The beginning...

My first foray into tube-based HiFi systems was with the Grant Fidelity Tube DAC-09 pre-amplifier, which is a hybrid design pre-amplifier with a tube-front end coupled with a DAC-based input. It also could act as a switch, and also feed in RCA-based signals through the tube --- acting a bit like a tube buffer. A nice review of the pre-amplifier can be found on DaGoGo. I used it for about 3 years before moving to a solid-state DAC for SMSL, it DAC-09 was excellent, but the tube sound did not fit well with some of the music I liked to listen to then --- heavy metal and electronica, the sound tended to get very muddy at times, sometimes I would bypass the tube for this reason.

Step up, DIY

At somepoint I was using a dual-mono block power amplifier setup from Temple Audio to drive my SABA speakers, and these had a lot of power --- even for 40W per channel. The input was provided by a pre-amplifier from ELEKIT, the TU-8500 which uses two 12AU7 tubes in the line stage amp. I built the TU-8500 myself, which was a lot of fun getting to understand more closely how a pre-amp works. I really really liked the TU-8500, and together with input from my SMSL M8 DAC, the sound was very pleasant. Unlike the DAC-09, the sound was not as strongly tinted by the tubes --- I never did any tube swapping here, sticking to the stock tubes which at the time of writing I can't remember what make they were.

The beast

Through a newsletter I found out that ELEKIT was releasing a new power amplifier based on the 300B tube amplification in a dual channel setup. The TU-8600 is a monster, and I think for ELEKIT the largest audio product they have ever designed at that point. I bought mine through a distributor in Poland (getAudio) and got the special offer that included some transformers from Lundahl (a Swedish manufacture of transforms and other electronic equipment), model LL2770. This version of the amp is known as the TU-8600VK.

Building this thing was tricky, as some of the parts are both heavy and delicate. Once assembled though, the build quality (choice of materials and design) was amazing. For this amp I initial bought some JJ 300B tubes, which worked fine and sounded reasonable. They were unobtrusive but for tubes tended on the boring side of things, for me.

After only a year of use though, the left channel tube broke --- a rather amazing experience, there must have been a crack in the glass and a slow leak of air was getting in, this led to sparks forming inside the tube. Before I could react though, one of the power transistors connected to the output stage of the tube blew, giving out the magic smoke. I had to go a fix this, before I could us the amp, but this wasn't too big of a deal thankfully.

I replaced the tubes with PSVANE T2, and have been using these ever since. The T2s are really really nice sounding, what impresses me the most is how quick they react and how much punch they have, especially for bass output. One negative of them though is that they suffer from microphonics.

I still use the TU-8600VK as my main speaker amplifier, and so far have not seen any reason to change this. I did move from using a SMSL M8 to a Audio-GB R2R R2 DAC, which was a fantastic upgrade --- I really like the idea behind R2R ladder DACs versus delta-sigma based chips from a purity idea. I realise though that this shouldn't have much effect on sound, compared to other components in your system like what speakers you use. I do believe though that higher grade R2R DACs with probably sound even better, but of course cost more due to the price of the resisters used in the ladder. I'm still waiting to get my hands on something like the Holo Audio R2R or a Soekris dac1541 R2R DAC which represent some of the highest performing R2R DACs available.

Loxjie P20

During the pandemic of 2020-202* (yeah, I'm a pessimist) I was working remotely and realised that I was really missing listen to music comfortably --- as much as I like my B&O headphones for travel, they aren't really great for long usage. Through a suggestion I was told to try out the Monoprice 1060C headphone, which is a kind of rip-off of the Audeze LCD-2 headphone (but cheaper). They are actually really nice, and the sound is very pleasant... I don't have much experience with headphones of this level. For the longest time I used Shure SRH440 for listening to music while commuting, but otherwise I didn't try out many other types of headphones.

To go with these LCD-2 rip-off headphones, I wanted a reasonable headphone amplifier. I found via Amazon that the Loxjie P20 were a nice tube-based headphone amp with reasonable power output. It was also pretty cheap at 99 Euro. I bought it and used it for a couple of months. During that time I came to really appreciate the importance of amplifier power output for headphones, the Loxjie could get loud, but I don't listen to music loudly. At my normal volume level, I found that a lot of the top and lower end just faded with the mids being overrepresented.

I bought a AK4493 based DAC, the SMSL Sanskrit 10th MKII. It isn't a jump-off-the-page kind of kit, and certainly is not comparable to my Audio-GD R2 DAC, but for this use case more then reasonable. Certainly I find I prefer AKM delta-sigma chips to ESS SABRE chips in sound character.

xDuoo TA-20

After some research for a new headphone amp with new power, I landed on the xDuoo TA-20. This amp was being recommended everywhere, but surprisingly was tricky to get in Europe for a reasonable price --- some places were selling it for over 600 Euro?! Eventually on eBay I came across and offer for the amp in like-new condition for 300 Euro... the price is a factor of 3 more then my Loxjie, but I was confident that beyond this, the next step for perceivable sound quality would be over the 1000 Euro mark, so for a long-term investment this looked OK to me.

I was very pleased, at my listening volume level, the sound is extremely even. The bass still punches and the highs don't fade off. I was listening to some Fleetwood Mac and was amazed to find that I was hearing sounds (extra tapping coming from the drums, string strums from the basses, etc.) that wasn't there before --- with the Loxjie or just my laptop's headphone output.

300B

These are massive tubes, which run at about 300 volts and can kick out some 40 watts. They are commonly used in single-stage class A power amplifiers, like the TU-8600.

My current collection of tubes are:

12Ax7

Also known as ECC82 in Europe, these tubes are popularly used in pre-amps/head amps/other smaller amplication systems. I started using these tubes when I got a deal off eBay for a xDuoo TA-20 head amp.

My opinons on the following tubes are based on my setup, where I have an AK4490-based DAC, the xDuoo TA-20 head amp, going into Monolith M1060c headphones. This setup tends toward slightly darker tones, so bright sounding tubes work better in this setup I feel.

My current collection of tubes are: