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Post subject: Fender Twin hum
Posted: Wed May 22, 2013 2:44 pm
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Recently I had all the tubes changed on my Fender Twin (red knobbed evil twin), but the same hum is still there. Is this normal? It seems like a lot of noise.

It doesn't matter which input I plug into, the hum is there.

I'm wondering if it's a grounding issue, or how/what to do to fix it.

I took a video of my amp, so you can hear the hum, to advise me: http://www.youtube.com/watch?v=ad_mXkUEqIM

Here are the specs for my particular combo: http://ampwares.com/amplifiers/fender-twin-red-knob-the-twin/

Schematics: http://ampwares.com/schematics/the_twin.pdf

Manual: http://ampwares.com/schematics/TheTwin_Owners_Manual.pdf


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Post subject: Re: Fender Twin hum
Posted: Wed May 22, 2013 2:51 pm
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Check the power supply caps.

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Post subject: Re: Fender Twin hum
Posted: Wed May 22, 2013 3:18 pm
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bluesky636 wrote:
Check the power supply caps.


How do I do that?


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Post subject: Re: Fender Twin hum
Posted: Wed May 22, 2013 3:36 pm
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Well, I would use an oscilloscope or DMM to see how much AC ripple was present across the caps. Or you could take it to a good amp tech. :wink:

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Post subject: Re: Fender Twin hum
Posted: Wed May 22, 2013 3:36 pm
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Do not look to me a fiter capacitor problem . Filter cap problem sound more bassy, 60 hz frequency . Look like you have some noise from neon light , halogene or something outside of the amp.

Or is a noisy preamp tube (s) .

Try the amp in other room . Are you sure electrical wall outlet is grounded , amp is grounded?

No mod in the amp or work before ?


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Post subject: Re: Fender Twin hum
Posted: Wed May 22, 2013 3:44 pm
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stratele52 wrote:
Do not look to me a fiter capacitor problem . Filter cap problem sound more bassy, 60 hz frequency . Look like you have some noise from neon light , halogene or something outside of the amp.

Or is a noisy preamp tube (s) .

Try the amp in other room . Are you sure electrical wall outlet is grounded , amp is grounded?

No mod in the amp or work before ?


AC power supply ripple is 120 Hz.

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Post subject: Re: Fender Twin hum
Posted: Wed May 22, 2013 4:20 pm
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stratele52 wrote:
Try the amp in other room . Are you sure electrical wall outlet is grounded , amp is grounded?


It sounds the same in every room. The wall outlets are grounded, for sure. The power wire coming off the twin as 3 prongs. What else can I do to check if the amp is grounded?

stratele52 wrote:
No mod in the amp or work before ?


No mods. I think this amp has always made a hum. It just gets soooo loud, that the hum is insignificant when playing loud, but I don't want to hear it anymore when I stop playing.


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Post subject: Re: Fender Twin hum
Posted: Wed May 22, 2013 4:24 pm
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If it bothers you and you are not capable of troubleshooting and repairing it yourself, take it to a good amp tech.

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Post subject: Re: Fender Twin hum
Posted: Wed May 22, 2013 7:49 pm
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Is that amount of noise normal for a combo like this, or is there something wrong?


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Post subject: Re: Fender Twin hum
Posted: Wed May 22, 2013 8:49 pm
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Definitely louder than any of my amps. The fact that the volume controls have no effect on the hum and it is common to both channels points to something after the volume controls that is common to both channels, either a tube or the power supply.

http://ampwares.com/schematics/the_twin.pdf

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Post subject: Re: Fender Twin hum
Posted: Thu May 23, 2013 6:34 pm
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I took it in to my local shop for repair today. Thanks


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Post subject: Re: Fender Twin hum
Posted: Thu May 23, 2013 8:47 pm
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Hope everything works out.

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