Melos user, please help!

[egg]

I just bought a second hand melos sha1. There is no problem when pair with hd600. When I pair it with HD25, or other low ohm earbud, there is a quite loud hmmm sound in the background(from no volume to high volume, in high volume, the hmmm will cover by the music, so it is not obvious. When playing quite music like piano solo, the hmmm sound can be hear which is quite disturbing.)

Is it normal??? Or mine melos has something wrong? Which part?

I am a newbie in audio equipment and please help.

Thank you.

 

[egg]

Is it due to the power cord or the tube?

 

[bozebuttons]

No this is not normal for a melos they are very quiet.
You may have a ground loop problem or a bad tube.
If not contact member Carlo as he mods Melos amps.

 

[Andrew Pielet]

Quick way to see if it is a tube- tap the tube w/ the eraser end of a pencil. You will hear the static if it is a bad tube.

 

[Hirsch]

Is the noise in one channel or in both? If in one channel, try switching the tubes. If the noise changes sides, you've got a bad tube. If the noise is in both channels, start looking for ground loops. A "cheater plug" that converts a three-prong plug to two prong may help if it's a ground loop (If this eliminates the problem, there's definitely a ground loop somewhere that you need to correct). I've also had situations where noise was coming in through the power lines. A good power conditioner can eliminate EMI/RFI noise coming in that way almost completely.

 

[egg]

Thank you for your help.

The hmmm is from both channel. I guess it is not the tube problem cos only the headphone with low ohm affected.

If it is ground loop problem, is it easy to fix, or need to send it to MAR for repairment??

 

[Hirsch]

A ground loop is part of setting the unit up. Make sure that all components connecting to Melos are connected to the same electrical outlet.

Unplug everything from the outlet, so that the Melos has nothing connected to it except the headphones. Does it still hum? If so, try the three-prong to two-prong adapter described above. If that fixes the hum, ground loop is confirmed.

MAR cannot repair a ground loop. It's a setup issue, not something wrong with the amp. It could also be related to your house wiring.

Another possibility is noise coming in through the power lines (I had an amp that had big problems with this recently). In that case, a good power conditioner may be worth trying.

The output of the SHA-1 should be able to power any impedance. Noise into a low impedance load might indicate an impedance mismatch in a pure tube amp, but the Melos is a hybrid and shouldn't have that issue.

 

[egg]

Thank you. I have tried the methods all you helpful members suggested:

1)I have tried the two prong plug, it can't eliminate the hmmm sound in any degree.

2)Make sure that all components connecting to Melos are connected to the same electrical outlet.

3)Unplug everything from the outlet, so that the Melos has nothing connected to it except the headphones. Hmmm sound exist as before.

4)the powder cord of my second hand melos is not the original one. I think it is a cheap cable. I also suspecting the problem is cause by that cable.

All I can find is another cheap powder cord, I exchange it to see whether the new cable can fix the problem or not, but it can't

5)I have try "Quick way to see if it is a tube- tap the tube w/ the eraser end of a pencil. You will hear the static if it is a bad tube." cos I don't really understand.

6) hmmm sound always coming from both left and right side of the headphone.

Do you figure out where the problem coming from?

Another question: there is two headphone jack, are they purpose for headphone with high ohm and low ohm? if so, which jack for which ohm? I observed that the hmmm sound is slightly louder when low ohm headphones plug in the jack in right hand side.

 

[Hirsch]

The cable is a passive component. It works or it doesn't, but it's unlikely to be a noise source.

Tapping on a tube is bad. Don't do it. You can damage a tube.

That said, it's possible that both tubes are bad. A replacement set could be worth trying.

The jacks are wired in parallel. They should sound the same, unless your unit has been modified.

You might want to try contacting Head-Fi member carlo through PM. He modifies Melos units, and may have a better idea where to look for the problem.

 

[Digital-Monk]

egg:

Did you ever find your problem? I have a similar problem, and feel it maybe the tubes, but want to confirm before I lay down cash for some new ones.

Thanks,
digi

 

[dsavitsk]

I am also a recent purchaser of a used melos. I have found that ety 4Ps (low impedence) have a bit of background hiss while 4Ss (high), do not. The hiss with the 4Ps seems to go away once volume is turned from 0. Also, Senn 600s do not. In my case, it is not annoying enough to consider it a problem yet, but i'll get there i'm sure.

-d

 

[carlo]

(thanks for the point to this Monk)

Play with the pots paralleled off the plate resistors if you have a blue board. These will be around your tube sockets. Otherwise, adjust the pots to the top left near the bias op-amp.

The problem could be the tubes, so buy new ones. Its worth having a backup anyway -> Old Stock Russian 6h23 works well in Melos and is relatively cheap.