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DT50 high noise floor (hiss) solutions
by GugaWedge on 2012-11-14 12:15:09.2220

Hi guys,

There are a bunch of threads that mention issues related to this one, so I was thinking if we can try to make one that can provide ideas on how to fix/workaround the issue.

I have an open support ticket with Line6 at the moment regarding this issue and will keep you updated on any solutions that might be coming from them.

Here is the transcript of the ticket so far: (This also details the issue that me and a lot of others are complaining about...)

Hi guys, Just bought a DT50 (to add to my collection of POD plus variax) and unfortunately is suffers from excessive "crackling" noise (sometimes refered as white noise, or waterfall sound). This is not my first tube amp, so I am guessing from experience that this is probably an issue with one of the tubes. I know I could get a ticket and get in touch with the nearest support center, but unfortunately the closest one is +1500kms away from where I live. (Welcome to Australia). So as you can imagine I really don't want to ship the amp there just to replace the valves. So if you guys can help me to narrow down the problem to a valve issue, I would be more than happy to replace them. I will try to give you as much info as possible on the issue: Amp is working fine (except for the noise...) in both channels, all the modes/voicings, both in low and normal power modes. With the power on and in standby mode there is no noise whatsoever. Turning the standby mode on, voicing 1, pentode, class A/B, there is no hum (just the normal from a tube amp) and a low crackling noise (sounds almost like static from an old radio). Changing to voicing II, the noise increases every so slightly. Voicing III is the worst one. Not acceptable. Voicing IV is on pair with Level I or II. Changing the mode from pentode to triode attenuates the noise somewhat. Changing class makes almost no difference. Changing Volume/Master level has zero impact on the noise. Running the amp with nothing plugged in, direct guitar or POD has zero impact. I have tried to remove the tubes and reinsert them (maybe they would have gotten loose during transportation...). This had a very minor impact on the noise, reducing it very slightly. Leaving the amp running for long periods also makes the noise reduce slightly but remains stable after 5 minutes or so. Ok I hope that is enough information so you guys can help me out to diagnose the source of the issue. Thanks in advance for your help. Cheers. Hugo Fonseca

After some more troubleshooting (and head scratching) here is some more info:

Removing either of the preamp tubes and turning the amp on makes the noise go away.

There is a slight difference in the noise volume between channels one and two with two being lower than one.

I have swapped the preamp tubes positions with a slight change in the volume of the noise.

I have tried electric contact cleaner with no success.

Found that moving the presence knob to a value higher than around 90% increases the noise even further. Decreasing pass that mark gets it back to the "normal" level. This variation is not linear. Constant up to ~90%, higher above it.

Please disregard the differences between channel one (A) and two (B). I forgot the fact that they save the tipology and so when I was switching between the two the tipology was changing also and that accounted for the noise volume difference.


How loud is the noise when using the amp? It is normal to hear hum/noise differences when switching topology and class on the DT Amps.

Can you hear the noise while you are playing the guitar?

The reason that you do not notice this on other tube amps is that the power class and rating is not changeable so you get used to the hiss or hum over time.

I.e. in class A on and setting III or IV you are going to hear hiss because your preamp and power tubes are juiced.

On Class AB with setting I is going to be relatively quiet.

Ultimately, there is no dead quiet tube amplifier. the DT amp just might be drawing your attention to the difference in noise floor because of the gain staging implications of changing the class and topology settings.

Can you post a sound clip of the issue?



Hi David,

As I mentioned I had several other tube amps including a twin reverb, a TSL 100 and an AC-30 (which have different levels of noise and/or hum), so I am aware of the typical noise floor on tube amps.

The hum level on my DT50 is fine and as you say changes with the different settings on the amp as expected.

What is not normal is high "waterfall style" constant sound, even with all the knobs turned to 0.

The noise is noticeable even when playing at low levels. When playing at higher levels the guitar sound drowns out the noise.

I will post a sound clip of the issue tonight so you can judge for yourself.



(File is attached)



As requested here is an audio of it. It was recorded with my phone from about 0,5m distance.


Sorry for the late reply. I don't hear anything out of the ordinary depending on your topology and gain settings. Can you hear the noise while you are playing?

You can hear hiss even with the knobs turned to 0 with the DT. This is the noise floor of the power amp.

Do you hear any pops, clicks, monophonic feedback, doubling sounds?



Hi David,

You can definitely hear the hiss while playing at low to mid volumes. It gets drowned out while playing at gig level, but it is still unusable since even muting the strings/using a noise suppressor on the effects loop won't silence it, so if for instance there is a quiet part on a song and you are playing live with a mic'd cab it becomes impossible to stop the hiss. Plus again makes it unusable for studio recording with a mic'd cab.

I have used some very noisy amps (ac30 comes to mind) and none was anywhere close to this.

Can you give any ideas on how to reduce the noise as in replacing valves with another brand or biasing the power amp ones lower? Maybe some other minor mods/tweaks?

I honestly think that the amp sounds great and am very happy with it, but the very high noise floor makes it unusable. from reading in the support forums there seems to be a bunch of other users complaining from the same thing. Also on general amp forums, every time someone is asking for advice if they should buy it or not, there is always someone advising against it because of the noise.

This are all customers you are losing because of something you are calling a "feature".

If you can somehow find a solution to reduce the noise (again no one is expecting it to be silent. some hiss IS expected), this may all be customers you are gaining back.

I would even be ok with some noise suppressor solution post power amp, so at least the hiss wouldn't be audible when not playing...



Ok,  that is all the conversation so far. When i have some time I will round up the other threads regarding the same issue and provide links for them.

I also have a set of 12AX7's (TungSol) coming and will let you know it it made any difference.

Any other ideas?



Re: DT50 high noise floor (hiss) solutions
by GugaWedge on 2012-11-15 03:02:14.9820

As promised here are the links to some of the other thread on noise issues with the DT amps:

Crackling & Popping Noise coming from DT25 Combo">">

DT-50 Digital Noise.">">

DT50 Too Noisy!">">

DT 50 2x12 combo hum in class a">">

DT 25 hummming">">

DT 50  background noise\">">

I am done with the DT50!">">

dt 50 2x12 motorboating!">">

DT50 crackling noise question?">">

Let me know if there are any other threads that should be in here...

Re: DT50 high noise floor (hiss) solutions
by DropTheSun on 2012-11-16 02:15:18.6900

My DT50 212 Combo has this "feature" aswell. Setting I and II has little "hiss", that i could say is the normal tube amp noise. But when changing to setting III, the "hiss-noise" raises so loud, that it disturbs playing in low volumes (and on gigs when the combo is mic'd). Setting IIII is almost as quiet as setting I and II.

I'm afraid that Line 6 is going to name this noise problem as a feature. Pretty irritating feature in 1600€ combo amp, don't you think?

Re: DT50 high noise floor (hiss) solutions
by GugaWedge on 2012-11-16 03:38:56.0750

Well, from reading the other threads, some users have had some success resolving the issue one way or another. Hopefully we can narrow down a solution to the issue, or/and Line6 can help us out providing a workaround/fix.

It is an amazing sounding amp that is a shame that something like this prevent it from being used in low volume/mic'd scenarios.

I am hoping that the rest of the DT owners will join their voices here so together we can work this out and maybe put some pressure to Line6. Unfortunately some of the previous owners of the amp were not so persistent and have already given up on it...

Re: DT50 high noise floor (hiss) solutions
by evilmikehoo on 2012-11-16 05:03:28.1140

I hear the voices of the dead thru mine. Guess I better not do what they keep telling me to do, tho, huh?

Re: DT50 high noise floor (hiss) solutions
by GugaWedge on 2012-11-17 03:48:53.8060

Troubleshooting basics:

Here is a list of basic traoubleshooting tips that might fix your specific noise issues with the unit.

1 - Reinstall firmware / Install the latest firmware / Install a different vesrion of the firmware.

This are all possible solutions to your problem. The DT series amps do a lot processing of the sound in software. They "model" the sounds of the amps in this process, including some noise properties. Trying different versions of the firmware or reinstalling a "faulty" one might have some positive impact on the noise level.

2 - Reseat the valves / Swap valve positions / Clean valve contacts

During transport your amp is shaken all over. It is possible that your amps's valves have rattled out of position and they are not seated properly. Removing them and placing them back on (after clenaing the contact with some electronic contact cleaner) might solve your issue.

No two valves (tubes) are the same, no mather how good is quality control. It is just the nature of they are made. Plus they all have the tendency to become microphonic with usage. If one of your valves is noisier than the other, swapping their position might have some positive effect on the overall noise level.

3 - Change valves / Rebias the power amp

Again your tubes might be faulty or they might just be noisy. Different brands of tubes have different noise levels (among all the other different properties), so changing valves might fix your noise problems. There are a few reports of fixed hiss problems by swapping the "preamp" (not really preamp) tubes for TungSol 12AX7's. You should always keep some spare valves, so it is worth a shot.

If you swap your power amp tubes (EL34's) it is always good practice to rebias your power amp section. Probably a good idea to pay an amp tech to do it unless you know what your doing. While it is there why don't ask hime if he has any ideas about reducing the noise levels. Maybe he will come up with something and you can share it with the community...

4 - Try a power conditioner / Voltage regulator

Unfortunately most of our hoses's electrical lines are terrible. That is a simple fact.

Test for ground in your wall socket. If your ground is not properly connected, you will have a lot of hum.

Changes in current/voltage will prevent your amp from performing at its best. Also spikes might even burn the fuse out in extreme events. A power conditioner and/or a voltage regulator will have prevent this and keep a nice steady feed to your amp. This may also improve noise issues.

5 - If the noise only happens when a guitar/pedals/effects racks/whatever are connected the problem is in your chain and not in the amp. Start eliminating things from the chain one at a time until you find the problem.

I think this will cover most common troubleshooting scenarios. If after doing any of this things your noise went away let us know so others can try it also.

Good luck.

Re: DT50 high noise floor (hiss) solutions
by GugaWedge on 2012-11-19 23:16:01.8490

Update from my ticket with Line6 support:


I can understand that hearing the noise floor change on the amp can be a bit jarring at first but I really don't hear anything from the recording that leads me to believe anything is wrong with the amp.

For instance high gain amps such as the Mesa Dual rectifier and even the Bogner Alchemist that we used to manufacture have a similar noise floor.  It's a byproduct of the power and preamp tubes being pushed hard to produce the gain levels in the amplifiers.

Understand I am not trying to be difficult, I would just hate to send you to a tech that will charge a fee to look at the amp when I don't believe anything is wrong. 

People on the forums have commented but in order to do the things that the DT50 does there is going to be a drastic difference in noise floor in some instances. This is not really something that can be overcome on the technical side. In short, tubes hiss.

You can hear this on many modern metal recordings:

This song was recorded with a Dual Rectifier check out the noise floor at the first of the song.

Definitely noticeable when not playing. On a lot of records this is gated or trimmed out in the recording software but this is a good example of a raw recording of this type of amp.   

You could put different power tubes in the amp but if you found a quieter set  you are going to loose some gain and the amp will not have the same kind of breakup.



And my reply:

Hi David,

Thank you for your reply and for looking into this.

I understand your point of about how different settings (in this case changing the amount of feedback that goes into the power amp valves) is going to have an effect on the amount of noise. But if the amount of noise would be related to how hard we are pushing the valves, shouldn't it increase/decrease with increasing/decreasing the volume/gain?

Also since the DT50 with the master volume knob pulled out and turned low is basically just using the power tubes to "warm" up the tone, they shouldn't be pushed hard enough on this mode to create the hiss.

I am no audiophile in the sense that I can't almost distinguish the tone differences between two valve brands of the same type. I listened to the link you gave me and I swear I can't almost hear any hiss.

To put this in perspective to you, if I am having a normal conversation in my room with somebody and I turn the amp on on type III (again with all controls at 0 and nothing connected to the amp) we have to raise our voices to continue! It is literally like listening to an old FM radio tuned in-between stations.

If replacing the valves with a less noisier brand will reduce the noise, even losing some of the gain/breakage when pushed/tone might be a solution, I will give it a try. I need spares anyway... I have a pair of TungSol 12AX7s on the way and will get a pair of EL34s to see if there is any difference.

I know you are not trying to be difficult and believe me I am not also. As I said I love the sound and the flexibility of the amp. If not for the noise it would be the perfect amp and I would recommend it to anybody.

Hopefully we can find a workaround and me and a lot of other users can be happy.


Hugo Fonseca

Re: DT50 high noise floor (hiss) solutions
by DropTheSun on 2012-11-21 03:48:32.0930

I manage to decrease the hiss of Voicing III on my DT50 212 Combo. I reseted (I don't know if this is the right word for it) the DT50 and that did the trick. Voicing III is still the loudest one, but much quieter now.

Here's what i did:

1. Push DT50/25 voicing knob DOWN. Now, at the same time push the Pentode/Triode knob UP. Keep them pushed at these positions.

2. Now Power up the DT50/25 and keep the knobs pushed. First all the lights on DT50/25 will be on, then some of them will go off.

3. After view seconds Channel A, Triode, Voicing I and Class A/B lights will go on.

4. Release the knobs. DT50/25 has been reseted to factory setup.

Re: DT50 high noise floor (hiss) solutions
by GugaWedge on 2012-11-22 03:59:09.0600

Great sugestion. Another thing that people can try...

Meanwhile I received a pair of TungSol 12AX7s and unfortunately one of them is microphonic. BUT here is the interesting thing. I used the other one to replace one of the original tubes and the noise was cut by half at least!! So definitely something for people having this issue to try. You should have spare tubes anyway so you don't lose anything by trying some new tubes out!.

I do have to confirm that as warned by Line6 suppor there was a loss in overall volume of about 5% and the tone changed ever so slightly (for the better for me since it gained clarity)..

Re: DT50 high noise floor (hiss) solutions
by nairraf on 2012-11-27 07:07:31.5350

Just thought that I would reply with my findings:

I have had a DT50 now for a couple of weeks, and noticed, like many of you, that the noise floor was quite high.

Based on my readings, I replaced the 12AX7's with Mesa SP12AX7's, and while it did take some of the noise out, it was not a huge difference.

I am going to try some JJ Gold's, and will reply back with those findings, but unfortunately, not a huge difference with the SP12AX7's .

Like many: voicing 3 is the most noisy.

NOTE: I have also updated to 2.0 (reflashed a couple of times just to be sure), as well as try the factory reset thing. Now, I find that it is usable, but my other tube amps are more quiet that this thing. But it really does sound great, really great in fact. Just too bad about the noise.

Re: DT50 high noise floor (hiss) solutions
by GugaWedge on 2012-11-28 20:17:47.2080

Sorry that replacing the 12AX7s did not make a difference to you. I have only tried with the TungSol ones so I can not confirm how noisy are the Mesa ones compared to the EH originals. Let us know how the JJ's go.

On my case it was a big difference. Still not quiet by any standards, but it is at least usable. Meanwhile my support ticket got escalated today... Not sure what that means, but maybe Line 6 is looking into it... fingers crossed....

Re: DT50 high noise floor (hiss) solutions
by CKro on 2012-12-06 22:06:09.2990


I just got my DT50 212. I noticed the the noise issue. #3 is the louder. When nothing is connected to the amp the noise is higher. When the HD500 is connected the noise is reduced. I've updated the firmware and the noise was reduced a little more. it sill there but is better now (3 is still the noiser). At very low gain (practically listen the string from my electric guitar) the noise kind of bother me, but i just play at that volumne when my little one are sleeping. With a no so low volumne, the noise is ok, even for quiet riffs is ok. Using my HD500, some of the effects cut any remain noise. The only thing that having crazy is when I change a present from high to low gain in my pod it makes me jump from my stool (that happened also with my normal amps, but this is worst). Overall, I'm happy with the quality and sound and the noise doesn't bother me too much to don't recommend it (I'm not so picky)

So summary: I think I reduced some noise with the update of the firmware and with pod in low gain effects (the high gain covers the noise, so is not a problem ).

I'm not a tube expert, it's just my experience.

BTW, the audio you uploaded Hugo, sounds louder than my noise in possition #3.

Re: DT50 high noise floor (hiss) solutions
by GugaWedge on 2012-12-07 21:38:23.7220

Glad that you are enjoying the amp. It is great!

I thought I would share with you the recording post pream tube change to a TungSol one. Conditions of the recording were the same (Typology III, Class A, Pentode, Gain at 20%, Volume at 50%, Master pulled out at 50%, recorded with a crap cheap computer mic). I didn't trim the beggining of the audio file so you guys can hear how quiet it is even without playing.

Let me know what you think.

The information above may not be current, and you should direct questions to the current forum or review the manual.