[rattesp]

My MKVI+ had the exact same problem. The hum from the transformer was so loud that I had to send it back to Little Dot. It seems they don't learn from their mistakes ... If I were you I'd ask for a refund.

 

[sebhoff]

Thanks, rattesp - that's an interesting comment!
I'll show the amp to the specialists at work today and will see what they say.

 

[LogicAudio]

Hum in there brings some possibilities to me:
 

1. transformers are winded unsystematically so they need more wire to reach the demanded coupling and the core saturates
2. transformer is starving some shellac so the windings get buzzed like piezoelectric and results in an unclean voltage
3. the PSU is not regulated. no Transformer can act as good and silent and linear as a good regulator
4. maybe a cold solder joint or something
5. try to give the tubes a finger fillip in case of a possible mica chip kinked in filament or somewhere
6. maybe your source impedance doesn't get along with device input impedance
7. if you're using 220V power, check the voltage with a multimeter to see if you have that 220 volts +-1% on the outlet. any voltage shortage may result in a much lower secondary voltage so the tubes won't be working in the optimum working loadlines which will result in an unintended hum on the plate output (also with 110v)

 

[sebhoff]

Thanks, LogicAudio for your input!
 
I've now spoken to our audio specialist at work. He confirms that the hum is from the transformer and that it *is* fairly loud. He also questions the claim by David from Little Dot that this is a "toroidal transformer". But he says that it's probably something I have to live with.
The low maximum volume seems to be due to the input level provided by the DAC. We tried it with a different headphone amp with the same result. Since I wanted to buy a DAC for work anyway, I'll just have to find one where the output level can be adjusted.
 
He did confirm, though, that the combo (LD MK9 + DT990) sounds great. 

 
 
The headphone amp he used was a model by Lake People. Interestingly, I immediately noticed something in the FLAC (some very high chirpy noise that must be an artefact of the FLAC-conversion) that I had never heard before. It seems that the Lake People amp produced the highs in a much more pronounced way than the LD. When I listened to the same position with the LD, I did notice the problem - but much less audibly so...
 
Sebastian

 

[sebhoff]

OK - quick update after one more week with the amp: I've now managed to change the gain settings in my Little Dot. There was some confusion because I was instructed by David from Little Dot that I would have to look for two red boxes with switches. But I simply couldn't find the second one. 

 In the end, I just set the switches on "high" on the single one I could get at - and now my amp produces more power. Good. I'll also get another DAC that should have a higher output level than my current one - this is likely to help further.
 
Soundwise, I feel that the amp produces more bass now than it did a week ago. But then again, this may have to do with the music I'm currently listening to. 

 

[Jasper9395]

Seems your enjoying the amp but could you give us some general impression of the character of the sound?

 

[sebhoff]

Sorry - I think I'm not experienced enough to do this. 

 Some time over the next few weeks, I'm planning to compare it to my only other relevant piece of equipment, a cheapo SMSL SAD-25 DAC. Once I've done this, I'll report back - but don't expect too much. In the meantime, I'm just enjoying what I'm hearing....

 

[sebhoff]

OK - after some more time with the LD 9, here's a quick update...
 
I'm generally happy with the amp, but there are/were two main problems:
1. transformer hum
2. a hum inside the headphones that turned up when the volume dial is past 70 
 
I have been able to solve the second problem: this goes away when I don't use USB as input method to the DAC (regardless of which DAC I use). I tried both a USB-to-Coax converter as well as a toslink cable - in both cases, the amp is completely quiet even at volume level 100. I don't know whether this is a problem of the LD amp or my computer (which has always been the source).
 
I have not been able to solve #1 yet, but at least I'm now closer to knowing what causes it... As soon as I remove the metal cover of the transformer, the hum is almost completely gone. It seems as if the cover works as a mechanical amplifier of the minimal vibrations that are produced by the transformer. Obviously, I won't want to use the amp without the cover - so I'll somehow have to find a way of absorbing the vibrations. Certainly not ideal but probably fixable...
 
Volume-wise, I've been fine since I bought a new DAC (and changed the gain settings). However, that DAC will need to be sent back (a Musical Fidelity V90-DAC) since the PSU produces a constant hiss that is not acceptable.
 
Sebastian

 

[MaDD0G]

Referring to the second problem, if your DAC usb input board has its own power supply, you can try to remove +5V pin from the USB cable. This should help to eliminate hum, that is transferred from the computer. At least it helped me. Sorry, cannot help with the transformer hum problem, I never never encountered this.

 

[sebhoff]

Ahh - that's an interesting suggestion! Thanks!
Sebastian

 

[Mr.J]

I came across this the other day. Maybe it will help you. http://rockgrotto.proboards.com/thread/4684

 

[derbigpr]

I don't want to sound like a hate, but this sounds like another poorly designed Little Dot. I've had 3 of them so far, the MKII, MKIII and MKV. All of them had problems. All hummed, buzzed, crackled, or in some other way underperformed. MKIII popped like crazy when turning it on or off with headphones plugged in, which is not supposed to be done, but it popped hard when plugging the headphones in and out when it WAS turned on, as recommended. It also distorted to hell and back when using it as a pre-amp. I ended up selling it because I was simply afraid to plug in any of my more expensive headphones. MkV hisses....no matter what I fcking do to it, it just hissed, but at least in other ways it works ok, most of the time, and actually sounds very good for the money. The only reason why I keep it.. MkII just combined faults from both amps. The biggest issue here is the fact that Little Dot company tries to convince buyers that all these issues are "normal". Well, they're not. I've had or still have Musical Fidelity, Pro-Ject, Rega, Nuforce and various other amps, including tube amps, and none of them had the issues. Plugged into same wall wart, used with the same DAC, PC, headphones, etc., all work perfectly while LD's don't. So the issue is in LD amps, there's a section somewhere inside that's poorly designed and is shared between various models, and no excuse is enough.

It's never good when you have so little confidence in a headphone amplifier that you're afraid to plug in your expensive headphones so they don't get damaged, and you unplug the headphone amp out of the wall when you leave your home in fear that the thing might catch on fire when you're gone because its freaking buzzing constantly, even when turned off. I also got lightly electrectured by the MkIII several times when touching the volume knob. You know those small shocks like when you touch the car and it shocks you...yea...very annoying. Sorry to do this, and I'm sure I'm an exception to the rule, but I have so little positive experiences and so many bad ones with LD that nobody could make me pay another one of their products. And it's sad because they KNOW how to make good sounding amps. They ALL sounded very good, but its the issues beside the sound quality that ruin the experience and just make the amps unusable for me.

 

[sebhoff]

I'm still looking for a solution to the transformer hum. A friend of mine has offered to make an aluminium replacement cover - this might help...
I'm generally happy with the amp - no hissing, crackling and the like, and the sound quality is fine. But the hum must go... 
Sebastian

 

[stuympy]

Has anyone tried to change gain? Are there switches like the IV?

David hasn't posted a manual yet

 

[guildenstern]

I don't want to sound like a hate, but this sounds like another poorly designed Little Dot. I've had 3 of them so far, the MKII, MKIII and MKV. All of them had problems. All hummed, buzzed, crackled, or in some other way underperformed. MKIII popped like crazy when turning it on or off with headphones plugged in, which is not supposed to be done, but it popped hard when plugging the headphones in and out when it WAS turned on, as recommended. It also distorted to hell and back when using it as a pre-amp. I ended up selling it because I was simply afraid to plug in any of my more expensive headphones. MkV hisses....no matter what I fcking do to it, it just hissed, but at least in other ways it works ok, most of the time, and actually sounds very good for the money. The only reason why I keep it.. MkII just combined faults from both amps. The biggest issue here is the fact that Little Dot company tries to convince buyers that all these issues are "normal". Well, they're not. I've had or still have Musical Fidelity, Pro-Ject, Rega, Nuforce and various other amps, including tube amps, and none of them had the issues. Plugged into same wall wart, used with the same DAC, PC, headphones, etc., all work perfectly while LD's don't. So the issue is in LD amps, there's a section somewhere inside that's poorly designed and is shared between various models, and no excuse is enough.

It's never good when you have so little confidence in a headphone amplifier that you're afraid to plug in your expensive headphones so they don't get damaged, and you unplug the headphone amp out of the wall when you leave your home in fear that the thing might catch on fire when you're gone because its freaking buzzing constantly, even when turned off. I also got lightly electrectured by the MkIII several times when touching the volume knob. You know those small shocks like when you touch the car and it shocks you...yea...very annoying. Sorry to do this, and I'm sure I'm an exception to the rule, but I have so little positive experiences and so many bad ones with LD that nobody could make me pay another one of their products. And it's sad because they KNOW how to make good sounding amps. They ALL sounded very good, but its the issues beside the sound quality that ruin the experience and just make the amps unusable for me.

 
I have only tried a single Little Dot product, the MkIII, which I bought secondhand maybe six months ago here ago on head-fi. I've had no problems with it, beyond an occasional susceptibility to RFI. My LD MKIII has worked steadily and reliably, no shocks or sizzles. It has cooperated with a few tries at tube rolling. It sounds good -- very very good. I have noticed that if the gain is set at highest settings, it can make typical ping-ing noises when plugging or unplugging headphones, but this is almost unavoidable given that the small signal tubes are almost all more or less microphonic. With gain set at 5, I get all the signal I need with my AKGs, and only a little bit of annoyance from microphonics when plugging or unplugging headphones. My amp hasn't "popped like crazy," and I hope it never does. Overall, then, so far, so good with my LD MKIII.