Seriously - the hiss!

Ok NDSP. I love the QC. It’s taken me a while (quite a while), but I’ve finally solved the ground hum puzzle. If you’d like to pass along to your support team. Ground hum can be eliminated by:

  1. Connecting an XLR cable out of the QC to a grounded device (in my case, a studio monitor). However, there are also conditions for that connection:
    a) XLR cable must be unpainted on its end.
    b) Device should be connected to the same power source (surge protecter) as the QC.
    A little crazy for an over $1800 device, but ok.

So now, what about the hiss? I love the QC so much that I don’t want to give up on it.
But why do I need a noise gate on absolutely any device in the path? A clean amp. Needs a noise gate. Otherwise, it’s just hiss.

And it’s not a defective unit. Sweetwater was kind enough to send me a second. Same issue.

So let’s resolve this.

  1. Provide a new grounded power supply to all current QC owners.
  2. Provide a firmware upgrade that doesn’t require a noise gate on every single device.

With those two solutions, QC is the winner in the modeler/profiler wars.

Desktop editor and plugin support can come in time. The interface itself is amazing.

But the noise. Just search Google for “Quad Cortex noise”.

Please NDSP, save the QC!

This is all on the website. It’s been designed like this on purpose. The alternative is potential ground loops when connected to external grounded devices. They had to make a guess that this is the most likely use case and design accordingly.


I dunno, man. Mine is very quiet, even the overdriven presets. No buzz or hiss. It’s certainly as quiet as my AX8 was. I only use a noise gate (moderate threshold) at the input of overdriven presets. My first guess would be a gain staging issue but I know you’ve gone over all of that. I’m sure it’s frustrating.

A note for others who might read this: cable issues can’t cause hiss!


This seems more like it should be a BUG report than a feature request. If “hiss” was a universal issue, you’d hear WAY more about it and it wouldn’t be a viable pro option for all the A-listers out there touring and recording with it.

I haven’t heard of other users needing a noise gate on clean amps. Hiss is unavoidable when dipping into high-gain territory, but should be manageable in most other cases. I think your issued may lie elsewhere. Gain staging is the usual main culprit, but I’m sure you’ve explored that already.

Can you give us an idea of your signal chain, guitar/pickup/preset-wise and the environment you’re using it in?


If I could offer a suggestion…try going through and turning each block off (bypassed) and on. If you find that your preset’s volume goes up, considerably, when a specific block is bypassed, that’s an indication that that is block reducing the signal. That means that other blocks down the line from the weak one (or the output section) are having to make up for the gain loss and are amplifying the noise floor in the process. As I’m programming, I like to occasionally bypass the FX block I’m tweeking to see if the volume stays roughly the same, the digital equivalent of unity gain. Obviously this wouldn’t hold true for somthing like a boost before an amp block. As long as you have a good strong input level from your guitar and each block is operating near unity, the QC should be very hiss free. Things like heavy compression, destortion and/or treble boost will also amplify hiss.


Thanks @PickinPete - I will give that a try!

@xush if you search Google for “Quad Cortex” “hiss” - it is quite common.

Of course! Keep us posted.

Totally agree, the noise is a problem for a lot of people (including me) and you can find a lot of people complain about it. (the most common complaint from what i see)

If i compare to my Kemper it’s very different, the Kemper is way quieter (noise gate also wy better imho) The QC seems very sensitive of his environment in comparison.

for the 100th time do not plug in your outputs from the QC to your amp/PA whatever until its finished booting, and then you wont have the hum.


They’re talking about noise-floor hiss, not grounding hum in this case


i think hte megadupe guy or whatever is conflating the ground hum issue and posts with the hiss problem so i am compelled to say the thing relating to the power up scan / power supply thing

personally i dont see the big issue and complaining about having to have a noise gate with a little more frequency to taste than what people are accustomed to doing. I dont even know why anyone would harp about having to put a gate in or whatever. I have had a ton of amps and i have been using various filters and gates over the years because i like my amp to make absolutely 0 noise. I dont care how quiet the thing is, i use a gate or something on every rig to clean it out totally. its part of having a rig and to some of us we want 100% clean quiet no hum, not even a low barely perceptible operational level. hmmm. use a block almost all the time. or carry my favorite rack solution everywhere i go…

first world problems

The Megadupe guy is talking about hiss.

The ground loop issue was solved by connecting an unpainted XLR cable to a grounded source. Which in itself is ridiculous. Axe-FX III, Kemper, Helix. None of them need this.

The hiss is very similar to a high gain amp hiss, but without the high gain amp. It is a known issue, yet for some reason QC owners feel the need to protect NDSP and not upset them or something. These are known issues.

Take the Plexi Bright model alone with a cab and set the gain at 2. Just that in the path. You will get hiss. A real Plexi does not do this at gain 2. Helix, Kemper, and Axe-FX don’t hiss at gain 2.

It’s an issue with the QC and hopefully can be resolved with a firmware update. That’s why this Megadupe guy posted it in feature requests.

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yeah you can use unpainted stuff or whatever complex way of addressing the ground issue, or you could not plug in your painted cables until its finished booting.

I understand this is about the hiss but you are bringing up stuff that is not about the hiss, conflating the two

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i can understand that there is more hiss on QC amps than what you would expect in real world, but real world or virtual QC world I use gates or filters 100% of the time, so im not really seeing a lot of value in making me not have to turn the knob a little further on the obligatory gate that I am always going to have in my chain no matter what.

I’m perplexed by QC noise complaints as I’ve had no problems with hiss or hum (except during boot-up). I’ve always used gates on higher gain presets, even on my Fractal and Line 6 gear. High-gain and/or compression will increase noise! It has to be how folks are setting up their signal virtual signal chains or a defect that only exists on some units.

Concerning coments about noise not existing in the real world. Have you ever plugged into an original Dual-Rectifier? :hear_no_evil::laughing:


As the bro has found people complaining about hiss, perhaps the rest of us need to post a load of threads declaring that we have no problem with hiss.


Indeed, I have a rev G at home. Last of the old 2ch duals

But how did they come to this conclusion?
Kemper, Helix, Fractal,… they all go the other way with no problems.
At home I always have to connect something via XLR, which is just stupid.
And at a gig? I tried the QC once at a gig, connected via XLR to the mixer and had an underlying hum I couldn’t get rid of → I put the QC back in my car, connected a Helix and had no problems…

@megadupe21 : The QC will not be fixed. I bought the unit over a year ago and love it for so many reasons. But it is unreliable and not gig-ready. Meanwhile, any hope in NDSP is gone as well.
It’s a good device if you only want to use it at home (and are willing to always use a noisegate + permanent XLR connection). For everything else, the device is unreliable and you should rather buy Kemper/Helix/Fractal.

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something something dont plug in the outputs until its finished booting something something

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So for one thing, that shouldn’t be necessary… With NO other modeler you have to remove the XLR cable to boot. No matter if 2000€ Fractal, or 130€ Harley Benton. I also can’t understand how you can just accept this as a customer.

In my case, however, the device was fully booted. The Ground hum was permanently present (with Ground Lift even worse than without). This was a smaller festival and exactly the same place and XLR cable played several modelers over the weekend (Helix, POD, Mooer, Kemper). Only the QC has made these problems and was not usable