Billm Blues Junior Clean Boost

One of the ongoing complaints about the Blues Junior is that it doesn't "step out" enough when you're going from rhythm playing to solo. If you're going from clean to distorted, a pedal is an excellent solution. The Fat switch gives you a boost in loudness and a bass boost, but it isn't quite enough to cut through the rest of the band. Players who have tried supposed clean boost pedals with the Blues Junior usually discover that if they're playing close to breakup, the boost isn't clean anymore when they cut in the pedal because it drives the preamp into distortion.

For everyone who has wished for more volume without a tone change, I hereby present the Billm Clean Boost module. It's one square inch, mounts right on one of the existing circuit board retainer screws, and all the connections are done from the top of the circuit board--no need to remove it or get to the back side. The clean boost module adds about as much additional loudness as the Fat switch, but without the bass boost, and it does it at any volume level, all the way up. It boosts clean signals or distorted, and doesn't change the tone. It does not suck tone or alter the Blues Junior's tone in any way when it is off. Like the Fat switch, the Clean Boost increases the gain of one of the Blues Junior's tube stages. But unlike the Fat switch, it doesn't increase distortion or boost the bass significantly.

The easiest way to use it is to wire it to the Fat circuitry, so it comes on with the Fat switch, for a noticeable boost in power. But you can also wire it in conjunction with a pull-up switch on the (Billm mod) presence control so that it comes on without the Fat switch or so the Fat switch comes on without the Clean Boost.

This is the Clean Boost module. It's 1 inch square and it connects to your amp in three places. All connections are from the top of the circuit board, so there's no need to get to the back side.

R3 is a thumbwheel trimpot that lets you adjust the amount of boost. If you're not running the boost along with the Fat switch, you'll probably leave it wide open. If you're combining the Fat and Clean Boost, and the jump in volume is a little too much, you can dial it back. This is probably a one-time adjustment for most users.

The Billm Clean Boost uses premium components, including a Bourns cermet trimpot for reliable, static-free operation, and a Xicon low-ESR (equivalent series resistance) capacitor for maximum efficiency. It switches in and out silently, with no pops or clicks. The active connection uses Mogami low-noise coaxial. This is mixing board/studio-grade cable. The control and power connections are stranded, Teflon-coated wire for ruggedness and resistance to the errant soldering iron when you install them.

Here's the Clean Boost module installed in a cream-board Blues Junior. This one is wired to go on with the Fat switch. I provide a longer hold-down screw with the kit, so that it remains securely in place. The back is cushioned to prevent buzzes and vibration damage.

The voltages on the board are low, so that you can adjust the boost trimpot safely, but always follow the rule of one hand in your pocket when reaching into an amplifier--and don't touch anything else!.

Although shown on a cream board, it works equally well on a green board, including those with existing Billm mods. For amps that already have the presence/bright switch, it can be wired to come on with the bright switch and/or with the Fat switch. I supply the module fully assembled and tested, with instructions and wiring options.

$40 plus shipping. Email me for details

The loudness boost, when combined with that of the Fat switch is dramatic. I made some tests with continuous, harmonic-rich tones, similar to what you'd get from a guitar, and wired one of my Blues Juniors so I could turn the Fat and Clean Boost on and off independently.

I tested 400Hz and 1500Hz tones, starting a higher volume level with the 1500Hz tones::

  400Hz 1500Hz
Starting Level 90dB 100dB
Fat Switch 99dB 107dB
Clean Boost 97dB 106dB
Both 105dB 111dB





As you can see, the boost is somewhat more effective at lower frequencies, but the 11 to 15dB of total gain is an amazing difference. The boost remains effective even at 12 and 12 on the volume controls (wear your earplugs!). The Blues Junior has some untapped power hidden away in there, and the Clean Boost module brings it out--dramatically.

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