Scratchy rattling resonance - diyAudio
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Old 11th September 2013, 01:18 AM   #1
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Default Scratchy rattling resonance

Hi newbie here.
While I have built a couple of guitar pedals and mic pre's I know jack about tube guitar amps.
I got a Peavy Valve King Royal8 5 watt class A design tube amp for recording used.
It only has two tubes, the pre/ pwr amp.
I'd like to be able to mod it a little but right now it has the Scratchy rattling resonance when I hold a chord or play the low end strings. It sneaks in after the initial strung pluck.
If I back the gain and volume down it is clean and sounds okay. Turn up to not even half way and in comes the resonance.

The volume brings out this rattling noise more than the gain, so too the tone control shunt to ground.

I have new tubes in it. They aren't vibrating. The amp is connected to a larger ext speaker.

I was hoping someone might know what this is a symtom of or a ball park idea on what to check as I need to fix it before making mods.

The cost of decent amps is beyond me and I don't really need lots of watts and weight for recording.

Thank you for reading

Last edited by Jinks; 13th September 2013 at 02:57 PM.
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Old 11th September 2013, 09:50 AM   #2
DF96 is offline DF96  England
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Should be in Instruments and Amps forum.

Click on the red triangle and ask the Mods to move it.
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Old 11th September 2013, 11:44 AM   #3
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Is the resonance also present withouth the input cable? And with other speaker?

This is to determine if the amp is in trouble per se or in the interaction with the other parts.

Good luck‼
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Old 11th September 2013, 12:39 PM   #4
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Hi Osvaldo,
not when guitar and cable not connected only usual hiss and hum.
Yes I thought was speaker at first but two other known good speakers still apparent. more so when lowering vol on guitar to clean it up a bit(not so much crunch)

Last edited by Jinks; 11th September 2013 at 12:43 PM.
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Old 11th September 2013, 01:11 PM   #5
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Sorry, I'm not musician, so I ignore the meanings of terms as scratchy, hash, etc.

Then, if when no cable to guitar the trouble disappears, then:
1) there is any undesirable interaction between them,
2) there is a short or open cable then receiving some kind of noise from the amplifier or any other source (AM FM Station for example), the causing the amp to oscillate.

Then, I suggest to test the amp with any other audio source: a radio, a microphone, etc, to test the amp itself.
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Old 11th September 2013, 11:10 PM   #6
kevinkr is offline kevinkr  United States
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Note if you have not gone through and replaced all electrolytics and any bad caps and resistors this could contribute to your issues.
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Old 12th September 2013, 06:30 AM   #7
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Thanks kevin, there is a possibility that the amp is a few years old though looks as new.
i guess if I replace them I can think about changing values to get a better tone.

Osvaldo, I have shielded my guitars and it does it on any I try with any cable I use. It also does it if I use an isolating transformer on the mains power or not.
I don't think it is an interference on the mains power line into the amp.

There is a fluro light in the kitchen down the hall. I'll turn it off and see just to make sure. Also I am on a completely different electrical circuit to the rest of the house
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Old 12th September 2013, 12:29 PM   #8
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As ham radio since 1987 and Electronic Engineer, I saw that fluorescent lamps sometimes generate EMI in radio receivers, but never in an audio amplifier. But actually I can't discard any hypothesis, mainly if you have those ******* electronic ballast in the lamp.
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Old 13th September 2013, 07:19 AM   #9
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I should also describe this rattling scratchy ticking buzz.
It comes in after a single strum on the strings holding the chord and stops before the final decay of the strum.

With no fluro lights it is still present.

most likely a failing component.

Looks like the solution is to upgrade components and make some mods.
I'd be better off building a better design! LOLOL.
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Old 13th September 2013, 12:12 PM   #10
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If the trouble appears after some time, it should be a defective component, try to replace electrolytics first. No need for mods, with only find defective element is sufficient.
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