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Post subject: Odd Amp Noise
Posted: Wed Oct 06, 2010 12:18 pm
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At least I think it is an amp noise. The amp is a Blues Deluxe Reissue with JJ tubes from Eurotubes. The 6L6GCs are biased at about 38 mA per tube at a plate voltage of about 406 volts. The speaker is stock.

Lately I have noticed an underlying "fizz" in the sound. It only occurs on the octave "A" at the 12th fret of the fifth string. You can hear it in both the clean and drive channel. Other then that single note, the amp sounds perfect. It is not fret buzz. I have also "de-buzzed" my room (although an occasional, random buzz appears if I crank the volume). It is not a microphonic tube. I have tapped each tube with the eraser end of a pencil and they are dead quiet. The noise is very faint but does rise and fall with volume changes. Again, I want to stress, it is only on that one note. Any suggestions on what to do besides a change in my medication? :lol:

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Posted: Wed Oct 06, 2010 12:28 pm
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Hi Bluesky,

It could be problem with the speaker (few months ago I've got and issue with my BDRI, noise with 1 valve and kind of saturation on G 3rd fret on E cord --> speaker). Try on another speaker if possible, however it could be a valve issue, microphonic is not only detectable by taping the valve.
Let us know.

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Posted: Wed Oct 06, 2010 7:38 pm
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Hi bluesky636,

This might sound strange, but it could be the chassis resonating. Since it only happens on that certain note, it could be a "sympathetic" vibration of something loose. Make sure that all of the chassis mounting screws are very tight, and the tube socket mounting screws too. Anything that's loose on the amp can vibrate only at certain notes. I am going by your description of the noise, it sounds just like a problem that I had on my little champ. I found that I could stop the "fizzy" secondary noise by pushing in on the bottom of the chassis. Tightening the screws got rid of the noise. Just a thought. :idea:

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Posted: Wed Oct 06, 2010 7:49 pm
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My HRDlx had a fizz and more fizz channel until I changed the tubes out. JJ's got rid of mine. Try touching the tubes one at a time with an eraser while playing the note. If it stops, it may just be tube rattle. Could be "cone cry" too.

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Post subject: PROBLEM SOLVED!
Posted: Wed Oct 06, 2010 10:14 pm
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shimmilou wins the prize for guessing closest to what the problem was.

I picked up the amp (No mean feat given the condition of my back!) and put it on my bench. I hit the problem note and there was the fizz underlying the note. So I pulled the back cover and swapped out V1 with the original GT 12AX7. I hit the problem note and the fizz was gone! I put the cover back on and put the amp back on the cabinet where it sits. I hit the problem note again and ..... damn! It sounds worse than before. :x

Back up on the bench she goes. I pull the back cover and replace the GT 12AX7 with the JJ ECC83S. I hit the note ..... and the fizz is gone. Put the cover back on, hit the note .... and the fizz is back. Hmmm. :?

I pull the cover again and start hitting the problem note. No fizz until I hit the string really hard when I heard a different buzz. All this time my wife must be wondering "What the hell song is he playing?" :lol:

So I start looking at the chassis and wiring harness. Hmmm. That harness really sticks out from the chassis. I run a straight edge sideways across the back of the chassis and notice that the edge hits several wiring harnesses and tie wrap heads. So I redressed all of the harnesses and rotated the tie wrap heads away from the back panel. And yes, the amp was unplugged and the caps drained while I did this. Running the straight edage across the chassis again showed nothing touching. I then remounted the back panel, but I also included a metal washer on the inside of the panel at each screw to space the back panel out a little bit while still maintaining electrical countact with the shielding foil on the back side of the panel.

I hit the problem note .... and no fizz! :) I placed the amp back on the cabinet, hit the note .... and no fizz! :D Problem solved! :D :D :D :D

So what does shimmilou get for a prize for being closest to solving my problem? Well, you can pick any Masterbuilt Strat you like and I will buy it for you. 8)


















Just kidding, but thanks for everyone's suggestions. :lol:

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Last edited by bluesky636 on Thu Oct 07, 2010 10:09 am, edited 1 time in total.

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Posted: Wed Oct 06, 2010 10:19 pm
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+1 to all recommendations thus far. I'd add checking the cabinet's baffle board and the speaker itself for loose mounting screws. The offending noise may be mechanical in nature rather than electronic, but it could be a microphonic tube. My '65 Princeton Reverb had a similar noise issue a while back -- a weird buzz on the low F#, G, Ab, and A notes only, played on a low E string. After troubleshooting with a wooden popsicle stick I discovered that one of the amp's original 6V6's had finally given up the ghost. After replacing both power tubes with another NOS matched pair, the noise vanished and never returned.

Best of luck, HTH

Arjay

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Posted: Wed Oct 06, 2010 10:36 pm
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Retroverbial wrote:
+1 to all recommendations thus far. I'd add checking the cabinet's baffle board and the speaker itself for loose mounting screws. The offending noise may be mechanical in nature rather than electronic, but it could be a microphonic tube. My '65 Princeton Reverb had a similar noise issue a while back -- a weird buzz on the low F#, G, Ab, and A notes only, played on a low E string. After troubleshooting with a wooden popsicle stick I discovered that one of the amp's original 6V6's had finally given up the ghost. After replacing both power tubes with another NOS matched pair, the noise vanished and never returned.

Best of luck, HTH

Arjay


Look just above your post. I posted the solution to the problem 5 minutes before you posted. :lol:

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Posted: Wed Oct 06, 2010 10:43 pm
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A day late and a couple of bucks short!

The story of my life, Bill!

:mrgreen:

Arjay

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Posted: Wed Oct 06, 2010 10:46 pm
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Hey man, I think you found the mystery resonance spike of your cab and guitar, that tickles a tube. Seriously, if the tube elements are at all loose, they can vibrate in sympathy at a certain frequency, like Shimmilou suggests. This is also affected by the resonance of your guitar. Looks like A(3) at 220hz, if your at standard tuning. I've had this happen with my guitar at D(3)293.656hz. It's pretty amazing to me, all of the things that have to come together to have this happen, synergy ! Fizz in the speaker would be a different story, but their resonance spike is usually around 100hz. Have you tried another cab ? Art LOL I've got to stop overthinking these problems and type faster. Glad you got it fixed !

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Posted: Thu Oct 07, 2010 10:15 am
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What is interesting is that the vibration was apparently not just causing a problem with that one note. Since my fix, I notice that all notes around the 12th fret and above are cleaner sounding.

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Posted: Wed Oct 13, 2010 3:56 pm
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bluesky636 wrote:
What is interesting is that the vibration was apparently not just causing a problem with that one note. Since my fix, I notice that all notes around the 12th fret and above are cleaner sounding.

This was good info, Bluesky.
Thanks for linking back to it.


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Post subject: Re: Odd Amp Noise
Posted: Tue Mar 27, 2012 4:09 pm
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I have a BDRI, and have the exact same fizz sound when I play an open A string. Tried different cables, different guitars, no matter. Taking a look at your solution now, hopefully is solves my issue...

Thanks!


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Post subject: Re: Odd Amp Noise
Posted: Mon Aug 13, 2012 1:45 pm
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I was convinced I had a power tube buzzing. It seemed to stop when I pressed with an eraser. Got a new set of tubes, same issue. So I have lived with it for a while, and got fed up last weekend. Took the chassis out and tightened every screw i could find. Most were very tight. There were two on the back side of the smaller transformer that were a bit loose. Also, the metal baffle around the speaker had several loose, that you can't get to without removing the chassis. Also found a guitar pick floating around in the cab.

Put it all back together, warmed it up and unleashed a series of A5's. Nothing is rattling or buzzing now except the dishes in the kitchen.

I don't know which screws were causing it, but after several hours of playing over the weekend I have no more strange fizzy sounds. I will sleep better now.


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Post subject: Re: Odd Amp Noise
Posted: Mon Aug 13, 2012 2:21 pm
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jpeake wrote:
Put it all back together, warmed it up and unleashed a series of A5's. Nothing is rattling or buzzing now except the dishes in the kitchen.

I don't know which screws were causing it, but after several hours of playing over the weekend I have no more strange fizzy sounds. I will sleep better now.


Outstanding.

Rawk on!

8)

Arjay

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Post subject: Re: Odd Amp Noise
Posted: Tue Aug 14, 2012 5:53 am
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A lot of people don't even think about tightening up screws on their amps an guitars, but it is an important thing to do. People forget how much vibration goes through there! I just tigtened up the whammy bar on my Strat and it seems to have helped with the tuning stability on it, of all things! I think most techs will tell you that one of the last things they will do on any guitar or amp repair is generally tighten things up.

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