Author Topic: Hum from active acoustic guitars  (Read 331 times)

0 Members and 1 Guest are viewing this topic.

Offline JordanD

  • School Prom Hero
  • **
  • Posts: 55
  • Good Vibes 1
Hum from active acoustic guitars
« on: November 14, 2017, 12:02:31 pm »
I couldn’t really find anything related to this specific problem, and I’ve done as much research as I can before asking so here goes;

We’re hooking up acoustic guitars directly into the PA system we’ve got (a Yamaha but can’t remember the model, it’s powered) and only from acoustic guitars. I don’t think it’s a single guitar issue because it happens with a variety of guitars from takamines to a Gibson with an expensive preamp and pickup in it.

Doesn’t matter where the gain’s set, and gets worse when the guitar isn’t played then pipes down while it’s being played but it’s not feedback because we get it even with the volume turned off on the guitar; just having it plugged in causes hum.

I really can’t get my head around it, any help is appreciated. Ps. Would a DI box help this issue?
You must be Born Again. - John 3v3
Gibson J-200
Gibson SG Special, Fender Super Champ x2

Offline Joerfe

  • Stadium Superstar
  • ******
  • Posts: 2504
  • Good Vibes 97
Re: Hum from active acoustic guitars
« Reply #1 on: November 14, 2017, 12:34:38 pm »
Grounding issue?
/Jesper

Sigma SOMR28H, Fender Classic '50s Tele, Fender Std Stratocaster, Gibson lpj '14, BOSS Katana 100-212 amp.
Me on da Soundcloud https://soundcloud.com/jesper-j-rgensen-11

Offline DarrellW

  • Stadium Superstar
  • ******
  • Posts: 1051
  • Good Vibes 42
  • What next???
Re: Hum from active acoustic guitars
« Reply #2 on: November 14, 2017, 01:05:19 pm »
Have they got the sound holes blocked with one of those disk thingies?
If not it could be as simple as they are picking up noise and the guitar body is amplifying it.
Freshman Apollo 4OC, 1970 Terada G703 classical, Squire Classic Vibe 50's Tele; 1963 USA strat.
Soprano, Concert and Tenor Ukes Amazon specials! Makala Bass Uke.
Blackstar ID Core Beam. FX: Electro harmonix 720 Looper, Zoom 505 II, Bespeco Volume pedal.

Offline Joerfe

  • Stadium Superstar
  • ******
  • Posts: 2504
  • Good Vibes 97
Re: Hum from active acoustic guitars
« Reply #3 on: November 14, 2017, 03:32:50 pm »
Have they got the sound holes blocked with one of those disk thingies?
If not it could be as simple as they are picking up noise and the guitar body is amplifying it.

That would be a feedback buster.
I use it when playing with the band. It seems to not be related to humming, but when it’s not on the guitar you are risking feedback from the monitors quite easily.
/Jesper

Sigma SOMR28H, Fender Classic '50s Tele, Fender Std Stratocaster, Gibson lpj '14, BOSS Katana 100-212 amp.
Me on da Soundcloud https://soundcloud.com/jesper-j-rgensen-11

Offline MrBumble

  • Pub Night Playa
  • ***
  • Posts: 117
  • Good Vibes 4
Re: Hum from active acoustic guitars
« Reply #4 on: November 14, 2017, 03:44:07 pm »
Grounding issue?

That's what it sounds like to me.

One question - have you used these guitars and leads satisfactorily with a different amplifier?

Offline stitch101

  • Stadium Superstar
  • ******
  • Posts: 4137
  • Good Vibes 134
Re: Hum from active acoustic guitars
« Reply #5 on: November 14, 2017, 04:55:48 pm »
Jesper is correct. The PA isn't grounded properly. Depending on the age of the PA there may be
a ground switch on the back to fix the problem.

Offline JordanD

  • School Prom Hero
  • **
  • Posts: 55
  • Good Vibes 1
Re: Hum from active acoustic guitars
« Reply #6 on: November 14, 2017, 06:47:51 pm »
That's what it sounds like to me.

One question - have you used these guitars and leads satisfactorily with a different amplifier?
sure enough, it’s only an issue with that one PA system
Any idea why this only manifests with the guitars though? And I’ll try to see if I can find a ground switch on the PA tonight
You must be Born Again. - John 3v3
Gibson J-200
Gibson SG Special, Fender Super Champ x2

Offline MrBumble

  • Pub Night Playa
  • ***
  • Posts: 117
  • Good Vibes 4
Re: Hum from active acoustic guitars
« Reply #7 on: November 14, 2017, 09:55:21 pm »
sure enough, it’s only an issue with that one PA system
Any idea why this only manifests with the guitars though? And I’ll try to see if I can find a ground switch on the PA tonight

Which inputs are you using?
Some have separate inputs for mic and line and it is possible that if you are using the wrong type of input the impedances will be severely mis-matched which won't help and you will need to turn the gain up which will amplify any induced hum and that won't help either.

Aalso if you are using a balanced input for an un-balanced signal (or vice-versa) that will lead to all sorts of problems. Most guitar inputs will be unbalanced.

Offline JordanD

  • School Prom Hero
  • **
  • Posts: 55
  • Good Vibes 1
Re: Hum from active acoustic guitars
« Reply #8 on: November 15, 2017, 10:49:19 pm »
Which inputs are you using?
Some have separate inputs for mic and line and it is possible that if you are using the wrong type of input the impedances will be severely mis-matched which won't help and you will need to turn the gain up which will amplify any induced hum and that won't help either.

Aalso if you are using a balanced input for an un-balanced signal (or vice-versa) that will lead to all sorts of problems. Most guitar inputs will be unbalanced.
I was getting ready to reply then I managed to get the manual up for the mixer, it turns out the inputs I'm using are balanced and I'm just putting a normal guitar cable in there, so that might be causing problems.

After a read one input is labeled super hi-z, which is unbalanced, so I might try the guitar in there, but it also put in my mind that I could use a DI to turn it balanced and put it straight in one of the mic inputs, but I don't really know which way I'd be better off doing it.

As for ground, I couldn't find any switch on the thing, so there isn't a whole lot on that end I could do really
You must be Born Again. - John 3v3
Gibson J-200
Gibson SG Special, Fender Super Champ x2

Offline Joerfe

  • Stadium Superstar
  • ******
  • Posts: 2504
  • Good Vibes 97
Re: Hum from active acoustic guitars
« Reply #9 on: November 16, 2017, 06:33:58 am »
As for ground, I couldn't find any switch on the thing, so there isn't a whole lot on that end I could do really

At least check the wall power outlet and the cable. There should be a third connector in both to supply the ground connection. At least that’s how it works in Europe.
/Jesper

Sigma SOMR28H, Fender Classic '50s Tele, Fender Std Stratocaster, Gibson lpj '14, BOSS Katana 100-212 amp.
Me on da Soundcloud https://soundcloud.com/jesper-j-rgensen-11

Offline JordanD

  • School Prom Hero
  • **
  • Posts: 55
  • Good Vibes 1
Re: Hum from active acoustic guitars
« Reply #10 on: November 16, 2017, 01:15:30 pm »
At least check the wall power outlet and the cable. There should be a third connector in both to supply the ground connection. At least that’s how it works in Europe.
well I'm in the uk, I'm no electrical expert (I'm trying lol) but afaik the top pin in our plug is for ground, the mixer and drum set/other stuff associated with the pa is all plugged into one big surge protected strip plugged into the mains outlet
You must be Born Again. - John 3v3
Gibson J-200
Gibson SG Special, Fender Super Champ x2

Offline MrBumble

  • Pub Night Playa
  • ***
  • Posts: 117
  • Good Vibes 4
Re: Hum from active acoustic guitars
« Reply #11 on: November 16, 2017, 02:15:10 pm »
First thing to mention is whatever you do don't be tempted to remove the earth connection to your big surge protected strip. This is an electrical safety "earth" and is distinct from the "ground" connection which is the signal reference. The safety earth is what protects you (and others) from getting a shock - potentially fatal - if anything develops a fault.

Some equipment separates the mains earth from signal ground and some doesn't. If your Yamaha doesn't have a switch marked "lift ground" or some similar terminology.

What is the model number of your Yamaha PA (and where in the UK are you)?

Offline JordanD

  • School Prom Hero
  • **
  • Posts: 55
  • Good Vibes 1
Re: Hum from active acoustic guitars
« Reply #12 on: November 21, 2017, 11:40:00 am »
Problem solved guys, by replacing most cables for the mixer, all the guitar cables and replacing my audio interface for the pc.
You must be Born Again. - John 3v3
Gibson J-200
Gibson SG Special, Fender Super Champ x2

 

Get The Forum As A Mobile App