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Post subject: Bj Hum
Posted: Mon Oct 27, 2008 6:04 am
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I have a new Blues Junior amp that I use with an LP. Recently, the amp has started to hum. The hum gets worse as you increase the volume. I have moved it around my basement and tried different outlets--but same problem. I hums both with both the guitar plugged in and without it plugged in. Though I can control hum when the guitar is plugged in by touching the strings.

So, it the amp picking up interference or is it an issue with the pre-amp tubes? Or something else?


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Posted: Mon Oct 27, 2008 8:57 am
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Most BJ's (and all valve ams!) hum a little bit - a bit of a feature!

Does the hum go after it's warmed up a bit?
have you tried different leads?
this might sound silly - buy one time I took all my tubes out whilst going over the amp, tightening screws etc. I noticed some extra hum when I turned it on. I turned it off, swapped the postition of the 12AX7's and this helped!
(vague advice - but hey, I'm no amp tech!)

Don't get greasy fingers all over the tubes! Use a yellow duster or something.

By the way - I took a photo of my current amp settings for your last post. Any help?

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Posted: Mon Oct 27, 2008 9:06 am
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ian sheridan wrote:
Most BJ's (and all valve ams!) hum a little bit - a bit of a feature!

Does the hum go after it's warmed up a bit?
have you tried different leads?
this might sound silly - buy one time I took all my tubes out whilst going over the amp, tightening screws etc. I noticed some extra hum when I turned it on. I turned it off, swapped the postition of the 12AX7's and this helped!
(vague advice - but hey, I'm no amp tech!)

Don't get greasy fingers all over the tubes! Use a yellow duster or something.

By the way - I took a photo of my current amp settings for your last post. Any help?


The settings helped a lot. Thanks. It only hums once the tubes have warmed up. I am going to take the amp upstairs to see if it is something to do with the wiring in my basement. Before doing so, I will switch the tubes around to see if that helps. It is just strange that this just started happening.


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Posted: Mon Oct 27, 2008 10:51 am
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You said the hum went away when you touch the strings?
That sounds like a grounding issue.

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Posted: Mon Oct 27, 2008 11:01 am
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Right. The hum is there if I don't have the guitar plugged in. The hum is reduced or eliminated when I plug in the guitar and touch the strings. It goes away if I turn the volume all the way down on either the guitar or the amp. The hum increases when I turn up the volume. I have tried different cables and have unplugged my Fulltone OCD pedal and run the guitar straight through. That doesn't seem to make a difference.

My understanding--which is very limited--is that hum that responds to volume increases or decreases is pre-amp tube issue.


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Posted: Mon Oct 27, 2008 6:54 pm
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OK. I am revising my earlier post after playing around with the amp. If there is nothing plugged into the amp is as silent. Once you plug in a cord, the amp begins to hum/hiss--even when there is no guitar on the other end.


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Posted: Tue Oct 28, 2008 7:57 am
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bluemoon wrote:
OK. I am revising my earlier post after playing around with the amp. If there is nothing plugged into the amp is as silent. Once you plug in a cord, the amp begins to hum/hiss--even when there is no guitar on the other end.


Let me guess, it really hums loud if you put your tongue on the end of the lead right?

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Posted: Tue Oct 28, 2008 8:05 am
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ian sheridan wrote:
bluemoon wrote:
OK. I am revising my earlier post after playing around with the amp. If there is nothing plugged into the amp is as silent. Once you plug in a cord, the amp begins to hum/hiss--even when there is no guitar on the other end.


Let me guess, it really hums loud if you put your tongue on the end of the lead right?


Not my tongue...my wife's tongue. Look I understand that if I touch the end of the lead, it will create a hum. That's not the issue.

But the hum is pretty loud with just the cord plugged in (and I am not touching the end of the lead) and it is loud with the guitar plugged in--no strumming. The hum diminishes if I touch the strings. The hum gets louder if I turn up the amp. If nothing is plugged in the amp is pretty silent, even when cranked.

I understand that most tube amps hum--but this hum is pretty loud.


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Posted: Tue Oct 28, 2008 8:07 am
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Cheap lead?

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Posted: Tue Oct 28, 2008 8:12 am
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ian sheridan wrote:
Cheap lead?


It is possible. I switched a few around and it did reduce the hum a little (I think)


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Posted: Tue Oct 28, 2008 8:16 am
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bluemoon wrote:
ian sheridan wrote:
Cheap lead?


It is possible. I switched a few around and it did reduce the hum a little (I think)


So based on the above is the assumption that it is either

1. bad leads
2. bad jack

But not the amp (other than perhaps the jack) and not the guitar.


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Posted: Tue Oct 28, 2008 8:31 am
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I get suspicious when there is no hum. No hum usually equals some kind of stifling!

I like a bit of humming/rattling/chiming. That's where it's all alive and the mojo is flowing.

I'm no jazz player though!

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Posted: Tue Oct 28, 2008 8:37 am
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ian sheridan wrote:
I get suspicious when there is no hum. No hum usually equals some kind of stifling!

I like a bit of humming/rattling/chiming. That's where it's all alive and the mojo is flowing.

I'm no jazz player though!


I can live with it. I might go out and get some news leads this weekend to see if that helps. At first I thought it might be the preamp tubes, but it doesn't sound like it is an amp problem.


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