Buzzes from amp...

[Jazzer2020]

I'm pretty sure I've nailed it this time. Up until tonight I thought it was a loose plastic knob on top of a volume/presence pot.

That's because when I put pressure on the knob the buzzing stopped.

 

But tonight, after pressing some of the other knobs and getting similar results I discovered it is the metal plate that all the pots go through that is buzzing.

After pressing down on the plate, the buzzing stops.

 

So basically you have your speaker grill cover and at the top of the speaker you have your row of volume/tone/presence pots.

It's the plate right above the speaker.

 

The amp is a beaut. It's a Fender Princeton II.

 

If anyone can steer me in the right direction here on how to fix this I would appreciate it.

 

I hope it's not too involved.

 

[AJ6stringsting]

Take it in to a amp tech for servicing. Later, if money and time permits, get a rackmountable noise gate or hush unit. Set the unit up in your effects loop ( if you got one) , set the gate up so it won't trigger (close) too soon. Then when you stop playing, you'll have no hiss or hum,

[WRGKMC]

From the description it sounds like a noise from Vibration, and not electrical hum. This is common in combos because the chassis is in direct contact with the speaker cabinet. The fix can often be simple. It may however require removing the chassis and shimming things to prevent the buzzes and rattles that can occur.. I've used things like electrical tape, rubber washers and sometimes just retightening the bolts that hold the chassis in. Each is different so I cant be real specific. The plate you're talking about sounds like its below the face plate and may just be a cosmetic panel. With the head removed, you can usually get a better look. It may need some shimming or maybe the head just shifted in the cab during shipment or transport and is just far enough away to buzz with certain guitar notes.

 

Most of the times these aren't hard to fix and with a little creative effort, you can fix them. Just make sure whatever you do is reversible. If you have two plates touching and buzzing, then something like tape can act as a shim and since its removable, it can always be reversed.

 

If this is an electrical hum through the speaker then its likely some ground or shielding issue. Many amps have PC mount pots and solder joints can crack. The only way to fix those is to have a qualified tech give it a look. Your issues does sound like a mechanical buzz from the read so that sounds like something most people can figure out. Those amps are super simple. Just realize the heads are held in with a long screw and a nut below. Don't loose the nuts because they are unique. You should only have to loosen them and then you should be able to shift the head around a small amount to get rid of any mechanical buzzing of the chassis

[Jazzer2020]

From the description it sounds like a noise from Vibration, and not electrical hum. This is common in combos because the chassis is in direct contact with the speaker cabinet. The fix can often be simple. It may however require removing the chassis and shimming things to prevent the buzzes and rattles that can occur.. I've used things like electrical tape, rubber washers and sometimes just retightening the bolts that hold the chassis in. Each is different so I cant be real specific. The plate you're talking about sounds like its below the face plate and may just be a cosmetic panel. With the head removed, you can usually get a better look. It may need some shimming or maybe the head just shifted in the cab during shipment or transport and is just far enough away to buzz with certain guitar notes.

 

 

Since I posted, I'm not sure it's the plate underneath the pots.

It may be the nut that secures the pots to the plate that has come loose.

 

Can someone please tell me an easy way to take off the plastic knobs on top of the pots?

They are all stuck!

Thanks.

[t_e_l_e]

the standard fender knobs do not have any small screws you would need to loose first

so if the knobs stuck, gentle with a srewdriver or scissor or small plier from underneath and push them a little up, move around so you don't push it always from the same spott. be gentle to not destroy the knob.

 

if you have raised them a quit bit they should then go off easily

[WRGKMC]

the standard fender knobs do not have any small screws you would need to loose first

so if the knobs stuck, gentle with a srewdriver or scissor or small plier from underneath and push them a little up, move around so you don't push it always from the same spott. be gentle to not destroy the knob.

 

if you have raised them a quit bit they should then go off easily

 

Woah, Hold on there. I have to flag that advice.

 

Fender Princeton II uses the older classic black top hat knobs that do have set screws.

I believe they are regular flat head screws. You'll need a small screwdriver to loosen them and then they should come off with no resistance

 

I am questioning your reason for removing the knobs.

 

You obviously don't know what you're doing. You don't remove the knobs to pull the head out and there's zero reason for removing the knobs unless you're changing pots. The only thing you'll wind up doing is removing the face plate. and you'll wind up having to remove the head to get all those pots back in place. There is no reason what so ever to remove the knobs.

 

The head comes out of the cabinet from the back. You go in above where the speaker is mounted and the nuts for the screws can be found at the 4 corners of the chassis. The screws that hold the head in place come down through the top of the head and go all the way through to the bottom of the chassis frame. They use machine screws with nuts that have lock washers attached to the nuts so they don't loosen up from vibration.

 

You need to use a Phillips head screwdriver on the top of the amp and hold the nuts from the bottom side inside the speaker cavity. .

 

I suggest you Google up some construction diagrams so you have some clue to what you're doing. Otherwise take it to a music shop. This should be a simple 10 minute fix in most cases .20 if you have a face plate that needs shimming.

[onelife]

Fender Princeton II uses the older classic black top hat knobs that do have set screws.

 

I can't say for sure but since the Ultralinear Silverface Fender amps used push on knobs (with the exception of the Master Volume control) I would suspect the Princeton II, which came later, would use them too.

[WRGKMC]

Most of these amps use the set screw type.

https://www.google.com/search?q=Fend...w=1280&bih=871

 

Their solid state lines had pull off knobs that really sucked because you'd throw and amp in the back of the car and they would fall off and get lost. I think that line of amps taught them where they could cheapen up and where getting too cheap hurt their reputation.

https://www.google.com/search?q=fend...w=1280&bih=871

 

Their guitars used push on knobs, but the better amps were mostly set screws. The pot shafts were also round metal so you had to use set screws. There's probably some cheaper junk they've made where they have splined pots or plastic but, the tube amps seem to stick with the traditional builds. All the silver faces I've owned used the same set screw knobs too. I haven't tried any reissues, but I'd think they would use the same parts to qualify as a reissue. Tube amps especially get hot and without set screws the knobs would go bad too easily. Solid state remains cool so you can use plastic push on junk.

 

 

Older amps used the white knobs and chicken heads. Both were set screw knobs.

[Mikeo]

Inside the reissues are a couple of printed circuit board. One is the amp layout or what would have been the turret board. The other the control knobs are mounted to. The whole thing gets connected with a bunch of short ribbon cables. The pots are kind of different than what ya might think

 

 

 

[Jazzer2020]

 

Woah, Hold on there. I have to flag that advice.

 

Fender Princeton II uses the older classic black top hat knobs that do have set screws.

I believe they are regular flat head screws. You'll need a small screwdriver to loosen them and then they should come off with no resistance

 

 

Holy cow Batman, you are both right.

Some of the knobs have screws and some do not.

The first three knobs from the left (those that are push-pull pots) have screws, the rest do not.

Who would have thought that?

 

As luck would have it, the one(s) I want to take off don't have screws.

 

 

I am questioning your reason for removing the knobs.

 

You obviously don't know what you're doing. You don't remove the knobs to pull the head out and there's zero reason for removing the knobs unless you're changing pots. The only thing you'll wind up doing is removing the face plate. and you'll wind up having to remove the head to get all those pots back in place. There is no reason what so ever to remove the knobs.

 

My reasoning is very simple.

You are making assumptions which shouldn't be made.

I am not trying to pull off the knobs to pull the head out!

 

I am trying to pull off the knob so that I can check to see if the nut that is securing the pot is loose, that's all!

 

[onelife]

... All the silver faces I've owned used the same set screw knobs too...

 

That doesn't mean all the silver face amps used the same knobs. The last of them, the Ultralinear ones, used push on knobs that are very difficult to remove (with the exception of the pull out Master Volume control that used the old style set screw knob).

[onelife]

Some of the knobs have screws and some do not.

The first three knobs from the left (those that are push-pull pots) have screws, the rest do not.

Who would have thought that?

 

That doesn't surprise me. I've seen several Fender tube amps that use different types of knob even though they both look the same. CBS must have saved just enough money to make it worthwhile in the mass production of all those boxes.

 

[Jazzer2020]

I am getting there slowly but surely.

Removing the knobs didn't help because the nuts were securely fastened and not vibrating.

 

Just now however I re-affirmed my first suspicion about the mounting plates vibrating (the plates that hold the pots at the top of the front face).

 

When I pressed down on the top of the amp, compressing the wood onto the very top of the plates, the vibrations stopped!

 

So now the source of the noise is locked in.

 

A couple of questions...

 

Is there anything to be careful about when I open up the amp?

I know when you open a TV there are some potentially lethal charges waiting for you.

 

Also, what would you use to bridge the top of the plates with the wood at the top

to cushion the vibrations?

 

Some type of foam?

Any other tips for this?

 

 

 

 

 

 

 

 

 

 

 

 

[onelife]

You might find this site interesting:

http://www.stratopastor.org.uk/strato/amps/prii/PRII_hub.html

 

Phil O'Keefe in the Studio Trenches forum has a PRII and may also be a good resource.

 

[Jazzer2020]

You might find this site interesting:

http://www.stratopastor.org.uk/strato/amps/prii/PRII_hub.html

 

Phil O'Keefe in the Studio Trenches forum has a PRII and may also be a good resource.

 

Thanks onelife.

I had discovered that site several years ago actually. I haven't visited it for quite a while though.

It's too bad there aren't any photos there of dis-assembly etc.

I might fire off some e-mails.