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Post subject: Fender Princeton 65 SS Amp is so noisy it's unusable......
Posted: Sat Aug 05, 2017 6:44 pm
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Location: Centerville Indiana
Ok,
I have an old Princeton 65 SS amp. It is so noisy it's unusable. I've resoldered and then replaced the power caps and no change. I've resoldered all of the connections on the PCB and it made no difference ('refreshed' the solder). I've tried several guitars, cables, etc, and can not change the noise that way. It's 60-cycle hum. I have conditioned power to plug it into, a shielded studio (HAM radio operators made that a necessity. I basically have a Farraday cage in my basement HAHAHAHAHA!), have tried it in several circuits, in several locations (inside and outside of my house), and no change.

I've also swapped out the input jacks and have not had any luck. Fender SS amps are 'noisy' out of the box but this is insane. ANY help would be appreciated. I was an electronics tech in the Army and work in the industry now, so I'm not a novice, but I simply cannot figure this thing out! I love the amp (when it works) but am about ready to set it on fire! Thanks in advance!


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Post subject: Re: Fender Princeton 65 SS Amp is so noisy it's unusable....
Posted: Sun Aug 06, 2017 7:42 pm
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Horrido! Erich!

Sound like the front end gain stage has a funky ss device in it. Which it is and how do you find a replacement is the question-of-the-day. Unfortunately.

There is no way (either button selection or input selection), you can get the amp to be noiseless?


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Post subject: Re: Fender Princeton 65 SS Amp is so noisy it's unusable....
Posted: Mon Aug 07, 2017 8:15 am
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I have literally tried everything to quiet the beast. I mean it had the 'normal' Fender SS noise when I first got it. I stopped playing it for a couple of years and decided to fire it back up and BAM! 'Stank Noise'. All day, all night. Regardless of any of the variables I try to induce the noise, reduce the noise, heck, blow it up, nothing changes.


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Post subject: Re: Fender Princeton 65 SS Amp is so noisy it's unusable....
Posted: Mon Aug 07, 2017 8:25 am
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For a couple of solid-state amps I fixed... I got a donor amp or chassis and replaced boards. This is $$ way to fix things and is only worth it for $$$ amps.

It's very hard to hunt down specific components, if you can't do differential diagnosis ( one setting works, one doesn't). Sorry...

:(


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Post subject: Re: Fender Princeton 65 SS Amp is so noisy it's unusable....
Posted: Tue Aug 08, 2017 4:04 pm
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My Princeton 112 Plus was hissy too. You know what helped? I changed the speaker to an Eminence Red, White, and Blues. It has a rolled-off top end compared to the stock speaker and it really cut the frequency where the hiss was worst.

Not really a solution but it made the amp a lot more pleasant.


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Post subject: Re: Fender Princeton 65 SS Amp is so noisy it's unusable....
Posted: Sat Aug 12, 2017 11:47 am
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Thanks, all. From the work I've done, I think I'm going to bypass the circuit traces on the board for the caps (bench style) and see if the noise goes away. I see some thermal stress near them and the marks are radial (which, methinks, means thermal shock from them). The old caps I pulled out didn't look bad but I couldn't get them to read right on a true cap checker so I 'assumed' they were bad. I wonder if I'm getting some signal leakage via a fault in the board. This sure 'feels' like a ground hum so I'm going to re-re-flow all of the joints and then see what happens (obviously, only one troubleshooting attempt at a time). I appreciate all of the advice!


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Post subject: Re: Fender Princeton 65 SS Amp is so noisy it's unusable....
Posted: Sun Aug 13, 2017 9:02 am
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I don't think bypassing traces will work.
Lets back up a bit on your symptom description. The 60 cycle hum. Is it affected by the volume control?
Does it make noise with nothing plugged into the input? There is a mute circuit switching on the input and power amp in jacks. It operates to quiet the preamps up to the main stage. Hiss should increase when you plug anything into the input, but what does it do for your hum?
Next, monitor preamp out signal. Is there hum there. Good luck.


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Post subject: Re: Fender Princeton 65 SS Amp is so noisy it's unusable....
Posted: Mon Aug 14, 2017 6:52 am
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Lets back up a bit on your symptom description. The 60 cycle hum. Is it affected by the volume control? ~ No. It's the same volume whether the amp is at 10 or just turned on with the volume at 0.
Does it make noise with nothing plugged into the input? There is a mute circuit switching on the input and power amp in jacks. It operates to quiet the preamps up to the main stage. Hiss should increase when you plug anything into the input, but what does it do for your hum? ~ Nothing changes when I plug something in. You can play through it, but the noise remains a constant.
Next, monitor preamp out signal. Is there hum there. Good luck. ~ I'm going to try this tonight. I've checked the muting 1/4" jack and everything checks out OK (I replaced the crap plastic ones with Switchcraft probably 7 years ago). I have been informed that the reverb tanks can go bad so I'll also (in a controlled way) unplug it and see if the hum changes. Thanks for all the input!!!!!!


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Post subject: Re: Fender Princeton 65 SS Amp is so noisy it's unusable....
Posted: Mon Aug 14, 2017 7:23 pm
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Hmm, do you think the mute circuit is working. You should get more hiss when you plug into the jacks.
If it hums in mute condition, then it's got to be in the main stage. While you changed the main caps, there is an op amp, U7, that is downstream from the mute transistor.
Don't pull u7 and run it empty. Its part of the dc balance feedback loop. Don't even modify the chip, use the original number if you replace it.

If the power supply for the op amps has ripple, it could cause hum in the main stage.
Look at C69 & 70 electrolytics, their associated zeners and 330 ohm resistors.


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Post subject: Re: Fender Princeton 65 SS Amp is so noisy it's unusable....
Posted: Sun Aug 20, 2017 3:13 am
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I have one of these Princeton 65 SS Blackface amps that I bought circa 2003. I used it a lot at home and recording but never have gigged with it.

Reading here, it looks a tall order to attempt to quiet it down...because what y'all are talkin about is beyond my skill set! The reverb has always noisy. I think mine has gotten worse over times of low usage...maybe I'm just more sensitive to noise nowadays.

The explanation about the mute function of the input Jack is greatly appreciated because I only noticed this last week. For my purposes, I suppose it's a better idea to seek out a less noisy alternative for my stereo at wet/dry setups I am working on.

That sais, maybe this Princeton is a candidate for working up my amplifier maintenance and repair skills :-)

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