Unity gain & other gear

Hey all, so I’m digging my QC quite a bit. But what I’ve noticed is when using it with an amp either just in front, or in 4-cable-method. The levels of distortion I get from the amp aren’t as high as when I plug just straight into the amp.

On QC to get the same amount of distortion from the amp (Diezel VH4, but it also happens with my other amps) I have to increase the output level by about 5-6dB.

So I checked the output of the QC versus my Helix and Kemper, and yes indeed - the output of the QC is a lot lower than other devices.

I also checked this with a Fryette PS-100, and I needed to set the PS-100 to be very loud to get the sort of levels I wanted, in comparison to the Helix and Kemper.

I think this is a pretty big deal, because it also affects your signal when using external pedals. If I put a tubescreamer in FX Loop 1, then I’m not getting the same level going into the pedal as I would just plugging my guitar into the pedal.

Is this a known issue, a design fault, a hardware fault, a firmware thing?? Has anyone experienced the same thing??

Is this to do with the existence of the output limiter? Can we get a unity gain mode?

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There’s some talk about this that might help here

I brought up this issue with them a long time ago when I couldn’t drive a Line 6 Powercab properly they claim it’s a line level signal and it certainly is not. You really have to crank the output levels until the meters are well into the red to even get close to pro line level.

One difference between the Quad Cortex and other modellers is that the volume knob is actually an attenuator at the end of the chain. So all the way up is unity gain. When I want a boost beyond that I just turn up the output on the amp block.

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Well even with the volume knob at full, the signal from the QC is still attenuated. It isn’t unity gain.

Hi, do you fell that using the QC in 4-cable-method with an amp sucks the output level in general? I tried to use the QC in 4-cable-method with my Mark V. I use the Send Level on my Mark V effect loop same as I do with my Helix FX. Now with the QC I have to reduce the Send level on my Mark V as well as the Send and Return levels of the QC to avoid clipping Input and Output of the QC. In results I get less output gain. Do you have any tips for setting in 4-cable-methods?

No tips from me really. I think Neural need to fix this in a firmware update.

This mean you recognize reduced gain too?

Yes. Absolutely.

I’ve done a few measurements on my QC. Using a pass-through lane and setting the input and output to levels to 0 dB give unity gain within 0.1 dB. So the unit itself doesn’t mess with the gain as far as I can see. Same for the USB interface levels btw.

A note on the QC meters though - Going into the red on the green/yellow/red meters does not mea nclipping, but follows (more or less) the recommendation for keeping studio signal levels.

The meters go from green to yellow at -10 dB (down from digital ceiling at 0dB) and from yellow to red at -8dB. When the meters hit the right edge, that is digital clipping (0dB).

On the outputs there are gain controls (in the I/O page) where you can boost the signal up to +12 dB. However if the input signal is strong and boost is applied the limiter kicks in so the QC doesn’t distort in itself.

So what are the analog output voltages from the QC then? Well I can’t measure the actual value right now, but read the QC specs, which states that the maximum output level (when the limiters kick in) on all outputs is +9.5 dBu (using outputs 3/4 with balanced 1/4" gives +15.5 dBu) all with output impedance 560 ohms. That’s plenty of juice!! In comparison The Axe III delivers +20 dBu while the Kempers delivers +4dBu.

So analog level wise the FXIII is “louder” than the QC which in turn is louder than the Kempers, into the same amplification.

When inserting modules in the QC lanes affects the levels in different ways. What I’ve done is to save new defaults for some modules so that the parameters (including in/out levels) suit my way of building a preset.

That’s not my experience.

Blank patch. Volume knob up full. All input and output levels set to 0dB. Input 1 running straight to output 3.

I get about a -5dB level drop in such a situation.

Sorry, I’ve read about your issues, but I can’t replicate that…

Edit - apart from the input and output gain controls, the only “invisible” parameter that could affect the internal level through an empty lane is the output block gain (accessed by long-pressing the lane output box) but for me, that defaults to 0dB in a new “unsaved” preset.

Yeah same.

I’ll do a video to show what I’m getting

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OK, some further testing and I can replicate getting a -6dB attenuation passing straight through the QC with all gain at unity! My findings points to the balanced TRS outputs 3-4.

AFAIK my audio interface (RME UCX) is electronically balanced and give the same signal levels using both TRS and TS cables in its I/Os. A properly balanced connection has the double voltage swing compared to an unbalanced signal - or vice versa - using only one half of a balanced signal (as when using a TS gear/cable into a TRS jack).

OK, so the tele part of input combi jacks 1-2 is TS - nothing to see there. The outputs 3-4 are TRS jacks. When I use a TRS cable in output 3-4 to my audio interface I get unity gain. When I use a TS cable, I get 6 dB less signal. This indicates that the 3-4 outputs don’t sense if the signal is balanced or not, so with a TS cable, you get half the output voltage and the (preferably output) gain must be boosted 6dB.

I assume guitar amps with FX loops etc are unbalanced which will require that 6dB boost to stay unity.

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Thanks for this info @hasse_fx . This helps me understand what I’ve basically already experienced. It makes total sense to me now with how you’ve explained it :slightly_smiling_face:

Here is a DIY-solution to get the full signal output from the QC for unbalanced connection. As it’s still unbalanced you get no noise cancelling.

https://www.soundonsound.com/sound-advice/q-there-better-balanced-unbalanced-cabling-solution

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