Can a choke "buzz"?

[tubenit]

Is it possible for a choke to buzz from speaker vibration?  What I mean by buzz is a buzz that is in the signal path and heard thru the speaker vs. a buzz that is mechanical and not in the signal path & not heard thru the speaker.

I don't normally think of the choke being in the signal path (like I would a capacitor being in the signal path), but I've seen B+ rail problems impact the signal before by creating oscillations.

I can resolve the buzz by pressing my finger or a pencil eraser gently on the choke most easily.  I can resolve the buzz by pushing gently in the middle (not sides or edges) of the chassis front panel, back panel or top. So something is being vibrated to buzz when the chassis is in the combo cab. Pressing gently on the choke or gently pulling up on the choke seems the easiest and most effective way of silencing the buzz.

As best as I can tell I've isolated this buzz to being more likely the choke (or a "microphonic" capacitor on the layout board).  It is only on the open A note/string on the guitar and is only heard as the note is beginning to fade.

I've effectively ruled out the guitar (it does this with any guitar).  I've effectively ruled out the speaker (it does this with any speaker in the cab).  I can't find any loose bolts/nuts on the choke or OT or PT that would explain this. Also it is not the tubes causing the buzz.

With the chassis out of the cab, I have chopsticked the beejebers out of everything and can't reproduce the buzz.

Ever heard of a choke having a mechanical buzz problem that is audible thru the speaker (signal path).  It's rated for 90ma.

With respect, Tubenit

[tubeswell]

... I can resolve the buzz by pushing gently in the middle (not sides or edges) of the chassis front panel, back panel or top. So something is being vibrated to buzz when the chassis is in the combo cab. Pressing gently on the choke or gently pulling up on the choke seems the easiest and most effective way of silencing the buzz. ...

Seems like its not the choke then.


Have you looked at very closely at the input jack tip switch contacts (to make sure they are closing properly)? Sometimes when installing jacks, the tip switch contacts can inadvertently become un-tensioned to the point where they don't close properly, or only close intermittently, and it can produce weird microphonic chassis effects. (A couple of seconds work with some needle-nose pliers and a flat head screwdriver can fix this)

[tubenit]

Not the input jack, speaker jack or FX jacks.

Ironically, "googling: can a tube amp choke buzz?" ........... brought me back to the forum and an old post by HotBluePlates confirming in reply #8 that a choke can buzz.

http://el34world.com/Forum/index.php?topic=622.0

It doesn't take much pressure on the choke to stop the buzzing. Even very slight pressure on the choke stops the buzz.  It takes more pressure on the chassis front panel to stop the buzzing. I think pressing on the chassis is preventing or lessening vibration to the entire chassis and and the choke.

I'll try some rubber/foam material that I have to isolate the choke to see if this resolves it (when I get a chance).

With respect, Tubenit

[sluckey]

I would completely remove the choke from the chassis. Set it aside and use a couple gator clip leads to connect it to the circuit. Still buzz?

[tubenit]

If the chassis is not in the combo cab, ........... there is no buzz. 

I think I'll try the rubber strips to dampen vibration first.  If that doesn't work, then I'll probably install a resistor in lieu of the choke and see what happens.  Might be somewhat of a challenge to safely try alligator clipped approach with the chassis installed into the cab?

With respect,  Tubenit

[sluckey]

Might be somewhat of a challenge to safely try alligator clipped approach with the chassis installed into the cab?

I have total confidence in your ability to safely do this.

[tubenit]

Well .............. rubber between the base of the choke and chassis did nothing to resolve it or even lessen it.

Looks like the bell (?) housing is vibrating on the choke.  A silicone cover for an iron skillet handle wedged between the choke and the OT next to has totally resolved the buzz.  Remove the silicone and the buzz comes right back.  Weird.

That's not gonna be the permanent solution to this but it narrows down the issue.

BTW, it isn't one of Hoffman's chokes.

With respect, Tubenit

[bnwitt]

I've had the same problem with my Mackie MCU control units in the studio.  They have a little surface mount choke in the power supply and they start vibrating and create a heck of a squeal.

[Ritchie200]

'Nit,
Is there a way to take it apart?  Might be able to identify the space causing the problem.  Or if you...OOPS! drop it, that may cure it.  Kind of like banging on top of the TV in the good old days!

Jim

[tubeswell]

Not the input jack, speaker jack or FX jacks.

What sort of jacks? Switchcraft Type #12A?

[tubenit]

All switchcraft jacks.  Yes, like in the photo for input jack, and fx jacks.  No shortening jack on speaker.  However, it's not the jacks. I've had those be a problem years past in other amps. That's not the issue in this case. 

I'm leaning towards trying Sluckey's suggestion and seeing what happens? I'm anticipating simply replacing the choke with another or a 5w/1k resistor.

I can press on the choke with my finger moderately and hear something clicking similar to what you'd hear with sheet metal clicking. Something seems to be loose in the choke assembly.  Pressing rather gently with a pencil eraser on the choke with the amp turned on stops the buzz and the silicone wedged between the choke and OT completely stopped the buzz.

With respect, Tubenit

[sluckey]

Post a pic of the choke.

[tubenit]

This is supposed to be a choke for Fenderish two 6L6 amps.   The silicon pan handle sleeve resolves the buzz completely. It doesn't take much pressure to stop the buzz.  Gently pressing a finger or pencil eraser will stop the buzzing noise. The wires from the choke go into one of the same grommeted holes used for the OT.

with respect, Tubenit

[92Volts]

Maybe you could apply silicone (or caulk, or hot glue) around the edge between the cover/mount and the rest of the choke? I'm not sure how much it would help but it's the easiest (if not the only) place you could apply it.

[sluckey]

It's OK to just replace the choke if you want to be done. I would probably pull the shell off and dip the entire choke into a can of varnish, suspending by the wires. Let dry thoroughly and reassemble.

[tubenit]

Guys, thanks for the suggestions and help!  It is always appreciated.

With respect, Tubenit

[Willabe]

I see where you have the pad wedged but when you say;

"Gently pressing a finger or pencil eraser will stop the buzzing noise."

Does it matter where you press on the choke? The frame or the end bells or doesn't matter? Just wondering.   

[Willabe]

I seem to remember a thread on Power Scaling/KOC forum years ago that someone had the same problem? Or maybe it was here?

The problem turned out to be that the little wooden wedge shims that are used to hold the chokes bobbin in place were loose. Although this might be loose winding's. Sluckey's suggestion would probably fix that.

I like just getting a new choke.
 

[CraigB]

Same choke, same issue - but mine ticked like a timebomb with trem engaged.  The choke was replaced and when I pulled the offending unit, I could shake it side to side and hear the coil banging around inside of the endbells.  These are easy to pull apart, just pry apart from the underside taking care not to scratch the laminations, and shove some slivers of circuit board material between the core and the coil and reassemble the frame/bells and set it aside for another project 

[tubenit]

Just got around to replacing the "buzzing choke" with one from Hoffman.  Issue completely resolved.

I don't know how a buzzing choke (that seems like a mechanicial/vibration issue) could impact sound and tone thru the speaker?  Having said that,  the amp does sound smoother to me for some reason?   Since I was already replacing the choke, I rerouted the choke wiring and kept it further away from the OT wiring.  So perhaps that made a difference?

Just thought I'd share the resolution in case someone else experiences something like this?

With respect, Tubenit

[jjasilli]

It's OK to just replace the choke if you want to be done. I would probably pull the shell off and dip the entire choke into a can of varnish, suspending by the wires. Let dry thoroughly and reassemble.

Ditto, though I was thinking wax - like done with pickups.  Wax might be better at filling voids & deadening vibration than varnish.  You need to fully immerse the choke and rotate it to get all the air bubbles out.

[EL34]

You can take the coverings off of a choke pretty easy

Bend the tabs on the bottom up
Spread the mounting legs out and pull that off

Pull off the two end bells

Don't scratch the laminations down to bare metal

Here's one I did to fix a dented end bell