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Blues Jr - Dial In the Tone -9

Posted by Jim Black on 7/11/2015 to Mods

I've got "Ice Pic Tones In My Ears."

Love It, Love It, Love It!

Remember last time I decided to change the tone stack mid capacitor to make the tone stack like a twin reverb. Boy, did it pay off. I'm hearing the classic fender tone coming through---Strong mids, punchy bass and shimmering highs. This amp went from thin and raspy to the beauty I had hoped for.

My friend, Garth came over and we A/B compared his blues jr to mine while I completed the mods. Also, further reading on the Billm website revealed more sources of high frequencies.

Read on while we wrap up these mods and review the changes we made...

Blues Jr - Tone Assement -8

Posted by Jim Black on 4/24/2015 to Mods

This week we take some measurements to see how far off we are from our goal. We need to ask questions like "Did I Accomplish what I set out to do?" "Is it just me?" "Am I asking too much?"

I fired up the Blues Jr and I must say this amp is dark! Way too dark for my taste. There it is, I just said it. My Taste I relied on Bill's comments to guide my decisions and found that we have different views about how the highs are defined.

" and the moderate highs keep the ice pick tones out of my ears."

Ice pick tones don't sound appealing.

Find out how we recover from a wrong turn..

Blues Jr. -- Speaker Selection -7

Posted by Jim Black on 4/10/2015 to Mods
The Billm mods website has a very long discussion about speakers for your Blues Jr.
 
My legacy came with a Jensen Special Design C12N. The frequency analysis I did showed that the lows and mids were well under the predicted level that the Duncan Tone Stack showed. I try some experiments to get the levels I want...

Blues Jr. -- Output Transformer -6

Posted by Jim Black on 3/27/2015 to Mods
The last mod for the Blues Jr. is the Output Transformer. This mod is the key to getting that nice tight low end I am looking for. The new transformer has slightly more loudness than the stock transformer and no distortion in the bass end.
 
Let's put one in my Legacy Blues Jr.

Blues Jr. -- Power Supply and Trimmer -5

Posted by Jim Black on 3/13/2015 to Mods
We go big with the power supply then things get a little scary when we drill holes in the PCB to add the bias trim pot.

Blues Jr. -- Tone Stack -4

Posted by Jim Black on 2/27/2015 to Mods
The chassis is on the bench and the PCB is partially removed so we are ready to actually start the mods.
 
A Word of Caution About High Voltages in Power Amps
Discharge high voltages before you start work on any amplifier. I show you how it is done.
 
The tone stack mod replaces two caps in the tone stack itself and two coupling caps.
  • C6 0.1uF Bass
  • C7 0.015uF Mids
  • C2 0.022uF Input Coupling
  • C8 0.022uF Output Coupling
The goal of the mods is to increase the bass and the mids. The choice of the components reflects this goal.

Blues Jr. -- Diggin' Deeper -3

Posted by Jim Black on 2/13/2015 to Mods
The back cover is off the amplifier after removing the rusty screws in the last installment.
 
I bought the basic and output transformer mods from the billm website in the hope that I can get a tighter low end and more headroom before the amp starts breaking up
  • Tone Stack
  • Power Supply Stiffener
  • Bias Trimmer
  • TO20 Compact Output Transformer
  • Swamp Thang Speaker

Let's see how to install the mods and set the bias...

First, we need to get the PCB out of the chassis. Here is a nice technique to remove the knobs from the panel.

Blues Jr. -- Get Into It -2

Posted by Jim Black on 1/30/2015 to Mods

I decided to do the basic and output transformer mods from the billm website in the hope that I can get a tighter low end and more headroom before it started breaking up.

  • Tone Stack
  • Power Supply Stiffener
  • Bias Trimmer
  • TO20 Compact Output Transformer
  • Swamp Thang Speaker

Before I could do anything, I had to get into the box. Check out what happens next.

Blues Jr. -- Billm Mods, Preparation -1

Posted by Jim Black on 1/16/2015 to Mods
Frequency response is what it is all about. Before I rip into the Fender Blues Jr., I want to document the frequency response from the factory.
 
I have decent ears and I can hear subtle differences; however, I can't do an A-B comparison on this mod. Only 250 of the Legacy Blues Jr were made. Even if I could find one for sale, I'm not sure I want to own two.
 
Thankfully, there are reasonably priced tools just for this purpose. Let's have a look on how to use them...

Blues Jr. -- Billm Mods -0

Posted by Jim Black on 1/2/2015 to Mods
Modifying a Fender Blues Jr - Getting Started
 
If you are like me and a million other guitar players, it all starts so innocently. You get your first guitar and amp and find out you want just a little bit different tone. So you buy a louder amp. Then you get that really cool guitar you saw Joe Satriani playing because you know that is all you need to get *that* sound. As we all know, it never stops once it starts.