Hum and noise problems

Q & A for building and interfacing your rack gear with Ground Control Pro and GCX-based systems.
JohnClark
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Joined: Tue May 05, 2009 2:33 pm
Location: The Lab

Re: Hum and noise problems

Post by JohnClark » Wed Apr 12, 2017 9:42 am

Wait, what exactly was the signal path for this test... with no cables connected to the loops there is no way you should be hearing any popping when switching loops.

Popping is usually due to a DC offset where the signal has a sudden amplitude shift. This is commonly due to a failing output decoupling capacitor in a pedal, on the other hand there is always a certain amount of pop with true bypass switching... it is a rather violent way of switching a signal path.

I wonder if perhaps you sound card is also overly sensitive to what usually goes on in a guitar signal path. Do you have any true bypass pedals to plug into this card to see if they do a similar popping? Is this soundcard input specifically intended for use with a guitar? Do you have something other than this sound card to test this rig?

I'm still not too sure what you are saying about the rear panel jacks on your GCX and how you are using them. No model of the GCX used these jacks as an In/Out without something connected to the front panel jacks. In fact, on yours these are both outputs after a pair of buffers. the Front panel Feedthru 1 input will feed both rear panel Feedthru outputs but this normalling isn't intended to be used as I think you are describing. If you are going to use the buffer(s) in your GCX, you need to use the front panel jacks as the input and the rear panel jacks as the output.

andefeldt
Posts: 25
Joined: Mon Feb 20, 2017 3:59 am

Re: Hum and noise problems

Post by andefeldt » Wed Apr 12, 2017 10:20 am

Exact signal path in the test:

Guitar -- pedalboard: Poly Tune (true bypass) -- CryBaby -- TC BonaFide buffer (true bypass without switch) -- Rack: GCX -- TC G-Force -- Sound card (Lexicon Alpha)

I don't have other sound cards available and unfortunately no amp at the moment.

I'll try plugin a true bypass pedal directly into the sound card to test this.
About the connection on the back, I'm using the wiring you wrote in another thread of mine. It works with the exact same result as if I plugged my guitar into the front and then from the back to loop 1. I don't wanna use the buffer, as I'm using a buffer on my pedalboard befrie the cable to the rack.

I still think I have some ground issues as my loop 1 (whammy) is humming when it's power supply is placed near my rack drawer or my GCX power supply is near the whammy...

andefeldt
Posts: 25
Joined: Mon Feb 20, 2017 3:59 am

Re: Hum and noise problems

Post by andefeldt » Wed Apr 12, 2017 11:10 pm

Noticed the signal meter (don't know the correct term) on the G-Force.

When activating a loop the meter shows a peak - it's getting a loud signal from the GCX. This happens even if the sound card isn't plugged in. So there's something going on here...

JohnClark
Posts: 7133
Joined: Tue May 05, 2009 2:33 pm
Location: The Lab

Re: Hum and noise problems

Post by JohnClark » Mon Apr 17, 2017 11:41 am

Lets try a couple tests... Please follow these connections.

Test #1
1. Guitar to Feedthru #1 on the front panel of the GCX.
2. Feedthru #1 on the rear panel of the GCX to Loop 1 In.
3. Loop 1 Send to Pedal #1 In.
4. Pedal #1 Out to Loop 1 Return.
5. Loop 1 Out to Soundcard Instrument Input.

Test for noise, or excessive popping when turning Loop 1 On or Off.

Test #2
If that is no good, try moving the buffer after Loop 1...
1. Guitar to Loop 1 In.
2. Loop 1 Send to Pedal #1 In.
3. Pedal #1 Out to Loop 1 Return.
4. Loop 1 Out to Feedthru #1 on the front panel of the GCX.
5. Feedthru #1 on the rear panel of the GCX to Soundcard Instrument Input.

Test for noise, or excessive popping when turning Loop 1 On or Off.


Let us know what you find.

andefeldt
Posts: 25
Joined: Mon Feb 20, 2017 3:59 am

Re: Hum and noise problems

Post by andefeldt » Tue Jun 13, 2017 5:40 am

Finally something has happened :D

The hum has stopped. I had a guy build me a metalbox for the power supply for the GCX which removed all hum. Outside the box the power supply causes hum :? Maybe not the most ideal solution but it works.

The click/pop sound is still there though. But I figured out what causes it. I was running my signal through the GCX and then through my TC G-Force and then out. I tried bypassing the G-Force and going straight from the GCX to my soundcard - No more pop sounds!

So I need to a add a bleed resistor somewhere, but where? In the jack going from the GCX to the G-Force? Or in the jack going from the G-Force and to my sound card? Or both places? And is a resistance of 100k enough or should I go 1M?

JohnClark
Posts: 7133
Joined: Tue May 05, 2009 2:33 pm
Location: The Lab

Re: Hum and noise problems

Post by JohnClark » Tue Jun 13, 2017 9:30 am

Good find on the noise source!

For the resistor mod, I would suggest running a 100K across the output of the G-Force... particularly if it is an early production unit.

Let us know how it goes!

andefeldt
Posts: 25
Joined: Mon Feb 20, 2017 3:59 am

Re: Hum and noise problems

Post by andefeldt » Wed Jun 14, 2017 5:40 am

Ok, I soldered a 100k resistor on the output jack cable from the G-Force (from tip to sleeve in the jack). That didn't help :|

It didn't make problem worse or anything, it just didn't do anything.

Should I do the input instead? Or input as well?

Anders

JohnClark
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Joined: Tue May 05, 2009 2:33 pm
Location: The Lab

Re: Hum and noise problems

Post by JohnClark » Wed Jun 14, 2017 12:43 pm

I'll have to admit, I'm at a loss here then.

If you only get the pop when the G-Force is in the signal path, well that points to the G-Force... older units did need this output mod, but without being able to get this setup under a microscope (OK, an Oscilloscope is probably a better tool ;) ) I just cannot guess as to why this occurs.

Have you gone back to an earlier idea and routed the buffer after the G-Force or just in front of the sound card input?

andefeldt
Posts: 25
Joined: Mon Feb 20, 2017 3:59 am

Re: Hum and noise problems

Post by andefeldt » Thu Jun 15, 2017 5:54 am

I just tried the two buffer tests you suggested earlier. The first one didn't help, but the second one did!

So now I just tried this which works:

1. Guitar to Loop 1 In.
2. Loop 1 Send to Pedal #1 In.
3. Pedal #1 Out to Loop 1 Return.
4. Loop 1 Out to Loop 2 In
5. Continue through all loops
4. Loop 8 Out to Feedthru #1 on the front panel of the GCX.
6. Feedthru #1 on the rear panel of the GCX to Soundcard Instrument Input.

So it appears that I need a buffer between the GCX and G-Force, right?

JohnClark
Posts: 7133
Joined: Tue May 05, 2009 2:33 pm
Location: The Lab

Re: Hum and noise problems

Post by JohnClark » Thu Jun 15, 2017 10:06 am

Earlier you said this...
andefeldt wrote:The click/pop sound is still there though. But I figured out what causes it. I was running my signal through the GCX and then through my TC G-Force and then out. I tried bypassing the G-Force and going straight from the GCX to my soundcard - No more pop sounds!
...but I don't see the G-Force being included in your most recent test, so I am unsure what it has proven. Was the the Feedthru #1 Buffer being used in the test I've just quoted to make the GCX quiet when running directly to the soundcard? If so then I would try adding the G-Force after Feedthru #1, and maybe try running the Output of the G-Force to Feedthru #2 before going to the soundcard.

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