Review on MT 602 Headphone Amplifier Tube 6J1 Preamplifier by Bill Sorenson

I tested this with Sennheiser HD6xx 300 ohm headphones and a Modi 3+ DAC as input. I compared the sound to my magni 3+ solid state amp using a custom made switch that allowed me to toggle the headphone output between two amps playing the same music and volume. It had more than enough power for the HD6xx. A pleasantly loud listening level had a volume at 10 o'clock. I had to set the volume to 12 o'clock on the Magni 3+ to get the same level. In terms of sound, the MT-602 really added some warmth with the standard tubes, with extended bass and reduced mids, with some loss of detail and soundstage. . It wasn't a huge difference and if I wasn't switching between the two amps it would be harder to tell but it was definitely noticeable. The Magni 3+ was brighter, with more mid-range detail, which I prefer for a lot of music, but I also liked the warmer tone of the MT-602 for a change. Roll up different tubes for different sounds. Changing them was pretty easy. I've tried several GE JAN 5654w bulbs and couldn't tell any difference from standard bulbs. A minor downside is the lack of a high/low gain setting, meaning it's not good for low-impedance headphones as they just deliver too much power. I tried it with some ATH-AD700x 38ohm headphones and at low and even mid volume levels I noticed an imbalance between the left and right channels, probably due to low level potentiometer variability, which is not uncommon in less expensive amps is. Here the Magni 3+ was significantly better, even at higher gain levels, without this imbalance. I suppose it can still be used with those low-impedance headphones, but the quality has suffered at lower volumes. Overall it was a good amp that added a touch of tube-like warmth with plenty of power. I thought it was a great $100 deal. Update August 21st: I had the opportunity to roll a few different tubes and noticed certain differences. I can update them after I have the opportunity to record them longer. Mullard M8100 from the 1960s - increased soundstage, with good bass extension. The upper mids were also enhanced and perhaps went beyond adding detail and adding some harshness to things like the vocals. This can be a little tiring during long listening sessions. It was good for classical pieces, both for a small group and for an orchestra. These were the tubes with the clearest difference to the solid state amplifier. Sylvania 6AK5 from 1953 - pleasant warmth for bass and mids. Decent soundstage. These were probably the best tubes I've tried for all the different styles of music I've listened to, from classical, rock, jazz, vocals, instrumental to electronic. The difference to the semiconductor wasn't as pronounced as with the Mullard, but I liked the sound better overall. Voshkod 6j1p-ev - Good mid-range clarity, noticeable on vocals or instruments like the cello when you need more clarity. Some bass extension, but not as much as the Mullard. Not as warm as a Sylvania or even a GE JAN 5654ws, but overall a nice sound somewhere between Mullard and Sylvania.