DT50112 + Helix=Fizz

[Rocco_Crocco]

I just bought a DT50 112. I am noticing some serious fizz when using the amp with Helix (I am using L6 Link).

 

Right now, I have the PV Panama preamp running into the DT.... fizz city. I would have thought a guitar speaker would remove most of the unwanted high end, but it doesn't. If I place a Hi/Low cut EQ block and set the Hi cut to even as high as 15k, it still makes a big difference in eliminating the fizz. That's a pretty high setting, so there is a lot of very high frequency information coming from the amp. Similar issue with most of the preamps and even full amp models I have tried. 

 

At first, I thought the stock L6/Celestion speaker was the issue, but if I use the built-in DT preamps, there is no fizz... the amp sounds as expected.

 

I don't mind including a high cut in my Helix chain, but this doesn't seem like normal operation for a combo amp with a guitar speaker. Anyone else notice this? I tried a Google search, but I am not coming up with much.

[psarkissian]

You are using a 50-Ohm mic cable for the Line 6 Link?

When was the last time the tubes were changed out?

Are they the specified tubes and bias (go to a Line 6 authorized service for that)?

Topology II and IV are the noisier louder ones for that extra crunch people like. Along with

Class, Triode vs Pentode,... they will all play a part in the noise floor level and distortion level

of the settings.

 

[Rocco_Crocco]

1 hour ago, psarkissian said:

You are using a 50-Ohm mic cable for the Line 6 Link?

When was the last time the tubes were changed out?

Are they the specified tubes and bias (go to a Line 6 authorized service for that)?

Topology II and IV are the noisier louder ones for that extra crunch people like. Along with

Class, Triode vs Pentode,... they will all play a part in the noise floor level and distortion level

of the settings.

 

To clarify... I am not talking about noise. I am taking about excessive high end (fizz) in the guitar signal. My original post gives details. This amp is not particularly noisy.

 

To answer your questions:

 

I am using a Line 6 Link cable.

 

I just bought the amp. The previous owner says he never changed the tubes. The preamp tubes are EH with "made in russia" stamped on them. I cannot see the power tubes through the cage well enough to see a brand, but there appears to be a green stamp of some sort on them. 

 

As far as topology, the TIGHT (1) setting seems to be an improvement over the other three, which all have excessive treble. Class a and ab,  and pentode/triode all have the issue.

[psarkissian]

Green stamp on the power tubes would be the EH head logo, it is typically green.

 

Fizz could be noise from lights, a filter capacitor getting old, or just old tubes. With normal use, tubes should be

changed out once every 18 to 24 months.  Tube amps in general will never sound like a solid state transistor based

amp, it's one the things people like about them.

 

Fizz (a form of noise) or any other noise that's excessive should be looked at by a Line 6 authorized service center tech.

https://line6.com/find/service_center/

 

I don't see a service history on it, so it's probably over-due for a tube change, bias and test by an authorized service center.

 

 

 

[Rocco_Crocco]

Thanks. I think I will order a matched quad set of powertubes so I only have to get it biased once. 

 

Again, though, I am not talking about noise. It's treble freqs in the guitar sound.

[Rocco_Crocco]

Amp was dropped off at an authorized repair center last week. Repair tech called me to tell me it is finished. The new power tubes have been biased correctly. He told me the amp was biased very high at around 43mv when he got it. After replacing the power tubes, the bias is now at 32.2 mv. Also, one of the preamp tubes was not working right so that was also replaced. I will pick up the amp on Thursday and am confident it will sound great.

[psarkissian]

Very good.