# My blues junior mod went bad



## Studiocat (Apr 24, 2007)

Hey guys

Just looking for any tips I can get before I take this to an amp tech.
I opened up my blues junior (green board Rev B) to do a few modifications, but I didn't get very far. 
I bought a few of Bill M's mod kits online, and he sent them over with lots of good instructions. The first mod I did was to change the input jack. Basically, you de-solder the crappy stock plastic jack, clip a jumper, and hard wire a connector directly to R1 and R2. Simple enough. Did that, quite nicely I thought, but now the amp is making a pretty loud hum. Like something is shorted out.
The new input works, but the hum remains whether there is a guitar plugged in or not. The only knob that has an effect on the hum is the reverb knob; it gets more or less high end buzz as I turn it.
Stupidly, I didn't test the amp after removing the circuitboard, which on these amps is a bit of a pain. So I don't _really_ know if the problem was there before I did the input jack mod. I most likely damage something during the disassembly process. I went over the major parts, to see if any of the big caps were loose, but found nothing obvious, like loose solder joints. The ground wire is still connected to the chassis.

I don't really know how a professional amp tech troubleshoots problems like these. All I have is a mediocre multimeter and a little bit of electronics knowledge. 

I would love any suggestions!!

Thanks so much
Adam


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## Studiocat (Apr 24, 2007)

Hey.
Solved, thanks to Bill M himself. Just needed to ground out the speaker jack that was hanging freely.
I sent him a few pics and he told me:

"Everything looks OK. You should ground the black speaker output wire to the
chassis, however, or the negative feedback loop won't work and may cause
some noise. Or just reinstall the jacks with the rest hanging out.

I had one customer recently who said that he had a lot of hum but that it
went away when I he put the board back in the chassis. When I test them, I
put a piece of cardboard behind the board so nothing shorts out and bring it
back towards the chassis, but don't re-bend everything to get it back
inside.

The two places where you're most likely to induce hum or buzz are the ribbon
cables for V1 and V3. You can temporarily shield them with aluminum foil
(grounded to chassis) to see if that makes a difference."


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## jcayer (Mar 25, 2007)

Good !!!

I just read your post... Not shure I could help but the first thing that came to my mind was to tell you to communicate with Bill M.

Now you can continue with the mods :smile:

Good luck on your project. :rockon:


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## Studiocat (Apr 24, 2007)

I'm totally pumped.
Just installed the presence control. Awesome. Tone stack mods next!

A


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## Gunny (Feb 21, 2006)

tone stack mod is a very good improvement. I'd recommend the bias adjust pot too. If you go for that but get stuck let me know. I've installed 3 of them for others...and I'm not far away.


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## Studiocat (Apr 24, 2007)

Wow - tone stack IS good. Just did that and the "twin stack" mod. Twin stack allows you to completely roll off the mids if you want to. When you set the tone knobs to zero now, the amp turns right off.

Doing the power stiffening mod now, and I'm just waiting for Bill to send me instructions to do the bias control on the green board. I have the trim pot but I got the cream board instructions by accident. 

A


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