[60] Mini-Booster: Fat and Fatter

Date: December 12th, 2007 | Comments : [16] | Categories: DIY.

Fat switch

Here is a quick mod for my Mini-Booster pedal, to add a switch for fattening the sound.

Basically, the circuit uses LEDs to drop the voltage from the power supply going to the Mini-Booster. Instead of 9v powering the booster, the pair of LEDs will drop the power to about 5.4v (if using typical red LEDs).

Less voltage = less headroom, and the circuit will clip with smaller signals. The boost is still basically clean but the lower headroom adds a bit of grit to the sound for mo’ phat boostin’.

No other changes are required to make this work with the circuit. Current draw is low and well within the limitations on the LEDs. The switch can be any common SPDT with a center-off position.

I actually prefer to use blue or white LEDs with this circuit because of their slightly higher forward voltage, which gives the switch settings a bit more impact.

The switch position as shown in the drawing is equivalent to the original unmodified Mini-Booster; both LEDs are being bypassed. The center-off position is the fatter sound with both LEDs dropping the power supply voltage. When the switch is to the bottom, you get a slightly subdued version since one of the LEDs is bypassed and only one is dropping the power supply.

This same circuit will work with the AMZ Mosfet Booster also. Enjoy!


16 Responses to “Mini-Booster: Fat and Fatter”

[257] michiel Says: 8:50 am, December 12th, 2007

Wow, great!

I have one question: when using a power supply, should’t there be a cuurent limiting resistor in there? I think there could be one between the switch and the second LED, that would insure that in full bypas, there no resistor and that when using ether one or two LEDs the resistor is always in the path.

[258] admin Says: 9:12 am, December 12th, 2007

The current limit resistor is already there in the form of R4 on the schematic:


[259] michiel Says: 4:33 am, December 13th, 2007

Aha, ok, so the LED will not draw enough current to make them explode.

Should have seen that myself. I am definitely gonna try this out.
With the MOSFET booster, the limiting resistors would be R2 and R4?

[260] jan Says: 5:47 am, December 13th, 2007

Thank you. I will try this with my Mosfet Booster. Where do I have to place this little circuit? At point A at the schematic? (because of the current limit resistor?
Thank you…

[261] admin Says: 2:26 pm, December 13th, 2007

It goes between the positive (red) battery lead and the power input on the pcb or breadboard.

@michiel: yes, R2 and R4 on the MosBoost will limit how much current can flow.

[263] Sam Says: 7:14 pm, December 20th, 2007

Would this be a correct wiring diagram?


[264] admin Says: 8:37 pm, December 20th, 2007

That looks like it will work.


[265] admin Says: 5:36 pm, December 23rd, 2007

I might add that this trick would work well with a fuzzface type circuit too!


[286] jdavyd Says: 1:21 pm, February 8th, 2008

what about a ‘sag’ pot a-la the fuzz factory?

[489] Анастасия Says: 9:01 am, July 29th, 2008

Хорошая тема, продолжайте. Иногда нахожу ответы, которые получить самой просто реально не хватает времени. Спасибочки!

[Google translation: Good topic, please continue. Sometimes finding answers that get the most just really do not have enough time.]

[758] alf Says: 9:58 pm, August 2nd, 2009

Would it be possible to use a pot instead of the switch & LED’s so you could dial in a desired amount of “fatness”?

[885] BoxOfSnoo Says: 7:33 am, December 16th, 2009

I have built this, but wonder if it’s safe to feed 18v into the circuit now. Will it actually drop the voltage to 9v with both LEDs on?

[886] admin Says: 6:37 pm, December 16th, 2009

It is safe to feed it 18v but that will negate much of the effect that we are trying to create. The volatge drop will be less than 4v and that will still leave the circuit powered by 14v, which will be missing the fat sound.

[1293] dmc777 Says: 11:27 am, August 24th, 2010

Jack, I just purchased the mini booster pcb as well as the First Issue newsletter. In the email I was sent a link to the thread for help about the minibooster but nobody seems to respond really. Is there anywhere else to get help?

I built mine with the buffer. Shouldn’t it not be True Bypass since it’s acting as a buffer? Also, I’d like to add a gain knob and/or possibly the mod above but don’t know how to go about it. I understand I connect the leds to the switch but don’t understand where to put the leads. I see it says between the positive red battery leads and the power input on the pcb. Would I have to drill new holes for this? Any help would be appreciated.

[1294] admin Says: 11:35 am, August 24th, 2010

You can send me an email from my support page at http://www.muzique.com/email.htm

I will answer any questions that you have.

As for the switch mod above, you would solder the LEDs to the new switch… bring 9v to the switch center log, and a wire from one side lug of the switch to the pcb. You don’t have to drill any holes on the pcb.

[526777] Steve Says: 7:28 am, January 17th, 2015

I built this mod for the Mini Booster. It works in that the LED’s are lighting up correctly (they take a second or two to light up, but I presume this is normal) – but I am not hearing any difference, even with both LED’s on. I’ve tried different colours of LED’s. Is it possible to use different kinds of Diodes that might make a more obvious effect?


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