EZ Pro Jr. noise fix & mod

I recently got a PJ and while it sounded good, I wanted it quieter. I also wanted to have a little more control over the gain in the amp so I had a look at the schematic and popped open the amp to see how it was laid out. I fixed both the issues in my amp for $3 in parts and no PCB soldering. The whole mod process took me about 15 minutes including waiting for the soldering iron to get nice & hot.

1. Noise:
Turns our Fender in their infinite wisdom of R&D decided the PJ doesn't need the green heater wires twisted together and routed separated from signal wires in the chassis like every other amp on the planet. In fact, they're run un-twisted, in parallel and zip tied tightly to both power and signal wires. Duh, Fender. I started by cutting the zip ties and moving the rest of the wires away and laying those wires close to the PCB and front of the chassis. Then, holding the heater wires apart (still attached on both ends) I started twisting the pair together at both ends working my way to the center. Then I routed them first from the lower tube socket PCB along the rear edge of the chassis, crossing other wires at right angles and keeping them toward the rear panel (or where it will be when buttoned up) to the power transformer. I then pushed the other wires together and tucked toward the top of the chassis but didn't zip tie anything together. I powered the amp up and it's not dead silent, but at least 90% better than it was stock.

2. Gain
The purple wire soldered to the speaker jack is a negative feedback to give the amp more gritty volume. After discharging the caps I simply desoldered the NFB wire from the speaker jack, then drilled a 1/4" hole next to the speaker jack in the bottom of the chassis for a small DPDT toggle switch. I then resoldered the purple NFB wire to one end-pole of the switch and found a small piece of almost-matching purple wire from my junk bin and soldered the center lug on the switch back to the speaker jack where the original NFB wire came from. Now I have my choice of Blackface NFB type gain or tweed style gain with the flick of a switch that's out of sight behind the back panel. As a little addition to control a little more noise, I made sure the NFB wire crossed the red & white wires running between the 2 PCBs at a right angle.

Works perfect, has nearly no noise and I have an option of how snotty I need the amp for different gigs. Cost was only the switch, some solder , a piece of scrap wire and about 15 minutes.

I also use a 60s era GE 5751 in V1 & a 1962 Wurlitzer/RCA 12AX7 in V2. EL84s are not matched Ruskie something or another. I'll be trying out some late 50s Dutch Gold Star Motorola 6BQ5s in there that came in a radio chassis I salvaged on a recent trash day.

I find when I'm messing around in tube amps that wiring placement makes a HUGE difference in the noise floor. Even PCB amps can usually benefit from some decent routing of the off-board wiring, especially the heater wires, NFB (if present) and signal wires. Originally, the Pro Jr. had ALL the wires zip tied together in one big bunch. AC, NFB, speaker, signal, heaters - EVERYthing. Way to go Fender. :speechles

I haven't done a lot of messing around with the amp since I closed it up because we have relatives here for the weekend and I don't think they'd appreciate me plinking for hours going back & forth with different tubes, settings and other junk looking for the 'Holy Grail of Junior Tone'. I did plug it in, let it get hot the other night and play around with it a little (about 3 minutes) and found that between the heater wire mod (quieter) and the NFB switch (different gain voices) that it's surprisingly versatile for doing so little work on it compared to what it was stock.

A picture's worth a thousand word (but that never stopped me from blabbing). Here ya go!

http://s233.photobucket.com/albums/e...na/amps/projr/

Cheers,
- JJ



Cheers,
- JJ

I wish I had read this a couple years back when I had 2 stock Pro Jr's. The hum used to drive me nuts.

I sold one and had the other coverted the other into a hand-wired 18Watt Lite.

Good job though! :bluesbros

Fun stuff!

I've seen hand-wired versions of the same Pro Jr. circuit stuffed in these, too.

That's actually why I bought this - to do a terminal board build.
I just figured since what I did was so easy that I'd share it with anyone who wanted to try a couple very simple things to get the biggest complaint these amps seem to have under control. From what I've heard since posting this in a couple places, some PJs respond well to this kind of tweak, others refuse to play nice. Couldn't hurt to try it though ... it's certainly cheap.

Cheers

Oh yeah...good info...but you mention that the NFB adds grit to the amp when, in fact, they're in place to clean them up. Just a detail really, anyone who knows enough to mess with the NFB already knows what they do, usually.

I'm still wanting one to mess with myself.

NT, your're right of course. I was getting the 2 settings mixed up in my head. The difference isn't what I'd call big in this amp, but it's just a little different and if you're listening to it with the knowledge that there should be something different, you'll hear it easily. I doubt someone who didn't know what I was doing while reaching back there would ever notice anything. Maybe, but not likely.

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Well, here's my gig report.

I like it.

I brought the HRDx along since that's been my main gig amp for a couple years now. I got snickers from the other guys in the band when they saw my 'tiny little amp' I planned on playing through.

At sound check I found the Pro Jr. worked just fine on about 2 or 3. Didn't need any more power than that (I mic). What was surprising to me was that I only had just a little guitar coming through the PA, this little sucker has balls. The cleans are where it's at with this amp. They're not crystal clear but what I'd call the perfect Fender cleans with just the slightest little bit of hair on it.

It takes my pedals in outstanding fashion. With no effects, I can cover the Robert Cray type clean sound with a Strat all day and do it VERY convincingly. With my home-built Bluesbreaker pedal clone, it sounds like the amp is screaming loud, but it's not. Think Dwight Yokum doing 'Long Cool Woman' with a Tele only I'm still using the Strat - nice. Overdrive to distortion tones going everywhere from Joe Walsh to Zep to AC/DC are covered by a Line6 Crunchtone Tonecore pedal. I set that on Blues2 and leave it. If I use the Crunchtone and Bluesbreaker together, it's as snotty as I ever need it to be. For certain songs, I'll replace the Strat with my old SG with humbuckers to get over the top if needed.

My bass player mentioned a couple times how good the amp sounded & both he and the drummer said a couple people asked them over the course of the night how I was getting all that sound from such a little box. The pedals help, but the amp delivers what the pedalboard pushes into it. I believe you can usually use a great amp and cheap pedals and sound pretty good, but reversing that equation doesn't usually work very well.

Overall, this is the best $200 amp I've ever played through. The tweaks I did aren't what I'd really call mods, but subtle improvements that keep the amp's core tone intact but make it nearly silent. I was pleasantly surprised to find the heater wiring twist kept it quiet at gig volume with neon light right next to me in a bar.

Dang I like playing through a little amp.
I REALLY liked it at 3am loading the van. :appl:

My wife even suggested I sell the HRDx and use the money to buy another small amp like the Pro Jr. since I could toss it behind the seat in the back of the van for a spare. I could see that, eventually doing turret board conversions on them.
Then the real fun begins. :odie:

Cheers,
- JJ

cool beans man. i used to mix a band from time to time that only used those amps, just like you, a little through the monitor and cranked through the house. they sounded great! that was when i started to realize that volume doesn't equal tone.

rock on man!

Hey JJ, I just did your two mods this week on my PJr. (re-routing the wires and the NFB switch) and I must say that it sounds great! Less noise and the breakup at full volume with the NFB off and everywhere in between is much smoother. Thanks for the ideas and posting pics of it!

Ya gotta love these snotty little boxes - heh? :biglaugh:

Seriously, When Fender claims it has a little Champ, a little Harvard & a little Princeton in there - it's the truth. When you consider those amps were originally designed for kids to haul to lessons and they ended up being used in so many classic recording sessions it really brings out how nice they really are. FMI doesn't have much choice in making them the way they do these days with ribbon cables and PCBs, but that doesn't mean some of us can't tweak them to bring back the old character of the classic circuits they're inspired by.

I'm just glad my wire-routing discovery has helped others. I'm no designer of much of anything, but I am happy to have helped.

Cheers,
- JJ

I'm still trying to wrap my head around untwisted heater leads!

I'll re-read the rest of this when I get unscrewed.
:D

Good work, JJ!

Quote:

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Originally Posted by Cygnus X1

I'm still trying to wrap my head around untwisted heater leads!

I'll re-read the rest of this when I get unscrewed.
:D

Good work, JJ!

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Yeah, untwisted is bad enough but to zip-tie power/signal/output wires and everything else together? That's like the Cardinal Sin of amp layout - even a newbie builder like me knows that!

At least it's an easy fix. :headbange

I just put in a Ragin Cajun today and I must say that it is the best thing you can do for this amp outside of these mods. Way better low end, the highs don't kill you, and it handles the amp's breakup perfectly. It's the perfect speaker for this amp (for me)!

voided3, what kind of material are you playing with your PJ?
I'm curious about how the Ragin Cajun sounds in different music types.

I go to school for music so it gets used for a lot of different things. I've brought it to class to play some jazz and I used it for another class to do a delta blues slide thing I wrote in open D. It's been to a few gigs (I only bought it late this summer) playing rock/pop/blues stuff as well. All of this was before changing the speaker, but I can tell now that it has the cajun it'll fill a room much better. The problem I was having with it was unless I had the volume maxed out and controlled the gain with my guitar, it didn't have any/much bottom end (and you probably know, a maxed out PJr. is noisy as heck). Now it has a healthy amount of lows at all volumes and the tone control is more usable to do things besides attenuating highs and the upper mid spike disappeared for the most part. Overall, it's very warm sounding but can still get bright while pushing more dBs than the stock speaker. Only downside: it weighs a bit more... boohoo.

Dynamic range is the name of the game - that why this little souped up 5E3 thing's such a popular idea - no NFB and an amp screamin' it's erm... things... off... provided it's built right (yer - not with wires indescriminately bundled/untwisted etc) is one of the most exciting things I've done with a guitar lately - it's like flicking a switch and the sustaaaaaaaaaaaaaaaaaaaaaain........... good shout! :D

I posted this over on the TDPRI a week or so ago, but I thought it might help someone here as well:

Well, I tried a trick today on my PJr I read about being used in Champion 600s on sewatt.com which is to install a bridge rectifier + a 1000uf cap inline with the AC heaters to convert them to DC. I just spliced it inline w/ the existing wires since there is plenty to work with. I hooked the two green leads form the PT to the AC input (~) on the bridge, then soldered the 1000uf cap across the DC (+ and -) outputs, then ran leads form the DC outs on to the bottom tube socket logic board. I have done this on my C600 as well and recall that if you hook up the DC outs backwards, the LED pilot light will not work since they have a polarity and run off of the same 6.3v heater feed, so you'll know you did it right if your pilot light goes on. Just in case though, I hooked up the DC outs using crimp on connectors like the ones they use on speakers so I could swap them if I hooked them up backwards. Besides splicing and soldering the components, all that is left to do is bolt the rectifier to the chassis. I didn't have any, but I know it can be wise to put some heatsink compound (same stuff used on computer CPU coolers) on the metal bottom of the rectifier to help dissipate heat generated by it. Considering the rectifier I used was rated for 50v and only is seeing 6.3v, I'd imagine that it would be ok.

With a gold series GT-12AX7R in V1 and an EH12AX7 in V2 plus a set of JJ EL84s, I fired up the amp and the idle noise has been greatly reduced from before, but bear in mind I have already doubled the first stage filter caps w/ a pair of Ruby 47uf 500v monsters and rerouted the factory bundled wiring. I got both the rectifier and the cap from Radioshack, just look for the 25 amp 50 volt one and a 1000uf 50v electrolytic cap. The cost was about $6.

Billm's other mods that include replacing the carbon comp caps with metal film will also help. If I am feeling adventurous, I'll go through and replace them someday to diminish the "hiss," but for now I'll use the amp as-is since the noise level is acceptable for the bar gigs and practicing it gets used for.

Oh yeah, I forgot to mention (and I don't know if they helped or not), but I put some snap on ferrite cores I had laying around on the power cord, too (one by the plug, one near the chassis). They help with radio interference which is an issue since I am using the amp in a city. They're relatively cheap and may be worth a try if you're getting some interference, but they won't help the hum, buzz, or hiss much if at all.