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View Full Version : Years of Amplifier Hum trouble SOLVED last night!



kissing
09-19-2014, 02:39 PM
I have always experienced a very unpleasant HUMMMMM when plugging in ukuleles into my small amps - the Roland Microcube and the VOX Mini.

For years I thought this must be due to some sort of electrical mismatch between piezo pickups and amps suited for electric guitar.

But I noticed that my Gibson Les Paul Electric guitar with humbuckers would also hum on my VOX Mini amp specifically, but not on any of my other amps. I initially thought it was because there was something wrong with my guitar, but when I took it to the guitar technician who opened it up and inspected all the wirings, it came back with nothing diagnosed...

Last night, I decided to try an experiment and used a different power supply plug on my VOX for the first time..

AND VOILA! NOISELESS AMPLIFICATION.
On both my guitar AND all my ukuleles!

I feel kinda angry that VOX would provide power supplies that would cause prominent EMI hum...

But I feel greatly relieved that a dilemma I've been having for years is solved.

If you get nasty hum on your amplifier, try changing the power supply!

http://i4.photobucket.com/albums/y121/pactio_kiss/20140912_014952_zps95634ad7.jpg (http://s4.photobucket.com/user/pactio_kiss/media/20140912_014952_zps95634ad7.jpg.html)

hollisdwyer
09-19-2014, 03:50 PM
So to be clear, you replaced the entire supply and just didn't fit new the plugs at either end?

coolkayaker1
09-19-2014, 04:41 PM
I need this advice, kissing. How does one change the whole power supply?

kissing
09-19-2014, 04:41 PM
Yes, I replaced the entire power supply with a generic one from the electronics store:

http://i4.photobucket.com/albums/y121/pactio_kiss/20140920_1205101_zps722781e1.jpg (http://s4.photobucket.com/user/pactio_kiss/media/20140920_1205101_zps722781e1.jpg.html)

Though the strange thing is, some adapters seem to emit hum more than others.
I had some other generic adapters lying around.. and they generated hum.

The one in the picture seems to be the "lucky" one that doesn't generate hum..

coolkayaker1
09-19-2014, 04:52 PM
Thank you, that photo helps. It's incredible that the generic, no name rather cheap appearing power supply made that much difference. Wow. But my amps hum, too, so maybe I'll have to try other power supplies. I think they sell power "conditioners" that change the waveforms from the wall plug or something. Maybe those work, too.

Rick Turner has always said to monkey with the power supply, as that's the culprit. The power going into the amp. I guess that's right.

vanflynn
09-19-2014, 04:56 PM
Thanks for the info. Humm is usually a ground problem and I would typically think it's before the amp.

Glad to hear a low $$ fix chased the gremlins away.

ricdoug
09-19-2014, 06:24 PM
I use batteries in those amps. No hum. Ric

kypfer
09-20-2014, 01:28 AM
I feel kinda angry that VOX would provide power supplies that would cause prominent EMI hum... It's highly unlikely that a small power supply like this would generate any level of EMI (electro-magnetic interference) hum, there simply isn't the power available to do so. However, a poorly designed power supply, with insufficient smoothing, or indeed an overloaded power supply (one that doesn't have sufficient power output capability for the job in hand) very often will cause hum. Alternatively, there may be other equipment in the vicinity that is generating EMI and this is being picked up by the power supply and fed to the amp.

Presumably the original power supply is the correct one for the job and hasn't been interchanged with an inferior unit, possibly by mistake. Does the power output rating on the power supply match the power requirements for the amplifier? If so, I suspect you may have just been unlucky and were supplied with a faulty unit originally :( Did you ever take up the issue with the original supplier?

Pleased you've got your problem sorted now :)

Ukuleleblues
09-20-2014, 02:49 AM
I've had good luck with the Danelectro DA-1 power supply. Everyone I bought is quiet. I bought one of the fancy brands, ones with multiple plugs and it hummed. You would think it would be better than the 1/3 price DA-1, it wasn't.

paw123los
09-20-2014, 03:00 AM
From my experience most of the time hum problems come from the power related issues. It could be not properly grounded outlet or faulty power supply. I also had problems with my amp - very loud hum whern instrument plugged in, but when I touched the amp chasis the hum would disapear. The problem was of course on the power side - but when you perform somewhere you never know what to expect on the venue. I have found a solution to that problem - Electro Harmonix Hum Debugger pedal - it just removes hum from the signal, even if it is bad grounding fault, and doesn't change the tone. I always take it with me when I play/perform in unknown place and it saved my life (or rather my tone) many times.

Skinny Money McGee
09-20-2014, 03:59 AM
Just to be clear as well, we are talking AC adapters (and the associated plugs), Not power supply's, right?

kypfer
09-20-2014, 10:20 AM
Skinny Money McGee wrote :
Just to be clear as well, we are talking AC adapters (and the associated plugs), Not power supply's, right? Not quite sure what is implied here ... an AC adaptor, "wall-wart" call it what you will, is just a power supply that is external to the equipment ... unless your definition of power supply is the mains AC supply to the building, be that from the grid or a generator?

In response #4 the OP shows a picture of his replacement "power supply" (his description) which clearly shows a device labelled "Battery Eliminator". I think the subject of the posting is fairly clear ;)

Rick Turner
09-20-2014, 03:05 PM
In electronics, the phrase "power supply" can have several meanings. "Wall warts" usually consist of a transformer to lower line voltage down to somewhere between about 5 Volts (USB) and 16 Volts. The output of the wall wart can be DC or AC. 9 Volts DC is very common for driving stomp boxes.

The issue in this case could have been that ground was lifted with the original wall wart and thus there was no connection to ground with perhaps inadequate shielding in the instrument(s). The grounding scheme in the new wall wart may have taken care of this. This can occur with any number of devices, and it usually points to shielding being incomplete or not properly connected somewhere up-stream of the amplifier.

Preamps and amplifiers also have "power supplies" inside that will deliver well regulated appropriate voltage and current to the internal components. In some cases, the internal power supply has to provide several different voltages to different sections of the circuitry. For instance, with the D-TAR Mama Bear, the wall wart delivers 16 Volts AC to the unit and the internal power supply then distributes five different voltages to the circuitry and LED indicator lights.

This stuff isn't as easy as you'd like it to be. If it were, everyone would be doing it!

Icelander53
09-20-2014, 04:41 PM
I use batteries in those amps. No hum. Ric

That's what I ended up doing also. But hell I would love to have humless plug in. Vox you are dummies. I contacted them and they just told me to send it back. I knew there was no problem with the amp though because it played quiet on battery power. Thanks for clearing this all up for me. I'm the total amature that knows more about Vox amps than Vox does. How stoopid is that?

Inksplosive AL
09-20-2014, 04:47 PM
Most instrument hum is caused by bad shielding allowing the instrument to pick up the 60hz pulse in the wiring of your home. 50hz if you're on the other side of the pond.

Apparently the new power supply is shielded better.

I love foil tape!

~AL~

Icelander53
09-20-2014, 04:49 PM
I also have a behringer that has no noise in the same outlets.

How do you use foil tape?

kissing
09-20-2014, 05:18 PM
Just to be clear as well, we are talking AC adapters (and the associated plugs), Not power supply's, right?

Yes, in my case I was referring to the AC adapter.

But it seems its a lot more complicated matter. I got lucky with my AC adapter fix :)

Skinny Money McGee
09-20-2014, 07:19 PM
Skinny Money McGee wrote : Not quite sure what is implied here ... an AC adaptor, "wall-wart" call it what you will, is just a power supply that is external to the equipment ... unless your definition of power supply is the mains AC supply to the building, be that from the grid or a generator?

In response #4 the OP shows a picture of his replacement "power supply" (his description) which clearly shows a device labelled "Battery Eliminator". I think the subject of the posting is fairly clear ;)

Since your interested, I was implying

The average of an AC current is zero. RMS means the square root of the time average of the square of the quantity, current or voltage. We do not use the term "rms power", but average power. On a resistor R, and current I(t)=Io sin(wt), the power is P(t)=(Iosin(wt))2R, and the average of the current is Io2/2. Plot it and you will see. So the average power is Pav=RIo2/2. You can introduce the rms current which is Irms=Io/√2, then you have the same formula for the average power you would get in case of Irms=Io/√2 DC current. Pav=Irms2R. It is said that the rms value of the AC current is equal to that DC current which would dissipate the same power on a resistor as the AC current in average.

I don't know how I could be anymore clear ;)

kypfer
09-20-2014, 10:01 PM
Skinny Money McGee wrote :

The average of an AC current is zero. RMS means the square root of the time average of the square of the quantity, current or voltage. We do not use the term "rms power", but average power. On a resistor R, and current I(t)=Io sin(wt), the power is P(t)=(Iosin(wt))2R, and the average of the current is Io2/2. Plot it and you will see. So the average power is Pav=RIo2/2. You can introduce the rms current which is Irms=Io/√2, then you have the same formula for the average power you would get in case of Irms=Io/√2 DC current. Pav=Irms2R. It is said that the rms value of the AC current is equal to that DC current which would dissipate the same power on a resistor as the AC current in average. Thank you for that, all neatly copied and pasted from https://www.physicsforums.com/threads/what-is-the-mathematical-relationship-between-ac-power-and-dc-power.707900/ ... if ever I need it I'll use it ... now, back to the original question ;)

Skinny Money McGee
09-21-2014, 03:27 AM
Skinny Money McGee wrote :
Thank you for that, all neatly copied and pasted from https://www.physicsforums.com/threads/what-is-the-mathematical-relationship-between-ac-power-and-dc-power.707900/ ... if ever I need it I'll use it ... now, back to the original question ;)

Damn, always someone who's too serious and spoils all the fun!

by the way, I wrote that on the physicsforums

kypfer
09-21-2014, 03:38 AM
Skinny Money McGee wrote:
Damn, always someone who's too serious and spoils all the fun! ... but making people think you are serious is the fun :rolleyes:

Skinny Money McGee
09-21-2014, 04:01 AM
Skinny Money McGee wrote: ... but making people think you are serious is the fun :rolleyes:

Nobody took me seriously except you. My original question was for the OP, and you barged in with a smart a.. response.

kypfer
09-21-2014, 07:45 AM
... and you barged in with a smart a.. response. :rolleyes:

Inksplosive AL
09-21-2014, 10:00 AM
I also have a behringer that has no noise in the same outlets.

How do you use foil tape?

Somewhere around here in the hoard I call home I have an old Boss Chorus pedal from the 80's. I got it from a friend who had issues with the old wiring in his house causing a hum with this pedal. His fix was to cover the pedal in foil tape it worked for him by shielding the unit from acting as an antenna picking up the hum.

Over the years with various guitars, amps and an old book I'll be damned if I cannot remember the name of about hot rodding electronic guitars I've learned most 50hz-60hz hum is being picked up by unshielded or bad solder joints. My most recent experience was with my Risa soprano that was unplayable until I shielded the jack area with foil tape.

After sleep and some thought I think the fact you mention about some ends for the power supply humming and some not shows us the power supply while it might be pushing this hum through the line is more likely acting as a broadcast station leaking this 50hz-60hz for something else to pickup. This could be the amp itself, the cord, the solder joint at the jack or pickup. I would start by lining all my instruments compartments with foil tape, but that's just what has always worked well for me.

http://forum.ukuleleunderground.com/showthread.php?72464-Risa-Stick-Amplifier-Buzz-Hum-Help-Plz

http://forum.ukuleleunderground.com/showthread.php?92068-Risa-electric-background-noise

Ukuleleblues
09-21-2014, 11:55 AM
I 've heard about the aluminum foil thing. You can wrap you head with it, over your eyes with eyeholes works best. Just start playing, no hum, plus you meet some very, very interesting folks. Lead or brass works well too. The brass gets a nice patina over time. :)

KaraUkey
09-21-2014, 01:25 PM
In my experience, ground loop currents are caused by stray currents in a conductor running between two points that are supposed
to be at the same potential (usually ground) but are not. It is a common complaint when you have the
sound output of a PC connected into an AMP. The problem can be solved by running the PC on its battery as ricdoug suggests OR you
can connect a ground loop isolator into the audio lead between the PC and the AMP.

Ground loop isolators are fairly small and inexpensive. They are available at most good electronic shops.

A lot of modern power supplies lower the voltage by clipping the AC waves. These power supplies are particularly
troublesome and can cause a lot of AC hum, 50 Hz or 60 HZ as someone else has pointed out, depending on where you are.
A transformer type AC adaptor isolates the AC input side and tends to have a lot less Hum, if any.