with the Apogee like I do with my other amps.
In the end, I find the Head-Direct EF1 to be a very nice amp in it's price range and well worth the $400 asking price. I would pick this over my Dark Voice 336i, Travagans or Meier Headfive (although the Travagans speaker output is great with electrostatic transformers for my basement rig). What I can't decide is whether it goes in my bedside rig or my basement rig - it gives me good reason to finally sell my DV336i except for the fact that I have twice as much $ invested in the tubes for the 336i than I paid for it.
The Head-Direct EF1 is a tube hybrid amp of their own design. It uses a dual channel opamp in the output stage and a 12AU7 type tube for the input stage. It uses the OPA275 opamp and the tube is reported to be a new production Chinese tube here on head-fi but the Head-Direct website says it is supplied with an RCA cleartop. Skylab had the chinese tube and he recommended the NOS RCA cleartop as well, so it may have been changed at that time. My tube doesn't have any markings and I don't have any spares for the EF1 right now. I do plan to try a cryo'd Mullard re-issue tube next week when my quad arrives for my Woo GES, and I have a pair of Amperex Bugle Boy 12AU7 coming too. I checked and found that we can use a 12AX7 in the EF1.
I really like the EF1 from the short amount of time I have spent with it (4 days of ear time since the 23rd when it arrived). I put over 80 hours on the tube (with 180 on the amp) at the time of the review, and have tried a selection of my favorite headphones and favorite music with it. I have to say Wow - this EF1 has crazy synergy with my APS V2 Denon D2000, like they were made for each other. It is also very good with my APS V3 cabled RS-1 and APS V3 Edition 9, although any synergy with my HD600 is not as remarkable. The remarkable thing is my Edition 9 are usually picky about amplification as they can sound boomy and dark with the wrong amp, but no such problem exists with the EF1. The EF1 with the HD600 is still very nice, but it doesn't knock my socks off like my more expensive amps, or like the EF1 with D2000.
In comparison with my Apogee mini-DAC headphone out, while the Apogee is technically very accurate and capable with these D2000, the EF1 conveys better emotion. The EF1 is also non-fatiguing, which the Apogee does to me with my D2000 sometimes. I have to say that the EF1 is a above that level of performance as far as listening fatigue, tonality and sound signature; and I liked that it is not too forward with my headphones. It has a relaxed smooth sound and is slightly warmer colored than my current SS amps (excluding the Single Power) with a seductive rich flavor. I previously compared it to like being a Mocha Latte (maybe with Kaluha) while the Grahm Slee NOVO was more like sparkling water (refreshing and clear and transparent with little taste of it's own). This does not mean to imply that the EF1 is dark or rolled off in the highs, which it is not; nor does it mean to imply that it is slow and thick sounding, because it is not. In rock music guitars are still crunchy, in jazz the saxophone is warm and breathy and reedy at the same time, hard strikes on piano keys don't drill into my head, and in electronic music like Infected Mushroom the attack is fast and punchy.
The EF1's soundstage isn't as wide or expansive as my single ended Woo WA6 Maxed w/PDPS and Sophia Princess rectifier ($1250) or my balanced Single Power Square Wave XL 2008 model with Blackgates (also $1250), but it sure is very enjoyable nevertheless. Instruments still have their place and position in the soundstage, it just doesn't have that same holographic 3D feeling that I sometimes get with the more expensive Woo WA6 or balanced Single Power amps.
At this point I prefer to listen to the EF1 above my Meier Headfive, Travagans Red/Green, or the headphone out of my Apogee mini-DAC which a few people have said is on about the same level as a Gilmore Lite. The only two amps in the house that I like more than the EF1 are the WA6 Maxed w/PDPS or Single Power Square Wave XL balanced at 3x the cost. The Dark Voice 336i is the odd duck out because of it's great synergy with the HD600, but it is not as enjoyable with the RS-1, Edition 9 or D2000 as they are with the EF1. I do have $120 worth of JAN CRC RCA 5692/6AS7G tubes in the Darkvoice as well, so it would be around the same price as the EF1 and typically sounds about as good as the Apogee head-phone out. But in this case the EF1 beats the 336i with three out of four of my top dynamic phones, and it's still close with the HD600 (which I am listening to now as I type this - and it is improving with more hours on the EF1 too). Right now the EF1 is still better with HD600 than the Apogee mini-DAC headphone out or my other lesser amps in the house. All four of those headphones have the APureSound cable on them, but the Denon D2000 and HD600 are both terminated with a 4-pin balanced neutrik plug and I use APureSound adapters to connect them to either single ended or balanced amps as needed. The RS-1 and Edition 9 are both single ended only.
As for the $400 loaner Grahm Slee beta NOVO that I recently reviewed, it is no longer here to directly compare amps. Nothing stood out as being particularly wrong with the NOVO while I had it, and it was also ranked similarly to the EF1 in comparison to my other amps. But the NOVO really benefited from an additional cost PSU to rise to the level that it did - which means it was no longer a $400 amp. The EF1 already seems to have a good PSU which is a large 15v 1.5A power brick that sits between the amp and the wall (about the same size as the power brick for my Single Power). The EF1 is being enjoyed here right now, and I don't believe I would give it up for the NOVO if someone wanted to trade amps with me.
The one complaint that I have is that there is a small amount of noise that can be heard with the volume all the way down, but it is quiet enough to be well below the music with full-size headphones, and was most noticeable with my Edition 9 but not hardly at all with my D2000. Skylab says, "According to Fang from Head-Direct, the reason for this is because they use an active volume control, which Fang says results a lot of sound quality benefit specifically from this design." The good news? With the Edition 9, I found that between 12 - 3 o'clock on the volume it was very quiet, so I used my Apogee mini-DAC as a preamp and controlled the volume with the Apogee like I do with my other amps.
In the end, I find the Head-Direct EF1 to be a very nice amp in it's price range and well worth the $400 asking price. I would pick this over my Dark Voice 336i, Travagans or Meier Headfive (although the Travagans speaker output is great with electrostatic transformers for my basement rig). What I can't decide is whether it goes in my bedside rig or my basement rig - it gives me good reason to finally sell my DV336i except for the fact that I have twice as much $ invested in the tubes for the 336i than I paid for it.
