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Hiss/ground problems on a LTA MZ2/40

Hi all,

I bought a MZ2 secondhand about 6 months ago, I used it some time as integrated and everything was good.

A couple of months I also purchased secondhand a ZOTL40, and when I hooked up the Microzotl as preamp I start experiencing some ground noise issues, which eventually by manufacturer recommendation were solved by unplugging the ground cable spade connector on the Linear power supply. That solved it.

I'd be curious to know if other owners have experienced a similar issue, and wether this is a safe solution or not, and what to do otherwise.

The system ran silent for quite some time, until I started noticing a noticeable hiss coming from the tweeter of my speakers (Tekton Double Impacts), nothing accentuated but eventually hearable from a few feet away.
Initially I thought was on the power amp, and sent it to the manufacturer for a check, but they couldn't replicate the issue.

The hiss can only be hard when plugged to the poweramp, otherwise MZ2 operations on headphone or integrated are dead quiet.

I have realised recently that swapping tubes from 12at7 to 12au7 has reduced the hiss. When hooking up other devices to ZOTL 40  (a phono amp, or a chord mojo) i haven't experienced any ground or hiss issues at all.
I recently have purchased an extra linear power supply, but the hiss is still there.

Just want to say that LTA has been extremely supportive, and helped me a lot trying to figuring out this problem on a long email exchange.

I'd be curious to know from other owners if they ran into something similar, and if eventually have sorted out a solution.

Many thanks.
any-major-dude
tuckia08
23 posts
 
Dude,

Are the MZ2 and amp plugged into the same electrical circuit? If they are on different phases of the supply AC hum can occur.

Also, is a WiFi transmitters anywhere near the equipment?

Have  you changed the octal tubes (6sn7 or 12sn7). Is the hiss even in both channels. Have you swapped tubes right to left.

Greg

any-major-dude OP
3 posts
 
Yes, plugged in the socket and currently on Isotek Sigmas GII mains conditioner. I also tried connecting to another socket via an extension, but can't say if in another circuit.

No Wifi Transmitter near the equipment, likewise I have tested many times by disconnecting all appliances near my amps.

Also repeatedly tried to swap tubes. from old to current production, left to right, right to left and as well on the octal ones.

The hiss is in both channels, the only thing that reduces it is when using lower gain tubes as the 12au7. It is still audible compared to when plugging my Chord Mojo into the ZOTL40, as then the hiss is a inaudible.

Prior the MZ2 ran without problem, but I had to disconnect the green spade connector in the LPSU in order to get rid of the ground hum. 

tuckia08
23 posts
 
My MZ2 exhibited something like a beat frequency with the fundamental a little less than 60 hz. Found out it was from the WiFi unit about 8 inches away. I moved it two feet away and the noise stopped. 
I ve had half of a 6sn7 fail and it started to hiss (tube rush) prior to outright failure. 
My microzotl preamp exhibited an AC hum in both channels, but unbalanced. It was traced to an internal jumper that wasn’t making good contact.
But I haven’t seen what you are hearing (synaesthesia?) before. 

Are your interconnects making good contact? Any broken ground wires in them (does happen). 

I’d try to figure out that AC ground hum problem first. Is it at 60 Hz?

Through my ordeals LTA was very helpful as well. Obviously something isn’t right somewhere. Keep trying.

Greg

any-major-dude OP
3 posts
 
I get this hiss problem with no source connected, swapped three pairs of 12sn7 and the factory 6sn7 all with the same result.

Only when swapping ecc81 to ecc82 the hiss is reduced, but still noticeable.

I also have it replicated when plugging the MZ2 into a tube low integrated directly in the line input, the cheap integrated is much quiter than the MZ2 it self.

The ground issue is more of a 50hz ground loop noise, eventually I had to disconnect the green ground cable in the LPSU.
After that the unit was silent for a little while.

I chatted with LTA regarding the ground problem, and as I understood it's a common issue with the LPSU, even though I haven't read similar experience. I am concerned on the safety of keeping the ground cable unplugged.
Bare in mind I live in UK, and not sure wether there could be any difference on how the unit will operate from US voltage.

Got my socket tested with one of these: https://www.amazon.co.uk/gp/product/B01L4PODU2/ref=oh_aui_detailpage_o06_s00?ie=UTF8&psc=1
and it's all good.

Just yesterday I read they now offer an upgrade for the Linear supply, which hopefully will get the ground problem sorted, I need to follow up with them, in that case I'll send also my unit for inspection.

Really love how the MZ2 sound otherwise, and getting this problem sorted will put some piece of mind. Otherwise I would consider selling.

I see you have the new LTA preamp, was considering that as un upgrade at some point.
kw6
691 posts
 
My MZ2 with stock switching power supply is only several months old using it with some amp. Using Magnepan speakers. Tubes are nos Mullards and Shaugaung Black treasure CV 181. I don't detect any noise.
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