Introduction

Head-Direct is an online headphone store which sells just about everything you need in order to get a serious listening rig. It seems that the guys behind Head-Direct are constantly developing new and interesting products for the headphone market. Today we will be taking a look at their newest products which is called the EF1. The EF1 is a hybrid tube amplifier meant for driving headphones.

The amplifier uses tube based amplification for the input stage and solid state op amps for the output. The tube can be easily swapped so that you can alter the sound. The thought behind the hybrid design is to combine the best of both worlds, the lush mids of tube based amplifiers and the clean output of solid state op amps. There are a few major benefits from having such a design. One is that the amp will sound good both with low and high impedance headphones, whereas most tube amps do the best with high impedance headphone. Another is that the tube buzzing is kept at a minimum which is nice if you like a clean output.

This little amplifier will run you $399 and is aimed primarily at audiophiles that crave good sound. The EF1 was a two piece design, you have an out board power supply and then the main amplifier unit. The "brick" PSU is, however, plenty capable of supplying the amp with more than enough juice.

Specifications

• Opamp: OPA275
• Tube: 12AU7 (SINO)
• Frequency Response: 20-30K Hz
• THD+N: less than 0.2%
• S/N: more than 95dB
• Input impedance: 50K Ohm
• Output impedance: 2–2K Ohm headphones
• Output signal strength: up to 15 Volts at 32 Ohm
• Input: RCA x 1
• Output: 1/4 headphone jack x 1
• Dimension: 110mm(W)x 50mm(H) x 270mm(D), or 4.33inch(W) x 1.97inch (H) x 10.63inch (D)
• Weight: 750g (without power supply)
• Accessories: 12AU7 tube, 18V AC power supply
• Origin: China (Hand built in Shanghai)

The tube is a 12AU7 so you have lots of options to tune the sound. When you order the EF1 you get both a new Chinese tube and a NOS (New Old Stock) RCA tube. The difference between the two is quite big, and the RCA tube outperforms its newer Chinese counterpart in every scenario. If you are going to get this amp be sure to pick up a NOS tube or two while you are at it.