Fender Pro Jr More Bass

[Paleo Pete]

I got a Fender Pro Jr at a yard sale sometime about July, under $50 I figure that's not bad...works fine after I re soldered all the tube sockets. I think I might have found 4 total that were good...It buzzed and crackled like a wad of aluminum foil in a microwave. Yeah I did that once...Worked fine after sniffing a little solder, now on to making it sound decent. It seems Fender workmanship and QC are not exactly great these days, if this is what they're putting out, I don't want a new one...and this one is marked Made in USA...ouch...

Not a bad little amp, and actually more wattage than I need for many of the low volume gigs we play, I could use my 6 watt Champ if it didn't sound like a cheesy 8 inch speaker. Almost no hum at all, which seems to be a big problem with these amps, a little hiss at times, but not bad, everything seems to work fine but not near enough bass. I'm spoiled, I've been standing in front of a Super Reverb for 15 years, and a Peavey MX and Kustom 2x12 cab for almost 20 years before that. Not having that 10 foot bulldog barking behind me is a let down...I know I;ll never get this thing to match that, but I'm sure it can get more bass. Plugged in with the Super Reverb and A/B switch, it sounds really thin and wimpy. I know the 10 inch speaker can produce more bass, I've used my 10 band Boss EQ several times, but it also increases volume. Don't need that.

From what I can tell the tone knob just seems to add treble, about halfway seems to work, bass seems to be fixed. The Super Reverb was the opposite, when I first got the thing (1973 silverface) it had overpowering boomy bass with the knob on 2 or so, out of control. One cap swap fixed that, now I run it about 6.

So I've searched the interweb quite a lot, found all kinds of pages with the same basic info on mods for this amp - bias, negative feedbak loop, gain, speaker swap - but not a thing about what cap (if it can be done) will give it more bass.

So far, I've disconnected the negative feedback wire, twisted the green heater wires and routed them away from everything else, and swapped the 13K resistor at R29 with a 22K, bias voltage reads -11.48 now, it was -7.5 with the 13K in there. Most articles I've read say these (and the Blues Jr) are biased way too hot, low tube life. No other mods, it sounds good, don't have the bucks for a new transformer or speaker swap. And I'd love to stuff a 12" speaker in the thing...

So is there a component somewhere I can swap that will let this thing produce more lows?

Schematic http://ampwares.com/schematics/pro_jr.pdf

This one has 1/22/97 written on the board, I'm assuming that's the manufacture date, it's the original Pro Jr, NOT the Pro Jr III. I don't know what revision, I can't find it marked inside anywhere, 12ax7a preamp tubes, EL84 power tubes.

I can't think of any other info you might need...ask if I missed anything. Everything on the board is marked, so finding R29 to swap and R21 and R22 to check bias voltage was easy, no problem finding what is where.

[Dave H]

For a test try removing C5. It is hardwired for full presence which could make it sound thin. Have you tried it through an external speaker cab with known good bass response?

Where is the volume control set? It is interactive with the tone control. It will sound thin if the volume is turned down. Try turning the volume up then reset the tone control.

[Paleo Pete]

For a test try removing C5.

I'll try that.

No I haven't tried it with an external speaker, the only one I have is 4 ohms, not good for a 8 ohm amp. Wish I had one, I think a 4x12 or even 2x12 would sound lots better. I know the 10" speaker will do better, the 10 band EQ shows me that.

I haven't played it at high volume, it's low volume gigs we usually do, haven't really had the chance, Even at a booking at a bigger place, only had it around 4 (out of 12).I plan to tinker with it at home later today, I can crank it a little here, but normally it's used at very low volume. As I said earlier, the 6 watt Champ can produce plenty volume, the 8 inch speaker just sounds like a cheesy practice amp in a big building so I had to give up on that. Tried it, volume at 8 was plenty, but just didn't sound good.

My one gripe is the way they built this thing...I don't like the tubes being on a separate board, should be mounted directly to the chassis, and the main board is a bear to get out, fits too tight. I guess it's not as bad as the Peavey Classic 30...took me 30 minutes to get one taken apart...

Thanks for the suggestion, it might be a day or two before I try it, I want to check it out a little after changing the bias to something a bit milder before I do anything else...

[Justin Thomas]

Is anyone out there building a Champ with a 15"? Just sayin... (builders: HINT HINT!!!) seriously, try the Champ through the Pro Junior speaker. And try the Pro through your 4R speaker. For the sake of a minute' s testing, you won't kill anything. Just don't dime all the controls to 12.

Justin

[Enzo]

Yes, a 4 ohm speaker on the 8 ohm tap isn't going to hurt it. I think a different speaker will have way more effect on your lows than looking for A cap to change. There is a difference between A 10" speaker doing better, and THIS 10" speaker doing better.

Try setting the amp near the wall, and see if that improves bottom end.

[DRH1958]

What about increasing coupling caps C1 or C6 to .02uF of maybe even .047uF and also C8 and C9 to .047uF? Add a little bass on the preamp and a little more on the output of the PI to the EL84s? Would that be enough? It's worked for me before, just not on this amp. Or would the bass just get muddy? I agree the speaker is the weak link, just exploring possibilities.

[Paleo Pete]

OK thanks guys, one at a time...

Dave H - you were right, I got to tinker a little this afternoon with nobody around and crank it, seems it does get better bass as the volume goes up. About half volume it starts to sound pretty good, 3/4 and up it sounds downright mean. Don't know how that will work onstage in a bigger room...I had read that not long ago too, and forgot it. Once I started playing it, I realized I Liked this amp when I first got it, but that's the only time I've played it even remotely cranked. Usually the volume level is more like 3 or 4.

Justin - I've been wishing I could put together the parts to build a 2x12 Champ for ages. I've run mine through the Kustom 2x12, it sounds loads better. Still a 4 ohm load, wouldn't have to change a thing but the cab, and I'd build it to use a 6L6 so the bias would have to be tweaked to suit that tube.. I've thought about trying it with the Kustom cabinet, just haven't done it, I'm not worried about 5 minutes, but I wouldn't run it for a 4 hour gig on a 4 ohm cab. I'm pretty sure it can handle a short run with a mismatch.

Enzo - You got the point as usual. A better speaker would make more difference than anything, and the factory ones aren't the greatest, I've already tried a 8 ohm 10 inch out of an old Yamaha amp, didn't make enough difference to notice so I put the stock one back in. I couldn't really tell I had swapped speakers for the most part. Problem is there's no way I can afford a better one to put in this amp, I'd probably go for a 12" and enlarge the baffle hole if I could.

DRH - I might try those options too, I'd be concerned about anything that might make it muddy. It already gets slightly flabby when dimed, but not in a bad way...Sounds a lot like the Super Reverb dimed if I run the bass a little hot. Gets a great overdrive sound above about halfway, and only gets flabby in the bass if I run the neck pickup, not unexpected. With the bridge pickup it does great at full volume. I was surprised how loud that is for a 15 watt amp...I'll have to see what I have sitting around for parts...

But with the bass being tied to the volume knob I may have a dilemma. If I find any one thing that can give me a little better bass response at low volume, (and if it sounds decent in a full band loud situation, which it didn't last time I tried it) I may have to make it switchable, so I can turn it on for low volume operation and off if I know I'll be able to crank it.

I haven't been able to put it in a loud situation since I disconnected the negative feedback, that should help at least "open it up some" as it's usually put. But so far at low volume it makes little difference. I still have to plug in the EQ, which drives the volume a bit higher.

Thanks for everything so far guys.