How can you eliminate/reduce hum in your amp, especially when cranked up?

[aiiiiee]

I have a VOX AC-15 that has a hum that takes over when cranked. Any suggestions? Thanks.

[daddymack]

check your grounding...does this happen everywhere or just at home?

[onelife]

Does the volume control on your guitar effect the amount of hum you are experiencing?

[WRGKMC]

If the hum is only there when you have a guitar plugged in or gain box turned on then its likely the shielding in the guitar that needs to be improved or the cable quality.

 

If you use a Fender style guitar with vintage wiring and single coil pickups they are known to have major hum issues. Shielding the wiring cavity with copper foil or conductive paint, or replacing the pickup wires with shielded wires are your only choices. (besides using humbuckers which use phase cancellation to kill hum)

 

The cables used should be 90% shielded or better too. Cheap cords are often only 70%.

 

A Vox is going to amplify any hum in your signal chain and make it more noticeable then most amps do. That doesn't mean the hum comes from the amp unless the amp is ungrounded.

 

If you use pedals, the other possibility is a bad wall wart. Pedals, especially buffered pedal like boss which are not true bypass, will hum badly if the wrong wall wart is used. Those pedals require a zero hum adaptor. If a generic 9Vdc pedal is used the pedals can hum badly whether the pedal is on or off. The AC ripple that's produced sounds exactly the same as if its coming from the amp's power supply except it disappears when you disconnect from the amp.

 

Overloading a multi pedal power supply can do the same thing. Spot one power supplies work well with normal pedals that normally run on a 300ma adaptor. Some pedals are major current hogs and can overload that adaptor. The company lists what pedals can and cant be run together without overloading on they're site

[arcadesonfire]

I was going to ask a similar question. I just moved into a new rehearsal space, and my amp is way noisier than in my old space. It's an old converted factory in Brooklyn, and I suspect its power routing isn't done very well. (I'm not an electrician/engineer in any respect and have no idea if building/power construction could matter at all.)

 

I've been using the very same Strat with single coils and a Traynor Bassmaster, always cranked to distort (with a THD Hot Plate). It seems noisier in this new place, even when I use pickup positions 2 or 4. I mean, yes, those positions produce much less noise than one single coil, but the amp is still noisier than it was in my old space or in my apartment. Also, when I rotate my body/guitar in relation to the amp, the hum volume changes significantly (as prescribed by the Biot-Savart Law iirc). This happens whether I'm plugged straight into the amp or when running through my pedals (all powered by a Voodoo Labs PP2).

 

I'm wondering if the Furman SS-B6 power strip could help. Anyone have any experience? (When I play in stereo with two amps via my Timefactor, I'll get a ground loop that is entirely eliminated by using an Ebtech Hum-x on one amp's plug, so I'm open to technological help.)

 

If there's something I can do to make my Strat more hum resistant, I'm open to it. (I've grown so fond of the poing of single coils over the years... I don't wanna go back to humbuckers!)

[arcadesonfire]

(Testing to see if my account works... cuz i've got a noise problem in my new rehearsal space.)

[onelife]

I was going to ask a similar question. I just moved into a new rehearsal space' date=' and my amp is way noisier than in my old space.[/size'] It's an old converted factory in Brooklyn, and I suspect its power routing isn't done very well. (I'm not an electrician/engineer in any respect and have no idea if building/power construction could matter at all.)

 

I've been using the very same Strat with single coils and a Traynor Bassmaster, always cranked to distort (with a THD Hot Plate). It seems noisier in this new place, even when I use pickup positions 2 or 4. I mean, yes, those positions produce much less noise than one single coil, but the amp is still noisier than it was in my old space or in my apartment. Also, when I rotate my body/guitar in relation to the amp, the hum volume changes significantly (as prescribed by the Biot-Savart Law iirc). This happens whether I'm plugged straight into the amp or when running through my pedals (all powered by a Voodoo Labs PP2).

 

I'm wondering if the Furman SS-B6 power strip could help. Anyone have any experience? (When I play in stereo with two amps via my Timefactor, I'll get a ground loop that is entirely eliminated by using an Ebtech Hum-x on one amp's plug, so I'm open to technological help.)

 

If there's something I can do to make my Strat more hum resistant, I'm open to it. (I've grown so fond of the poing of single coils over the years... I don't wanna go back to humbuckers!)

 

 

Can you eliminate the hum by turning the volume control on your guitar all the way down?

 

[daddymack]

the Strat is easy...shielding the entire cavity with metal tape [al or cu] will eliminate a bunch of the transient hum. Make certain your ground lead to the bridge is stable. You can't eliminate all the 60Hz hum, but you can diminish it with extreme prejudice.

Are there fluorescent lights? Ceiling fan? Bad juju, bwana...

I run into reversed AC lines and improper grounding all the time. Just corrected it at our rehearsal space. Had the owners of two different clubs correct their power issues as well. You can buy a basic AC outlet tester on line for about $5. Well worth it.

I do use a Furman power conditioner strip for my amps, PA and monitors...expensive but worth it.

[WRGKMC]

I always get a laugh when people blame hum on AC. What do you think an outlet is supposed to provide DC?

 

Hum either comes through the power supply into the circuit or its generated through the air.

 

AC Filters remove noise that isn't supposed to be on the line, spikes, stray EMF waves, anything that isn't AC 60HZ. That don't remove the 60 cycle hum. AC cant work in circuits without having a change in polarity.

 

If the ground and polarity are good, the outlet itself is not the source of the hum.

 

AC Alternates in current and as it does it generates and external magnetic field around all wires. This electromagnetic force (EMF) is the same as any other radio wave except its 60 cycles falls within the same frequency range as the audio spectrum or 20~20Khz.

 

Audio circuits are susceptible to these waves. The EMF passes through the air or in the case of a ground loop the chassis passes low levels of AC generating EMF in the circuitry and the amplifier picks it up like a radio antenna and amplifies it. The waves will pass through any weakness in shielding and get amplified by the amplifier circuits. The more gain stages, the louder the hum winds up being.

 

The reason different room hum at different levels is due to the EMF levels in a room. If the walls and ceiling have allot of wiring, the EMF is going to be greater. There can also be other devices on the line or in close proximity to the amp which can either increase the EMF levels or send noise through the line which the power supply cant adequately smooth into clean DC.

 

One fix for EMF is to have armored cable in the building. Old homes like the one I grew up in had armored cable throughout the house and that armor was grounded at the breaker box. Those were the days before three wire grounding became the building code. Most homes today have your regular Romex cable which is unshielded.

 

There is no protection from the wire emitting EMF in the air. Most business with 220 voltages for AC units and equipment have building codes require much of the wiring to be armored or pass through grounded pipes. This is can prevent fires and limit the EMF emissions.

 

In most other buildings the only thing that can protect your audio gear from EMF is to have all audio input cables and amp chassis well shielded. Any direct hum from an outlet is purely a power supply issue. If the caps are weak they will fail to smooth the AC ripple into solid DC. Ground loop pass AC through the shielding/chassis which normally acts as a ground shield, but when that chassis is passing AC it emits EMF in close proximity to the circuits instead of acting as a ground to drain the waves off safely to ground.

 

There are other types of hum but they are usually cased by circuit failures and the AC input is bridging the power supply through shorts into the circuits. These rarely last very long before the circuit is toast.

[onelife]

Electromotive Force (EMF), measured in Volts, is the voltage developed by any source of electrical energy such as a battery or dynamo. It is generally defined as the electrical potential for a source in a circuit. EMF can be AC or DC but it is not entirely correct to say it is the same as any other radio wave.

 

I believe the previous post is referring to Electromagnetic Radiation (to use the proper terminology). Before I switched to noiseless pickups, I used to refer to my old Stratocaster as a "radiation detector" which it did very well.

 

It is possible that the "hum" referred to in the OP is a result of poor filtering in the amplifier's power supply, it happens from time to time, which is why I asked if the hum goes away when the guitar volume is turned all the way down.

 

 

I generally try to differentiate between "hum" and "buzz" when describing the annoying unwanted sound of a guitar rig. It helps determine if it is a power supply issue or noise being picked up by the guitar.

 

If it is hum and the level changes with the volume control on the amplifier then it is usually a filter in the B+ supply (on a tube amp) and if it does not change with the volume control then it is likely the filter for the power tubes' bias supply.

 

 

 

 

[1001gear]

Where does transformer hum come in?

[onelife]

Where does transformer hum come in?

 

 

There is some electromagnetic radiation that emanates from any power transformer - including the transformers on power poles. This radiation can generate an electric current in a coil of wire. Getting too close to the transformer with an electric guitar pickup will result in hum.

 

 

 

 

[daddymack]

thanks for the detail explanation, but all you had to say was: If the ground and polarity are good, the outlet itself is not the source of the hum.

Which was the point I already made.

[1001gear]

 

 

There is some electromagnetic radiation that emanates from any power transformer - including the transformers on power poles. This radiation can generate an electric current in a coil of wire. Getting too close to the transformer with an electric guitar pickup will result in hum.

 

 

 

 

Don't guitar amp transformers introduce hum into the audio; At least the good sounding ones?

[onelife]

it's part of the mojo

[daddymack]

bottom line...if you eliminate all the extranea, take your amp to a qualified tech to check it.

[WRGKMC]

It shouldn't with a properly designed amp. When designing an amp the transformer is usually on the AC end of the chassis and on the outside of the chassis. Your preamp is usually at the other end of the chassis, away from the power supply. Its also encased in soft iron or Mu Metal to keep the magnetic flux contained within its core.

 

Its the first gain stage, (the input to the amp) that's most susceptible to hum because it takes small signals and raises them up in gain high enough for the next stage to amplify. EMF induces hum is usually in the microvolt ranges. The power amp signals needs to be line level which is in the 1~2V range so EMF isn't likely to generate audible hum directly into the power amp because its simply too weak a signal.

 

Again, with most amps, youll have the AC at one end, Preamp at the other and the higher gain stages, like power tubes wind up close to the AC components and power supply because they aren't as susceptible to EMF induces hum.

 

AC coming into the amps power supply gets converted to clean DC before it gets near the amplifying components. The exception being Tube Filament circuits which use low voltage AC to heat them. The wires for those filaments are usually twisted and tight against the chassis so it absorbs the EMF the wire may generate. The twisting helps to phase cancel, Plus the tubes which actually do the amplification are on the outside of the chassis.

 

Amplifier Transformers can generate hum in other circuits if they are in close proximity, like having a stomp box sitting on top of a tube amp. Allot of that has to do with how well the circuit is protected by its own chassis. I used to have issues with the old EH units which had stainless steel boxes. Stainless doesn't shield as good as other metals and a strong filed could pass through it to the circuit inside.

 

The fix was to simply move the box to the other end of the head or change its angle to minimize the hum.

 

Allot of it has to do with the type, size and voltages of the transformer too. I've gotten hum from many tube amp transformers before. They are usually large and step the voltages up to 200~600V.

SS amps run on low voltages. If the circuit runs on 24V or less there isn't going to be much EMF generated from the wires feeding the power supply. Many manufacturers don't even bother putting the transformer on the outside of the chassis. They can PC mount many at one end of the board and there's sufficient distance to prevent hum from being an issue.

[WRGKMC]

I was just expanding on the causes which seem to be a mystery to many.

 

By the way, a good way to find hum sources is to use a portable AM radio tuned between stations on the low bands and use the antenna as a probe. When you get close to a hum source you'll hear it.

[WRGKMC]

When you drive around listening to AM radio you often hear AC static when driving past certain AC lines and transformers that emit high levels of EMF.

 

I've often wondered if I had a battery operated amp in the middle of a desert thousands of miles away from civilization whether I'd hear AC hum when I plugged a bare wire into the amp. I suspect I would. The AC grid covers most continents and the ground itself is a conductor.

[onelife]

I always get a laugh when people blame hum on AC. What do you think an outlet is supposed to provide DC?

 

I don't laugh when people make mistakes simply because they don't understand a concept or don't use proper terminology.

 

 

Its the first gain stage, (the input to the amp) that's most susceptible to hum because it takes small signals and raises them up in gain high enough for the next stage to amplify. EMF induces hum is usually in the microvolt ranges. The power amp signals needs to be line level which is in the 1~2V range so EMF isn't likely to generate audible hum directly into the power amp because its simply too weak a signal.

 

Again, with most amps, youll have the AC at one end, Preamp at the other and the higher gain stages, like power tubes wind up close to the AC components and power supply because they aren't as susceptible to EMF induces hum.

 

AC coming into the amps power supply gets converted to clean DC before it gets near the amplifying components. The exception being Tube Filament circuits which use low voltage AC to heat them. The wires for those filaments are usually twisted and tight against the chassis so it absorbs the EMF the wire may generate. The twisting helps to phase cancel, Plus the tubes which actually do the amplification are on the outside of the chassis.

 

Once again you are confusing EMF (Electromotive Force), which is a difference in electrical potential - often referred to as Voltage because the potential difference is measured in Volts - with Electromagnetic Radiation. Radio waves are one example of Electromagnetic Radiation.

 

Sometime Electromagnetic Radiation is referred to as EM Radiation or as EMR - but not as EMF, as you erroneously stated, because that would be confusing.

 

I tried to point this out in a subtle, non-condescending manner in Post #10 of this thread but since you have, on several occasions, chastised other posters for not understanding or using proper terminology in their statements, I feel I must be more forward in my approach.

 

 

Amplifier Transformers can generate hum in other circuits if they are in close proximity, like having a stomp box sitting on top of a tube amp. Allot of that has to do with how well the circuit is protected by its own chassis. I used to have issues with the old EH units which had stainless steel boxes. Stainless doesn't shield as good as other metals and a strong filed could pass through it to the circuit inside.

 

The fix was to simply move the box to the other end of the head or change its angle to minimize the hum.

 

Allot of it has to do with the type, size and voltages of the transformer too. I've gotten hum from many tube amp transformers before. They are usually large and step the voltages up to 200~600V.

 

SS amps run on low voltages. If the circuit runs on 24V or less there isn't going to be much EMF generated from the wires feeding the power supply. Many manufacturers don't even bother putting the transformer on the outside of the chassis. They can PC mount many at one end of the board and there's sufficient distance to prevent hum from being an issue.

 

 

It's obvious that you understand the concepts but, as you have pointed out on several occasions, unless you use the proper terminology your meaning may be lost and your credibility may be brought into question.