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Post subject: Anyone have a tried and true fix for the Pro Junior hiss?
Posted: Fri Jan 29, 2016 2:26 pm
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Hi everyone... I picked up a used Pro Junior MIA yesterday and it has the dreaded hiss. I knew a lot of these had that problem, but I got a good deal on it and thought I might could work through it. It is practically mint and even still has the clear sticker over the logo. Does anyone might know where I can find out a good fix? I've looked all over the web, but have seen people describe it different and conflicting ways to try and fix. I'm sure someone has it out there, there was just so much information on this I couldn't find the right answer. I'll tell the issues with mine and maybe someone here can help or point me in the right direction. The center screw was definitely an issue. I pulled it back a little and that cut down the buzz down a lot. The buzz/hum is still there after the tubes warm up, but its not as bad with the center screw out some. The hiss it has is not terribly bad with the volume all the way down, but increases as the volume increases. It also has a static type interference sound to it. And this is without anything plugged in, just amp to outlet. I've checked the tubes, and they seem fine. I've seen where to twist the grounds and possibly changing tubes, but it seems like that works for some and not for others. I'm basically just wondering if anyone has had experience and luck fixing the issue. I'm also wondering if maybe a noise gate will help. But if anyone can help, it would be greatly appreciated!


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Post subject: Re: Anyone have a tried and true fix for the Pro Junior hiss
Posted: Fri Jan 29, 2016 7:38 pm
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I went to John Fromel and got his supreme upgrade kit for CVR. Perfect! Fromel also makes a special kit for your amp..


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Post subject: Re: Anyone have a tried and true fix for the Pro Junior hiss
Posted: Fri Jan 29, 2016 8:37 pm
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Ok cool. I'll definitely check that out. I appreciate the info. I've been reading that certain tubes can cut it down. I'm thinking that's my first step, but I'm gonna wait and see if some other knowledgable folks chime in. I don't really have money to be throwing around buying different things to try, so just trying to figure out the best course of action. If someone has had luck with certain tubes, let me know which ones.


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Post subject: Re: Anyone have a tried and true fix for the Pro Junior hiss
Posted: Sat Jan 30, 2016 11:54 am
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Hiss is a demon that rides along with high gain. The best approach to start is to use a low noise preamp tube such as a JJ ECC83 gold pin.
You can look at the comparison chart for preamp tubes at Antique Electronics.com. They show the gold pin JJ appears to be lowest noise.
A 12AY7 or 12AT7 will lower the gain and noise. It might be a worthwile tradeoff.
Plate noise from the preamp tubes can be reduced with metal film resistor upgrades .
JJ EL84 power tubes will give a more musical tone for clean play.

But if you can get into the chassis, you can cut the gain of the power stage and the noise as well by changing the feedback resistance. The current feedback resistor is R27, a 100K resistor.. You can piggyback another resistor on top of it to lower the gain.
You can also series a 1K resistor with a 100K trim pot to piggyback on R27.
This lets you dial in the precise amount of gain/noise balance. Dial in less gain and noise for recording, or select high gain for dramatic live play.


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Post subject: Re: Anyone have a tried and true fix for the Pro Junior hiss
Posted: Sat Jan 30, 2016 5:49 pm
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Thanks for all that info TimsAudio! I know the hiss is part of things, so you can't totally get rid of it. I don't mind some. This has a little too much though. I'm gonna put some new tubes in as soon as I can and see if that makes a difference. I'm sure it will considering what I've read and your advice. If that can cut it down some, I will be happy and not go changing things around on the inside.


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Post subject: Re: Anyone have a tried and true fix for the Pro Junior hiss
Posted: Mon Feb 01, 2016 2:36 am
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jones2278 wrote:
I've checked the tubes, and they seem fine. !



I don't know how you can check the tubes for a hiss ? Only new tubes will tell.
Clean tubes 's socket. Re-tension contacts.


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Post subject: Re: Anyone have a tried and true fix for the Pro Junior hiss
Posted: Mon Feb 01, 2016 2:08 pm
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You might find some helpful info in these pages:

viewtopic.php?f=13&t=56947

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Post subject: Re: Anyone have a tried and true fix for the Pro Junior hiss
Posted: Mon Feb 01, 2016 4:53 pm
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Strattele52... That was stating I checked that they were seated properly and working.

Miami Mike... Thanks for that link. A lot of good info on there.


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