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Acoustic Variax 300 Hum
by yrjo on 2010-12-20 08:26:24

Hello every one,

First time on this forum because i'm having troubles with my Variax 300.

When i'm recording the guitar i get a lowend hum. The only way to get around it is using a lowcut filter on my preamp.

I don't have this problem with my other gear when it's connected to this preamp so the problem must lie in the guitar.

I tried different things:

  • External DI
  • Preamp DI
  • Different cables , xlr, mono trs, stereo trs
  • With powersupply connected
  • With battery power

But the problem still occurs.

So i'm thinking the problem may be in the guitar it self.

I also thightend the output jack and took a peek inside but no loose connections.

I'm hoping someone can help me get rid of this annoying hum.



Re: Acoustic Variax 300 Hum
by amx05462 on 2010-12-20 13:36:53

in most cases  hum  is  usually  a ground  problem. check the ground  on your  output  jacks.



Re: Acoustic Variax 300 Hum
by JellyWheat on 2010-12-20 13:52:49

I experienced the same problem with my Variax Nylon 300. It ended up I was sitting too close to my tube amp. The RF energy radiated by whatever circuit those guitars uses is incredible, and was being picked up by my amp. Five feet made all the difference in the world!

I looked inside my Variax Acoustic once, and there was a coil of spare wire (I'd say 12" to 18" of it) in about a 4" coil fastened to the underside of the top of the guitar. A natural antenna, if you ask me. Anyway, I'm just suggesting that you experiment by sitting farther away from your preamp/amp setup and see whether or not that has any effect.

My $0.02/YMMV

JellyWheat



Re: Acoustic Variax 300 Hum
by amx05462 on 2010-12-20 14:45:37

sounds  like a good  suggestion.    like  i said  before   line  6  arent  guitar  builders.  what   would  possess them  to put that  much  unshielded  wire  in there  is beyond  me.



Re: Acoustic Variax 300 Hum
by JellyWheat on 2010-12-20 15:00:37

(8>*}... and, as I have said many times before, O all-knowing One:

...I'm no tech dude, but it surprised me, too, especially since the wire had been coiled through one of those "ceramic magnet" thingies [ferrite chokes] that they put on the end of some computer connections I have seen.

but what do I know?

JellyWheat

[NOTE: veiled reference to O all-knowing One alludes to amx05462...]



Re: Acoustic Variax 300 Hum
by amx05462 on 2010-12-20 15:29:32

well i think  we  both   know  better  than to do something  like  that  my friend



Re: Acoustic Variax 300 Hum
by JellyWheat on 2010-12-21 13:52:03

(8>ɞ}... if I'm not mistaken it was the noted Chinese physicist Dr. Xiang Li Ho who first explored the hi-pass filter effect of ferrite beads and their use in attenuating RI, in a paper entitled simply: "Hum"...

FYI/FWIW/

JellyWheat



Re: Acoustic Variax 300 Hum
by yrjo on 2010-12-23 02:06:43

Hi Guys,

I think it's time for an update.

First of all,thanx for the suggestions! I

put some of them in practise and this is what i found out.

  • Moving away from monitors didn't work. that
  • Grounding was correct

Both ideas where allready checked before posting my question. But thanx anyway, there are alot of people out there that don't know that.

What i did was the following; opened the back of the guitar and removed the glue so i could untangle the wires inside.

I removed the magnetic round ring and removed the coil from the wire.

What an inprovement, much better but still not good enough!

There's still some background hum i want to get rid off. In other words, there's more work to be done.

Today i'm going to try what happens if you sperate the power wires from the signal wire and if that isn't the trick i'll make the signal wire a shielded wire by turning a wire around the signal wire which is going to be connected to ground at the input of the guitar.

The electronics compartment isn't shielded either so that could be another thing to look at later in the day.

I'm going to do tests after each step so that it's clear what helped and what not.

Bye for now. Greetz Yrjo



Re: Acoustic Variax 300 Hum
by amx05462 on 2010-12-23 02:10:19

well good  luck  and if you come up  with a  soloution   please  post   it  for  others  who  may  have this  problem  to see.



Re: Acoustic Variax 300 Hum
by JellyWheat on 2010-12-23 04:45:42

!(8>*}?... you might want to consult that scientific paper I referenced earlier...

Just Google...

...Ho: "Hum"

JellyWheat

[Sorry... the devil made me do it!!!]



Re: Acoustic Variax 300 Hum
by yrjo on 2010-12-24 04:17:50

Hi all,

@Jellyweat: i searched google and didn't find the artical you mentioned. But i found this on wikipedia instead: http://en.wikipedia.org/wiki/Ferrite_bead

Whati understand from that artical is that they are used as low pass filter. But the problem with my variax is a low-end hum. Probebly all acoustic variax guitars have this problem. I did tests all afternoon and i think i found the sourch of the problem which lays in de construction/ lay out of the pcb,  positioning of the cables and the piezo input.

As a mentioned in my previous post the first thing i did was remove de coils from the 4 white cables. The coil around the Ferrite bead could be left in place but the other bigger one has to go. This decreases the lowend hum.

The next thing i did was to get the power cables away from the signal cable, i removed the signal and earth wire from the connector and braided them together, reconnected them to the connector and taped them to the lower side of the body. The power cables where guided to the upper side of the body and fixed with some tape. This is a minor improvement and could be skipped.

But when i was testing this, i found the biggest cause of hum. My hands got near the piezo cable and the hum got worse!

So i thought this is it! Disconnected the pieze cable and put some insulation around it and reconnected.....hum....

The next step was to follow the piezo cable in the hope of finding the sourch. It turned out to be the input for the piezo cable and the grey extension cable to the pcb. I taped it all up in insulation tape including the connector on the board. This helps alot!

That's why i think the problem is in the design of the pcb.All the wires are on the same side of the board, powerlines, signal and earth cables are so close together that they are a recipe for interference.

The hum isn't completly gone, at least it's workable now. The hum shows on my vu at max -50db, when i use my lowcut filter it's completly gone and dead quiet. Even with the filter on the guitar sounds full and warm so i'm sort of happy now.I did all my tests with max volume on the guitar, biggest body size, mic slider down, compression 50% and100%, reverb off.

I can only hope that a designer from Line6 would try and fix this problem in future and sell the new pcb to their customers.



Re: Acoustic Variax 300 Hum
by JellyWheat on 2010-12-24 04:36:07

yrjo:

You sound a lot happier now. Good for you! Your persistence has explained a mystery to all of us!

Merry Christmas

JellyWheat 




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