buzz in Princeton Chorus

[Billy_in_KC]

It's probably been discussed before, but I can't find anything specific through the searches.

I've got a '98 Princeton Chorus; and it buzzes.  Sounds about like 60 Hz.  Don't have a scope.  Buzz is independent of input.  Buzz does not change with changing position of any pot or channel. 

Sometimes buzz goes away temporarily with application of a little mechanical shock.  But, only temporarily.  It always comes back, so --

filter caps or ground loose somewhere?

I do have a good DVM.

Everything I've ever heard about these amps is that they should last forever if they're treated right, but this one has been hauled around to open jams on a regular weekly basis for the better part of ten years. 

I've got experience in the electronic/electrical field, so I don't think this is just a disposable chunk of gear.  If I could get pointed in the right direction I think I could fix this.

Then if I do get it fixed, I'm going to search again and look up the thread where someone was talking about upgrading by putting in some higher efficiency speakers and adding that preamp stage.

Thanks in advance for any help!

-Billy Joe in Kansas City

[Enzo]

Pull the chassis.  There will be a pair of main filter caps standing near the center of the board, if I recall the layout.  Dismount the board flip it over and resolder them.  I'd bet my lunch money that is your problem.

After restirong hte board to poistion, run a large glob of silicone sealer or hot melt between them to glue them together into one mass.  Also run a bead around the base of each.  Those measures will help prevent them shaking around and cracking their solder in the future.

And for the record, that would be 120Hz hum in this case.

[Jack1962]

Pull the chassis.  There will be a pair of main filter caps standing near the center of the board, if I recall the layout.  Dismount the board flip it over and resolder them.  I'd bet my lunch money that is your problem.

After restirong hte board to poistion, run a large glob of silicone sealer or hot melt between them to glue them together into one mass.  Also run a bead around the base of each.  Those measures will help prevent them shaking around and cracking their solder in the future.

And for the record, that would be 120Hz hum in this case.

Good advise from Enzo , that is the best place to strat ,since your allready in there check all the other solder joints and clean all input and outputs(1/4 " jacks) and do all the general inspection stuff , a small hum is common in most amps, but this amp is usually pretty quiet. Good Luck


                                   Rock On

[Billy_in_KC]

Thanks Enzo and Jack. 

I pulled the chassis Saturday and did not see any physical defects but that does not mean that they are not there;  I know it wouldn't take much of a crack to cause a problem so I'm going to try the re-solder tonight. 

The silicone fix for stabilization may have to wait for material on hand but thanks for the tip it looks like a good idea.

I'll re-post and let you know what happened.

-Billy Joe

[Billy_in_KC]

Nothing was visibly apparent, but I resoldered both caps at anode and cathode.

Sounds just like new. 

Thanks again guys.

[Jack1962]

That's what were here for, bro  :tu:

[NA_NC_MX5_DRVR]

Hello All

This is my first post. I am having 2 issues with my Princeton chorus. 1 I get a hum similar to what the original poster is having and 2 the reverb is noisy. I have the spring reverb in my unit. I have already had the chassis and PCB out to replace the volume pots with audio taper pots. when testing with the chassis out the chassis actually vibrated. This is an early black knob  may be a late 80s or early 90s unit. I would like to pull the chassis this weekend and re-touch the solder on c60 and c59, Is there a way to test the caps while I am in there? I re-touched R106 and R107 as I saw a you tube video of someone having a noise problem so I thought I would do some Preventive soldering here..

Any ideas on what to look for on the reverb? I may have strained the cheesy cable that goes to the reverb on the 1st opening of the chassis.

Thank you in advance. This forum is great.