My MK IV SE arrived Friday, but sadly it's been plagued with a problem I'm unable to pin-point. The first evening of firing it up I enjoyed a listening session of sonic bliss. Even straight-out-of-the box - with an also brand new HD 650 and source (the Little Dot DAC_I) - the sound was very impressive. It was more engaging, alive, detailed and realistic compared to anything I'd heard up until this point - this is the closest I've ever come to feeling like I'm listening to a live performance from audio equipment.
However, the next morning - eager to repeat the experience - I fired the amp up and left it playing to warm-up and continue the burn-in while I went about the morning's duties. Upon putting the phones on my head to settle down to another listening session, I could hear a very clear rustling/crackling/squeaking sound coming from the left channel. I could hear this noise with the volume set to 0 and the source turned off. I wasn't too worried initially, I'd read many accounts of tube pins becoming oxidised during transit, and so got to work cleaning all tube pins with isopropyl alcohol. This didn't solve the problem, so I decided to try swapping the tubes around (driver first, power second) so see if I had a dodgy tube. I also checked the gain switches and moved them back and forth several times. None of this made a difference either.
To cut a long story short, I repeated swapping tubes and moving the gain switches a good number of times to try to pin-point the issue. During this trouble-shooting, the issue moved to the right channel and then back to left, however I have never heard the noise from both channels during the same listening session. I have also been unable to identify a gain switch or tube as the cause, because while the issue did move back and forth channel, it does not move with the adjustment/re-positing of any of these components. I have followed literally every recommendation in the troubleshooting guide (swapped fuse, power plug, checked tube jumper position and turned off all electrical equipment in vicinity and moved the amp to a different location), I've also tried the HD 650 in a different amp and used a different source with the MK IV to be sure.
Today I purchased some electrical contact cleaner to clean the tube pins, sockets and gain switches as I understand this can be more effective at cleaning electrical components than isopropyl alcohol. I've been in touch with David who directed me to follow the trouble-shooting guide but hasn't offered any other suggestions so far. If the contact cleaner doesn't do the trick (I'm doubtful it will as the tube pins look clean to me), then I see no alternative than to send the amp back, and I'll be insisting Little Dot pay postage.
If anyone has any further ideas or tricks I'd be grateful to hear them. I'm loathed to send the amp back, as after hearing its potential, I'm really keen to start enjoying it.