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PostPosted: Tue Oct 04, 2011 9:20 am 
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World Tour
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I have been experiencing major noise issues with my Line 6 HD500 and the JVM using a 4 cable method to hook it up. On the high gain channels, I was getting some serious hum and a notchy cocked-wah resonance effect leading to feedback. The indications were that this related to a ground loop somewhere in the hookup.

I managed to address the problem using a Behringer HD400 hum destroyer between the cables in/out of in the Amp FX Loop, thereby breaking the ground loop - very effective at getting rid of hum (but not hiss). However, I have been a bit concerned by the impact on my tone from putting this unit (effectively a transformer) inline. This certainly causes a level drop and may be pulling on my tone too.

Santiago (JVM designer) had suggested in other posts that disconnecting the ground (shield) from one side of the patch cables used in the hookup could break the problem ground loops. I have been reluctant to carve up my main performance cables but realised today that I didn't have to.

Instead. I went out today and bought four 1/4" Mono Jack sockets and some short crocodile-clip cables (from my local Maplin store here in the UK). I then improvised two cables, each using two 1/4" mono jacks and a croc clip cable linking the 'tip' connections only. The ground tag on each socket was left unconnected. I was left with a pair of 'ground lift' cables for testing with.

Next step: I plugged short pedal hookup cables into the JVM 'Send' and 'Return' sockets and then plugged them into the jacks on one side of my home-made ground-lift cables. Then I plugged the two leads that would normally go into the amp loop into the jacks on the other side of my home-made cables. The upshot of this was that each cable in the amp loop wound up with a broken ground connection.

I then turned the master back up. The result? Hum gone - certainly as much as with the Hum Destroyer inline. Hiss remained (as expected) but the gate on the MultiFx could now take care of that. Anyone wanna buy a hum destroyer?

Next step is for me to go back and buy a (plastic/non-conductive) case for the jacks to go in. I will then solder some wire in place of the croc cables and job done.

I have considered breaking the ground on cables themselves but I think it will be more flexible to use a box ... in case I run into some unexpected circumstance where I am forced to put the grounds back. Not sure why I would want to right now though. If after a period I don't get any problems I will attack the cables and remove the grounds from those.

Thought this might be useful as information and a test procedure for anyone trying to fight with Noise on the High Gain Channels. You could try breaking grounds like this on any of the signal cables for testing - i.e those connecting amp and effects. Just keep the JVM master down. If your amp is not a JVM and has a master volume before the effects loop you should be carefull as, if cables short out during testing, you will hear a BIG noise.

Do NOT break the ground connection on your speaker cables. This will likely damage your amp.
Do NOT break the main ground connection into the amp as this is very dangerous.

@Casey_Butt: you are the acknowledged ubertech on this board. Is there any other safety point that you want to make here? I think we are safe but would not like to toast anyone inadvertently. I would appreciate your view.

_________________
JimBOB

-------------------------------------------
Amps:
Guitars:
    70s hard-tail Strat with EMG 89/SA actives. Gibson "The Paul" with bridge P-Rails, Triple-shot, Roland GK-3 and Torres Tone Mods. Gretsch 6119 Tennessee Rose. PRS SE Semi-Hollow w/Bigsby, Squier Affinity Tele, Falk "Splitter"
    Taylor DN3 Acoustic w/Rare Earth Blend, Ovation Celebrity 6/12 Acoustic, Sigma Acoustic, Gibson LG-0, Martin 000X1AE, Rally Resonator, Stretton Payne 12-string.
FX:
    Line 6 HD500 - 4CM & MIDI switching, Joyos galore! T-Rex Moller, TC Flashback X4, MXR '78 Distortion, modded 90's Crybaby, Boss GT8 (retired)


Last edited by jimsreynolds on Wed Oct 05, 2011 6:26 am, edited 2 times in total.

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PostPosted: Tue Oct 04, 2011 10:20 am 
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Looks safe enough to me ...by not connecting the grounds on the jacks you're simply breaking any potential ground loops the same way you would be if you disconnected the ground lines (shields) in the cables themselves. If you hard-wire them and put the jacks inside a box you'd make yourself a convenient little ground loop breaker for your effects loop ...probably cheaper than buying a separate supply and more convenient than running them off batteries.

_________________
_ JVM410H: "Blackface" Clean channel, "Plexi" Crunch channel, stock-ish OD1 channel, "Dual Rec" OD2 channel, 3rd stage bias pot with switchable 100nF bypass cap, switchable 470k/470pF "treble peaker", OD1/2 Orange and Red extra gain pot, signal boost into power amp, PI voltage set to 2203 levels, 5H choke w/ 50uF on screens, -ve feedback pot.
_ Peavey Windsor head rebuilt to 2203/1959 specs (switchable between amp specs with switchable FX loop, resonance control and -ve fb pot)
_ 1960A cab with Celestion G12-65s and G12-75Ts in X-pattern, Peavey JSX cab with Celestion G12M's (UK 6402 cones)
_ Fender Deluxe Reverb clone head
_ Fender Pro 185 (rebuilt) - open back 2x12" with Jensens
_ Ibanez TB15R


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PostPosted: Tue Oct 04, 2011 11:09 am 
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World Tour
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Location: Essex, UK. Maybe.
Casey_Butt wrote:
Looks safe enough to me ...by not connecting the grounds on the jacks you're simply breaking any potential ground loops the same way you would be if you disconnected the ground lines (shields) in the cables themselves.

Phew ! [smilie=gt-happyup.gif]


Casey_Butt wrote:
If you hard-wire them and put the jacks inside a box you'd make yourself a convenient little ground loop breaker for your effects loop ...probably cheaper than buying a separate supply and more convenient than running them off batteries.


I think that is where I am going ... or alternatively get a pair of Inline Jacks and plugs and have them as adapters to plug onto the end of the loop cables is the other option.

Thanks Casey.


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PostPosted: Wed Oct 05, 2011 3:25 am 
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Thanks for the info and good write up [smilie=gt-happyup.gif]

_________________
::: JVM410 head,modded:- 5H choke, Caseys Mods :- Plexi cap, -ve feedback, Dual Rectifier, Blackface, 1 wire Randy Rhoads, Plexi, Metaled Out ModPI Boost, OD Channel Gain Reduction Mod
::: AFD100, DSL100W head (no C83), Fender Champ 12
::: 1960AV w/greenbacks, homemade 2x12 Celestion Golds (100W)
::: Gibson Les Paul Standard, Dimarzio SD bridge Pup,Standard neck Pup.
::: Tokai Strat with Dimarzio SD, Epi SG-400 Iommi, Hondo Les Paul, Alhambra Acoustic fishman Pup
::: PodXTLive fully loaded, Vox V848 Clyde McCoy Wah Wah, Korg Pitchblack and Snark Tuners

It's better to fail in Originality than to succeed in Imitation ...


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PostPosted: Wed Oct 05, 2011 6:34 am 
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Thanks Andy.

One Minor gotcha to add.

If you have a disconnected ground in the loop (as per above) and for some reason you remove cable 2 in the 4CM (MultiFX Send -> JVM Input) then you will get lots of hum and noise and your guitar will no longer be heard.

By removing cable 2 (the one with the ground intact) you effectively break all ground connections between the MultiFX and JVM and this means that the circuit is not complete. You would always want to leave one ground in there.

The only reason I can think of you might want to do this is if you were planning to use your MultiFX preamp modelling direct into the Power amp and skip the JVM Pre-amps completely.

Here, you would just use two cables: 1 being from Guitar to MultiFX Input and 2 being from MultiFX Output into the FX Loop Return on the amp. If you do plan to do this: Use normal cables without a ground lift. If you have noise problems (and generally you will not in comparison to 4CM), try a Hum Destroyer or similar.

Some people out in modelling world do this cause it is a simpler setup and it works for them. Personally, I have this like ... JVM ... and I plan to use it all!!!!

_________________
JimBOB

-------------------------------------------
Amps:
Guitars:
    70s hard-tail Strat with EMG 89/SA actives. Gibson "The Paul" with bridge P-Rails, Triple-shot, Roland GK-3 and Torres Tone Mods. Gretsch 6119 Tennessee Rose. PRS SE Semi-Hollow w/Bigsby, Squier Affinity Tele, Falk "Splitter"
    Taylor DN3 Acoustic w/Rare Earth Blend, Ovation Celebrity 6/12 Acoustic, Sigma Acoustic, Gibson LG-0, Martin 000X1AE, Rally Resonator, Stretton Payne 12-string.
FX:
    Line 6 HD500 - 4CM & MIDI switching, Joyos galore! T-Rex Moller, TC Flashback X4, MXR '78 Distortion, modded 90's Crybaby, Boss GT8 (retired)


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PostPosted: Thu Oct 06, 2011 3:49 am 
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Location: Essex, UK. Maybe.
Ok. Built the box. Ain't that sturdy but shouldn't really need to be. Pics attached in case anyone wants an easy project and fix.

First pic is the test cable lash up I describe above.
Attachment:
IMAG0031.jpg
IMAG0031.jpg [ 1.02 MiB | Viewed 5280 times ]


Second pic shows the required parts (plus drill, bit, soldering iron and solder). Box should be plastic to avoid ... ground loops! Ignore the different styles of jack. They are actually the same, and were what the shop had in stock.
Attachment:
IMAG0032.jpg
IMAG0032.jpg [ 1014.83 KiB | Viewed 5280 times ]


Drilled the holes in the plastic box and mounted the jacks with the 'tip' tags facing up. Take care that the jacks don't touch. Linked the 'tip' tags with hookup wire.

Attachment:
IMAG0038.jpg
IMAG0038.jpg [ 733.32 KiB | Viewed 5280 times ]


Final build, with pick for scale (Dunlop Jazz III XL - my fave [smilie=icon_cool.gif])
Attachment:
IMAG0037.jpg
IMAG0037.jpg [ 664.65 KiB | Viewed 5280 times ]


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PostPosted: Fri Feb 24, 2012 2:24 pm 
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Jerry's final thought:

After using the box for a few months without issue, I decided to make life easier for myself and broke the grounds on my FX Loop cables. Same result - no hum!!!

All good.


JIM


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PostPosted: Sat Feb 25, 2012 12:39 am 
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Jim,

So you broke the grounds on your FX Loop cables. Sounds good, but...uh...how do I do that? Lol. Newb here. :)

I'm sure it's quite simple (probably just unscrewing the cover, pulling back the outer sleeve, and snipping something....) but I'm not sure.

Thanks,
Kevin

_________________
Amps:
JVM 410H/1960A
Hot Rod Deluxe

Guitars:
Fender Am. Special Strats (2)
Epi Joe Bonamassa LP
Epi LP Custom Silverburst
Epiphone Dot

Pedals:
TC Flashback Delay
TC Corona Chorus
Fulltone OCD
Fulltone Fulldrive 2
Fulltone Deja Vibe
Suhr Riot
GGG Bluesbreaker clone
Line 6 M13


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PostPosted: Sat Feb 25, 2012 7:34 am 
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Sure yeah. It might be worth testing with croc clips as per above first before butchering cables but if you want to cut to the chase. Maybe start with a busted cable for practice if you have one. Bear in mind that you may need a soldering iron too. You will definitely need some insulating tape ...

I will start with basics in case you (or others) need the orientation.

Cable Construction 101
Standard guitar cables carry two connectors internally:

  • A thin central core cable surrounded by plastic shielding. This is the signal cable and carries your beautiful music to your mighty amp.
  • A shield just inside the outer layer of the cable. This can be braided or just a bunch of loose strands of wire arranged around the edge. This is the ground connection.

The braid or strands of the ground connection get twisted together before they are soldered onto the jack.

The signal cable connects to the smaller 'tip' connection on a standard 1/4" jack. The Ground connects to the larger 'shield' connection on the jack.

There are some great pictures of guitar cable construction on the page here --> http://www.ultimateguitartone.com/how-t ... cable.html

How to Break the Grounds
You only need to cut the ground connection at ONE END OF THE CABLE. It still provides shielding benefits with just one end cut.

OK, start by unscrewing the cable housing and remove any cable strain-relief devices and any other plastics covering up the soldered connections.

To sever the ground cable connection. You need to make sure that there is absolutely no contact between the stranded/braided ground and any metal terminals on the plug. I suggest that you cut as close as possible to the cable outer wrap using a sharp wire cutter (a small side cutter or similar).

Use insulating tape to carefully mask off areas where there might be a risk of metal touching the remaining braid cable. I wrapped a layer around the base of the cable so only the signal connection was exposed. Think about how tape will be pushed around as the cable flexes and try and insulate accordingly.

If the ground connection is soldered hard-down onto the jack connector it may be impossible to get a cutter in cleanly. In this case you would need to use a soldering iron to release the ground connection from the jack before you cut. Head up the solder as quickly as possible and remove the braided/shielded cable. Avoid plastics with the iron and take care!


Last edited by jimsreynolds on Sun Feb 26, 2012 12:41 pm, edited 1 time in total.

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PostPosted: Sat Feb 25, 2012 12:31 pm 
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Thanks Jim! Excellent work (as always) making it easy to understand. I'm sure I'll be doing this when the JVM replacement gets here.

_________________
Amps:
JVM 410H/1960A
Hot Rod Deluxe

Guitars:
Fender Am. Special Strats (2)
Epi Joe Bonamassa LP
Epi LP Custom Silverburst
Epiphone Dot

Pedals:
TC Flashback Delay
TC Corona Chorus
Fulltone OCD
Fulltone Fulldrive 2
Fulltone Deja Vibe
Suhr Riot
GGG Bluesbreaker clone
Line 6 M13


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PostPosted: Tue Oct 30, 2012 3:41 pm 
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Location: Essex, UK. Maybe.
For completeness: JL on the Blackstar forum made a variation on my ground lift box by creating his own cable 'stubs' from a jack and a plug and short cable lengths. Pix are here for anyone who is interested ... http://www.blackstaramps.com/forum/view ... f=2&t=1455


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PostPosted: Mon Nov 26, 2012 9:10 am 
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World Tour
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Another device, this time a product, that is designed to nail hum from ground loops .... the Humdinger. Isolating transformer based. Provides a single ground lift connection. Pricey but provides a powered buffer which may (or may not) reduce any tone suck associated with the transformer. You pays yer money .....

http://www.thegigrig.com/acatalog/master_HumDinger.html


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PostPosted: Sun Mar 10, 2013 6:43 pm 
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Jim, you made my day!!! I has a real bad time with my JVM squealing - i was searching for a solution, asking al techs i know - no one had help and i was considering giving up using theamp, though it is sounding great...... I broke the shields and: Much less hum, no siren-like sueal any longer..... and now we start a brand new realationship, the amp and me. Thank you!

Zam

[smilie=gt-happyup.gif]


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PostPosted: Mon Mar 11, 2013 5:16 am 
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[smilie-rock] [smilie=gt-happyup.gif]

Do love those 'good news' stories!

Glad the fix worked for you. I really get the feeling that many of the 'squealies' that people seem to suffer are due to excess noise leaking into the amp input through ground loops, crappy cabling, grumpy pedals or whatever. On the high gain channels it can be really difficult to defeat without messing with the gain (on the knob or with mods or with tubes or whatever) . That is not always a good thing.

Just for my understanding ... was it 4CM that you fixed with this or was there some other kind of ground hum? Useful to know.

_________________
JimBOB

-------------------------------------------
Amps:
Guitars:
    70s hard-tail Strat with EMG 89/SA actives. Gibson "The Paul" with bridge P-Rails, Triple-shot, Roland GK-3 and Torres Tone Mods. Gretsch 6119 Tennessee Rose. PRS SE Semi-Hollow w/Bigsby, Squier Affinity Tele, Falk "Splitter"
    Taylor DN3 Acoustic w/Rare Earth Blend, Ovation Celebrity 6/12 Acoustic, Sigma Acoustic, Gibson LG-0, Martin 000X1AE, Rally Resonator, Stretton Payne 12-string.
FX:
    Line 6 HD500 - 4CM & MIDI switching, Joyos galore! T-Rex Moller, TC Flashback X4, MXR '78 Distortion, modded 90's Crybaby, Boss GT8 (retired)


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PostPosted: Fri Apr 25, 2014 2:42 pm 
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Location: Ottawa, Canada
Thanks for the advise! I've been experiencing problems with my amp using the 4CM but it was mild and intermittent. I built a box similar to yours and everything is working great now!
Since my problem was intermittent I put a switch on it to connect disconnect the ground so I could easily swap between the two while it was happening. That way the rest of the guys in the band wouldn't be standing there with a grumpy look while I'm messing with cables. I also hard wired the output cables directly into the box. I like the idea of the box so I don't have to modify any cables and make notes of which cables are lifted and which ones are not.

Thanks again, I probably would have ditched my FX board if it wasn't for you.


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