Helix Amp Models Producing DC

[deadpool_25]

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[BenIfin]

Just so I'm clear on the bottom line here:

MP reported what seems like a bug and the Line6 crew are looking into it.

Is that correct?

Yep.

 

[banned]

That’s absolutely what an FFT will do when there is DC present though. It can’t show 0Hz but these behaviours are typical for when DC is present. It’s a strong indicator for it, and is easy to verify. Jay’s issue is it doesn’t conclusively show that it IS DC, but something like that would be externally unlikely to be anything else in the circumstances. As confirmed by the other graphs, which honestly shouldn’t come as a shock to anyone.

I made one initial assertion which was true then, and true now. I checked analog outputs, and got a result that I now can’t receate. It’s likely that I made a mistake on that one. Thankfully others have gone to the trouble of checking, which is a helpful thing to do as far as troubleshooting goes.

The analog outs has no real bearing to this as far as I’m concerned though, because the problem itself lies within the amp modelling, not the D/A or analog path. Whether or not DC is detected after the analog outputs does not change the fact that some models are producing it when they (probably) shouldn’t be. This is the part that should be fixed, and what the OP is laying out (I didn’t mention the analog outs at all there because I’d already isolated the problem to elsewhere).

Nobody's faulting you - you don't need to justify anything. You did great work. Thanks for helping the modeling community!

And thanks goes to Jay as well - but maybe an adjust to communication style would be appropriate.

This is my present impression of Jay -

 

[DLC86]

Hey ... multi-colored, bolding and bold-underlining is my gig .... ok

And while you're at it, don't even think of going the bold underlined italics :)

You learned that by doing this kind of stuff, ain't it?

 

[Orvillain]

You learned that by doing this kind of stuff, ain't it?

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Ben looking through the font colour palette:

 

[timbuck3]

I used ChatGPT to tidy up what I wrote and make this post a bit easier to digest, hope that's not a problem (I think its easier to read and understand this way but some of the tone of what I was saying is very slightly altered due to being made more concise):

Description of the Issue:

While exploring some of the newer Bogner XTC amp models in the Helix platform, I discovered unusual behaviour that doesn't align with how the actual amp should perform. Using an FFT display (Pro-Q), I noticed two types of noise:

1. Broadband noise (ripple) – common and intentional to Line 6 modelling, can be turned off.
2. DC offset – visible as energy at the far left of the FFT (essentially 0Hz).

Unlike ripple, which can be disabled, this DC offset remains, and it’s present in the output of certain amp models even with ripple turned off. You can see that behaviour in action here, across various settings. Pay attention to the input and output meters - all of this noise and DC is produced when there is no input at all:



Why This Is a Problem:

• DC has no place in an audio signal. In a real amplifier, DC is filtered out by design (e.g., by capacitors and the output transformer). Driving a speaker with DC would move it in one direction and cause it to stay there, preventing it from functioning properly.
• Audio modelling consequences: If the DC offset is present beforenonlinear processes like saturation or compression, it could cause:
  • Asymmetric or unintended distortion
  • Incorrect dynamic behaviour in the modelling
  • Audibly, it may contribute to clicks and pops when switching amps/settings – likely caused by sudden DC shifts moving the speaker cone abruptly.
• Confirmed in multiple models: Beyond the Bogner XTC, I’ve confirmed the issue in various other Helix amp models, including several Marshalls, Mesa models, Cartographer, and others.
• Power amp related: This appears tied to the power amp stage in the modelling; preamp-only models don’t show this behaviour.

Why It Should Be Fixed:

• Realism: DC offset would not be present in a properly functioning tube amp output. Its inclusion contradicts the goal of realistic amp modelling.
• Performance impact: The DC may be causing audible artefacts (clicks, pops) during amp changes and might affect tone in unpredictable ways.
• User experience: Even though DC can be filtered after the fact, the root cause should be addressed to ensure proper, consistent behaviour in the model itself.
• Legacy product support: While newer Line 6 tech (e.g., the Stadium series) may avoid this entirely, current Helix users should not be left with a compromised experience, particularly since the fix likely falls within current DSP capabilities.
• Potential impact on tone: Fixing the issue could alter the tone of affected models slightly, but that’s only because the current tone may already be subtly incorrect due to the unintended DC presence.

Summary:

I’m raising this not as a nitpick, but because it potentially affects the fundamental accuracy of the amp modelling on Helix. I believe Line 6 should investigate this DC offset issue and implement fixes where practical, both for sound quality and user confidence in the product.:

The amps I've noticed with noticeable DC (not just noise from ripple but where DC remains when ripple is at 0):

- 2203 (and all Marshall's besides the JTM45, Park P75 and 2204)
- German Xtra Red + Blue (XTC)
- Cali Texas (Mesa Lone Star)
- Cartographer
- The older Panama 5150
- Cali IV
- Grammatico
- Fullerton
- Super Vib
- Mail Order Twin

Hey line 6 I think you should this poster a helix studio to demo… better use of a demo unit then so many yt influencers. Seems he knows what to look for and would likely be a good candidate

 

[KingsXJJ]

Hey line 6 I think you should this poster a helix studio to demo… better use of a demo unit then so many yt influencers. Seems he knows what to look for and would likely be a good candidate

I second this @Digital Igloo

 

[timbuck3]

I second this @Digital Igloo

Forgot the word send in my sentence to send this poster a stadium unit. Sorry

 

[KingsXJJ]

Forgot the word send in my sentence to send this poster a stadium unit. Sorry

You can always hit edit and add it in afterward bud.

 

[Dom Mcsweeney]

To be 100% fair, I think Tim is just trying to make this place feel more like a comment section on facebook.

 

[Mongillo19]

To be 100% fair, I think Tim is just trying to make this place feel more like a comment section on facebook.

He's succeeding

 

[timbuck3]

You can always hit edit and add it in afterward bud.

That edit ability only lasts for lik he movede 10 minutes after posting

 

[timbuck3]

To be 100% fair, I think Tim is just trying to make this place feel more like a comment section on facebook.

Huh? I was just saying the detail of the op in finding this possible issue is what a company needs from a user on their products

 

[Dom Mcsweeney]

Huh? I was just saying the detail of the op in finding this possible issue is what a company needs from a user on their products

I know

What I wrote was not related to your point, it was a joke.

The Type O and your additional comment to correct the Type O.

On facebook, it's just normal to see so much of this happening - mainly because phones are such terrible devices for writing.

 

[deadpool_25]

That edit ability only lasts for lik he movede 10 minutes after posting

Not on this forum. At least not for me. It lasts forever as far as I can tell.

 

[KingsXJJ]

Not on this forum. At least not for me. It lasts forever as far as I can tell.

Same here.

 

[timbuck3]

Same here.

Not for me for some reason

 

[Frodebro]

Not for me for some reason

That's weird. I just went way back in my post history, and stuff from six months ago can still be edited.

 

[DLC86]

phones are such terrible devices for writing.

What a boomer comment! Phones are perfcetly usbale foenwirtsing

 

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