[DT25] Loud "thump" when turning on and switching between triode and pentode

[Shaamaan 1]

Quite recently my DT25 has been acting weird.

 

First, it started with an unusually loud "thump" when turning the speaker on from standby (after the DT warms up a bit of course in standby). Then I've noticed sounds that shouldn't be there when strumming chords on a clean setting (single strings sound OK). And I've noticed that switching between pentode and triode modes also causes an unusually loud "thump". Finally, a worrisome "thump" is also heard if I disable the AMP on my POD500.

 

In general, I've come to somewhat fear these thumps, as it seems to me something isn't working (or isn't operated) as it should. I cherish my DT and would prefer it to keep rocking on. Any idea what it could be and what should I do to alleviate the problem?

 

EDIT: I've realized I've never updated the firmware on the DT25. While the problem above doesn't seem like a firmware issue, I'm also kind of wondering if I can even DO a firmware update with "Dream Rig"...?

[psarkissian 362]

Are they the factory tubes?

How old are the tubes, when were they changed out and biased last?

 

[Shaamaan 1]

14 hours ago, psarkissian said:

Are they the factory tubes?

How old are the tubes, when were they changed out and biased last?

 

 

That's... actually a good question. I bought the DT used, so I don't really know (if memory serves the information from the seller was that these are stock tubes). As a "basement" player, I use the DT sparingly (compared to stage / pro musicians anyway) so I was under the impression the tubes should be good for a long while. As such I haven't touched them at all. The only thing I ever did was fastening a few, somewhat loose, screws which caused a notable buzz - but this was after I bought the unit.

 

Do you think it's the tubes?

 

EDIT: One more thing to note: I just turned on the DT, waited for it to warm up, then turned on the speaker - all of this WITHOUT turning on the POD, so there was no input. Not only did I get the scary "thump", but there was also notable "noise" from the speaker, like uneven scratching sounds...? Just putting this info out there, in case it helps identify the problem or confirm any existing suspicions...

[psarkissian 362]

Scratchy noise sounds like popcorn?

 

[Shaamaan 1]

5 hours ago, psarkissian said:

Scratchy noise sounds like popcorn?

 

Not... really. More like a rodent that got into the speaker and was trying to get out? It's very intermittent and... just a little bit scary.

 

...no, I do NOT have a rat problem, and yes, I checked. ;)

 

EDIT: The thumping, at least when turning on, appears to... come and go? I just came from work and, after reading your post, figured I'd try to record the strange noise with my phone. To my surprise, the amp didn't make any noises when switching on from standby. There were still very minor occasional scratches / artefacts however, albeit I was unable to catch them. At this point I'm starting to think I might be haunted! O_o

 

EDIT 2: OK, so right now it seems that just after turning the amp on, everything is fine (I could swear I tested it in the morning before going to work and it was bad straight after starting it tho). However, if I play for a bit, it's as if some kind of charge was building up in the amp, causing the "thump" and weird noises, even with no input. If I turn it off and shortly after turn it on again, the issues persist. This effectively means I can't play for more than 10-15 minutes before the noisy artefacts become very distracting. :(

 

EDIT 3: I've recorded (alas, with my phone) two very different cases of the noise produced by the amp. Do note that in both cases the audio is recorded by keeping the phone close to the amp - these aren't VERY loud, but quite notable when playing in a quiet room. The first file (Noise 1) was recorded after turning the amp on after it had a little bit of a rest. There's some "popcorn" sounds, but also some other weirdness. The second file (Noise 2) was recorded after the amp was used a bit. During both recordings the POD was turned off, so there should be no input coming into the DT.

 

Noise 2.mp3

Noise 1.mp3

[Shaamaan 1]

I've had the laps replaced and it's all good now. I did NOT expect old lamps to cause such... specific noises. Oh well, lesson learned.