SOLVED Pedals hissing less first in line compared to FX loop?

[Fama]

Hello! I've built the Aion Anubis (https://aionfx.com/app/files/docs/anubis_documentation.pdf) a while back and it's very noisy when I use it in the FX loop of a Quad Cortex.

The Body control also affects this hiss tremendously. There's a specific sweet spot around 3'o'clock where the hiss is reduced dramatically.

I also noticed that if I use the Lightspeed clone I built (Southern Lights from Fuzzdog, Lightspeed specs) the hiss is decreased substantially while the sound is similar - with more gain, if anything.

Here's the sample using a looper feature, I tried to add comments to Soundcloud but apparently I got blocked by their spam filter after three comments.

https://soundcloud.com/user-913671490%2Fanubis-hiss-sample%2Fs-CZlZD8Gy0lq

I'll list the riff repeats:

1st: All pedals off
2nd: Just the Lightspeed
3rd: Anubis with Body set to sweet spot
then I turn the Body control down, you can hear a massive increase in hissing
4th: Anubis with Body turned low
5th: Lightspeed + Anubis with Body turned low - the hiss disappears almost completely even though it sounds almost identical otherwise, maybe a bit more gain.

I've tried with some buffers before the Anubis but I don't think it has helped much. I use a 1Spot Pro CS 12, most pedals are daisy chained, I give the Anubis it's own isolated power but that doesn't make any difference.

How could I get rid of the hiss? Is it an impedance thing? Or would a small buffer pedal help?

One obvious answer is "put it in front", but I would like to be able to use effects on the QC before the Anubis, like pitch shift, octaver and so on.

Edit: Actually the Aztek Sunn (https://www.dropbox.com/s/2avxcdetkyk59ez/Aztek Sunn Doc.pdf?dl=0) from Moonn is acting in a similar way.

According to the manual, the QC send outputs (which I'm using) have an impedance of 560 ohms.

 

[Fama]

Do you get the hiss if you just use the FX loop as a return? (No send from the Cortex, just plug your pedal chain into the FX return instead of input).

No, that doesn't cause hiss. When testing I've always had the pedal output plugged into Input 2, and then switch between guitar to pedal, or guitar to Input 1 and then route it Input 1 -> Send 1 and plug Send 1 to the pedal.

FWIW I haven't figured anything else out, the Clandestine Preamp doesn't seem like a great solution either since it adds too much hiss to keep as always-on. It's not boxed yet so that could be part of it, I'll box it up when I get more black footswitches, and I can then also play around with switching the JFET around (I socketed it) to see if some other one is lower noise, and then solder that in. But from googling it seems the original also hisses, at least for some users. To clarify this is just normal hiss, FX loop or not makes no difference there - it does remove the "weird hiss" I get with the Anubis, but if I can't fix the normal noise it's not a working solution for me.

 

[JTEX]

Your pedals hiss when in the FX loop because the FX Send is noisier than a guitar's bare output, due to suboptimal circuit design. Perhaps not enough to be an issue on its own, but it gets magnified to the point of annoyance by any gain-based pedal that follows it (compressors, distortion etc). This cannot be fixed unless you mod the FX Send.

 

[Fama]

Your pedals hiss when in the FX loop because the FX Send is noisier than a guitar's bare output, due to suboptimal circuit design. Perhaps not enough to be an issue on its own, but it gets magnified to the point of annoyance by any gain-based pedal that follows it (compressors, distortion etc). This cannot be fixed unless you mod the FX Send.

But if it's just about noise, why would something like a cranked Secret Preamp get rid of the noise?

Edit: FWIW as an update to the last previous post I made, switching the JFET to a 2N5457 got rid of most of the noise, and now I pretty much run it as an always on tone enhancer thing.

 

[JTEX]

Secret Preamp

Maybe the cranked pre lifts the signal level enough that a subsequent, noisy pedal can be dialled with less gain, this cutting its own noise production? I don't know the Quad Cortex, but doesn't it have a level control for the FX Send? If it does, try cranking that one up and reducing the gain of the noisy pedals. Your issue could be just gain staging-related.

 

[Fama]

Maybe the cranked pre lifts the signal level enough that a subsequent, noisy pedal can be dialled with less gain, this cutting its own noise production? I don't know the Quad Cortex, but doesn't it have a level control for the FX Send? If it does, try cranking that one up and reducing the gain of the noisy pedals. Your issue could be just gain staging-related.

No, here's a sound example. I used the modded Cthulhu-fuzz, essentially something between a fuzz face and a muff, but with the gain dimed all the time - so the example is more extreme than how it normally would be. I turned the noise gates off too.

1st is the Cthulhu alone.
2nd I turn on the Secret preamp (it's before the Cthulhu, otherwise it doesn't remove the noise).
3rd I put on a noise gate.

https://soundcloud.com/user-913671490%2Fcthulhu-noisetest%2Fs-yv7bKHWxP4r

I could set the preamp to unity too, and it would still do the same thing. Or even quieter than unity. I'm not sure what's happening, but running the signal through the pedal filters something out of it that is there otherwise. Other pedals also work, like the Lightspeed or a treble booster, but I use the Secret preamp since it sounds really nice.

 

[JTEX]

No, here's a sound example. I used the modded Cthulhu-fuzz, essentially something between a fuzz face and a muff, but with the gain dimed all the time - so the example is more extreme than how it normally would be. I turned the noise gates off too.

1st is the Cthulhu alone.
2nd I turn on the Secret preamp (it's before the Cthulhu, otherwise it doesn't remove the noise).
3rd I put on a noise gate.

https://soundcloud.com/user-913671490%2Fcthulhu-noisetest%2Fs-yv7bKHWxP4r

I could set the preamp to unity too, and it would still do the same thing. Or even quieter than unity. I'm not sure what's happening, but running the signal through the pedal filters something out of it that is there otherwise. Other pedals also work, like the Lightspeed or a treble booster, but I use the Secret preamp since it sounds really nice.

Oh wow. Drastic. It almost sounds to me like the FX Send has some out-of-band noise (above 20k) that gets demodulated and made audible by the Cthulhu. Try a 220pF to maybe about 1nF cap across the Cthulhu input just for troubleshooting.

 

[Fama]

Oh wow. Drastic. It almost sounds to me like the FX Send has some out-of-band noise (above 20k) that gets demodulated and made audible by the Cthulhu. Try a 220pF to maybe about 1nF cap across the Cthulhu input just for troubleshooting.

Do you mean in series? I could give that a try for sure. So far the same thing has also happened with the Aion Anubis (https://aionfx.com/app/files/docs/anubis_documentation.pdf - it's much better with the Body control at a certain point) and Moonn Aztec Sunn (https://www.dropbox.com/s/2avxcdetkyk59ez/Aztek Sunn Doc.pdf?dl=0). I think both of those have electrolytic caps at the input, I wonder if that could affect it. Not sure about the Cthulhu since it was modded and made into a PCB by someone on Discord.

 

[JTEX]

Do you mean in series? I could give that a try for sure. So far the same thing has also happened with the Aion Anubis (https://aionfx.com/app/files/docs/anubis_documentation.pdf - it's much better with the Body control at a certain point) and Moonn Aztec Sunn (https://www.dropbox.com/s/2avxcdetkyk59ez/Aztek Sunn Doc.pdf?dl=0). I think both of those have electrolytic caps at the input, I wonder if that could affect it. Not sure about the Cthulhu since it was modded and made into a PCB by someone on Discord.

Parallel capacitor! Right across the input jack of your pedal. Easiest would be to open up the male jack plugging into the pedal (assuming it's not molded) and just put a cap between tip and sleeve. Hold it there by hand, just to see if it makes a difference.

 

[Fama]

Parallel capacitor! Right across the input jack of your pedal. Easiest would be to open up the male jack plugging into the pedal (assuming it's not molded) and just put a cap between tip and sleeve. Hold it there by hand, just to see if it makes a difference.

Thanks! I'll give it a try tomorrow probably.

 

[Fama]

Well it was more "week and a half" than tomorrow, but @JTEX I think you might be correct. I first tried with the Cthulhu, but I think it has some other grounding issues too because it just gave a nasty sound whenever I was touching the input jack with a cap, or the ground jack with a finger even. I'll check that separately to make sure it's well grounded.

However, I also tried the Aion Anubis which originally spawned this whole thing, and for sure a capacitor across the input jack removed the noise! I used a 27nF cap because the QC send impedance is 560 ohms only - I used a basic RC filter calculator for this, although I'm not sure if it's that simple. And if I were to solder something like that in, does that mean that if I plugged a guitar straight into it with pickup impedance in the 20k range, it would go to shit since the filter moves to like 350Hz?

I guess I could maybe try rigging up a socket for it and just try to remember it if I ever use the pedals outside of the QC or sell them...

Edit: A 1nF cap still helps quite a bit, 2.2nF pretty much fixes it but then that might be too much already for some guitar mics.

 

[JTEX]

Well it was more "week and a half" than tomorrow, but @JTEX I think you might be correct. I first tried with the Cthulhu, but I think it has some other grounding issues too because it just gave a nasty sound whenever I was touching the input jack with a cap, or the ground jack with a finger even. I'll check that separately to make sure it's well grounded.

However, I also tried the Aion Anubis which originally spawned this whole thing, and for sure a capacitor across the input jack removed the noise! I used a 27nF cap because the QC send impedance is 560 ohms only - I used a basic RC filter calculator for this, although I'm not sure if it's that simple. And if I were to solder something like that in, does that mean that if I plugged a guitar straight into it with pickup impedance in the 20k range, it would go to shit since the filter moves to like 350Hz?

I guess I could maybe try rigging up a socket for it and just try to remember it if I ever use the pedals outside of the QC or sell them...

Edit: A 1nF cap still helps quite a bit, 2.2nF pretty much fixes it but then that might be too much already for some guitar mics.

I'd fix the root cause: the QC send. Just add a 10nf or so cap across it, if it has a 500-ish ohm output impedance.

 

[Fama]

I'd fix the root cause: the QC send. Just add a 10nf or so cap across it, if it has a 500-ish ohm output impedance.

That would probably be the correct way to go about it, but I don't feel confident enough in my abilities to not mess up anything soldering a cap inside a 1600€ piece of kit.

I ended up modding a cable, I had a WIMA 22nF cap (so -3dB frequency is around 13kHz, should be just fine) that just fit inside the cable itself (it was already my designated QC cable since I tried if the "ground canceling" thing would fix the buzz, but it did not - now it's my designated send cable) and that fixed all the noise from the Aion Anubis. Thank you again @JTEX, this has been puzzling me for literally years at this point, and now I finally have the answer!