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DT-50 Digital Noise.
by jcurry on 2011-11-06 15:06:27

The DT-50 212 is my first tube amp, so maybe this is normal, I don't know. I've had this amp for about 3 days. I played it for about 2 hours today and started to notice this periodic digital noise coming from the amp. To troubleshoot I started by disconnecting the guitar, unplugging the L6 connection that is plugged into an HD500, and finally unplugging everything else that was going to the same power strip.

So, nothing is plugged into it, and there are no other devices plugged into the same power strip. it's quiet for about 5-10 seconds and then theres about 3-4 seconds of what sounds like digital noise. it's quiet, but easily heard when practicing by yourself in an otherwise quiet room. The master volume control has no effect on how quiet or loud the noise is. The amp was also very hot, so I put it in standby mode. There's no noise when its in standby mode.

After leaving it in standby for about 20 minutes I turned it back on and I didn't hear anything. The only other thing I can remember about it was that it was in 'low power' mode for the 2 hours I was using it. Can that cause issues if used for too long? Of course, there's always the possibility that there's something around here causing interference that the amp is picking up.

Any suggestions would be appreciated. Thanks.



Re: DT-50 Digital Noise.
by jcurry on 2011-11-06 15:35:03

Oh, I forgot to also mention that I firmly believe that it shouldn't have anything to do with the power in my house or a grounding issue. My house is only 6 years old with all 20 amp wiring and circuits. I have also had a Line6 Spider II and a SWR Working Mans 15 bass amp plugged into the same power strip for the past 6 years where the DT-50 is now and they never had any weird issues like this.

Again, if I leave it in standby for a while the noise goes away, but after a while it starts coming back. Is this something that happens when the tubes get too hot?

I've seen a lot of posts complaining about the factory tubes. Should I just replace them?



Re: DT-50 Digital Noise.
by bartpuglise on 2011-11-07 03:29:51

It's quite possible that it's the 12ax7's in your amp I had my DT50 head for a month or so and started getting noise. Replacing the tubes solved that issue. Make sure your firmware is all updated as well and get yourself a DMX XLR cable for your L6 link I had a real strange feedback sound that drove me nuts and after replacing cable it went bye bye. Best of luck with your DT once you spend some time with it you'll appreciate it!



Re: DT-50 Digital Noise.
by jcurry on 2011-11-07 06:35:58

Thanks for the suggestions.

I'm not sure what a 'DMX' XLR cable is, but I did get an AES/EBU cable for the L6 connection like it suggests in the manual. It's made with the Mogami 110 ohm 3080 cable and Neutrik gold connectors. I disconnected the cable from the HD500 but I didn't disconnect the cable from the amp, I guess it could be acting like an antennea of some sort? I did notice that 'normal' amp noise and hiss drops significantly when I disconnect the HD500.

I also updated the firmware to v1.30 the day I got it. So, unless it's a bug in the latest update, that can't be it.

I'll be testing it again today. I will probably remove the HD500 entirely just to make sure its not that or the cable its using. I guess if it's a tube that's not a huge problem. They seem cheap enough to replace. There's just such a huge variety of 12AX7 tubes out there. I wouldn't know what to get.



Re: DT-50 Digital Noise.
by bartpuglise on 2011-11-07 08:18:40

Yes the aes/ebu cable is a Data cable which is what a DMX cable is as well. You may be getting noise off of your patches. Try plugging directly into the amp. I ordered tubes from www.tubedepot.com there is a lot to choose from. I have used Sovtek in the past so that's what I put in my DT50. Also the pre-amp tubes need not be biased. If you search the threads you'll find a lot of info on biasing. Every tube amp I've owned had some noise but nothing annoying. Rock on!!!



Re: DT-50 Digital Noise.
by jcurry on 2011-11-07 08:30:34

A friend of mine who owns a DT-50 112 suggested these tubes, which is what he replaced his factory tubes with.

http://tubedepot.com/jj-ecc803g.html

and

http://www.tubedepot.com/bsct-el34-sed.html

He also suggested having the bias set to 35. Why do you say that the bias doesn't matter?

Do the 12ax7's need to be matched? balanced triodes? both? Hi Gain? Low noise and Microphonics? All of the above? I've never ordered tubes, I don't know what any of that means other than it costs a bit more.




Re: DT-50 Digital Noise.
by jcurry on 2011-11-07 09:30:50

OK, more information...

The noise continues when absolutely nothing is connected and all knobs are at 0. Its the loudest when set at Model III, Pentode, class A/B, but can be heard when these switches are at ANY setting. Right now it sounds like a game of space invaders. pew pew shhh pew shhh .... Not real loud, but definitely annoying. I wish I had a microphone, I would record it and post it. Also, it definitely seems worse than yesterday.

I removed the back of the amp and tapped on the 12AX7's with the eraser end of a pencil and got no response at all, so it's not microphonics.

Do you think it's the tubes? Which ones? Should I just replace them all? Is this a warranty issue?



Re: DT-50 Digital Noise.
by jcurry on 2011-11-07 10:04:16

OK, it's going to the shop tomorow morning. I called a local warranty repair place that I found on the Line6 site and talked to them about it. He had me test a few things including the direct out on the amp, the noise ALSO comes out of the direct out. He said that it might be a transformer or the power supply. But, it's under warranty so it doesn't really matter what's wrong with it.

I'll report back once it's fixed.



Re: DT-50 Digital Noise.
by ethyl80 on 2011-11-07 12:11:29

was your cell phone near it when you were playing?



Re: DT-50 Digital Noise.
by jcurry on 2011-11-07 12:25:37

How 'near' would it have to be to cause problems? It's not sitting on it. It's sitting on my desk a few feet away. I thought about that at first as well. I even did tests where I held the phone near it and had it check my mail and stuff and it did not appear to be the cause.

I think that warrents further investigation though. I might try a few things later.



Re: DT-50 Digital Noise.
by bartpuglise on 2011-11-07 14:18:40

That swoosh sound is exactly what my DT50 head was making! I replaced the 12ax7's and that sound went away! I then replaced the power tubes. The only tubes that need biasing are the POWER TUBES and the bias setting is 35 milli-volts



Re: DT-50 Digital Noise.
by jcurry on 2011-11-07 14:28:04

Well, I've had it on for the past 2 hours and it must know that I was going to take it to the shop because it hasn't made a single odd noise. Doesn't that just figure? I let it warm up for 10 minutes before taking it out of standby. I let it sit for another 30 minutes with nothing plugged in. I connected it to the HD500, let it sit for another 30 minutes. Rocked out with it in low power mode at around 10 o'clock for another 30 minutes, and it's been quiet the whole time. WTF?! I wanted to do some tests like shutting my phone off when it was making noise, disabling the wireless on my laptop, etc... Basically anything that could be causing interference.

This might be a dumb question, but like I mentioned previously, I know jack about tube amps. Do tubes require any kind of 'burn-in' period?

I hear what you're saying about the tubes, it just seems standard practice to replace the tubes in this amp right away. Maybe it's just me, but you would think for a $1500 amp it would come with decent tubes from the factory.




Re: DT-50 Digital Noise.
by bartpuglise on 2011-11-07 15:39:09

Yeah no s**t that's my only gripe about the amp also the telex is thin and there are no corner guards but...... Hands down best sounding rig I've ever owned. I also run a DRZ attenuator that really makes it sound bad ass but replacing tubes is a small price to pay I don't think a cell phone or wireless laptop is the issue. Well best of luck make sure you run per-amp models on your HD500 I think they sound much better!



Re: DT-50 Digital Noise.
by Nick_Mattocks on 2011-11-07 16:01:22

The bias setting for the DT-50 is actually 36mV



Re: DT-50 Digital Noise.
by jcurry on 2011-11-07 17:33:08

Thanks Nick, I'll remember that if I order new tubes.



Re: DT-50 Digital Noise.
by jcurry on 2011-11-11 14:13:23

Well, I talked to the guy at the shop and of course it hasn't been acting up since the first day it was there. Figures...

He is going to swap out all of the tubes anyway and I am going to re-flash the firmware when I get it back to see if that helps. I saw another thread on here where that made a difference. I think new tubes will make a big difference too since it seems to be the general opinion of all that the ones that it comes with aren't the best.



Re: DT-50 Digital Noise.
by snooze12 on 2011-11-12 08:48:35

Do the DT25 is less noisy than the DT50?



Re: DT-50 Digital Noise.
by jcurry on 2011-11-12 13:20:30

I don't know man.You should probably start a new thread for that question. It's not relevant to my issue.



Re: DT-50 Digital Noise.
by jcurry on 2011-11-28 13:03:02

I'm happy to report that the issue seems to be completely fixed. Like most other noise related issues, a brand new set of tubes cured it. Line 6 sent the repair shop a new set of Electro Harmonix tubes and it's been silent ever since. They replaced both 12AX7's and both EL34's since they weren't able to determine which ones were causing the problem. Luckily the issue was discovered within the 90 day warranty on the tubes so this didn't cost me anything.

I have both sets of tubes that I can use as a backup, but I plan on buying some others as well.





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