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DT50 Noise Floor vs. DT25 Noise Floor

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After waiting 6 weeks I finally got my DT50-112 back, and it's just as noisy now as it was when I took it in.  Being that my tech couldn't find any reason for the noise, and having heard similar complaints about the noise in these amps from other owners, I'd begun to wonder if playing at practice volume while hearing fizz and whoosh and buzz (and even before I plug in too) was just the way this amp was built.  After all, it's a high-gain hybrid yadda yadda...

 

Then I ran across a used DT25-112 at a local store, and found that this amp has about one-tenth the noise that mine does (and this would be in either LPM or regular mode).  Even in voice III, which we all know is the noisiest, I practically had to stick my ear on the grill cloth in front of the cone to hear the noise.  In other words, this amp has an appropriate level of noise (very unlike mine).  At half the watts of a DT50, somewhat less noise is to be expected, but this is totally night and day, and my frustration level with my own amp is soaring.

 

So before I ship this puppy back to Line 6 with angry letter, does anybody out there know if these 2 amps I've played are representative of their brethren?  Are all DT50's noisy beasts while the DT25's are just fine?  Or are some amps just plain noisier with no real explanation why?  Or is my theory that something is wrong with my amp the best bet here?

 

THANKS!

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DT50 has a noisefloor that is a bit higher than the DT25....I have both a DT50 112 and a DT25 head/cab...The EH12AX7s were my problem in my DT50....It was noisy the day I got it and after some consult with some of the Line 6 engineers I switched out the 12AX7s for Mesa SPAX7s....Night and Day....With the stock EH 12AX7s it's not usable and annoying...

 

I have been an engineer for many many years and I really do not understand why this Line 6 tech that is new to the forums comes off talking about how these amps are designed for certain tubes that are matched in non-linear regions....I guess he is paid to scare those that don't know better...I think he is just tired of seeing the stupif lollipop people do with their amps...That was true 40 years ago and it's still just a true today...just now there are more dumb people that have access to Google...

 

I have been running my DT50 on Mesa tubes for nearly 5 years....current set is over 2 years old....That is the reason I use them....I have been using them in ALL of my amps since the mid-80s....I trust Robotube as I used to get the curve-traces from them back in the day...

 

The DT25 is quieter....The main reason is that it has a solid-state buffer feeding the phase inverter....DT50 has a 12AX7 single triode buffer for that and that is always going to have more noise than SS...In my own opinion, the DT50 has a bit more mojo than the DT25....DT25 is just a bit underpowered for band situations IMHO...clean tones don't spank as well as they do in the DT50...That's just power...

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DT50 has a noisefloor that is a bit higher than the DT25....I have both a DT50 112 and a DT25 head/cab...The EH12AX7s were my problem in my DT50....It was noisy the day I got it and after some consult with some of the Line 6 engineers I switched out the 12AX7s for Mesa SPAX7s....Night and Day....With the stock EH 12AX7s it's not usable and annoying...

 

I have been an engineer for many many years and I really do not understand why this Line 6 tech that is new to the forums comes off talking about how these amps are designed for certain tubes that are matched in non-linear regions....I guess he is paid to scare those that don't know better...I think he is just tired of seeing the stupif lollipop people do with their amps...That was true 40 years ago and it's still just a true today...just now there are more dumb people that have access to Google...

 

I have been running my DT50 on Mesa tubes for nearly 5 years....current set is over 2 years old....That is the reason I use them....I have been using them in ALL of my amps since the mid-80s....I trust Robotube as I used to get the curve-traces from them back in the day...

 

The DT25 is quieter....The main reason is that it has a solid-state buffer feeding the phase inverter....DT50 has a 12AX7 single triode buffer for that and that is always going to have more noise than SS...In my own opinion, the DT50 has a bit more mojo than the DT25....DT25 is just a bit underpowered for band situations IMHO...clean tones don't spank as well as they do in the DT50...That's just power...

 

Another discovery that I find unexpected came when I plugged into my ancient, beat up Fender Bandmaster bottom, which has two 12" Utah speakers in it.  Not only did the noise floor drop off (perhaps as much as 40%), but I got more highs out of it too.  This totally stumps me!  If the speakers have more high end, wouldn't we expect the noise floor to increase?  So did the load change from 8 ohms to 4 ohms reduce the noise?  Or is it because the noise got split between two speakers, with maybe some wave cancellation working in my favor?  The Celestion sounds better, though.  Fuller.

 

I thought you were using GT's?  I tried replacing the 12AX7's with a GT and a mullard, but heard no difference so I put the EH's back in it.  I'm going to replace all 4 tubes in one shot this weekend and see if that makes any difference, but I suspect that the tubes in there now are nearly new so I'm not holding a lot of hope.

 

So the difference in the noise floors--If you can recall back to when you first got the DT50 with the original tubes, would you say that noise level is many times more than the noise level of the DT25?  A subtle but noticeable difference is not what I'm hearing--I'm talking about a huge difference in noise between the 2 amps--that's what I heard.  You alluded to as much, but with some gray area...

 

THANKS!

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DT50 has a noisefloor that is a bit higher than the DT25....I have both a DT50 112 and a DT25 head/cab...The EH12AX7s were my problem in my DT50....It was noisy the day I got it and after some consult with some of the Line 6 engineers I switched out the 12AX7s for Mesa SPAX7s....Night and Day....With the stock EH 12AX7s it's not usable and annoying...

 

I have been running my DT50 on Mesa tubes for nearly 5 years....current set is over 2 years old....That is the reason I use them....I have been using them in ALL of my amps since the mid-80s....I trust Robotube as I used to get the curve-traces from them back in the day...

 

The DT25 is quieter....The main reason is that it has a solid-state buffer feeding the phase inverter....DT50 has a 12AX7 single triode buffer for that and that is always going to have more noise than SS...In my own opinion, the DT50 has a bit more mojo than the DT25....DT25 is just a bit underpowered for band situations IMHO...clean tones don't spank as well as they do in the DT50...That's just power...

 

Well, replacing all 4 tubes unfortunately failed to surprise me.  As I predicted, I've still got whoosh, hiss, and buzz.  I put in a GT matched PI, a Mullard 12AX7, and two EH power tubes.  I was surprised that I had to adjust the bias as much as I did--apparently these tubes vary quite a bit.  But noise-wise there is no change (or it got slightly worse).  The whole amp does seem a tad brighter and louder (which is good), and volumes in my different patches are less consistent with each other than they were.  So new tubes equals new tweaks, I guess.  

 

At least now I'm absolutely certain that tubes are not at fault here.  

 

The noise is now to the point where I'm forced to use voice I whenever I'm not playing to a backing track, but even the noise in this voice, which didn't seem too bad before, is both annoying me and causing me to play louder.  It's confounding for me because the L6 authorized repair center didn't cure the noise.  He says he's done trouble-shooting, and says that from here the only option is to send it back to the factory.  I may consider a different tech before sending the amp back to line 6.  

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Hello!

 

I know this is a fairly dated post - but how did this end up with your DT50?

 

I had exactly the same experience - hearing a new DT50 at Guitar Center - was near dead quiet compared to mine - so I did new tubes etc etc etc - no real difference. Did you send/get your amp back? Any change?

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