John Darko
Musical Fidelity’s X-Tube is a tube of tubes. It’s a tube buffer that sits in the signal path between the source device and the integrated amplifier (or pre- and power amplifier) to 1) improve the impedance relationship between those two devices and 2) infuse the sound with a little E88CC triode tube flavour.
One very popular source device of the last 12 months is WiiM’s Ultra streaming DAC. I wondered if the X-Tube might fatten up its sound, especially when running the WiiM as a pre-amplifier directly into a power amplifier. I often hear DAC-direct setups like this as quick but thin, but more times than not, I return an analogue pre-amplifier to the chain.
There was only one way to find out…
I was in Lisbon when the X-Tube was announced. Would Musical Fidelity send a sample unit to me in Portugal asap – so that I might take a listen with the WiiM Ultra and shoot some photos – and then send a second unit to Berlin for the video treatment and further listening? Yes, they would. The plan was set within 24 hours; so hats off to Musical Fidelity for its speedy response and double unit dispatch.
Then things began to fall apart.
FedEx bounced the Portuguese-bound unit between its delivery van and the Lisbon depot for five straight days. I was home for at least three of those. Then, for a further five days, the world’s best-known courier company sent me email notifications stating that the package would be delivered ‘tomorrow’. That tomorrow never came.
I flew back to Berlin and two days later, cameraman Olaf stopped by for a full day of b-roll shooting (Patreon timelapse video here). We left the X-Tube for the final hour. Not only did I want Olaf to film its unboxing and setup, but I wanted him as a second pair of ears.
An AudioQuest Evergreen interconnect joined the WiiM Ultra’s output to the X-Tube’s ‘input’ RCAs. An AudioQuest Thunderbird interconnect took the analogue signal the rest of the way to Technics SU-R1000 running as an integrated amplifier. Here, we used the X-Tube’s ‘output’ RCAs.
Then I hit play.
Was there a night and day difference? Nope.
More audible than any fattening of the sound was a new noise: a hum that spilled almost evenly from both loudspeakers. This hum became a proper growl when moving the Ultra to pre-amplifier duties and re-purposing the SU-R1000 as a power amplifier.
Time to troubleshoot.
I tried a different interconnect between the X-Tube and the Technics…and the hum roared on. Thanks for nothing, Cambridge Audio. /jokes
Could it be the overall setup?
I moved the ‘output’ cable to the ‘bypass’ RCAs that are internally wired to the input RCAs to bypass the tube board completely — and the hum all but vanished.
With the output cable returned to the ‘output’ RCAs, I tried a different power amplifier: the Mola Mola Perc. My X-Tubed system still hummed.
The way I saw it, the X-Tube was unusable. That was Saturday.
On Sunday, I made a Patreon-only video about my initial experiences with Musical Fidelity’s tube of tubes, not to throw them under the bus but to ‘show’ the hum (Olaf filmed it) and to make the point that when reviewers are met with unexpected behaviour from a review sample, their first response should be to contact the manufacturer and not hang them out to dry on YouTube.
I also sent the video to my Musical Fidelity contact, who described it as ‘fair’. Perhaps my sample is faulty. It might have been damaged in transit. Only a replacement will tell.
This morning – Monday – I made three more changes to the system. The first was a new source device: I swapped out the WiiM Ultra for the Grimm MU2, and the hum was as loud as ever. Oof.
I then swapped out the Technics amplifier for the Luxman L-505z integrated and heard no change to the hum’s presence. Yikes.
Lastly, thinking it might be the power conditioning, I moved the X-Tube’s power cable from an AudioQuest Niagara 1200 to the wall. And. It. Still. HUMMED. 😫
What we have here is the first half of our forthcoming YouTube video’s story. A replacement X-Tube will provide the second. Hang tight.
Further information: Musical Fidelity
