Hum problem @180Hz

[phvdv]

Hello,

After analyzing the hum in my guitar circuit with an oscilloscpe, the frequency of the hum I'm experiencing is at 180Hz.
Does anyone has any idea where that might come from and how and can solve it?
My strat has the QTB mod already and that hum is driving me nuts...

Thanks,
Philippe

[wolf]

phvdv
Wow, getting fancy - using an oscilloscope. Well if we are getting into serious science, then here's something you might find interesting.

If I have done my calculations correctly, and if 60Hz hum produces a 60Hz note, it should produce a frequency between B flat 58.270Hz and B 61.735Hz.

A note of 180Hz is between F 174.614Hz and F# 184.997Hz.

Perhaps this will help you determine if the frequency of the hum is precisely what the oscilloscope says it is. I have rarely used oscilloscopes but I know they can be tricky. To me it is easier to say that the oscilloscope might not be set correctly as opposed to explaining a 180Hz hum. (Even a hum second harmonic (if there is such a thing) would be 240 Hz).

As I previously stated, my calculations might be inaccurate and so, anyone else is more than welcome to join in this discussion.

[RandomHero]

I've always been interested in this. Something I'd like to try sometime is record some 60-cycle hum on my computer and then do some modulation to makes some synthy notes out of the annoying noise; although you're right Wolf about the B and Bflat. That's what my electronic tuner registers when there's nothing plugged into it.

[wolf]

RandomHero
Wow - I'm glad I got my calculations right.

For those who are wondering about this, the 12 note chromatic scale is based upon the 12th root of 2 which equals 1.0594630943593
The note 'A" (I forget whether this is A above middle C or whatever) but one of those A's has a frequency of 440Hz.
The next higher note (B Flat) has a frequency of 440 times the 12th root of 2 or about 466.164Hz. The next note (B) has a frequency of 1.05946309..... times 466.164 or about 493.88Hz.
As we work our way up to the 12 note of the chromatic scale (12 notes = 12 frets) we return to A but an octave higher and this note would have a frequency of 880Hz.
Every note that is one octave above another note, has a frequency twice as great as that lower note.
So, 'A' another octave higher would have a frequency of 1,760Hz. The 'A' one octave after that is 3,520Hz.
If nothing else, this is the calculation that determines the placement of frets on the fingerboard of a guitar.

[jester700]

There can be harmonic components to 60 Hz hum - at 120Hz, 180 Hz, 240Hz, and on up. I've recorded various instances and frequency analyzed them in Adobe Audition, which is nice because all the partials show up as spikes. As to where it's coming from - it could be many things. I'd do some troubleshooting and turn all the things in your area off & on to suss this out. Also play with room position. Eventually you should find the culprit(s).

[phvdv]

Wolf:
It's not a question of getting fancy - it's a question of being desperate... :-) I'll try out the F and the F# thing.

Jester700:
Together with the oscilloscope, my friend also brought a UPS. After plugging my amp into the UPS and shutting down the main powerswitch, the hum was still there... which leaves me one possible explanation: the high power line for the railroad near my yard (25kV AC).

After surfing for a while, I found out that you can experience hum on all the harmonics: 60Hz, 120Hz, 180Hz, 240Hz, etc etc and that the odd ones are "nastier" then the even ones.

Anyway, I could build a Faraday cage around my basement or... I could switch to flute, trumpet or saxophone, but I'm too hooked on my guitars.


Thanks,
Philippe

[jester700]

Is the hum there when you turn the volume on the guitar down? If not, it's the pickups. If so, is it there when you pull the guitar cord from the amp's input? If not, it's the cord. If so, it's the amp. But where in the amp? It may be possible to shield whatever is acting like a hum antenna.

And whaddaya mean FLUTE? There's always an acoustic guitar!

[phvdv]

Jester700:

The hum does diminish when I turn down the volume, so I do suspect the pickups (Lace Sensors, very good pickups but not noiseless). Maybe I should try out some noiseless pickup (Fender Hot Noiseless, Kinman, Bill Lawrence).
If I pull the cable from the amp, I don't hear anything anymore, but could it be possible that, by removing the cable from the (amp) plug, the (amp) circuit is opened and therefore nothing is amplified anymore?
And for the cable; I've been testing with three different cables, but all of them don't seem to be "top notch". I could try another, more adequate cable, but which one?
And for the amp, it's a Marshall AVT275 - could one suppose that the circuit is shielded ?

Thanks,
Philippe

[RandomHero]

Most "input cut" circuits on amps lay both contacts on the ground of a mono plug, so if there's a plug in there, the preamp will be on and taking in whatever noise is making it's way in through the cable.

I can't imagine why pickups would be the problem, especially Lace Sensors, and to my knowledge if they were it would still be your standard 60-cycle hum. The AVTs are very quiet, to my experience... do you have access to another guitar you might test it with?

[phvdv]

RandomHero:
I have another Strat, QTB'ed and also with Lace Sensors and a stock American Telecaster... They all behave in the same way...

"Most "input cut" circuits on amps lay both contacts on the ground of a mono plug..."
You've lost me here a bit...


Thanks,
Philippe

[RandomHero]

Ooooh! I think I misread you. Okay, "If I pull the cable from the amp, I don't hear anything anymore, but could it be possible that, by removing the cable from the (amp) plug, the (amp) circuit is opened and therefore nothing is amplified anymore?"

With most modern amps, there is a circuit that shorts out the preamp volume to nothing when there's no plug in the amp. So yes, you're right; if you pulled the plug the amp automatically shuts off, helps with noise problems onstage.

[jester700]

The kicker is that the hum drops as your volume control does. This points to the guitar. I'm not familiar with the lace pups, but other humbuckers, normal or stacked (noiseless singles), aren't perfect. They only work when they're "hearing" the same noise signal - this is why the noise changes as you change position. This kind of EMF "buzz" has lots of harmonics (as you experienced).

I just took my Yamaha Pacifica 921 (H-S-H, and all 5 switch positions are humbucking - the middle pup is a stacked bucker) and recorded some buzz generated by my PCs 2nd monitor - a CRT (my main monitor is an LCD, which doesn't cause this). The noisiest position is the bridge bucker alone. It's a DiMarzio Steve's Special, which is not fully humbucking, if you're familiar with this pickup. I held it so the pickup face was perpendicular to the CRT, then moved it so one coil was further than the other. I got quite a difference in the min. and max. buzz generated. Are you ready? 18dB! and the harmonics are almost equal in level from the fundamental at 60Hz out to 3.5k, where they start to roll off. Pic here:
www.playhousemm.com/images/Image1.gif

[wolf]

How about eliminating the "input cut" amplifier circuit by placing a ¼" plug into the amplifier input? Yes it will not have the same impedance as the guitar and it might introduce slightly more hum but it would allow a better test for amplifier hum. I suppose even an entire guitar cord could be used but I feel this would introduce even more hum into the amplifier circuit.

[phvdv]

Jester700:
So, changing to noiseless pickups will not solve the problem? It seems that even a "full flavoured" humbucker is subject to hum.

Wolf:
Sorry, but I have no clue what you're explaining (unfortunately I'm a chemist, my knowledge of electronics is very limited). Could you elaborate a little more please?


What about the idea of building a cage with cupper mesh to put my amp in and grounding this cage?


Thanks,
Philippe

[wolf]

To tell you the truth, I was unaware of this feature on modern amps until Randon Hero said:
With most modern amps, there is a circuit that shorts out the preamp volume to nothing when there's no plug in the amp.
Basically, this would narrow down the hum problem to the amp (which it probably is if you've tried other guitars).
Then again, it isn't necessarily the amp if power lines in your area are causing interference.

[RandomHero]

Simple; take a crappy patch cable, and lop off one end, twist and solder the lead and braid within a half in or so of the plug, and use your new "dummy plug" in the amp's input. If massive noise shows up, I'd go as far as to say your amp is the problem. (If you can't kill one of your patches, desoldering the tip from a sleeved one will work too. The main point is just to get a plug with nothing attached into the jack to see how your amp reacts.)

[wolf]

Random Hero
Good idea but wouldn't that have the effect of shunting the input jack - basically doing what that other connection does when the is no plug in the input jack?

How about soldering a resistor (maybe 10 K to 20 K) on that patch cable to act as a dummy load in place of the guitar?

[jester700]

phvdv said:

Jester700:
So, changing to noiseless pickups will not solve the problem? It seems that even a "full flavoured" humbucker is subject to hum.
Thanks,
Philippe

How well a bucker works is dependent on 2 things: 1) How similar the coils are, and 2) How similar the noise signal is that they pick up. A stacked bucker has coils that are closer together than a normal one (so does a side-by-side that fits in a single coil space, BTW). So they will hum SLIGHTLY less at certain positions, because they'll "see" a more similar noiseprint. My "normal" bucker has mismatched coils for sound reasons, but that means it also bucks less noise than most normal humbuckers.

[UnklMickey]

180Hz hum? wow thats atypical.

usually 60Hz, or 2nd harmonic 120Hz from full wave rectifier. 3rd harmonic 180Hz doesn't usually show up as a prominent component unless you have a motor or a 3phase transformer.

if you have a fan in your amp disconnect it temporarily. if the fan is the source, replace or move it.

if the fan is not the source, determine if it's environmental background by taking guitar and amp to a friend's house and see if the hum is significantly less there.

if your house is the problem you may not have to move. depending on the source i have some suggestions on how to cure the problem.

[phvdv]

randomhero:
I think I don't have to do the test you're describing: just by plugging the cable into the already give some hum - hum that disappears immediately as soon as I touch the ground part of the plug...

unklmickey:
There IS a fan inside my amplifier - but I don't see how I would be able to disconnect it: I only see 4 screws on top of the amp and I'm not even sure that by unscrewing them, I'll get access to the wiring...
I took my amp and my guitar to a friend's house (as a matter in fact, I did it yesterday evening), and there was less hum.

Today I took my amp and guitar outside, in order to be closer to the railroad's powerline: with the cable plugged into the amp but not in the guitar, the hum was present and got worse if only walked 4 feet towards the railroad.
Afterwards, I continued to do some testing in the basement (where I usually play) and bizar stuff is going on: there are moments that I wouldn't here a thing (and is that nice!!!) and then 180Hz hum kicks in, for a number of seconds and then disappears again, and so on and so on... Any thoughts???

Thanks,
Philippe

[jester700]

Seems like whatever's causing it is cycling onn & off. Can you hear any transformers powering on & off? Anything in your house? A/C? I'm wondering if there might be more than one source for the buzz.

[UnklMickey]

Philippe,

let's start by trying to determine if the cycling of the hum is caused by the trains, or a problem in some device or appliance in the house (or the wiring to the device).

we'll ignore the possiblilty of the fan being the source of the problem unless it cycles off and on (or low speed to high speed) along with the quiet and hum.

is there a marked increase in the speed of rotation of your watt-hour meter feeding the house when the hum is present? (a sign we have something correctable)

having a friend help you with this (one person watching the meter and another listening for the hum, both with 2way F.R.S. radios) makes it much easier.

if the presence of the hum correlates to an increase in power consumption in the house, obviously this points to a local (in the house) problem. We'll then then proceed to determining which device or appliance is the culprit and also if it is the DEVICE or the WIRING TO IT that is the problem.

worst case would be if external events (like the train passing by) correlate with the hum. (consider moving!)

I'd be particularly suspicious of motor driven devices like air conditioning, whole house fans, refrigerators, washers, dryers, etc.

p.s.

I'm sure you're already aware of the sonic danger of touching the TIP of that open ended 1/4" cable you had plugged into your amp. -- hope the amp volume wasn't turned up too high.

[RandomHero]

The solution is obvious. Sheild your basement.

[wolf]

unklmickey

phvdv said he was touching the ground part of the plug which would reduce the hum.
As I mentioned earlier, (and RandomHero later added to this idea), how about plugging in a ¼" jack with a 25K to 50K resistor soldered to the terminals? This would be a good "dummy load" for the amp and would certainly narrow down if it is a guitar or amp problem.

[UnklMickey]

wolf said:

unklmickey

phvdv said he was touching the ground part of the plug which would reduce the hum.
As I mentioned earlier, (and RandomHero later added to this idea), how about plugging in a ¼" jack with a 25K to 50K resistor soldered to the terminals? This would be a good "dummy load" for the amp and would certainly narrow down if it is a guitar or amp problem.

yes, i understood him touching the shield portion of the cable. my p.s. was just a left handed, after-the-fact caution to him and everyone else about the mostly obvious effects of touching the tip of cable with the amp volume up.

sorry if i confused the issue.

your idea for a 1/4'' plug (i assume you meant plug) with a resistor between the terminals is not bad, but i suspect in Philippe's case, the problem MAY not be in the guitar or the amp or even in the cable. it is sounding more and more like either an extremely strong EMF or the house ground is being modulated by heavy cyclic loads combined by a poor wiring scheme for the neutral and ground connections.

if you or any other members have the time, you might experiment with the following:

1 - - 1/4" plug only (no connections between elements)

2 - - 1/4" plug with 33k resistor connected between elements

3 - - 1/4" jack with 33k resistor connected between elements, plugged into guitar cable (other end of cable plugged into amp)

4 - - 1/4" jack with short between elements, plugged into guitar cable (other end of cable plugged into amp)

5 - - modified guitar cable with 33k resistor separating the shield of the cable and the shield of the plug on the guitar end of the cable. this would simulate a poorly grounded guitar.

6 - - normally connected well sheilded guitar, amp, cable.

compare the amount of hum in each case with the same settings on the amp.

which ever one of the first 4 most closely resembles #6 would be a good choice as a dummy load.

admin said:

The solution is obvious. Sheild your basement.

YIIIKES! hold the phone there.

the solution may not be as obvious as it seems!

assuming that it is EMF and is not within his control, (e.g. the train) shielding his basement would be probitively expensive! moving might be a cheaper option.

if it is EMF and within his control, correcting the problem at the source might be cost efficient.

if it is not EMF, but rather a modulated ground in his house, shielding his basement won't help.

let's take this one step at a time before we jump to any conclusions.

[phvdv]

I did touch -accidently- the "hot" part of the cable plug, which made my wife go "YEEEEK"... :-)

Anyway, it seems that I have a lot of testing to do: there is RandomHero's test with the cable, further to be refined by the unklmickey and the other tests unklmikey mentioned (looking at the watt-meter).

What does "the house ground is being modulated by heavy cyclic loads " mean

Thanks,
Philippe

[lbw]

Lace sensors aren't as quiet as people think they are. I also live in a high EMR area. The neck pickup on my PRS is more suceptable to noise than the bridge. It's more about pickup design than anything else.

Why not take yourself, your amp and your guitar somewhere far, far away and see if the problem is environmental?

[jester700]

phvdv said:

I did touch -accidently- the "hot" part of the cable plug, which made my wife go "YEEEEK"... :-)

Aaaahh, the little moments we guitar guys live for.... ;D

[phvdv]

jester700:
:-) indeed

ibw:
I tend to believe that the Lace Sensor are more quiet than normal designed pickups, but I also believe that they're NOT noiseless (@ all).
I have the far far away test already in my mind.


Thanks,
Philippe

[UnklMickey]

phvdv said:

What does "the house ground is being modulated by heavy cyclic loads " mean

i'll get into it in detail if seems likely this is the cause in your situtation, but in a nutshell, if the electrician who wired your house tied the neutral and ground together at the load end of a long run, part of the current is flowing through the ground conductor. this causes the voltage at the load (device) end of ground wire to be not at true ground, but in some cases, several volts (ac) above ground. (modulated). this voltage on the ground wire is not present when the device is not drawing current. cyclic referring to turning on and off.