Noise in guitar amplifiers

[Zander]

Hi,

Last week I had my first full band session in my new studio. While tracking guitars I have encountered noise problems from the guitar amps. I tried three amps and all had noise issues some worse than others. The noise was worse with the players’ effect pedal so I suspect ground loops. The noise was not different with a direct cable vs my patchbay tie lines. The noise was better when I disconnected smps adapters. The effect pedal were plugged in the control room the amps are located in another room.

I have another session by the end of the week so while I sort out the noise problem. I would like to use a quick solution for the noise like an audio isolation transformer. What is generally specced for guitar isolation trafo’s? Can I use edcor 1:1 10k:10k?

Any pointers on where to start on finding the noise source? It’s a bit better when I turn off my hvac system, but not quiet enough. I have the option of inserting a mains isolation transformer in my electrical system (different panels and labelled sockets for audio and dirty power)...

 

[ruffrecords]

Looks like you already have some idea of the sources. Next job is to find out where it is getting in. Sounds like there is a longish lead between guitar/pedal and the amp which would be my first suspect. If the guitarist goes in the room with the amp does the noise disappear or decrease?

Cheers

Ian

 

[Newmarket]

Well - electric guitar set ups tend to be noisy wrt pro audio specs.
Typically you have a high impedance source susceptible to picking up any sort of interference around (passive guitar pickup) that is unbalanced (balanced is inherently possible but for 'historic' reasons unbalanced is the norm) and that is fed via single core unbalanced cable into the amp which may be set to a high gain !
How bad is the noise you are getting and is it hum / buzz / 'white/ hiss ?

 

[Zander]

@Ian: I will check again if it’s better with shorter leads but I think we tried without a satisfactory result.

@Newmarket:  It’s a nice mix of all the sorts you mention. Most noticable is a 6k noise with it’s harmonics. I’m used to regular guitar amp noise but this is something else. I need to edit out noise in between notes, more than normal.

Zander

 

[peterc]

Single coil pickups picking up fluorescent lights or computer monitors maybe?

Try and eliminate all sources of interference.

 

[tony hunt]

6k? Yeah, that sounds like something "external".  I get some of that from modern lighting, even LED lamps. Those spiral energy saving bulbs are the worst, or a dimmer circuit somewhere.

Guitar amps are great at picking up neighbourhood noise too. In one place I got the taxis louder than the guitar.
Sometimes the orientation, also in relation to the player, can make a difference.
Also I find I need to keep my distance from them. I drive amps and magnetic compasses crazy.

 

[Newmarket]

6k? Yeah, that sounds like something "external".  I get some of that from modern lighting, even LED lamps. Those spiral energy saving bulbs are the worst, or a dimmer circuit somewhere.

Yeah - LED lighting can be problematic particularly if it is 'low voltage' ie there is an external "SMPS" block to run the lamps.
If that is noisy then there is a large loop area to transmit it !
This experience comes from EMC lab testing so it's a fairly controlled test.

Also consider noise sources on any adjacent floors esp downwards assuming the amp is nearer the floor than the ceiling.
It's easy (for me anyway to forget that ceilings and floors can be transparent to radiated noise.

 

[Zander]

Thanks for the advice people!

I have tried a shorter lead. No succes.
I will turn everything off but the breaker for the socket where the guitar amp is plugged in tomorrow. For now I can make a scifi soundtrack just by moving around.
Also when I touch the volume knob on the guitar there is less noise, i tried this with a few quitars. Is this a safety earth issue?

 

[Newmarket]

Also when I touch the volume knob on the guitar there is less noise, i tried this with a few quitars. Is this a safety earth issue?

No. That is expected. When you are near the guitar but not touching it then you (basically - not a complete treatment here of course) act as an antennae and a source of noise that the guitar can pick up. When you touch the volume control (or strings / bridge etc.) then you 'ground' your body since an electric guitar should normally have it's metal hardware etc connected to the 0V connection - normally there's a wire under the bridge that connects it to the shield / pot case etc.
The sometimes misunderstood point is that you are grounding yourself through the guitar. NOT that you are grounding the guitar through yourself 
To illustrate - if you are near the guitar and touch another grounded piece of metal - rack / mixing desk chassis etc. then the noise should still decrease.

 

[JohnRoberts]

Guitar amps operate at high voltage gain with signals from high impedance, unbalanced pickups.

So by definition there will always be a lot of noise.

Mains frequency noise from lighting (dimmers, fluorescents, etc) can often be reduced at the source of the noise. 

Humbucking guitar pickups can be quieter, but sound different (no free lunch).

JR

 

[BluegrassDan]

Cell phones in close proximity can be problematic.

 

[Audio1Man]

Hi Zander
You should always have your handy dandy Spectrum Analyzer in your tool kit. This is a small plastic AM  LOOPSTICK battery operated RADIO. This is a GREAT NOISE HUNTER, tune it to a blank station and then start a search to locate the noise source.  You can also run it up/down the AC Power cords to see conducted line noise.  Many noise sources are in places that you can turn off or move away from.
Good hunting. Duke

 

[Newmarket]

Cell phones in close proximity can be problematic.

Yes - and pretty much anything else electronic.
I had a mysterious periodic click with a strat type (ie 3 x single coil) guitar.
Eventually I thought about it occuruing about once per second.
It was - of course - my quartz watch with the clicks sync'd to the second hand.

 

[Michael Tibes]

I think there are a lot of possibilities to investigate:

-What is the noise of the amp on its own with / without a guitar?
-Does the noise change when the guitar is moved / turned?
-Is this basic setup already noisy or is the noise introduced by effects?
-What kind of pickups do you use?
-What happens if the pedals run on batteries?
-Are there an switching type power supplies involved - if yes, do they cause noise?
-Is there a particular pedal creating noise, maybe even in bypass?

...and so on.

My approach would be to break things down as much as possible in order to locate the source of the noise and figure out whether things can be improved. Also if possible I try to keep the signal path to the amp as short / clean as possible, preferably just a cable, only plugging in pedals that are actually in use. BUT there are endless possibilities, and anything can be right if it fits the song - so unfortunately there might not be 'the one' recipe.

Michael

 

[Zander]

For my Hiwatt custom 100:
Ok. So I switched everything off in the electrical panel except the ac circuit where the amp is plugged in. No noise there.
Put all lights and other ac socket circuitry back on.
No noise.
When I put my hvac system on the noise is back, high pitched note.
With an Orange rockerverb 50 combo. I followed the same procedure. Here I notice a bit noise when the circuits where smps adapters are plugged are turned on.

Noise is worse with longer leads, effect pedals and single coil pickups.

So I assume the easiest, not cheapest, solution is a mains isolation transformer? Or maybe a couple smaller ones just for the amps? I don’t have issues other than in guitar amps in my studio.
For the longer leads (gtr player in the control room, amps in an isolation room) I would like to try audio isolation transformers? Any suggestions?

 

[Newmarket]

Are those observations re HVAC with / without guitar plugged in (and Vol pot open) ?
Suggest to determine if HVAC related noise is conducted or radiated ?
If radiated then isolating transformers might not be of much benefit ???
I'd suggest at least trialling before spending money on that approach.

For the long cable run I'd suggest to start with active DI.
Really you want that signal to be low impedance as well as impedance balanced.
A passive transformer solution to wind down the impedance will also wind down the level requiring more gain at the other end.
I'm assuming passive Hi-Z guitar pickup output.

 

[Zander]

No noise with the pot down. So radiated noise. Thank you. If I move around with the guitar the noise only decreases with turning not moving closer or further away from it...

Yes all passive pick ups. I only have passive DI’s and two active (bo hansen di) at my disposal right now.

I will test out the active di’s tomorrow.

In the mean time any other suggestion about isolation trafo’s?

 

[Newmarket]

No noise with the pot down. So radiated noise. Thank you. If I move around with the guitar the noise only decreases with turning not moving closer or further away from it...

Yes all passive pick ups. I only have passive DI’s and two active (bo hansen di) at my disposal right now.

I will test out the active di’s tomorrow.

In the mean time any other suggestion about isolation trafo’s?

Good info. I've built a DIY Bo Hansen circuit DI too using the OEP transformer.
The issue I see for you using the Bo Hansen is that while it has an active front end and will present a good high impedance to your pickup, that feeds the transformer and (assuming you've used one of the specified types - IIRC 5:1 or (OEP) 5.45:1 - then you're knocking your signal down by around 14dB.
Intended to DI into mic amps. On that note - are yours wired for Phantom power only in which case you'll need a power/cable solution to sort that.

Would they be going straight into the Guitar Amp input ?
Mic Input transformer reversed going into High Impedance - result ?
I don't know - maybe one of the 'Iron Experts' on here can contribute 

 

[abbey road d enfer]

No noise with the pot down. So radiated noise. Thank you. If I move around with the guitar the noise only decreases with turning not moving closer or further away from it... 

So it really looks like EMI (magnetic field picked-up by the gtr pick-up's - see the pun?)

Yes all passive pick ups. I only have passive DI’s and two active (bo hansen di) at my disposal right now.

A DI won't change a thing since the noise is in the gtr.
Can you compare with a gtr equipped with humbucking p/u's?
Some single-coil-equipped gtrs have RWRP sets, where one of the pick-ups is wound in contrary direction to the other, so when both are selected, hum is cancelled.
Alternatively, some guitars have a built-in humbucking coil (MusicMan).
You may want to try to shield the guitar with a large piece of sheet steel, like 1.5mm thick, but I think you need to identify the offending apparatus and either replace them or relocate them.

In the mean time any other suggestion about isolation trafo’s?

A passive electric gtr wants to see a very high impedance (500k-1Meg), that NO transformer is able to match. That's why passive DI's are such tone-killers for el gtr.

 

[Newmarket]

Sounds as if the only 'real' solution is to resolve the problem at source - which seems to be the HVAC (?)

Assuming you have different clients coming into the studio (or is it private use ?) then it's impractical to evaluate and shield every electric guitar and bass.
Alternatives ? Got any noise gates ?
Or if post processing / mixing ITB then noise gate / filter plug ins (preferably with 'look ahead' so all the attack of a note gets through). It's all hassle and compromise though.
Best get rid of the noise source ( but you know that anyway).
Good Luck.