Blues Junior Billm Mod with Audio Samples

I love my Fender Blues Junior. My parents gave it to me as a Christmas gift back in 1999 and became my first tube-driven amplifier. It has a beautiful clean to slightly overdriven tone that I’ve never tired of. But….

…despite its glassy yet smooth tone perfect for classic rock and blues, the Blues Junior isn’t without its flaws. After playing other amps of equivalent size, I started to notice that the Blues Junior didn’t have enough low-end punch. Although it features a 12″ speaker, it didn’t produce the bass that I thought it could. I didn’t know that there was any way to fix this flaw, so I lived with it. Until now, that is.

I found Bill Machrone’s Blues Junior Modification website. Known simply as Billm by many of his fans and customers, Mr. Machrone offers modification kits to anyone savvy enough with a soldering iron. The kits include electronic components such as capacitors, resistors, potentiometers and the like, as well as instructions on how to install them in your Blues Junior. Mr. Machrone’s site promised improved bass response. That’s what I wanted, so I performed the modifications found in Billm’s basic mods kit with the help of my father.

I couldn’t just perform the mods and let my memory of the old sound compete against the high expectations of the new sound. I’m too much of a nerd for that. I wanted to capture the sound of the Blues Junior before and after the modifications were completed.

I used my loop station to record a 20 second guitar riff used it to record 5 different amp settings before I modded the amp. By doing so, I removed performance differences from the equation. Then, I performed the modifications and re-recorded that same riff with each of the five amp settings. Here’s what I recorded:

Test 1 – Before the modifications:

Test 1 – After the modifications:

I started with the treble, bass and middle knobs set to exactly midway through their sweeps. I felt this setup would give us enough gain to sound good and also allow plenty of room to crank the knobs for later tests. Notice that the master and volume knobs are set to a modest level. I’m not interested in a high-gain distorted sound until the very last test. As you can hear, the bass in the “before” example is weak, while the bass in the “after” example is very strong. I could hear the difference immediately.

Test 2 – Before the modifications:

Test 2 – After the modifications:

For test two, I turned the bass all the way up. Yes, the knobs do go to 12. That’s two higher! Anyways, even with the bass cranked, the “before” example sounds like a little guy trying to sound like a big guy. The “after” example is strong and probably too powerful for my tastes, but it is nice to know that I have that kind of extension in the bass now.

Test 3

Test 3 – Before the modifications:

Test 3 – After the modifications:

In test three, I cranked the treble all the way up. I wasn’t expecting to hear much of a difference since Billm’s mod kit didn’t say anything about the treble side of things. Earlier in this article, I used the term glassy to describe the Blues Junior’s un-modded high-end and I’m glad to hear that the added bass in the “after” example has buffed the jagged burrs right off the treble. The highs are now crisp and smooth.

Test 4

Test 4 – Before the modifications:

Test 4 – After the modifications:

For test four, I cranked the mids all the way. Of all of the before-and-after comparisons, this is the least noticeable.  Although the “after” clearly sounds better because of the bass, the mid-range has that same nasal sound in both examples.

Test 5 – Before the modifications:

Test 5 – After the modifications:

Test five shows why there can always be too much of a good thing. I cranked the volume, which saturates the preamp stage with gain, and left the treble, bass and middle knows at 12. I also backed off on the master know so I could keep roughly the same output volume as the other tests. The distortion in the “before” example has a clear articulation to it, while improved bass in the “after” example simply muddies the sound up. In this case, the “before” example is better but I could easier get a more focused distortion sound by rolling back on the bass and mids a bit.

The modifications improved the amp’s sound much more than I could have hoped. What fascinates me is that the modifications were purely electronic. I still have the same speaker and cabinet, just different capacitors and resisters in a few places. Amazing.

I enjoyed performing the mods so much that I ordered a presence control and a new input jack. I can’t wait! Thanks Mr. Machrone, you rock.

For more information about me and the guitar lessons that I give in and around Baltimore, visit

5 responses to “Blues Junior Billm Mod with Audio Samples

  1. I remember when you got the Blues Junior for Christmas. We packed up my truck to head back to College Park and I didn’t account for the fact that the Blues Junior was slightly larger than your old amp — and it busted the window crank on the passenger’s side!

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  3. Blues and Classic Rock riffs sound awesome on my stock BJ sounds. It has a very sweet and creamy mid range tone and sustain with the right pedals.. However the lack of tone control on the stock amp makes it a one-trick pony in my view. While I wouldn’t want to lose what the amp is already good at;doing by modding it, I want to add more tone versatility for other types of music (e.g. Country, Pop, Jazz).. Thanks for taking the time to provide such good examples of your results and for documenting them so very well. Most excellent work! More than other reviews, you have given me a lot more confidence in proceeding with the BillM mods. BTW, It would be interesting to hear your findings in the event that you ever decide to also change the output transformer as BillM recommends.

    • Don, thanks for stopping by. I’m glad that you found this demo helpful. I’m surprised more people don’t use a looper to conduct A-B test like this. Oh well…
      Anyway, if I ever perform another BillM mod, I’ll definitely do another demo like this one. Good luck with your mod. As long as you’re good with soldering iron, you’ll be fine. If not, practice on a Radio Shack electronics kit.

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