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Old 11-18-2019, 09:01 PM   #1
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New Man Cave 60 hz hum in guitar amp


Hi all. My first post. I am an electrical engineer retired but not an electrician for residences. As the subject says, I have a 60 hz hum issue in guitar amps in a man cave I just finished building.

A little history. There is my primary 12 year old house. The breaker box was full. So watching a YouTube I took on the task of an add on sub-panel adjacent to the primary box. I used two sets of Romex cabling to run 240 vac to a ductless climate control system. And a second circuit with a single breaker for the 120 vac wall outlets. (The primary breaker feeding it is a 100 amp in the main panel). I also have a second shed with a light and socket that I moved to the new sub-panel to make room for the 100 amp).

In the cave I have some overhead incandescent lights and a small 2 cu ft refrigerator.

What I'm suspicious of with my guitar amps making 60 cycle noise is one thing that troubled me when I added the sub panel in my garage. The new panel only had one bar to install both neutral and ground wiring. Rather than the main panel which has both a bar for neutral and a bar for ground.
However, the main panel has a shorting bar going directly across from neutral to ground essentially making it one. So since the distance to the main and sub-panel is about 12 inches, I figured putting the neutrals and ground on the one bar wouldn't be a problem. However I also read that with a shorting bar setup like this, there should only be one point where the grounds are.

A bit more info, if the amplifiers have no guitars plugged in they are silent. But when I plug in a guitar or a bass, I can tell with the pickups and the cord I get the hum. I touch the strings and I'm creating a ground silencing. I just have a sense that there is some sort of grounding problem going on.

Further testing and I tried a couple of different guitar cords and it's possible I might just have some cords that are in need of repair. Or also possible is that the Carvin bass I have has a bad ground connection inside. I need to do some more exluding. I plan to move the bass amp temporarily into my house as a test. If the noise follows, then it's not the AC power.
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Old 11-18-2019, 09:19 PM   #2
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Re: New Man Cave 60 hz hum in guitar amp


Moving the operation to the main house would be a good exclusionary move. At least, then, you would know that your instruments or speakers or cords need attention. Or that you need more diagnosis on your grounding.
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Old 11-18-2019, 10:23 PM   #3
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Re: New Man Cave 60 hz hum in guitar amp


You need to buy a ground bar kit for that subpanel. Install the ground bar, move the grounds to it. Then remove the neutral bar grounding screw or what ever the ground connection is.

You want those neutrals isolated from the grounds in a subpanel.

Edit: that 2 sets of cables to take 240v to the HVAC may also be a problem. Does it ask for two feeds in the instructions or are you trying to use cable you already have.

Last edited by Oso954; 11-18-2019 at 10:46 PM.
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Old 11-18-2019, 11:28 PM   #4
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Re: New Man Cave 60 hz hum in guitar amp


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You need to buy a ground bar kit for that subpanel. Install the ground bar, move the grounds to it. Then remove the neutral bar grounding screw or what ever the ground connection is.

You want those neutrals isolated from the grounds in a subpanel.

Edit: that 2 sets of cables to take 240v to the HVAC may also be a problem. Does it ask for two feeds in the instructions or are you trying to use cable you already have.
Essentially this is the 8 space panel I bought. You can see it has a single bar for neutral/ground.



I think you might have misread my "2 sets of cables". One of the cables is for 120 VAC. And the other is used for single phase 240 VAC. In other words, the second Romex for 240 VAC, I have Black and White conductors going to Line 1 and Line 2 from a dual breaker and ground conductor tied to Neutral/Ground bus. Then I use a Whip with 4 conductors to tie black and red to the two lines and the neutral wires are all commoned together at the cave and the grounds are all tied together. So I am tying the neutral white to the those and the bare copper to the green ground. At the climate control I have Line 1 and Line 2, Black, Red and Neutral white, and Green ground. But in essence, Neutral and Ground are shorted together at the sub panel. and simply routed independently to the cave 60 ft away.
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Old 11-18-2019, 11:46 PM   #5
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Re: New Man Cave 60 hz hum in guitar amp


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Originally Posted by Oso954 View Post
You need to buy a ground bar kit for that subpanel. Install the ground bar, move the grounds to it. Then remove the neutral bar grounding screw or what ever the ground connection is.

You want those neutrals isolated from the grounds in a subpanel.

Edit: that 2 sets of cables to take 240v to the HVAC may also be a problem. Does it ask for two feeds in the instructions or are you trying to use cable you already have.
See attached drawing for how the main and sub panels are wired up. Since it's bus barred together at main I don't see what difference it makes tying the neutrals/ground together at sub panel. Except that it creates two points, twelve inches apart, where ground and neutral are shorted together.
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Old 11-19-2019, 12:05 AM   #6
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Re: New Man Cave 60 hz hum in guitar amp


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Originally Posted by Oso954 View Post
You need to buy a ground bar kit for that subpanel. Install the ground bar, move the grounds to it. Then remove the neutral bar grounding screw or what ever the ground connection is.

You want those neutrals isolated from the grounds in a subpanel.

Edit: that 2 sets of cables to take 240v to the HVAC may also be a problem. Does it ask for two feeds in the instructions or are you trying to use cable you already have.
Ok. I just read an article that clarifies this and it agrees with what you are saying from a safety point of view. The neutral and ground at the "service" panel must be separated so it can't create a sneak path in the event of some external fault (like water shorting).

No problem for me to separate the grounds from the neutral. I will do that tomorrow. But I'm dubious that this is what would be causing 60 cycle noise at guitar amps. Just a safety precaution.
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Old 11-19-2019, 12:19 PM   #7
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Re: New Man Cave 60 hz hum in guitar amp


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Ok. I just read an article that clarifies this and it agrees with what you are saying from a safety point of view. The neutral and ground at the "service" panel must be separated so it can't create a sneak path in the event of some external fault (like water shorting).

No problem for me to separate the grounds from the neutral. I will do that tomorrow. But I'm dubious that this is what would be causing 60 cycle noise at guitar amps. Just a safety precaution.
There are other reasons as well why you don't want current on the bond wire(EGC)!

Current on the EGC is the #1 problem for noise in PA systems/guitar amps etc.
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Old 11-19-2019, 12:50 PM   #8
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Re: New Man Cave 60 hz hum in guitar amp


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There are other reasons as well why you don't want current on the bond wire(EGC)!

Current on the EGC is the #1 problem for noise in PA systems/guitar amps etc.
I went ahead and separated the ground wire from the neutral bar on the service panel.

I also noticed a lot of my noise was coming from multiple sources. First a new bass amp that I'm still learning how to control that has a Gain and a Master Volume. And various tone buttons/knobs etc. Too much gain on the preamp (and it's a pretty loud amp) and any noise from the guitar side or cable will be magnified to the speaker. I also switched to a strat I have with humbuckers and plugged it in and it is much more quiet than the Carvin bass. So even though the Carvin uses Humbuckers, I am suspicious that there is a loose ground internally and that is on my list of things to look at.

Add to that, most of my guitar cables are 10 or more years old and I really need to go through them and repair or replace as necessary.

So I think we can call this a resolved issue and I appreciate all the feedback!
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Old 11-19-2019, 01:42 PM   #9
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Re: New Man Cave 60 hz hum in guitar amp


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I went ahead and separated the ground wire from the neutral bar on the service panel.
When you say service panel, what are you talking about ? Is it the main panel or sub-panel ?
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Old 11-19-2019, 01:59 PM   #10
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Re: New Man Cave 60 hz hum in guitar amp


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I went ahead and separated the ground wire from the neutral bar on the service panel.

I also noticed a lot of my noise was coming from multiple sources. First a new bass amp that I'm still learning how to control that has a Gain and a Master Volume. And various tone buttons/knobs etc. Too much gain on the preamp (and it's a pretty loud amp) and any noise from the guitar side or cable will be magnified to the speaker. I also switched to a strat I have with humbuckers and plugged it in and it is much more quiet than the Carvin bass. So even though the Carvin uses Humbuckers, I am suspicious that there is a loose ground internally and that is on my list of things to look at.

Add to that, most of my guitar cables are 10 or more years old and I really need to go through them and repair or replace as necessary.

So I think we can call this a resolved issue and I appreciate all the feedback!
Good to hear.
Just to start you off, when using pre/post volume, you want the post volume high and the pre volume low (or the volume you want to play at) for a clean sound.
For a distorted sound (rock/metal), you want to overdrive the input (the pre is higher than the post. Very few bass players distort their sound.

I haven't personally ever liked the 'built' in distortion sound on any amp. A nice pedal does that best. And very few bass players distort their sound anyways. (Although Deep Purple comes to mind)

Your bass may not be shielded (common on cheaper instruments), or the shield wire came off where it is soldered on the the foil.

For this type of stuff, find yourself a good musicians forum. Lots of good info there for signal related stuff. But careful what you rely on with them for thou, most of those guys would have had you buy a $3000 Line conditioner to correct the EGC current noise issue.
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Old 11-19-2019, 02:10 PM   #11
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Re: New Man Cave 60 hz hum in guitar amp


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Good to hear.
Just to start you off, when using pre/post volume, you want the post volume high and the pre volume low (or the volume you want to play at) for a clean sound.
For a distorted sound (rock/metal), you want to overdrive the input (the pre is higher than the post. Very few bass players distort their sound.

I haven't personally ever liked the 'built' in distortion sound on any amp. A nice pedal does that best. And very few bass players distort their sound anyways. (Although Deep Purple comes to mind)

Your bass may not be shielded (common on cheaper instruments), or the shield wire came off where it is soldered on the the foil.

For this type of stuff, find yourself a good musicians forum. Lots of good info there for signal related stuff. But careful what you rely on with them for thou, most of those guys would have had you buy a $3000 Line conditioner to correct the EGC current noise issue.
Well lo and behold I took the plate off the Carvin bass and one of the wires is broken off. A ground wire to a pot. LOL.
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Old 11-20-2019, 11:44 AM   #12
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Re: New Man Cave 60 hz hum in guitar amp


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Well lo and behold I took the plate off the Carvin bass and one of the wires is broken off. A ground wire to a pot. LOL.
Glad you found the potential problem.....but if the problem still persists after you fix the broken wire then you might want to make sure all the electrical equipment in your instruments and sound system is electrically sourced from only one circuit.

Multiple circuits feeding one sound system can cause the ground loop and hum you experienced.

Good luck.
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Old 11-20-2019, 12:47 PM   #13
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Re: New Man Cave 60 hz hum in guitar amp


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Glad you found the potential problem.....but if the problem still persists after you fix the broken wire then you might want to make sure all the electrical equipment in your instruments and sound system is electrically sourced from only one circuit.

Multiple circuits feeding one sound system can cause the ground loop and hum you experienced.

Good luck.
Thanks. Yes that is a good point. And yes that will be the case for me. And that's pretty typical for me. Years ago, in fact in the 70s, I built a quad box extension cord with 8 ft on it. I've been using that forever to source my power from one point and bring it out to my amps/effects etc.
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Old 11-20-2019, 01:19 PM   #14
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Try adding ferrite beads to input cord, power cord etc. You can add them to both ends see if it helps.
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