Mod Your Fender Pro-Jr!

Hi, in this instructable i will show you ways to mod your pro-jr to change the sound in pretty much every ways. this instuctable also regroup lots of information

I will cover easy to hard mods, how to bias it properly, route wires to reduce, see remove hum, hiss and oscillation. ADD/REMOVE GAIN and a lot more!

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Doing these mods WILL void the amp's warranty, if you don't feel confident enough to mod your amp, get it to a tech.

If you do one or some of these mods, you agree to indemnify and hold harmless to the author(ME) if something goes wrong.(see step 3)

Step 1: Open Amp

Follow steps in pics. YOU MUST BE LOGGED IN TO SEE INSTRUCTION IN THE PICS(you cant see all of the text if you're not logged in)

I recommend that you do all of the pcb mods at the same time, i did 'em on 3 times and broke a ribbon cables connection, no big deal. i soldered it back in place and it worked fine.
If after the mods the amp sound bad or even doesn't produce any sound(it won't happen if you are careful), you probably broke the ribon cables connection. Solder it back!

      Questions?

Step 2: Make/Change Speaker Baffle

The baffle in there is made of a very bad material, it doesn't sound good. Changing it with a nice one made out of pine will make your clean sound sweeter and warmer, vibrating.

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Step 3: Discharge Capacitors

AMPS CONTAIN DEADLY VOLTAGE, IF YOU DON'T FEEL CONFIDENT ENOUGH TO DO THE MODS, GET IT TO A TECH OR DON'T DO THE MODS AROUND THE PCB!

Here's how to discharge Filter caps Safely.

TO DISCHARGE THE FILTER CAPS: remmelt from http://remmelt.com/ (nice website btw)constructed a low tech but very effective tool. he got some nice wire in pretty yellow and a 5 Watt 15K Ohm resistor. In combination with a pair of alligator clips and some shrink tube it looks like the pic. You can use a resistor like the one in the tool and use it like the tool but I HIGHLY recommend that you build yourself one since it won't cost more, it'll be easier to use, a lot safer and a lot prettier. build one.

discharging:
with both leads of the tool, touch both leads of every Filter Caps(big ones) for about 30 secs until there isn't much electrical current in, 30 seconds should do, you should check with you multimeter, if you don't have one, I don't know why you are doing these mods, GET ONE NOW! its one of the most useful tool you can have in electronic. After a having discharged the caps, Take an alligator clip with one end clamped to the chassis, the other to one lead of the cap. Don't take these off until you're over with the mods.

Discharging Caps is Extremely important, They can hold a deadly voltage long after the amp was unplugged.

Step 4: Access the Pcb

Look at the pic.

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Step 5: Tone Mods

Look at the Pic, Follow the link will explain it more and show you how to adjust bias with a trimpot so you can tweek it. I found it a lot easier the Put a Fixed resistor, see for yourself.

http://machrone.home.comcast.net/~machrone/bjr/pjmods.htm

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Step 6: Adjust Bias

The bias in this amp is set way too hot, every one owning a pro jr that can use a soldering iron should do that mod, the mod consistof changing a resistor:  R29, its a 15k resistor, changing it to a 18k-20k lets the tubes cool down and won't affect tone, it will highly increase tube life!


Here i changed mine for 20k, its perfect.

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Step 7: Add a Line Out

I have not added a line out to my amp since I don't need one, but if you do, Here are some useful links, If someone does the mod, please, post a comment! tell us what values you used! The values shown in the pic should be a good start, it may even be perfect.
    Thanks.

http://www.singlecoil.com/docs/out.pdf

http://www.diyguitarist.com/GuitarAmps/LineOutBox.htm

http://sound.westhost.com/vda.htm

Step 8: Add/Remove Gain

R6: Controls BreakUp, right now it's set to 56K.
More gain: increase the value, i don't recommend going much higher than 80K
Less gain/more clean headroom: lower the value, don't go lower than 10K

My Pro-jr sounds really warm and clean, it breakups at about 6(volume) my R6 is at 22K
I like it clean to use my effects(fuzz, overdrive, booster...). At 22K I still have natural overdrive, it's not completely clean(good thing) I can get a quite nasty overdrive, don't be scared to lower value, yes you get more clean headroom but you won't say goodbye to overdrive.

Step 9: Negative Feedback Loop

Thats an easy mod. Its the negative feedback loop wire, without it, the amp works just as well but it won't sound the same, more VOX like. Remove the purple wire from the pcb  to the speaker jack, to test if you like, unsolder it from the jack, if you don't like the sound, solder it back, if you like both sounds, you can add a spst(single pole single throw) switch, any on/off(2 lugs) switch will work, solder the purple wire to the 1st or 3rd lug of the switch and connect the 2nd lug of the switch back to the jack where you first unsoldered the wire from, drill a hole in the chasis  (drill it before soldering the switch) next to the speaker jack if you don't want the line out jack mod, if you did the mod, solder the switch next to this one.

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Step 10: Tubes

Google for good tubes combination, you should find LOTS of forums that answered these questions. 

As with speakers, you can't know what you'll like until you tried, so buying a couple of different brand and models and spend a few hours to swap until you are happy is a good idea.

I have 2 EL84, 1 ECC81(12AT7) all JJtubes and an old RCA 12AX7, It doesn't sound harsh as I experienced with the groove tubes. sounds warm, clean, very musical, with TONS of Sparkle.

Step 11: Change Speaker/remove Magnet Cover

The stock speaker in the Pro-Jr. is harsh, I changed mine with a weber sig10s alnico

ceramic vs. AlNiCo.
Ceramic: stronger magnet, more focused, Later Breakup, More balanced.
AlNiCo(aluminum-nickel-cobalt): Warm, early Breakup, compressed at high volumes, more squishy.

How to choose?
Take the one you think will suit your tastes better, a used one would be a good idea, if you don't like, from what you heard from your amp with the speaker, you can find comparisons on forums from people who tried the speaker and another one, to know how they compare.
                                 YOU CAN'T KNOW UNTIL YOU TRY IT ON YOUR AMP!!! YOU CAN'T, YOU NEED TO HEAR IT BY YOURSELF.  
descriptions and reviews gives a good idea PERIOD. you can't know until you tried.

You can google ceramic vs AlNiCo guitar speaker to get better comparison.

from what i heard, i was sure i'd like Ceramic better over AlNiCo, guess what, i don't.
I have a weber sig10s alnico and it sounds warm and it has tons of sparkle. i love it. 
If someone gets a weber alnico speaker, the magnet cover is too big, it won't fit.
here's how i removed it:

1) get a big flat screw driver and a hammer.
2)find a good/comfortable position.(between you knees)
3)put screwdriver tip over small tab(see pic)
4)Hit screwdriver with the hammer to straighten the tab. Be careful not to slip and CRY BECAUSE YOU DESTROYED YOUR SPEAKER.

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Step 12: HUM!

EVERYBODY SHOULD DO THAT MOD! iT'S AN EASY MOD!
90% of the hum coming from this amp is due to the bad lead dress!

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Cut the cable ties holding the two green heater wires together and twist them together like in the picture


while unscrewing the midle screw down the back panel i realized that it was too long, as i was unscrewing it, the hum lowered, check for yourself, if it does the same, check for a smaller one but you probably wont find find one that match so you might want to cut the end or grind it, if it doesn't affect hum, leave the long screw as it is.

Also, all ribbon cables should run smooth without any sharp turns as seen in the pictures

Step 13: Thanks To:

EVERYBODY THAT POSTED MODS AND INFORMATION ABOUT THIS AMP ON THE WEB, I SPEANT HOURS READING WHAT YOU GUYS WROTE,
THANK YOU!

IF YOU FOUND THIS USEFUL, CONSIDER POSTING SOMETHING TO THE DIY COMMUNITY!   Also, if you have questions or if you did a mod, Post a comment! 

THANKS!