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]

Anyone? I'll probably try building a veroboard buffer once I get more input/output jacks. I also have some old pickups I could use to try and rig up a "pickup simulator", but I'm not sure if either of those would help, or what the issue is.

 

[giovanni]

When you say light speed + Anubis what do you mean?

 

[Harry Klippton]

I understood it to mean Greer light speed and aion fx Anubis

 

[Fama]

I understood it to mean Greer light speed and aion fx Anubis

That's exactly right, running the Greer Lightspeed clone at ~around unity and gain low into the Aion FX Anubis. It's a bit more gain but there's much less hiss.

 

[giovanni]

Have you tried isolating all pedals? The fact that the one pedal is isolated doesn’t protect it from ground loops. Electromagnetic fields are tricky.

That said, the hiss is really strange, I’ve never heard anything like it.

 

[Fama]

Have you tried isolating all pedals? The fact that the one pedal is isolated doesn’t protect it from ground loops. Electromagnetic fields are tricky.

That said, the hiss is really strange, I’ve never heard anything like it.

No, that's a good point. But it's still weird why it differs in the FX loop. I don't really know too much (yet) about pedal electronics, but impedance would be my first guess - I've got some more pedal parts now so maybe I'll try building a buffer or something with a high output impedance to test that too. But for sure I'll try the isolation first!

 

[giovanni]

Regarding your impedance hunch, do you have a schematic of the pedal? If the body knob can affect the impedance then your hunch is right. Otherwise I wouldn’t bet on it.

 

[Fama]

Regarding your impedance hunch, do you have a schematic of the pedal? If the body knob can affect the impedance then your hunch is right. Otherwise I wouldn’t bet on it.

Here's the schematic: https://aionfx.com/app/files/docs/anubis_documentation.pdf (page 5)

I don't think it increases impedance, it switches between two different caps.

 

[giovanni]

Oh I see. That definitely affects the input impedance. Big time. It’s also a traditional fuzz circuit which was probably designed to run immediately after the guitar. What’s the Aztek like? I couldn’t open the pdf for some reason, can you post a pic of the schematic? If that’s also a traditional fuzz we may have a pattern.

However I still have no idea where the noise is coming from or why it goes away with the other pedal in front. I still wouldn’t rule out a ground loop. The fact that the issue only occurs in the loop doesn’t rule that out and doesn’t confirm that it’s a matter of impedance, especially since it doesn’t go away if you put a buffer in front. Finally the fact that you get the same hiss with a different pedal may actually be confirmation that you have a ground loop: the noise may be coming from the ground loop and some combinations of pedals may trigger it. That’s usually how ground loops present themselves.

I would try a few things:
* make sure you have isolated power to all pedals and a supply that can provide enough current to all (since you are using a digital effect, that could very well be an issue)
* simplify your signal chain as much as you can and find the minimal setup when this occurs
* remove one element at a time from the chain to see if it makes a difference (sometimes it’s not the noisy pedal that’s the problem) and let us know
* try a different outlet or even a friend’s house (to remove your house as a potential source of the noise)
* I would also try a different amp just in case

Good luck!

 

[jhaneyzz]

Sounds like a bad solder connection to me.

 

[Fama]

Oh I see. That definitely affects the input impedance. Big time. It’s also a traditional fuzz circuit which was probably designed to run immediately after the guitar. What’s the Aztek like? I couldn’t open the pdf for some reason, can you post a pic of the schematic? If that’s also a traditional fuzz we may have a pattern.

However I still have no idea where the noise is coming from or why it goes away with the other pedal in front. I still wouldn’t rule out a ground loop. The fact that the issue only occurs in the loop doesn’t rule that out and doesn’t confirm that it’s a matter of impedance, especially since it doesn’t go away if you put a buffer in front. Finally the fact that you get the same hiss with a different pedal may actually be confirmation that you have a ground loop: the noise may be coming from the ground loop and some combinations of pedals may trigger it. That’s usually how ground loops present themselves.

I would try a few things:
* make sure you have isolated power to all pedals and a supply that can provide enough current to all (since you are using a digital effect, that could very well be an issue)
* simplify your signal chain as much as you can and find the minimal setup when this occurs
* remove one element at a time from the chain to see if it makes a difference (sometimes it’s not the noisy pedal that’s the problem) and let us know
* try a different outlet or even a friend’s house (to remove your house as a potential source of the noise)
* I would also try a different amp just in case

Good luck!

Thanks for the suggestions!

To cover your suggestions:

1.) I used just the QC (which has it's own power supply) and a couple of taps from a Truetone CS 12, which claims to be pure isolated power. So the Anubis is getting 100mA, and the other pedal I use to test is also getting 100mA, and the power supply should be able to handle all that and much more.

2.) Guitar -> Anubis -> QC, no hiss.
Guitar -> QC -> Anubis -> QC, hiss.

3.) I didn't try a different outlet yet, but I guess that could possibly be related?

4.) I don't have other amps, I only have the QC.

Well I do have an ancient Zoom G2.1U but there's no FX loop in there.

Sounds like a bad solder connection to me.

I don't quite agree since it doesn't make sense to me - why would a bad solder connection act up in the FX loop but not straight in? It's not related to the volume the pedal is getting coming in either. I did pop open the Anubis to check that the pots and in/out jacks make connection to the enclosure (pots, yes, jacks, probably yes but not quite 100% sure since the holes are bigger than the jacks themselves?) and noticed I had done a really shitty job with the soldering. The 9v wire came off the 3PDT breakout board when I pulled on it a bit! I fixed the issues I saw, but it didn't make any difference at all with this issue.


I did some more testing with the Informant Overdrive (1981 Inventions DRV) I just built, since that one is buffered, to see if it makes any difference. And it didn't really make any difference. I think the buffer is maybe increasing the signal level slightly, but that just means that I need to turn the gain down a bit on the Anubis to match. Otherwise it's all the same, hiss in the loop, no hiss without the loop. And similarly in the loop the hiss disappears if I turn on the Informant (at as neutral settings as possible, so gain at 0, vol at unity and cut somewhere around middle because it boosts the treble if I don't cut it). And even if I put cut down to 0, it boosts the treble, but not the hiss, so it's not related to cutting any hiss frequencies.

One possible clue I found is that in the loop if I have both pedals turned on and dime the volume on the Informant, the Anubis starts oscillating I think? It sounds like a circular saw. But then I'm not 100% sure if it's a clue or it's just how the Anubis is with a powerful enough input signal. It's way beyond any normal use settings.

Here's the Aztek Sunn schematic - it's not a basic fuzz in the sense that it's based on the Acapulco Gold, but maybe "close enough".

If the issue is indeed a ground loop, is there anything I can do to verify or fix that? The output from the pedals comes to the QC input 2 which does have a ground lift option, but toggling it on and off makes no difference. I'm not completely sure if it matters for a TS plug at all or if it's just for XLR. Maybe I could see if I could borrow a DI box or something and test whether using that and going as XLR in might make a difference.

 

[Fama]

If it's impedance related, shouldn't the buffer "hide" the output impedance of the loop since it's always on (informant schematic https://docs.pedalpcb.com/project/PedalPCB-Informant.pdf)? That's why I'm doubting whether it's just an impedance thing. I'll get the FX layout test board (input/output/volume on a board) soon so I can try doing breadboard experiments too to figure this out.

 

[giovanni]

This is really puzzling to me. As you mentioned, if it was an impedance problem it would go away with any buffer in front of the pedal. Did you try putting a buffer both in front and after?

I think a ground loop is also unlikely at this point since you tried with fully isolated supplies. I don’t know how the QC supply is but I assume it’s also isolated.

 

[Harry Klippton]

If you just put a patch cable in the effects loop with no pedals, does it hiss? I have an amp that hisses even if I just plug a cable into the return jack due to a ground loop so I don't use the loop on that amp

 

[Fama]

This is really puzzling to me. As you mentioned, if it was an impedance problem it would go away with any buffer in front of the pedal. Did you try putting a buffer both in front and after?

I think a ground loop is also unlikely at this point since you tried with fully isolated supplies. I don’t know how the QC supply is but I assume it’s also isolated.

I'll try with buffer before and after if that makes a difference.

The only very weird thing is that why does the hissing stop when I turn another pedal on? I have a Clandestine Preamp in the build queue too, so maybe I'll just have to start keeping that always on as the first in line to "fix" this issue

If you just put a patch cable in the effects loop with no pedals, does it hiss? I have an amp that hisses even if I just plug a cable into the return jack due to a ground loop so I don't use the loop on that amp

It actually does hiss a little bit. Not sure if it's a ground loop thing, it could just be down to the preamps on the output/input since they are digital. But the hiss is not very loud, so I don't think it should be amplified so much by the Anubis if there wasn't some weird interaction going on (and again, why is the body control making such a dramatic difference?). And the same hiss should still there with any other pedal turned on before the Anubis, if it was just down to that.

I noticed in the manual that the sends are mono, but they are actually ground canceling (or ground-compensated?) outputs, so I bought a TRS-TRS cable and soldered one side to bridge sleeve and ring so it becomes a TRS-TS cable. Sadly it didn't help with this issue at all, though.

 

[giovanni]

All you describe makes this sound more and more like a ground loop. The patch cable, the interaction with the body control, the pedal in front that “fixes” it: ground loops are notoriously “mysterious” with the noise sneaking into your signal chain in very specific conditions that don’t seem to have any logical connection. Again, I could be totally wrong, but this seems like the most plausible explanation. And it’s not really satisfactory and definitely sucks!

 

[Fama]

All you describe makes this sound more and more like a ground loop. The patch cable, the interaction with the body control, the pedal in front that “fixes” it: ground loops are notoriously “mysterious” with the noise sneaking into your signal chain in very specific conditions that don’t seem to have any logical connection. Again, I could be totally wrong, but this seems like the most plausible explanation. And it’s not really satisfactory and definitely sucks!

Hmm, it just hit me that the Anubis is pretty much the only pedal I've built which actually also works with a battery, would that solve a ground loop issue?

Edit: Quick test with a battery, Anubis as only pedal in line. Still hissing.

 

[giovanni]

Hmm, it just hit me that the Anubis is pretty much the only pedal I've built which actually also works with a battery, would that solve a ground loop issue?

It’s worth a shot but my guess is that the loop itself has a ground loop.

 

[szukalski]

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).