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EHX Switchblade noise and bleedover problems, how to fix??

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Hi,

 

I usually post over in HCAF but I thought you nice, knowledgeable people may be able to help.

 

I'm using an EHX Switchblade to A/B between my my guitar and bass live.

 

I use the same wireless and TU2 on both guitar and bass, and the switchblade goes to my guitar FX and out to the amp, while the bass is sent to a Sansamp and direct to board (I use bass on 2 tracks per set, so it's not workt bringing a bass amp.)

 

For ease of set up on my board, Output A of the Switchblade is sent to the Bass DI, and B to the guitar gear. Although, I'm sure this doesn't, or SHOULD'NT matter.

 

I'm getting a lot of hum going to the DI when the guitar channel is selected, and I'm getting the bass bleeding over to the guitar amp when that is selected. It's also causeing earth problems. I've got a hum destroyer on the guitar side which quietens that down, but that doesn't want to work on the oposite channel.

 

Any ideas? Can the Switchblade be modified at all? I'm 99% certain that it's at fault, and whatever is causing it to bleed over, is the issue.

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The switchblade is basically a stompswitch in a box and a couple of jacks. If you're getting bleedover then the switch is the only culprit, unless there's wires inside that are touching and that seems very unlikely.

 

The hum issue is almost certainly a ground loop problem. Try flipping the "ground lift" switch on your SansAmp bass DI and see if that reduces the noise.

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Ground lift on the Sansamp helps, but doesn't cure it. I'm not sure that the ground lift is a proppa ground lift on those tho, because it's also the Phantom Power on switch.

 

I used to use a True Bypass looper in the same way as the Switchblade (as in, just use the send jack as a signal splitter. Had the same issues with bleed and noise.

 

Isolated A/B it has to be then?? Looking at the Radial Bigshot, cos the Lehle Little Dual costs too much :(

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The hum is being created because you have your PA and Guitar amp plugged into two

different outlets. Those outlets have different lengths of wiring in the building back to the

Fuse box. One of the two has more resisntance and one if grounded better.

This creates a difference in potential between the two.

 

When you connect your wires to your guitar amp and the PA, you are bridging

the two outlet grounds and allowing current to flow from one to the other and you hear

it as a hum. You can float the ground of one outlet or the other with a ground removal adaptor,

but this is risky. Many have gotten zapped off a mic on stage because of poor grounding so

this isnt advisable. The only good way is to put the guitar amp and PA on the same outlet so

there is no difference in potential between the chassis of the amp and the chassis of the PA,

Or when you switch the AB box, also unplug the wire going to the amp or PA completely so

they arent grounded together.

 

The bleedover may be a capacitive bleedover in the box. The input signal strength may

be great enough that the signal jumps the contacts through capacitence between the contacts,

or theres additional circuitry in the box that allows leakage. Some wireless receivers put out a hefty signal

that may be too strong for the box. If it has an output attenuator try turning it down. You want to match the

strength of the Reciever to a guitar plugged in direct and not use the receivers gain control as a booster.

 

Other than that, You could build your own A/B Box with a DPST or 3DPST switch

You could use plastic jacks that dont ground to the box leaking a ground from one chassis to another,

and instead of just switching the hot wires on and off, the switch would also remove the ground from

on one output or the other when it isnt in use, thus removing the ground loop between the amp and PA.

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Cool, that's told me a few things I didn't know!

 

The bleed over thing, it's not due to the wireless because it's the same with a cable. I'm thinking that I need an isolated a/b box, the looper I had before and the switchblade are litterally a switch and some

Jacks, nothing else. I've been looking at the Radial Bigshot ABY as it has a ground lift and iso transformer. Would those cure it? I wouldn't get a mic zap because I'm not using a mic! And even if I was, my instruments are

Wireless anyway so it can't do me any real damage if I do get a little

Shock!

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Dont know if a different AB box will work.

Best thing to do is plug the PA and the Amp into the same outlet

so there is no ground loop.

 

Heres a quick diagram of what is happening

[ATTACH]347055[/ATTACH]

 

As I explained in the previous post, its the Ground wire, the shielding on your guitar cables when you have the amp and PA plugged together through the A/B box.

 

Since each outlet has a difference resistance to ground, the two outlets

are at different ground potentials. When you connect the Chassis of the amp

to the chassis of the PA the two outlets pass voltage. The one thats more

grounded will short the less grounded equipment to ground and voltage flows.

 

Since the voltage that passes through your outer shielding of your

high impedamce cables, it generates an AC radio wave in the Hot wire

inside the cable that is heard as hum. Instead of the shielding acting as

a shield it becomes the cause of the hum which you hear in your amp

when the signal wires amplified.

 

The only way to prevent this with both shielded portions of the

guitar cables connected to the AB box, is to disconnect the shielded

connection to one side of the other when one is connected.

 

When the PA is connected, The ground and hot wire are disconnected

from the A/B box. When the amp is connected, The PA cables hot and ground

wires are disconnected.

 

In order to do this, the Jacks cant be your standard metal type screwed

to a metal box. The shielding of the two cables will always be connected that way

setting up the ground loop.

 

What you need are the plastic jacks. The guitar input can be metal so

your body touching the guitar strings helps to ground the box hum down.

 

Then you use a switch with doubble the connections.

An AB box normally only needs a single switch blade

to connect to one output jack of the other. (If its got LED's

the it uses two sets of switch blade switches.)

 

It needs an extra set of switch blades to make an break the

ground connection and the output jacks need to float and not be grounded

to the chassis.

 

Heres an example of what I'm talking about.

 

[ATTACH]347056[/ATTACH]

 

Once either the PA or Guitar amp are connected to the guitar,

the box gets grounded through the guitar jack which is metal and grounded to the box. When the switch is tripped the ground source changes from the PA chassis to the Amp chassis as do the hot wires.

 

Trick is both the signal and ground are switched, and only one ground

can be supplied to the box at a time, not both which creates the loop.

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OK...I'll have a look at those PDFs... but surely a different AB with a ground lift on one of the outputs would solve it then??

 

The Switchblade does indeed have plastic jack sockets, my DIY True Bypass looper (which I used previously) has all metal jack sockets....

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OK...I'll have a look at those PDFs... but surely a different AB with a ground lift on one of the outputs would solve it then??


The Switchblade does indeed have plastic jack sockets, my DIY True Bypass looper (which I used previously) has all metal jack sockets....

 

No it may not. You're assuming a ground lift is the same thing as fixing a ground loop.

They are two different things. The main problem you have "is" the ground loop, not the pedal.

Put the amp and PA on the same outlet and you fix the problem.

You shouldnt be running gear with a ground loop in any case. Thats band gear setup 101.

 

If you have a volt meter, set it for AC. Unplug the PA and amp cords and place the probes

on the two sleeve connections (not the tips) You should not read any voltage on the meter

if the gear is on the same outlet. If they are on different outlets, you will likely read a voltage.

You hear that voltage as a hum. If the voltage is high, you have a dangerous situation for you

and your gear, if its low it may just be an annoyance.

 

When you have voltage passing through the shielded cable its emits 60hz EMF, a radio wave that surrounds your signal wires.

You have to remove that voltage from the wire by removing the ground loop to kill the hum.

On top of that, you have some amps that dont ground their chassis. Amps that have Plasitc input or output jacks

usually identify those kinds of amps. The sleeve of the input jack gets grounded further back in the curcuit

so any ground loop may be adding voltage to those circuits that shouldnt be there.

 

In any case, Fix your ground loop.

I posted a diagram that can allow you to run an A/B box where there is a ground loop involved.

The "Only" way you can remove the ground loop is completely removing the ground.

The only other way is to run the PA head or Guitar amp groundless.

Not a good thing. I recently replaces the cord on one of my amps because the ground

plug had been snapped off. i was always getting sappes on that thing and it had allot of buzz

when running overdrive boxes. With the new cord all those problems went away.

 

The thing I didnt mention with my sketch of a ground loop removal, if that ground loop voltage is high,

and you touch both sets of strings on your guitars at the same time, you can get zapped.

Its like walking up to a mic and zapping your lip because the amp and PA are on different outlets.

Same cause, same effect. Fix your ground loop.

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Unfortunately, you're assuming that I/we have a hand in where the PA is drawing it's power, we don't. We only ever play venues with in house or hired in rigs, and 9 times out of 10, the backline and FOH are powered by different mains rings :(plugging the PA into the same outlets as the backline is just simply not an option)

 

I'm also having a lot of ground loop problems in building my rack based rig. This is a separate issue, a totally different

Set up, not involving the A/B and DI, a guitar only rig. Everything is running from the same AC outlet... So I'm even more

Confused now :( I've even seen BLUE SPARKS coming off the rack rail in my setup, this scares me to the point of abandoning the project. But SURELY this can

Be made to work hum-free and safely???

 

I think I probably need to take some pics of how I've got things set up for you to have a look at!

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Didnt know it was the house system PA you were running on. I'd still see if you can run an extension.

 

Otherwise, Get an isolation transformer based noise filter for your guitar amp then and float the ground.

The Iso transformer will lift your guitar rig complete off the buildings AC circuit grid. Its a 1:1 transformer

so the voltage remains the same. I have a couple at home I run mt recording gear on. I take them to gigs.

They are the best solution for those kinds of problems.

 

http://www.tripplite.com/en/products/model.cfm?txtModelID=227

 

Why not just dump the idea of using the AB box, and plug the guitar into the

Guitar amp and the bass into the PA? Whan you take the instrument off, just turn the volume down?

Is there some great need for the A/B Box other than you have one and want to utilize it?

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Problem is, what's powering the PA? The desk may be on a different mains rig to the amps, then you have the monitor system which is connected too. I just don't think it's practical to even think about using the same power as the PA, as in many cases, that might not even be using the same power for all of it's components.

 

For rehearsal, yeah with a pa mixer/amp, but this band doesn't rehearse, so will never be in that situation.

 

The noise filter thing on the guitar amp: I've got one of those Behringer hum destroyers (HD400) on my guitar channel, and it's done the trick, but I can't get the second channel of that to have any effect on the bass side.

 

Live, I just can't be dealing with cables, so want to use the same wireless system on bass and guitar. It's also been advised I could just pull cables out of one or other inputs when not in use...which would work, until I forget in the heat of the moment, and end up playing with nothing coming out....and that WILL happen...probably every show :( It's all very busy onstage, so would prefer to keep the simplicity of hitting a button and being ready to go. For example...a laptop faffs, drops a track sooner than it should and I have to rush a guitar change....99% chance I'm gonna run back on and forget to plug the guitar amp back in, go in for the big intro and:...... Embarassing! I don't want to go down that route.

 

I also don't want to ditch the wireless for either the Bass, or indeed both instruments. A cable is an emergency go-to... it's not practical with all the movement onstage. I spend probably 85% of a show away from my amp/pedals position, and with 2 vocalists throwing themselves about too...me wobbling around with a cable around everyone's ankles is a recipe for a pile up! :lol:

 

I've also come across a cool sounding thing which needs the a/b connected in this way, I run a Devi-Ever bass fuzz on the bass channel, andi in one song I have started flipping the guitar signal to the bass channel for the first beat of every forth bar of the verses, for this big sub thing. I happened across the idea and it really sounds good. I simply slide the chord down the neck via the bass fuzz/DI. You can feel the drop through your chest, even from onstage... Very effective! But this is a recent thing, the problem was there before.

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Once either the PA or Guitar amp are connected to the guitar,

the box gets grounded through the guitar jack which is metal and grounded to the box. When the switch is tripped the ground source changes from the PA chassis to the Amp chassis as do the hot wires.


Trick is both the signal and ground are switched, and only one ground

can be supplied to the box at a time, not both which creates the loop.

 

Just re-reading this post and trying to digest it! Sorry, I'm a little slow.

 

So, If I'm right here, the switchblade is only swiching the hot signal, and not the ground...so that kinda makes sense becasue this ground loop is always there.

 

If it totally swiched the whole signal from output A to output B, then obviously the ground will be connected only to the path I want to send the signal to, yes? Which is how I want it to be! I want to send 100% of the signal to the guitar amp when using guitar, and 100% of the signal to the bass DI when using bass.

 

I don't know if I'm right here, but surely the bleedover problem is a symptom of the outputs not being switched totally independantly of eachother?? If the unit was switching the signal properly, then each ouput would only see the signal when connected... am I making sense??

 

What I need to do is take a gut shot of the pedal, and then we can assitane what the hell it's ACTUALLY doing? :lol:

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Right: This is the offending article! I usually run Output A to the Bass DI (Sansamp Paradriver DI via a Devi Ever Bass Fuzz), and Output B to the guitar (Bad Monkey, Pod XT Live and JCM800 2204). No reason for this setup other than the way the patch cables sit on the board.

 

EHXSwitchblade1.jpg

 

And this is how it's wired internally:

 

EHXSwitchblade2.jpg

 

I AM a total novice with this stuff...but it appears to me, that the ground connection is common across both outputs, and only the hot wire is switched. So...this must be the problem?

 

What do I do to fix this, and I'm assuming that once fixed, the bleedover thing will also be fixed, as I'm guessing it's that common ground connection that's at fault there too???

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Thanks for posting the picture. Just as I suspected. :cop: You're right, the ground is not switched. Since the jacks are plastic, they aren't directly grounded to the case, that's what the extra dark blue wire that goes to the switch is for. The switchblade could easily be wired to switch the ground lead too, BUT that is likely to cause an audible "pop" or "click" noise through your guitar amp and/or PA system when you switch. It should also be possible to rewire this to ground out the un-used output, but again, that may cause unintended problems.

 

The signal bleed over just should not be happening, the stompswitch is defective, it simply can't be anything else. The only other thing it could be is some sort of capacitive or inductive coupling between the A and B sides, that's extremely unlikely with a line-level audio signal. Replace the switch, and I'd bet ALL these problems go away.

 

Are you using an XLR cable to connect the SansAmp to the PA board? One of the purposes of a direct box is to "break" ground loops and prevent this sort of thing from happening.

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I also don't want to ditch the wireless for either the Bass, or indeed both instruments. A cable is an emergency go-to... it's not practical with all the movement onstage. I spend probably 85% of a show away from my amp/pedals position, and with 2 vocalists throwing themselves about too...me wobbling around with a cable around everyone's ankles is a recipe for a pile up!
:lol:
.

 

The wireless has nothing to do with the hum problem. You already told me the hum is there weather you use the wireless or not.

 

 

Again, I gave you the cheapest option and that is to rewire the exhisting switch.

It only takes a few solder connections that need to be added and I already posted the diagram.

The exhisting ground wire needs to be removes, and you need to connect them through

the extra open poles on that switch. Its about a 30 second fix and you're good to go.

 

The other fix costs money,

Please read what posted here again carefully.

Even if you fix your AB box problem, you should get one of these AC Isolation Transformers.

With all the crappy wiring and beat up AC outlets you find ins clubs and gigs, these are insurance policies that

your gear wont be damaged by bad power outlets.

 

 

Get an isolation transformer based noise filter for your guitar amp then and float the ground.

The Iso transformer will lift your guitar rig complete off the buildings AC circuit grid. Its a 1:1 transformer

so the voltage remains the same. I have a couple at home I run mt recording gear on. I take them to gigs.

They are the best solution for those kinds of problems.

 

http://www.tripplite.com/en/products...txtModelID=227

 

Those are filters for your AC jack not the input of your guitar amp.

Also dont confuse these with normal AC filter like Furman Rack filter and other

computer grade filters. that use chokes and caps to filter noise and protect against surges.

Those will not stop a ground loop. Only an ISO transformer can remove the ground loop safely and they

also have the filtering of a normal AC filtering as a bonus.

 

In any case, If the rewiring of the switch doesnt completely fix your problem, then this type of AC filter is all you have left as a fix.

 

(As a note, My company Canon sells allot of their own AC filters to protect the high end electronic gear we sell to customers.

I have many decades of experience with these type filters and what thay can and cannot fix and its why I mention the Iso transformer type.

Our company saves millions of dollars a year on repair costs by having the AC lines filtered so we include the filters

with the purchase of the expensive gear we sell.)

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yeah i usually have the Sansamp running on Phantom Power, so XLR all the way with that.

 

Hmm...popping would not be good with that thing I'm now doing with the guitar in one song :(

 

Dunno what to think now. Of course, it COULD be a knackered switch...but I did have exactly the same problem with bleedover when I was using a TB Loop box as an A/B before.

 

What problems could re-wiring the unused ground cause?

 

If this can't be made to work, I don't mind getting a propper isolated ABY or something...but I don't want to spend the money if that's not gonna work either.

 

Here are shots of the looper I used to use for this job anyway...just so you can see....

 

TBLoop1.jpg

TBLoop2-1.jpg

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Dont know man, I've played out for a living for over 45 years under all conditions and never found running an extension cord to the PA outlet a problem

when it was needed. The only times it was an issue is if the circuit breaker wasnt strong enough to handle the load, then you'd have to split them up.





I wasnt talking about a hum destroyer, Noise filter or Hush box. I would have mentioned one of those if I thought it was a fix.

I have a HD400 myself. All those are is gate. They gate the input to the amp when the input signal drops below a threshold you set

and kill noise when you arent playing.
Those help hide the symptom. They do not fix the cause of the hum.


What I'm talking about is a very specific isolation transformer for the AC outlet input to your guitar amp that

removes the ground loop and cleans up the AC input to your amp.






Cant help you there. Playing live requires you to be able to walk and chew gum and have your shit wrapped tight at all times.

I've posted 3 different solutions to your problem that will work. All I can do as a certified electronic technician who repairs gear for a living

is give you the facts and tell you the best way to fix the problems. You can choose to use them or stick with your noise issue.





The wireless has nothing to do with the hum problem. You already told me the hum is there weather you use the wireless or not.



Again, I gave you the cheapest option and that is to rewire the exhisting switch.

It only takes a few solder connections that need to be added and I already posted the diagram.

The exhisting ground wire needs to be removes, and you need to connect them through

the extra open poles on that switch. Its about a 30 second fix and you're good to go.


The other fix costs money,

Please read what posted here again carefully.

Even if you fix your AB box problem, you should get one of these AC Isolation Transformers.

With all the crappy wiring and beat up AC outlets you find ins clubs and gigs, these are insurance policies that

your gear wont be damaged by bad power outlets.



Get an isolation transformer based noise filter for your guitar amp then and float the ground.

The
Iso transformer will lift your guitar rig complete off the buildings AC circuit grid
. Its a 1:1 transformer

so the voltage remains the same. I have a couple at home I run mt recording gear on. I take them to gigs.

They are the best solution for those kinds of problems.


http://www.tripplite.com/en/products...txtModelID=227


Those are filters for your AC jack not the input of your guitar amp.

If the rewiring of the switch doesnt completely fix your problem, then this is all you have left as a fix.

 

I dunno... I just feel that there should be a better way around this than plugging into the same outlet as the PA...I mean...which part of the PA do I take my extension from...the Desk, the FX rack, the amps??? Surely those are NOT gonna be running off one outlet? And what happens when it's a festival or other big venue?? I just do not see it as being that simple. Yes...with a mixer amp setup for a small bar gig or something, but theres no way you'd be running a 10K+ full rig off one outlet? Not wanting to sound obtuse at all, but I really wouldn't know where to start with that one. Also time is not always on your side. When it's a festival situation and some clown has only budgeted 15 mins for changeover/line check time, you've got no hope in hell of messing about trying to do this....and likely the crew are gonna get pissy with you for even suggesting it :(

 

I've also got a Rocktron Guitar Silencer, and a Hush IICX...but I know those won't cure the problem...or even hide it well. The HD400, as you know, is a copy of the Ebtec Hum Eliminators...which conversly, work on ground hum, and not hiss/noise like the gates/hush things do....AS I UNDERSTAND IT anyway. I could be wrong, as I said..I'm quite a novice with this so....please correct me if I'm wrong.

 

But yeah... So looking at the pic of the switchblade....and your PDF....I can connect the input ground to the switch, and from the switch to the outputs in exactly the same way as the hot wires are yes? From the middle or the right hand terminals...does that matter??? I'll need one extra piece of wire, and 30 seconds to do it all in...is that correct? I don't wanna get it wrong and fuck it all up! haha

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Heres how you rewire the pedal so the grounds are switched.

The white area is where the wires are removed from the one jack.

The yellow wire is added and the purple and brown wires are resoldered to the switch.

This will remove your ground loop issue and should stop the bleedover problem.

 

EHXSwitchblade2.jpg

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Heres how you rewire the pedal so the grounds are switched.

The white area is where the wires are removed from the one jack.

The yellow wire is added and the purple and brown wires are resoldered to the switch.

This will remove your ground loop issue and should stop the bleedover problem.


EHXSwitchblade2.jpg

 

Wicked...This is what I though I probably needed to do....but wasn't totally sure I was right as I've never done this before. I've only ever really made/repaired cables and resoldered broken joints on things like this.

 

That's fantastic mate, thanks!!! I'm gonna try that and report back!

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My fix, keep ground rings, add ground to center pin in middle. Cross top left to bottom center, bottom hot to top center. Grounds inactive cable preventing noise, no pops!

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