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Post subject: Princeton 112 Plus Amp Volume Problem
Posted: Sat Mar 02, 2019 9:59 am
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The volume control on this amp is too sensitive. Turn it up to about 1 and the amp is almost full blast. What can I do to modify and where can I buy the parts? Maybe a different value volume pot?


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Post subject: Re: Princeton 112 Plus Amp Volume Problem
Posted: Sun Mar 03, 2019 2:31 am
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Joined: Fri Feb 05, 2010 4:31 am
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Location: Province de Québec, Canada
It is a 63 watts amps, very powerfull to play in bedroom level.

Volume pot could be dirty making a short and give you high output at 1 ?
Spray only good contact cleaner like Deoxit, cheapest may not work; you must go inside the amp

Volume pot can be ok too for this powerful amp ?
Volumes pots look to be a "B" pots on shematic, not sure, print is bad. "A" pot could work better if available for this amp.

If you don't have any skill in electronic, don't work on it.
Use the gain volume on the amp.
Or;
Buy a volume pedal and put it between Send and Return jacks, it will work fine at cheap price


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Post subject: Re: Princeton 112 Plus Amp Volume Problem
Posted: Sun Mar 03, 2019 6:17 am
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Pot has been cleaned and is not scratchy. The amp has always been this way. It's part of the design but I was looking to modify so I could have some better control of the volume level. I use the preamp jack to send preamp signal to the main mixer.


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Post subject: Re: Princeton 112 Plus Amp Volume Problem
Posted: Sun Mar 03, 2019 6:21 am
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Any skill in electronics ? Soldering ?
Are you able to go inside the amp to replace volume control if available ?


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Post subject: Re: Princeton 112 Plus Amp Volume Problem
Posted: Sun Mar 03, 2019 6:25 am
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Yes, I would change the pot if necessary. I don't what pot to use. Maybe a different taper?


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Post subject: Re: Princeton 112 Plus Amp Volume Problem
Posted: Sun Mar 03, 2019 6:28 am
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I'm sure there are thousands of these amp out there. Someone or Fender must have come up with a fix for this annoying problem.


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Post subject: Re: Princeton 112 Plus Amp Volume Problem
Posted: Sun Mar 03, 2019 6:38 am
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Changing value of the pot don't work.
Audio A pot is the one to use.
if it is this pot in your amp without the amp in front of me, I don't know witch mod to do or if you can you make a easy mod yourself ?


Volume pot use ont your amp ;

2 038658 CONTROL RTRY 50K 30C R16,31 (CLEAN/DRIVE VOLUME)


Service manual here,

http://bee.mif.pg.gda.pl/ciasteczkowypo ... Manual.pdf


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Post subject: Re: Princeton 112 Plus Amp Volume Problem
Posted: Sun Mar 03, 2019 6:42 am
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Bronx68 wrote:
Yes, I would change the pot if necessary. I don't what pot to use. Maybe a different taper?


"A" log pot .

Look here;

https://darrenriley.com/product-categor ... tiometers/

http://www.guitarpartsresource.com/amp_electrical.htm


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Post subject: Re: Princeton 112 Plus Amp Volume Problem
Posted: Sun Mar 03, 2019 8:56 am
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Location: Denver, CO, USA
Volume control in the loop is the way to go.

A box, 2 jacks, and a volume pot (and you're already willing to buy a pot). You can buy preassembled or slap it together yourself.

Guaranteed effective, and easier, quicker, and less likely to damage anything compared to taking the whole dang PCB out of the amp for a mod that might not work.
-----------------
Many Fenders are designed to have abrupt/touchy low volume response.

My cynical assumption is that's intentional marketing. Guy walks into a store and compares a Fender to a "brand X" amp. The Fender roars to life and at "1" it's louder than the other amp at "3". Guy thinks "wow, at "10" this Fender must be loud enough to play Madison Square Garden!"


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Post subject: Re: Princeton 112 Plus Amp Volume Problem
Posted: Sun Mar 03, 2019 12:53 pm
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Strayedstrater, As you suggest I would add a volume pedal or make one except I use the preamp output jack to go to the band's main mixer.


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Post subject: Re: Princeton 112 Plus Amp Volume Problem
Posted: Sun Mar 03, 2019 12:55 pm
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Also agree this was probably some misguided attempt at marketing the high volume of the amp.


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Post subject: Re: Princeton 112 Plus Amp Volume Problem
Posted: Sun Mar 03, 2019 1:28 pm
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First check the pot for damage. These models are prone to failure by pulling off the knobs. It pulls the shaft slightly through the plastic wiper disk.
Gently pull on the knob and see how much the knob pulls out. If one or two pots have more than the others, it may be a problem. It allows the wiper to lose contact and go full volume.
Also, changing the taper of a feedback type volume control can yield very different results than the traditional voltage divider controls.
A better way is to just tack some resistors across the op amp to lower their gain.
R13 , a 220K is the feedback resistor for the Clean channel.
R6, a 15K is the feedback resistor for the first stage op amp.
A safe bet is to add the same value in parallel to drop the gain in half. Scrape and tin the resistors on the board and keep the leads of the add-on short. Its a sensitive circuit.


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