I have a problem with a piezo pickup harness kit (from CB Gitty) I wired up. In short, it sounds great when the volume pot is turned all the way up, but when turned down just a little, there is a very distracting hum.
I have spent hours pouring over the forums looking for leads, and can tell you this:
* I have quadruple-checked each connection, the schematic, and have a solid solder joint grounded to the back of the pot which I sanded beforehand.
* I seriously doubt I cooked the pot. I am using a 25W soldering iron and it takes a while before any connector is hot enough to solder.
* a wires were tinned before soldering.
* When I run an extra ground jumper between the input jack and back of the pot, there is no change.
*The hum disappears when my hand touches the input jack, and the noise gets noticeable louder when I grab the pair of wires going from the jack to the pot.
* Wiggling wires and connections makes no change.
*There is no change when I try my amp In another outlet, another house circuit, straight to the wall, or with a surge protector.
* Another guitar with a preamp going through the same cords to the same amp makes no hum at all.
I am stumped. I am beginning to wonder if it is a bad pot. Any help would be appreciated.
Hi Scott,
I don't know if your issue has been resolved--too many sub-replies to filter through.
If it has, then let my reply be of use to others stumpling upon this thread.
Two possible issues I can see here.
1. I saw no mention of you grounding the guitar to itself.
This is paramount in ANY electric guitar. In solid bodies, we solder a wire from the volume pot to a screw we put in a body cavity somewhere. On a tremolo guitar--that wire is soldered to the spring claw.
On a CBG, you would use the same technique. Find a spot inside the box, drill in a small wood screw and solder a wire from the volume pot to that.
2. I don't know how long your wire harness is, but the longer the wires are--the better chance of hum.
The prime suspect is usually the leads going from your volume pot to output jack. Make sure they are as short as possible.
In solid bodies, we shield our cavities with either condyctive paint or copper foil.
Not practical in s CBG, so try this trick: insulate the entire harness with a sheet of copper foil.
just lay it over the whole harness and adhere it to the surrounding wood.
Thanks, Bernie. With the advice of others,I was able to resolve the hum problem. I likely had more than one issue, but the problem was resolved by grounding the amp which did not have a ground prong from the manufacturer (a peavey from the 80's). I was also likely wrestling with a cold joint on the back of the pot from an under-powered soldering iron, and my leads to the jack were likely too long. Now, it sounds fantastic. Thanks for the advice!
The hum seems to be resolved, and it appears there may have been more than one issue causing it. When i first started trouble-shooting, I fixed what was likely a cold joint, and that improved the buzz, but it was still bothersome. Just to be sure, I changed the piezo (had another on hand) and didn't get improvement. I shortened the twisted wires from the pot to the jack from about 12" down to about 4"(somewhere I read a description of a commercial piezo harness with 12" of wire for easy placement in any guitar, so I thought 12" would be fine). That seemed to have helped quite a bit, but there was still a hum.
Also, in tracing the ground all the way back to the power source, I discovered my old peavey amp from the late '80s did not have a three-prong ground wire plug so I upgraded that to a modern power cord with a solid ground to the metal frame of the amp.
Now, the only time I get a hum is when the amp is cranked to 11 and the pot on the CBG is < 8 or 9. Even then, the hum is greatly reduced from when I started trouble shooting. It sounds great and I'm hum-free if the amp is below 10, regardless of where the pot on the CBG is set. And now, my amp is safer and I have some experience under my belt.
Thanks to everyone for their advice, especially @Ron "Oily" Sprague for his numerous suggestions,
I just wanted to thank everyone again for all of your help in getting rid of that distracting hum. I have been playing around with my new CBG and am thrilled with how great it sounds. The piezo is still a little hot on the treble, but i love the results overall. A liitle volume from the amp and some mellowing through a chorus pedal makes this old cedar box sound amazing. Of course, now I have plans for a few others, an amp, a stomp box, and, and, and....
many thanks for starting and working through this thread. I have had the same issue on both of my 'electrified' builds so far. Based on your checklist I am working my way through and hopefully going to significantly reduce my hum too!
I also thank those who have imparted your knowledge it why I love this site! always willing to share and problem solve!
The only way I was able to work through it was with the advice of experienced people who offered their insight -- great people. I can tell you two things: 1. It is so much more enjoyable to play with the hum gone. 2. I am pretty confident I had multiple issues and am almost certain a main issue was an under- powered soldering iron that could barely reach melting point, especially given the mass of the pot (25 watts). I experienced a significant improvement when I went to a much higher wattage. With the amp grounded, it totally went away. In that regard, this thread is misnamed :)
Keep at it -- it will be worth it. By the way, are you using a 3rd-hand to keep the joints immobile when you solder?
not using a 3rd hand but i have drilled some holes in a scrap bit of wood and pushed the pot and jack into them so that they are held firm. bought a soldering iron with adjustable temperature, went over my joints again while doing that i discovered my rookie mistake. I had soldered the wire the wrong way round on the jack. as it was a second hand batch given to me by a friend I foolishly though that the black wire he already had soldered on to them was on the correct lug. swapped that over and all fixed (feeling a bit sheepish)
as a side note my wife was annoyed that I was on here reading up when I should've been working....until I was able to go and fix the problem. she now asks why I hadn't checked on here in the first place. haha
Well, it would appear tht I have about 1 Ohm of resistance (if I'm correct) though each joint and circuit with the pot on full. The only solder joints I have not yet checked are at the leads connecting to the piezo disc's leads. I covered those fragile leads/joints with shrink tubing, but it looks like I need to carefully disassemble to check those joints. Resistance though the pot appears to steadily change from 1 to 1k at the jack when the knob is turned.
Replies
I don't know if your issue has been resolved--too many sub-replies to filter through.
If it has, then let my reply be of use to others stumpling upon this thread.
Two possible issues I can see here.
1. I saw no mention of you grounding the guitar to itself.
This is paramount in ANY electric guitar. In solid bodies, we solder a wire from the volume pot to a screw we put in a body cavity somewhere. On a tremolo guitar--that wire is soldered to the spring claw.
On a CBG, you would use the same technique. Find a spot inside the box, drill in a small wood screw and solder a wire from the volume pot to that.
2. I don't know how long your wire harness is, but the longer the wires are--the better chance of hum.
The prime suspect is usually the leads going from your volume pot to output jack. Make sure they are as short as possible.
In solid bodies, we shield our cavities with either condyctive paint or copper foil.
Not practical in s CBG, so try this trick: insulate the entire harness with a sheet of copper foil.
just lay it over the whole harness and adhere it to the surrounding wood.
Hope that helps.
Also, in tracing the ground all the way back to the power source, I discovered my old peavey amp from the late '80s did not have a three-prong ground wire plug so I upgraded that to a modern power cord with a solid ground to the metal frame of the amp.
Now, the only time I get a hum is when the amp is cranked to 11 and the pot on the CBG is < 8 or 9. Even then, the hum is greatly reduced from when I started trouble shooting. It sounds great and I'm hum-free if the amp is below 10, regardless of where the pot on the CBG is set. And now, my amp is safer and I have some experience under my belt.
Thanks to everyone for their advice, especially @Ron "Oily" Sprague for his numerous suggestions,
Anyway, you people rock. Thanks again!
Scott,
many thanks for starting and working through this thread. I have had the same issue on both of my 'electrified' builds so far. Based on your checklist I am working my way through and hopefully going to significantly reduce my hum too!
I also thank those who have imparted your knowledge it why I love this site! always willing to share and problem solve!
Keep at it -- it will be worth it. By the way, are you using a 3rd-hand to keep the joints immobile when you solder?
not using a 3rd hand but i have drilled some holes in a scrap bit of wood and pushed the pot and jack into them so that they are held firm. bought a soldering iron with adjustable temperature, went over my joints again while doing that i discovered my rookie mistake. I had soldered the wire the wrong way round on the jack. as it was a second hand batch given to me by a friend I foolishly though that the black wire he already had soldered on to them was on the correct lug. swapped that over and all fixed (feeling a bit sheepish)
as a side note my wife was annoyed that I was on here reading up when I should've been working....until I was able to go and fix the problem. she now asks why I hadn't checked on here in the first place. haha
! Can't live with 'em, can't shoot 'em...
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