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Post subject: My BDRI is making strange buzzing noises!
Posted: Mon Jun 27, 2011 5:52 pm
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Hey guys,

I bought a ~ 2008 blues deluxe reissue combo used a couple of months ago. I bought all new tubes for it soon after, and I live in an apartment so sadly I haven't put much time on the tubes at all. Every now and then the amp will make a quiet higher pitched static/buzzing noise. Sometimes this can turn into a VERY loud, lower pitched buzz/hum. The buzz goes away if you turn the standby on, and then off again. This buzz occurs without anything plugged into the input jack or effects loop as well.

I'm hesitant to take it to a tech b/c it's one of those "every now and then" things that of course won't happen when he's looking at it. So, does anyone have any idea what this can be? As you can see I've done a good bit of trouble shooting to try to isolate the problem, but I don't know what could be causing this.

Thanks!

Dylan


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Post subject: Re: My BDRI is making strange buzzing noises!
Posted: Mon Jun 27, 2011 9:24 pm
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Maybe a preamp tube acting up. If you still have one of the original preamp tubes, try it in each preamp position one at a time to see if the noise goes away. Try V1 first. :idea:

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Post subject: Re: My BDRI is making strange buzzing noises!
Posted: Tue Jun 28, 2011 9:24 am
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Yea, the preamp tubes have less than 20 hours of play on them, but one could still be acting up.... The problem is that the buzz goes away if I turn standby on and then off, or if I turn the amp off and then on. So, if I turn the amp off to change out the tube, I won't be able to tell immediately if that fixed the problem, because that always fixes the problem. Is it safe / possible to change out a preamp tube with the amp turned on (and standby off)? That way I could change it while it's actually buzzing, and see what happens.... I feel like I remember reading about pulling tubes with the amp on to try to isolate the problem tube. Is this true?

thanks


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Post subject: Re: My BDRI is making strange buzzing noises!
Posted: Tue Jun 28, 2011 9:50 am
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No, turn off power before removing or installing tubes, we don't want to start calling you "Sparky". It is OK to turn the amp on with the tubes already removed, but don't change tubes with the power on. Besides, the tubes get hot, let them cool before grabbing them. When switching the standby switch, you are removing and reapplying high voltage to the tubes, momentarily stopping the noise. This is why I suspect a preamp tube. It could even be an output tube, but more likely a preamp tube. Yes, it may mean swapping a tube and playing for awhile to see if that one was the problem or not, V1 is the usual suspect, far right tube looking at the back of the amp. :idea:

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Post subject: Re: My BDRI is making strange buzzing noises!
Posted: Tue Jun 28, 2011 2:25 pm
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I thought maybe preamp tube too, but it buzzes with volume all the way down. Does this indicate a power tube instead?

Thanks


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Post subject: Re: My BDRI is making strange buzzing noises!
Posted: Tue Jun 28, 2011 2:32 pm
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Could be. Only one way to find out. :wink: Or, we could just keep guessing.....

- It could be ants.
- Maybe someone has a noise generator and they are just messing with you (I've done this)
- Aliens?

Who knows? Try the preamp tube and work your way up to the output tubes. Or, start with the output tubes, either way. :idea:

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Post subject: Re: My BDRI is making strange buzzing noises!
Posted: Tue Jun 28, 2011 2:41 pm
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shimmilou wrote:
Maybe someone has a noise generator and they are just messing with you (I've done this)


Me too.

H-P signal generator, 20-watt linear amp, feedhorn concealed in a tree.

Lotta fun, lotta fun!

:lol: :lol: :lol:

Arjay (the vengeful neighborhood Tesla)

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Post subject: Re: My BDRI is making strange buzzing noises!
Posted: Sun Jul 03, 2011 3:49 pm
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I thought tubes at first too, just because they're the usual suspect. However, I've had tubes go bad before, and this sounds much more like a 60Hz hum or grounding issue... The strangest and most important clue to me is that when you turn standby off and then back on, the buzz stops. Something about flipping the switch off and on fixes it. Is there possibly any connection between that and a grounding issue, bad solder joint, etc? I'm just trying to find another way to figure this out than changing tubes, because the problem occurs very infrequently, and I don't play enough to find out if my tube swap has made a difference. A trial and error tube swap, when the problem only occurs every couple hours of playing time, could be a very timely and possibly unfruitful process. If it comes down to this I guess I'll have to try it, but any other trouble shooting ideas will be appreciated as well.

Thanks


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Post subject: Re: My BDRI is making strange buzzing noises!
Posted: Sun Jul 03, 2011 4:02 pm
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dgcobb wrote:
The strangest and most important clue to me is that when you turn standby off and then back on, the buzz stops. Something about flipping the switch off and on fixes it.


The most significant thing that occurs when the amp is switched into standby is the B+ voltage to the power tubes is interrupted. Your symptom (a recurrent buzz that ceases when the amp is cycled into standby and back to operate) would point me to the power supply -- possibly a filter cap heading south. Fender's OEM filter caps are not premium components and their durability is a ever-diminishing finite quantity -- the newer amps more susceptible than older models, it seems.

Arjay

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Post subject: Re: My BDRI is making strange buzzing noises!
Posted: Mon Jul 04, 2011 7:04 am
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Good suggestion Retroverbial,

However, if changing preamp tubes is too much trouble for the OP, and he doesn't want to take the amp to a tech, then it would be near impossible for him to change the filter caps. I think that he may be looking for a magic incantation that requires no effort. :?

Maybe there are some druids among the forum members that can help. :lol:

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Post subject: Re: My BDRI is making strange buzzing noises!
Posted: Mon Jul 04, 2011 2:52 pm
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AbraCaDabra. Shazamm. Kalamazoo. Amp noise be gone!

Did it work? :lol:

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Post subject: Re: My BDRI is making strange buzzing noises!
Posted: Fri Jul 08, 2011 9:37 am
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Thanks Arjay. Your answer really helps me narrow this down. I may end up taking it to a tech and giving him the advice you gave me. If I knew how to change a filter cap I'd just go ahead and do it.

It's not that changing preamp tubes is too much work. I've changed my fair share of tubes, and it only takes a second. It's that I wouldn't be able to tell if changing the tubes worked or not b/c the problem occurs so infrequently, and therefore I wouldn't be able to isolate which tube is bad. So changing the tubes might just be a waste of time. Also, I just don't think it's a tube issue b/c these tubes are basically brand new, and it frankly doesn't sound like a tube issue (I've had my fair share of those too).

I'm with Arjay on it being a power issue. I've heard a similar noise coming from equipment with grounding issues before, and that is what this sounds like. However, I don't know much technical stuff, so I can't begin to isolate what would be causing a grounding issue with my amp. Filter cap.... anything else? I just want get a good grasp of my issue, and isolate this to a few possibilities so I know what to tell a tech to look for.

Thanks


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Post subject: Re: My BDRI is making strange buzzing noises!
Posted: Fri Jul 08, 2011 10:23 am
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While there may be grounding issues at play, filter caps are an altogether different situation. It works thus: the AC line voltage hits the amp's power supply tranny first, where it is stepped up in amplitude and farmed out to various sub-circuits in the chassis via multiple taps on the tranny's secondary winding. The high-voltage portion is routed to the rectifier (either a tube or a solid-state diode stack) to be converted to DC. However, the output from the rectifier is not pure DC (yet) -- it still contains some AC "ripple" voltage which, if not removed, will cause a number of problems. So after rectification, this high voltage is passed through a bank of capacitors which filter out the AC ripple and shunt it to ground, while the "purified" DC is then ready to be applied to the tubes. A voltage-dividing network within the filter-cap section provides the correct amount to be used by the plates, cathodes, grids, etc. If a filter cap goes bad or becomes weak, the voltage it provides is no longer usable to the components which rely on it. In a worst-case scenario, the cap shorts directly to ground and the runaway voltage destroys anything in its path (until finally the fuse, thermo-coupler, or circuit breaker blows, which by then is likely too late).

HTH

Arjay

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Post subject: Re: My BDRI is making strange buzzing noises!
Posted: Fri Jul 08, 2011 1:07 pm
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Cheap fix if your building has iffy power - Ebtech makes an isolated power thingy called Hum X. When faced with buzzing amps, plugging this inline can sometimes get rid of the buzz.

Please note that this is transformer isolated power and not the same as lifting the ground.

At $60, great for the gig bag for bars with questionable power. Has eliminated buzzing noises in amps that were fine in other places.

http://www.ebtechaudio.com/humxdes.html

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Post subject: Re: My BDRI is making strange buzzing noises!
Posted: Fri Jul 08, 2011 1:40 pm
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nedorama wrote:
Cheap fix if your building has iffy power - Ebtech makes an isolated power thingy called Hum X. When faced with buzzing amps, plugging this inline can sometimes get rid of the buzz.

Please note that this is transformer isolated power and not the same as lifting the ground.

At $60, great for the gig bag for bars with questionable power. Has eliminated buzzing noises in amps that were fine in other places.

http://www.ebtechaudio.com/humxdes.html


+1

My Furman performs similar functions.

Arjay

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