Noisy Fender Princeton Chorus

[Doc74]

Hi all

I have a mid 90's Fender PC that, besides its nice cleans and warm chorus tones, also has a not so nice buzz and hiss. Oh yes, both.

With nothing plugged in, turning on the amp you can hear a faint buzzing sound. It's not very loud but it's there and clearly audible. Kinda like interference. It needs to be pretty quiet around to hear it so it's really not rattling the windows.
Turning the dials doesn't affect this.

Playing a guitar through it makes it inaudible.

Plugging in a guitar, any guitar with any cable, adds hiss, like white noise.
Turning the dials does affect this. It drowns in the music when you play unless you play at low volumes, like bedroom practice where it is very noticable with slow pieces or between songs. Or of course when you crank the amp in which case the noise is very present when not attacking the strings.

Altough it has a seperate overdrive channel, this is virtual as the amp really is a single channel amp.

Turning the gain past 5 with the volume at 2 creates way too much hiss. Gain closer to 10 is a joke. This is all with low volume, on high volume it's insane.

This is the amp manual if someone cares to take a look.

http://www.fender.com/support/manual...ton_Chorus.pdf

The amp does work. The cleans, the chorus, the reverb heck even the overdrive.
It all sounds great if it wasn't for all this extra noise.

I've tried the amp in many different outlets in the house with no change and I've used a small outlet testers with 3 lights on the back to try various outlets.
All seems normal except that the tester packaging says it can't detect faulty ground...so how do I detect this?

Someone told me that it might be the filter caps?

I do suspect it might be the house wiring since I have a small 15w ultracoustic Behringer amp and, albeit to lesser extent, it has the same hiss. It also has the same buzz with nothing plugged in but because of its size or lack thereof you need to put your ear close to hear it.

The Fender has been sitting in a room for many years and I've just recently aquired it. It's 13 years old and my guess is that it wasn't powered up for half that time at least. It still looks brand new. As does the 2 button footswitch.

Oh yesterday I took the amp apart and cleaned the top of the circuit board with contact spray.
I also did all the pots annd input jacks but it didn't change a thing.

I don't know how to troubleshoot this baby and there's no techs in my neighborhood so any advice you can give me is welcome and very appreceated.

[Enzo]

Without hearing it, it is hard to tell what is wrong and what is you noticing the normal amount of noise a guitar amp makes.

AMps make a little background sound. Hum comes from power supply ripple and from grounding issues for the most part. Open the amp and pull the main board. Are there not two larger can caps side by side in about the center of the board? Resolder them.

Gain and hiss go hand in hand. The higher you turn the gain, the more noise there will be. You could have a noisy part of course, but most any high gain channel will hiss when turned up.

I rarely find an amp sounding good with the gain at 10. But 10 will sure max your hiss for you.

Ungrounded wall outlets will not make the amp hissy. It might potentially add to the hum, but not likely that here either. Most amps hiss, and I had a Behringer acoustic amp in here last week that hummed. As far as I could determine, the amount of hum was normal - I could not find any way to reduce it other than cutting traces and re-engineering the grounds. And it hisses when you crank it.

Filter caps will not affect the hiss, they could be responsible for hum. But try the resolder on them that I mentioned.

[Doc74]

Enzo thanks for the reply! Maybe the amount of hiss is normal. I asked other users of this amp and they claim that on the clean channel it's dead quiet. I'll try to resolder the two caps.
i had heard that gain is noisy but I did not know it was this noisy, that's a shame, I won't be using this much I'm afraid.

You have a shop in Lansing? I'm in Ann Arbor, maybe I should drop by with it.

Thanks again!

[Enzo]

You are welcome to do that. My shop is open musician hours, 6:30PM until dawn Mon-Fri

Shiawassee Technical Services
5223 South ML King
Lansing, MI 48911
517-882-2544

We are an authorized service center for many major brands (including Fender, gold level) and some odd ones too.

If you come to Lansing, you ought to make time to visit Elderly Instruments while you are here. Especially if you have never been there. Check them out and note their hours:

www.elderly.com

[shredmaster]

I've a PC, its also fairly hissy, I put this down to transistor shot noise.
My own amp has developed a fault in the chorus circuit though, and for some reason, though it can be heard through the headphone socket, does not reach the main speakers.

[Enzo]

Hi Shredmaster, welcome to the forum. May I suggest at this point you might get more response if you start a new thread for your amp instead of adding onto the end of a 6 month old thread.

Are both main speakers producing sound? If I recall, on that amp like most chorusing amps, there are two power amps, one per speaker, and the chorus only comes out one speaker while the second speaker remains dry signal. That way makes more sonic interplay instead of just having a chorus blended into one signal with the dry. if that output channel or its speaker dies, then no chorus. The opposite would be if teh dry chanel died then all you'd hear would be the chorus effect without dry, until the chorus was turned off. With chorus off, both produce dry.

Just a thought. If it is overly hissy, I usually suspect an op amp before most everything else.

[shredmaster]

Its always been fairly hissy, but no more than other tranny amps I've played through.

Hadn't checked if both speakers were producing sound, no. That would explain why I can get chorus through the headphones but not the speakers. Thanks.

I didn't consider it important enough to start my own thread though...

[Enzo]

How important are half the threads? Threads are cheap, feel free to use them.