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SnailSpace View Drop Down
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    Posted: 11 February 2024 at 5:08pm
Hello everyone,
Long time no see! So since I last posted I’ve generally been running my system quite low and tinkering with EQ and it all seemed nice but I recently had some Feedback/grouding issue with my Shure Head Cart, it was only in testing the cart on different Turntable, Channels etc to diagnose if it was cartridge or system I noticed another problem.
One of my channels on my Behringer NU6000 INuke used for x4 Bass that I noticed a hum on just one of the channels when turned up full gives off a hum.
The Amp was bought second hand and I can’t remember if I tested it with a single Bass speaker at full Volume at the time so not sure if it was an existing amp problem.
I’ve checked all my leads when setting up.
I’ve had a quick swap of Channel A & B leads to see if it isolated the problem but still exists.
As I have short runs on a patch panel fan out I presume I need to test speakers with a straight cable run to channel to find out if there is a problem with the patch cables.

I suppose my question is what are common problems that cause Hum on Bass amps?


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Conanski View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Conanski Quote  Post ReplyReply Direct Link To This Post Posted: 11 February 2024 at 7:14pm
Disconnect everthing from the amp except the speakers, is there still a hum?
If yes the problem is internal to the amp.
If no then the problem is with one of the signal cables or an upstream device.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SnailSpace Quote  Post ReplyReply Direct Link To This Post Posted: 11 February 2024 at 7:45pm
The only other thing going in is the DSP, didn’t think to try the DSP output.
Ok makes sense Check DSP Outs and then check channels direct to speakers.

Ok will do some further trouble shooting!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SnailSpace Quote  Post ReplyReply Direct Link To This Post Posted: 10 March 2024 at 12:26am
Okay so it’s not a hum!

 I thought a Hum was coming from my Bass amp but I isolated each amp/channel and with all other amps off I have located it to a speaker effecting the sound.

So when I played a song with just the Bass amp on one of my Mid speakers in the dual box (215s) also reacted and it had a signal coming through when I crank the channel on the Bass?

It sounded like a crunchy wobble I thought it could be torn but no it’s ok not torn - it is distortion.

Channel One on the amp (the Left stack) is clean but Channel Two on the amp (the Right stack) the Left Mid is alive whilst using Bass Amp.

So I then isolated the Mid and ran just that Mid amp and tried each channel and it’s definitely the Right Side Stack and Left Speaker in my 215.

Does this hint to a wiring problem internally in the 215 box or with it coming through on and effecting the Bass amp/channel does it point to something on the Patch Panel Fan out sharing a Speakon plug maybe? If one wasn’t properly insulated and touching the other? Could that cause distortion?

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Post Options Post Options   Thanks (0) Thanks(0)   Quote RoadRunnersDust Quote  Post ReplyReply Direct Link To This Post Posted: 10 March 2024 at 12:48am
Probably means you’ve smashed the VC into the backplate of the magnet and deformed the former
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SnailSpace Quote  Post ReplyReply Direct Link To This Post Posted: 10 March 2024 at 1:10am
Sorry could you break that down Roadrunners dust? The VC? Deformed the former?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RoadRunnersDust Quote  Post ReplyReply Direct Link To This Post Posted: 10 March 2024 at 1:39am
Voice Coil

The former is the cylinder of material that the voice coil wire is wound around. If it gets deformed then it causes buzzes, scraping noises, etc.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SnailSpace Quote  Post ReplyReply Direct Link To This Post Posted: 10 March 2024 at 2:02am
How could I have done that?

 What causes that? Physical handling or wiring?

 Does that mean I need a new driver?

(The driver may have already been like that maybe I just haven’t noticed it until recent maybe?)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RoadRunnersDust Quote  Post ReplyReply Direct Link To This Post Posted: 10 March 2024 at 2:19am
Over-excursion usually, either too much power or too low a frequency 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SnailSpace Quote  Post ReplyReply Direct Link To This Post Posted: 10 March 2024 at 2:46am
Maybe it was already damaged before I fit it as I can’t understand how I would have over excerted it as I’ve been running everything very low so as not to damage anything!

Also why is it doing it when I tested just the Bass Amp with all other amps turned off? 

 Can it be repaired?(I feel like I need to sit down for this news :( ha!)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Conanski Quote  Post ReplyReply Direct Link To This Post Posted: 10 March 2024 at 3:03am
Originally posted by SnailSpace SnailSpace wrote:

So I then isolated the Mid and ran just that Mid amp and tried each channel and it’s definitely the Right Side Stack and Left Speaker in my 215.
So one of 2 drivers in the same box is noisy? If so that potentially indicates a damaged driver, these were bought used correct so it's anybodys guess how they were treated. 

What model is this driver... are they Peavey? 
Few things you can do... 

1. Put a little chalk mark on the frame edge of driver to inticate which side is at the top. Now remove the driver and check that the tinsel leads aren't touching the cone, if they are bend them back a little and reinstall the driver. Is the noise gone?
2. If the tinsel leads are not touching the cone, rotate the driver 180 degrees and reinstall it with that mark at the bottom. Sometimes the suspension of old drivers will sag and allow the voice coil to rub slightly, and rotating the driver can relieve it. 
3. If the driver is a Peavey with the field replacable baskets, it will have 3 bolts attaching the magnet to the basket. Mark the magnet and frame so you know which orientation it currently has, unbolt the bagnet and lift it off. Inspect the voice coil for signs of rubbing, and clean out the gap in the magnet with a piece of masking tape folded back on itself so it's sticky on both sides, any debris in the gap can cause rubbing noises. With that done bolt the magnet and basket back together but rotate the magnet 60deg from where it was, and reinstall the driver for testing. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SnailSpace Quote  Post ReplyReply Direct Link To This Post Posted: 10 March 2024 at 3:21am
Ok thanks RoadRunnersDust & Conanski, I did take a look at replacements, Baskets & repair kits and I think it’s pot luck if they came on the market as a driver or basket and repair kits are discontinued and a recommended alternative and £150! At that price I’d just look for a pair on the market.

But before any of that I will try the tests/cleaning method put forward by Conanski first!

Thanks 
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