Noisy Effects Loop

[TexasFM3]

Hey All -

Gotta strange problem - My Duel Rec - is noisy as all when I use the effects loop. I thought if I changed out 12ax7 Tube in spot V4 that this would make the problem go away - but it did not do anything. On the clean channel - it is silent as all. Its only when I move to channels 2 and 3 that I get a hiss.

I thought it must be coming from my pedals so I put a noise decimator in the loop and turned it all the way up... still had noise? The only way to kill the noise is to unplug the cables.

I then thought it was the monster cables - but I use another set and the noise is still there. It seems that as soon as I plug in the 1/4 jacks the noise is present.

I unplug the effects loop and the amp is quite as all on all channels.

This is a Parallel effect Loop unit and not a Serial effects loop.

Any ideas are much obliged.

Thanks

FM3

 

[elvis]

Ground loop

 

[TexasFM3]

Ground loop

Thanks - but I am not sure what this means or how to do it.

In the simplest test that I have done - I take a 6ft cable out the send from the back of my Duel Rec to a Boss RV-3 input. I take the RV-3 output and run it back to the amp's return. I get NOISE! Removing the cables I get all quite.

How do I ground the loop?

When you say ground the loop is this something for a amp tech to do. I wish I could work a circuit board but cannot.

Any insight is much obliged.

FM3

 

[domct203]

Ground loop

Thanks - but I am not sure what this means or how to do it.

http://en.wikipedia.org/wiki/Ground_loop_(electricity)

How are you powering that pedal?

Have you tried just a cable from send to return (no effects)? If there is no hum with only a cable then it's not the amp.

Dom

 

[elvis]

+1

You want to look at where noise is injected. In particular, if you find that your low gain channel is quiet, but the high gain channels are noisy, then noise is being injected into the preamp front-end. This usually happens from a noisy guitar or pedal that is in front of the amp input. If turning the volume all the way down on the guitar fixes it, it's the guitar. If not, keep looking. NOTE: Do not look for noise problems without a guitar plugged in. That just leaves the amp input floating and allows for it to pick up noise from the room. Plug a guitar in and turn the guitar volume all the way down.

Once you get to the loop, the guitar signal has been gained up by the preamp, and it is much more difficult to inject noise into the loop unless you have a really noisy pedal in the loop. And that would be equally noisy on all channels.

A ground loop is where you have more than one path to AC power. For example, if your amp plugs into the wall, but no other path exists (either no pedals are used or all pedals are powered) by batteries, then there is only one way for ground current to travel - out the amp's power cable. So no ground loops are possible.

OTOH, if you use any other AC line-powered gear (wireless, AC-powered pedal or switcher loop, AC-DC pedal power, rack effect, etc.) then you can get ground current running between the two AC power plugs through the pedals and/or amp. Since this path may run randomly along the amplifier's internal circuitry, it could be injected into the preamp even though the effect in question is connected to the loop.

Easiest way to debug: Dom's advice first. Rule out the amp with a cable in the loop.
Next, plug one effect at a time into the loop and see when you get noise. Best bet is that it's an AC-powered pedal. Power those with batteries or an ISOLATED DC supply like a Pedal Power 2. If you have a rack unit or your pedal is AC, not DC powered, then you will want to try an isolation transformer like Ebtech HE-2. This breaks the direct path between the AC line supplies with a transformer.

 

[TexasFM3]

Dom and Elvis -

Thanks for the insight - I am happy to report that it is NOT my AMP!

I took a chord and plugged the send to the return and viola - quite as all.

I started missing with my cables and placed a battery in my RV3 and quite as well.

So now I need to investigate the board. I have a SKB-PS45 and it seems that the ports on the board are the problem. When I simply have a chord between the board and the amp - the amp is loud as well. This just by plugging a single cable in. It seems that this is the culprit, but now I need to know why. At least I have whittled it down.

Thanks gentlemen

FM3

 

[elvis]

Definitely sounds like a ground loop. Is the SKB board plugged into AC mains? What happens if you unplug?

 

[TexasFM3]

My setup is as follows -

I have the SKB pedalboard as the main plug i use for my setup and plug that into the wall. I then use a extension cord and connect the duel rec plug of the amp into the wall wart connections directly on the board itself. I then have two other wall wart effects that I plug into the other two wall wart connections. I then have 5 boss pedals that I also plug into the 9v outlets on the board. The only plug drawing juice from the wall is the board connected to the wall and this feeds all other plugs.

I am not sure where a ground loop would come from as me reading up on this it seems that this becomes a problem when I use 2 different plugs into 2 different outlets?

FM3

 

[elvis]

Having equipment plugged into different mains outlets can make ground loops worse, but is not a necessary condition. It's a design problem with the equipment and with a general misunderstanding of what ground means in AC mains.

You also have a bunch of other junk in the picture. I am not sure if the SKB power supply to the pedals is isolated or not, you should check. If not, you might want to add an isolated supply like a pedal power 2. But short-term, disconnect the pedals until you get the amp + board quiet.

You can try to kill the ground loop between the board and the amp by either breaking the signal path with isolation transformers (Ebtech HE-2 is great) or possibly by addressing the GND path in the mains with something like a HumX on the amp's AC power cord.

 

[Blaklynx]

Have you simply tried powering the amp from another power point?

I power many pedals but always power the amp from another power point. I've never had ground issues.

For basic safety, avoid powering so many things from one power point. The total current draw of all the equipment may overload the power point causing the circuit to trip or worse still cause a fire.

 

[elvis]

I'm not sure what the power standards are in AU, but in USA it's 110VAC with either 15A or 20A breakers. This is a minimum of 1500W, so you should never overload a circuit.

Plugging into multiple AC outlets increases the chance of ground problems, so I recommend against it. For example, if one AC outlet is on a clean line, but the other is on a line with a compressor (AC unit, refrigerator, etc), then you will get large, noisy ground current. Or, if both are on the same circuit, but tapped in at different physical locations, and there is a heavy load or ground current downstream, then there will be different voltages at the two outlets.

Best to stick to the minimum possible.

 

[TexasFM3]

Well I think I tracked down the issue -

It seems that the SKB is the culprit in this. The patch bay that it has is the cause of the issue I am having. So I have stopped using the patch bay of the Pedalboard and simply using it as a powerstrip. I then plug my cables directly into the pedals rather than the patch bay.

The results are ions better than what it was before.

I am happy with the result.

Elvis - I started from ground zero like you said and took everything apart. I then did one pedal at a time and was able to track the problem down to the patch bay on the board. So thanks for the insight.

FM3

 

[elvis]

Glad it worked.

Rock on!

 

[Blaklynx]

I'm not sure what the power standards are in AU, but in USA it's 110VAC with either 15A or 20A breakers. This is a minimum of 1500W, so you should never overload a circuit.

Plugging into multiple AC outlets increases the chance of ground problems, so I recommend against it. For example, if one AC outlet is on a clean line, but the other is on a line with a compressor (AC unit, refrigerator, etc), then you will get large, noisy ground current. Or, if both are on the same circuit, but tapped in at different physical locations, and there is a heavy load or ground current downstream, then there will be different voltages at the two outlets.

Best to stick to the minimum possible.

Hi elvis,

Power in AU is 240VAC. Standard circuit breakers are 10A for power points. Generally there may be 3~7 seperate lines for power points depending on the house size and how many power points are wired. Where high loads are required for AC's and ovens, 15A is used and these are always on seperate lines. For light switches, they have their own lines, too.

Everything else you said applies and makes sense.

Glad the OP figured it all out.

 

[TexasFM3]

OK - I officially have a total silence - a almost scary quiet amp now.

I found out the problem with the board. I don't know why - but I have a fix in place that works.

So I was powering all my stomp boxes through the power of the SKB board, as follows.

BEFORE preamp -
digitech whammy to a wall wart plug
digitech EX7 to a wall wart plug
Boss Tuner to 9v plug
Boss Super Distortion to 9v plug
BBE Sonic Stomp to 9v plug
ISP Noise Decimator to 9v plug

In Parallel Effect Loop
Boss Digital Reverb/Delay to 9v plug
Boss Super Chorus to 9v plug

The above for some reason caused all kinds of noise though the amp.

Taking Elvis's info above - I dismantled everything and started from ground zero. As soon as I plugged either of the pedals that I have in the effects loop into the onboard 9v plug - the noise would start. When I tried 9v batteries it was silence as anything, sure I could use 9volt batteries but the freaking RV3 is a battery eater. Hell I would go broke buying freakin 9v batteries for sure. So I investigated on further.

I dug out of my old cable box my old Roland wall wart boss power supply w/ 3 power extension cable and plugged the wall wart into the board and used this to power the 2 effects loop pedals.

I am talking Vacuum Quiet. WOW.

So for some odd reason - effects through the loop when using the power from the 9v onboard plugs creates a "ground loop". So moving these effects off the 9v plugs of the board and using my original boss power supply into the last Wall Wart plug of my board breaks what ever was going on and VIOLA sweet silence.

Sure I have a extra wall wart to tote around but **** I will take that over the noise any day of the week.

Thanks again for all the help gentlemen.

Rock on!

FM3