Space,

Hum happens whether gtr is connected or not (same amount). Happens the same on all 4 Topologies.

Just reseated all 3 tubes and no change. Hum still there and same amount. Tubes are not microphonic.

Cannot tolerate this hum when amp is sitting beside me at home. Like I said, it does get masked with the band. Dead quiet in Pentode / Class AB.

For my take, it shouldn't be huming like this.

Hey STPLE,

Nope I do not have a resolution on this yet and I am thinking seriously about sending the amp in for service under warranty. It must be a hit or miss thing as I don't see a lot of people complaining about it. Below is what has happened to me so far ....

Note: this is with EVERYTHING turned off (all knobs at "0"), no guitar plugged in ... Basically just the outbput power amp to the speaker.

I will also tell you that I returned the first DT25 head that I bought and got a 2nd one .... same problem.

1) On ALL 4 Topologies (NFL I, II, III, IV) Pentode and Class AB is pretty much dead quiet

2) On ALL 4 Topologies, Triode mode produces hum most noticeable at Bedroom Levels. At gig levels not so much because the higher volumes masks out the hum, but it is there.

3) On ALL 4 Topologies, Triode plus Class A produces slightly more hum. Definitely noticeable (and annoying) at bedroom levels.

4) NFL III produces the loudest of the 4.

I replaced all the stock tubes with Vintage Amperex. No difference. Hum still there. I also tweeked the bias ... same problem.

I also noticead that it "appeared" to increase slightly with the Firmware 2.0 update, although I think this is an output power problem and I don't think the firmware update does anything to the power section ??? (not 100% sure on that). So this in itself doesn't explain why it appears to be more noticeable now?? Maybe it's just my imagination?

I had some correspondence with Line 6 Tech Support (through a support ticket), but in the end they didn't offer much if any explanation. I sent them several audio files of the hum issue during the discourse.

Some here on the forums say "this is normal" but I don't buy it .... or I should say, I still think my amp is humming more than it should, especailly for a $1000 piece of gear.

Since I have SV212 as a backup I am thinking I should send the head in and see if they can fix it, or best case scenario, replace it yet again with one that doesn't hum although I doubt they will do that?

I think it may be a bad batch? .... but again, no recalls, and no heavy complaints on this forum about the hum, so I am scratching my head a bit?

In my office, working on my computer, I could NOT have this amp sitting beside me, turned on, set to Triode and Class A. The hum is totally, noticeable and annoying. I just can't wrap my head around the suggestion that this is "normal".

All that being said, I do like the sound of this amp. I am glad I got the head and cab as I prefer it to an open back combo.

I generally have the amp set for Pentode and Class AB (actually Pentode and Class A is ok, very little hum but still there). At band levels I generally use NFL III in Pentode mode and Class A.

Unfortunately I live a bit remote and my local L6 dealer doesn't stock these amps, so I have no way to compare my DT25 head with others in the store.

Lastly, I have had a few direct online chats with other DT25 owners who have said they have no hum in the same conditions that I get it in. So agan, scratching my head.

The big downside with sending it in is the likelyhood of a long (or very long) wait to get it back.

Sorry the news couldn't have been more positive.