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Post subject: Pro Jr. hiss and hum
Posted: Fri Jul 20, 2007 1:33 pm
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Location: South Orange, NJ
Got a new Pro Jr, great tone BUT it hisses like a snake when I turn up the volume to get that crunchy sound. I also hear a lot of hum (both sounds are present even with the guitar cable unplugged from the amp.Anyone know of an easy way to remove these sounds?


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Posted: Fri Jul 20, 2007 1:49 pm
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Part of the problem is the circuit the amp is plugged into. Many times one circuit powers more than one room in your house and major appliances share it. TV's, computers, lights, refrigerators, etc. on the same circuit will cause this.
I just recently had a dedicated circuit run for just my guitar gear.


Another cause may be a grounding issue in your house.

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Posted: Fri Jul 20, 2007 1:56 pm
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Here's what I did about it. It's not perfect, but it's a noticeable improvement.

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


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Posted: Fri Jul 20, 2007 2:07 pm
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Might want to swap out the pre-amp tube. My pj is pretty quiet.


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Posted: Fri Jul 20, 2007 3:33 pm
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I went through most of my preamp supply and they all hissed in the PJ but were quiet in other amps.

It's just the luck of the draw with PJs. Some hiss, some hum, some do both.

Finicky little buggers!


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Posted: Fri Jul 20, 2007 4:30 pm
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I hoped that Billm would show up around here. :wink:

I'm one of the lucky ones with a PJ that has no hiss, hum or rattle.


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Posted: Mon Jul 23, 2007 5:19 pm
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Thanks for all of the advice. Gee, in my book it seems like the Pro Jr. suffers from poor design. There shouldn't be that much variation in production. PLus, to cheap out on resistors - using carbon instead of metal film, c'mon! I'm a degreed EE, and used to design audio amps for Crest Audio. I'm torn between bringing this thing back to GC and trying to find a decent one, or cracking it open and firing up my soldering iron. I'm really disappointed in Fender.


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Posted: Tue Jul 24, 2007 10:22 am
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Remeber that there's a long tradition of using carbon resistors in guitar amps. Some think that it adds to the tone (I'm not one of them).

I've been puzzled by the variability of Pro Juniors for years. But if you get a good one, it's a superb little amp with great tone.


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Posted: Mon Nov 12, 2007 9:29 am
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Ok, Billm - I'm going to try your mods. I've got the Pro Jr. cracked open on my bench. From what I can tell so far all of the hiss, and most of the hum, are coming from the first tube stage - turning down the volume pot gets rid of 90% of the foul noises. Wish me luck.

Any advice on tube types? Are there 12AX7s that have lower noise - without sacrificing gain? Mine came equipped with GT/Sovtek tubes.


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