Author Topic: Single-coil-like hum from an Excel? (Read 665 times)

bsee · « **on:** January 22, 2014, 07:13:40 AM »

So, I have been enjoying getting used to the 2000 Excel fiver I picked up a couple weeks ago. I took it to a gig on Saturday night and I couldn't use it. As soon as I plugged it in, I got an awful hum. The other bass I had with me was a Zon Sonus with single-coil Bartolinis and I had no issue with it as long as I had both pickups on even. If I pushed the pan one way or the other, I got the same hum. I was surprised to get this from an Excel since I thought the pickup was hum-cancelling. I'm wondering if there might be something off with the electronics, or if something else was going on.

This is the same rig I played the Excel through at a rehearsal without an issue. I have also been playing it in the living room through a Baby Blue II and never noticed anything out of the ordinary, though the amp is a bit noisier as it could use a bit of tech love. At least, I didn't notice anything unusual about the noise floor until I looked for it after the gig experience.

The only things that are different that I know of are:
1. The power circuits themselves.
2. I forgot my surge protector for the gig, so it was plugged straight into the wall.
3. The noise sources in the room. Obviously, there's going to be neon and such in a barroom.

The gain is about the same as we keep the stage volume in check when we gig.

Any ideas on what the cause might be or how to combat it?

Thanks!
-bob

lembic76450 · « **Reply #1 on:** January 22, 2014, 09:38:34 AM »

Bob, is there a ferrite bead in the electronics cavity? They help with noise.

http://club.alembic.com/Images/16271/16909.html?1109872910

bsee · « **Reply #2 on:** January 22, 2014, 11:46:29 AM »

I'll do a cavity search. Thanks, Kenn.

mica · « **Reply #3 on:** January 23, 2014, 04:14:00 PM »

Is the hum directional? Can you rotate different directions and find a null? That would indicate the humcanceller is disconnected from the pickup coil and the pickup will have to be replaced.

Or does it increase with the proximity of your hand to the pickup or electronics back? That indicates the pickup may be plugged in backwards. If the friction lock looks right, remove the housing and reverse it (instructions in FAQ). If the friction lock isn't aligned to lock, just plug it in correctly.

bsee · « **Reply #4 on:** January 23, 2014, 09:20:30 PM »

There is a ferrite bead on the wire. I'm iffy on the construction in there, though, because there's nothing to restrain it and the bead is free to flop around. It has enough weight to it that it could bang into the boards attached to the tone controls. The board attached to the treble control has a little bit of wobble to it when touched - not sure if maybe the bead knocked it loose or it is meant to be that way. In any case, is there any reason why there shouldn't be a foam wrap on it to provide a little protection?

As far as I can tell, the hum doesn't react to hand proximity, but it might be directional. I will have to get the full rig set up to confirm, because it just isn't that pronounced in the living room with the Baby Blue to say for sure.

It may be early next week before I know for sure.

Thanks!
-bob

mica · « **Reply #5 on:** January 24, 2014, 05:09:08 AM »

Is the wobble from the board to pot connection or from the bushing of the pot connection to the top wood? The cells of the wood do compress over time under the pressure of the nut, so you may just need to tighten. I'd check all the nuts, including the output jack. Heck, I check the strap pins or locks as well,

There usually is a piece of foam on the ferrite bead, so you should replace that. The adhesive can fail after enough years go by. It's not really for hum rejection, it's for RF.

Let me know if you can find a null. What is strange is that it should be acting like a single coil pickup anywhere if the humcancelling coil became disconnected.

bsee · « **Reply #6 on:** January 24, 2014, 07:39:09 AM »

The wobble is the board vs. the pot. The pots are all solidly connected to the top. It's got maybe a 16th to an 8th inch of play if you manipulate it from the trim pot. The whole board can wiggle, and only in the one plane where you'd expect it to be possible. In any case, I'll look for some foam I can use.

Is there anything that could be going on with power input that could bring about the hum? That was really the only thing different at the gig. I tried to see if it was directional there and it didn't seem to be.

Thanks
-bob

bsee · « **Reply #7 on:** January 26, 2014, 03:05:51 PM »

Looks like the hum is very directional. In the basement with the full rig today, it was prevalent with the pickup facing the amp and gone with it facing away. Looks like I will need to be emailing Mica about what it takes to get a replacement pickup. I may take the opportunity to investigate a replacement for my custom bass and a couple other minor issues while I'm at it....

Thanks all!
-bob

mica · « **Reply #8 on:** January 29, 2014, 04:44:10 PM »

There should be no pot/board wobble at all. The terminals are soldered and there are 2 stabilizing pins that come off the back plate of the pot. Can you see if there are missing solder joints? (!)

bsee · « **Reply #9 on:** January 29, 2014, 05:51:50 PM »

First,Mica, thanks for the cure little package of screws and foam pieces!

I will have to take the pot out to see that.there isn't much extra space there and that board with the trim pot is fairly large. I will take a look when I return home, and see if I can maybe take pics or a short video of the motion.

I should point out as well that the hum is at a fairly high frequency. It's been a while since I experienced single-coil hum, and I don't recall it what frequency it represents with.

Thanks for your continued support!

-Bob

mica · « **Reply #10 on:** January 29, 2014, 06:31:04 PM »

Hum is low frequency, like 60Hz, 120Hz, etc. If it's high frequency, then we are dealing with something else altogether. Does the character of the noise (that's what we'll call it if it's high frequency) change when you change the treble or bass controls?

Glad you got the package!

bsee · « **Reply #11 on:** February 06, 2014, 10:07:30 PM »

Now I'm confused.

At rehearsal, I went about checking details. I found that I only had higher frequency directional noise when within about two feet of the amp head. This noise had the same character as what I had at the gig that started this mess. In that case, though, it was non-directional and distance didn't matter.

I don't recall any change as I rotated controls, but I don't think I was as diligent as I should have been in testing this aspect of the issue. I will do better this weekend.

Is there any possible explanation in the environment, the cabling, or the power feed that could explain the problems at the gig? The fact that my other bass made a very similar noise in that situation when on one single-coil pickup really makes me wonder if it was related to the environment. My other question is whether a potential loose connection in the preamp related to the moving circuit board could have been in a bad connection position at the gig, but was okay at rehearsal? This is a long shot since the issue occurred with either bass at the gig. My guitarist was playing a strat and had no issues, so I am leaning toward a power input issue if that sort of thing could explain it. Maybe a shared ground with some kind of lighting item?

I want to gig this bass, but I need to understand the what went wrong so I can trust it. We've got a Valentines Day show at a new venue and I'll bring it with me for at least a sound check, but I'll be prepared to put it right back down if there's an issue.

Thanks!
-bob

keith_h · « **Reply #12 on:** February 07, 2014, 05:08:21 AM »

If you were near any neon lighting, computers/terminals or motors such as blenders there could be enough interference to appear non-directional. Another area to consider is stage lighting.

Keith

jazzyvee · « **Reply #13 on:** February 07, 2014, 06:16:39 AM »

This may or may not be of any help but its useful to know where the sources of noise may be. When I bought my Series bass guitar a few years back I was plagued with a sizzling noise from it and could not work out what it was.

It never happened on my other guitars but when ever I used the series I guitar I would get this sizzle. Eventually i took the DS-5 to get checked out in case of problem with that and they put in more smoothing capacitors but it made no difference. Eventually I found the cause to be the powerline ethernet over mains adapters I was using to transmit the internet signals round the house. When I turned them off there was no noise problem. These days I have a filter and surge protector mains plug board and recently upgraded the powerline adaptors and even without the mains filter leads they are significantly quieter but not completely silent.

http://www.pcworld.co.uk/gbuk/powerline-home-networking/xx_7090_70097_xx_xx/xx-criteria.html

Jazzyvee

mica · « **Reply #14 on:** February 07, 2014, 01:22:30 PM »

It seems like you should pull the wiggler and make sure there are sound solder connections there. Without overnighting it's not practical to send the guts here before your Feb 14th gig, but do remember there is no charge to test any Alembic product.

Also, 2 feet away? Is it me or isn't that sort of close? Is it possible to stay three feet away (which still seems close to me)?