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A Mod for the Fender Blues Jr.

meh 9/2001
 
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First Impressions

First of all, to my ears there wasn't a huge difference. The modded amp is definitely a little "chunkier" at high volumes, and has a bit more gain and overdrive. This was most noticable when it was really cranked. Also, it seemed to have a better "clang" when played at lower volumes. The amp did not seem noticably noisier afterwards, which is always a good thing.

Other Modifications

I still wanted a bit more gain, (and as I already admitted, I'm a fiddler) so I made the following circuit changes as well.

  • Effectively lowered R13 to about 10K by jumpering it with an 18K resistor.
  • Jumpered R18 (= 0 ohms). This unbalances the PI a bit, as is done in the old circuits. While the 9K/91K split plate load is a good "hi-fi" improvement from an engineering POV, it is not the same as the "old stuff."
  • Replaced R26 with a 10K pot = "Presence". I used a 14mm pot and squeezed it into the space above the "FAT" switch.

Note (9/2007): I've since also made Bill M's tone stack and reverb mods to it. I like the new (old?) tone stack, but it's a bit bass-heavy for me, so I may tweak it some more. The reverb mod (changing it to the later, post-MV return) was a definite improvement. I'll update the schematics and record new sound clips when I get some free time. ;-)

Schematics

Here are partial schematics with the modifications shown:

The input section

The output section

Sound Clips

Here are some sound clips of the end product. I'm using Phillips 6BQ5 NOS output tubes and the Weber 12F150 (formerly wC12N) speaker.

The amp was miked using an SM57 into an older Mackie mixer then into a mid-fi cassette deck. The tape was then sampled using a run-of-the-mill Sound Blaster 128 card.

The guitars (a Fender American Standard Telecaster and a middle-aged Ibanez solid body) were plugged directly into the amp with no effects. Let's not discuss the quality of the playing (or lack thereof) please!

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