[toufeeq]

You could send that 5998 to me for further evaluation.. (and letting it bake for another 72 hours might help, if not you might have a bad tube) ;(

I know its recommended for the 6SN7 tubes to be burned in for 72 hours but does that apply to the 6AS7 tubes as well? That seems like a recipe for overheating?

 

[JKDJedi]

I know its recommended for the 6SN7 tubes to be burned in for 72 hours but does that apply to the 6AS7 tubes as well? That seems like a recipe for overheating?

Good question for the 6as7 guys, and although I wouldn't leave a 6as7 tube on for 72 hours, a humming tube that I might end up throwing away? Yeah, I'd let it burn in good before going that route.

 

[DenverW]

That’s a long time for the amp to be powered on and while it would probably be fine, I wouldn’t recommend it until a last attempt. As I mentioned in my pm I would try some different inexpensive power tubes with different gains and see what that does, I’ve got some tubes that always hum together but don’t with different combinations.

 

[Xibipiio]

Nevermind, it returned after 5 minutes. So on power on and while it is warming up, there is no hum. The hum sets in after 5-10 minutes of use.

Oh man, sorry about that...for a minute there I thought we’d solved it. All I know to do is swap in new tubes and see if it helps.

 

[sennfan83261]

I know its recommended for the 6SN7 tubes to be burned in for 72 hours but does that apply to the 6AS7 tubes as well? That seems like a recipe for overheating?

Personally, I wouldn't burn in power tubes (6AS7, 421A, 5998, 6080, 7236, etc.) for that length of time unattended for safety reasons, which is why I never seen anyone recommend burning in power tubes outside of this thread. Strange that the OEM tubes that came with your unit exhibited hum unless you didn't burn in the OEM 6SN7 tube before. Did you check your signal chain? If you are using a DAC or your motherboard, did you hook it up to another amp? Did you plug in your Darkvoice to another outlet? Is your source plugged into a different outlet from the Darkvoice (i.e. noise from ground loops).

 

[toufeeq]

Did you check your signal chain? If you are using a DAC or your motherboard, did you hook it up to another amp? Did you plug in your Darkvoice to another outlet? Is your source plugged into a different outlet from the Darkvoice (i.e. noise from ground loops).

I have a Schiit MODI 2 as my DAC and I use a RCA splitter from out RCA out to feed the Darkvoice and a Schiit Magni. When I plug the headphones(Senn HD6xx) to the Magni, I get no hum and it is clear. I tried my Audeze LCD-2Cs as well and got the hum on the DV but not on the Magni.

The DV is plugged directly into the wall and is separate from the power strip for the Magni/Laptop.

At this point I think I have one of three options:

1. Try the 72 hr burn-in process with the tubes I have (Tung Sols; 6SN7GTB and 5998)
2. Get a different 6AS7 or 6080 power tube
3. Try the Fitz mod which would probably be my last resort.

 

[sennfan83261]

I have a Schiit MODI 2 as my DAC and I use a RCA splitter from out RCA out to feed the Darkvoice and a Schiit Magni. When I plug the headphones(Senn HD6xx) to the Magni, I get no hum and it is clear. I tried my Audeze LCD-2Cs as well and got the hum on the DV but not on the Magni.

The DV is plugged directly into the wall and is separate from the power strip for the Magni/Laptop.

At this point I think I have one of three options:

1. Try the 72 hr burn-in process with the tubes I have (Tung Sols; 6SN7GTB and 5998)
2. Get a different 6AS7 or 6080 power tube
3. Try the Fitz mod which would probably be my last resort.

I would do 2 and 3 in that order. As for 2, RCA 6080's are cheap and plentiful, so I would go with that it you just want to test only. Or, if you want a solid backup to your 5998, then there's Tung-Sol 7236's.. As for 1, I wouldn't burn-in a power tube and leave this amp unattended unless you have fire insurance . Anyways, if you did the Fitz mod and still hear noise, then it is likely you have busted power tube. In my case, when I heard static (not a hum) on my modded DV, I quickly found out that it was a NOS RCA grey glass 6SN7 that I picked up for a song. The arc'ing when turning the volume up and down was cool to watch but I quickly discarded that bum 6SN7.

 

[toufeeq]

I would do 2 and 3 in that order. As for 2, RCA 6080's are cheap and plentiful, so I would go with that it you just want to test only. Or, if you want a solid backup to your 5998, then there's Tung-Sol 7236's.. As for 1, I wouldn't burn-in a power tube and leave this amp unattended unless you have fire insurance . Anyways, if you did the Fitz mod and still hear noise, then it is likely you have busted power tube.

Yes, I think I will get a cheap power tube to test. I have the OEM 6SN7 and swapping it in didn't take the hum out so I suspect it's the power tube.
Definitely, wasn't planning to burn in the power tube. Seems like a recipe for burning down the house.

 

[toufeeq]

Oh man, sorry about that...for a minute there I thought we’d solved it. All I know to do is swap in new tubes and see if it helps.

I used the DV for around 5 hours yesterday and the hum is now considerably reduced. So maybe the burn-in is probably the best option here.

 

[JKDJedi]

I used the DV for around 5 hours yesterday and the hum is now considerably reduced. So maybe the burn-in is probably the best option here.

And if you change your mind the offer is still up for me to test that out for you. My tests last for a year or so ...

 

[toufeeq]

And if you change your mind the offer is still up for me to test that out for you. My tests last for a year or so ...

Hah! I will keep that in mind.

 

[cddc]

And if you change your mind the offer is still up for me to test that out for you. My tests last for a year or so ...

Only one year???...that is a very irresponsible tube tester, trust me.

Be sure to send the tube to me instead, I will test it for 3 years and make sure I run it everyday...

 

[JKDJedi]

Only one year???...that is a very irresponsible tube tester, trust me.

Be sure to send the tube to me instead, I will test it for 3 years and make sure I run it everyday...

L M F A O ....

 

[Gallic Dweller]

toufeeq,
the Fitzmod should have been your the first thing to do. I get the feeling that a lot of you don't want to get into soldering. The Fitz mod is not hard at all and there are lots of visuals to look at at on You Tube. You would be surprised how buying a decent solder station can save you lots of money used to remedy non audio problems.

The one small sweet spot - use resistors to attenuate the pot/get rid of the pot and install a 50K Alps Blue transforming the sound by shunting the pot with Z foil resistors, take a look at www.world-designs.co.uk FAQ section, very clear instructions, do not use an Alps Blue by itself - you will be disappointed/buy one of Valab 23 step attenuators around $20. Get rid of the hum and open up the D/V with one of the pot options - then you will know just what the D/V is capable of.

 

[toufeeq]

toufeeq,
the Fitzmod should have been your the first thing to do. I get the feeling that a lot of you don't want to get into soldering. The Fitz mod is not hard at all and there are lots of visuals to look at at on You Tube. You would be surprised how buying a decent solder station can save you lots of money used to remedy non audio problems.

The one small sweet spot - use resistors to attenuate the pot/get rid of the pot and install a 50K Alps Blue transforming the sound by shunting the pot with Z foil resistors, take a look at www.world-designs.co.uk FAQ section, very clear instructions, do not use an Alps Blue by itself - you will be disappointed/buy one of Valab 23 step attenuators around $20. Get rid of the hum and open up the D/V with one of the pot options - then you will know just what the D/V is capable of.

Thank You. I have done soldering in the past so I can definitely do it. The real problem is that there are no real good instructions on doing the Fitz mod online. There are bunch of threads on Head-fi and some pics on Google Images. Everyone seems to be talking about this mythical process but nobody actually has instructions on doing it. Just for that I'm tempted to put together a HOWTO on this if I can kinda piece together all the info.