Friday, 10 November 2017

EHX "Booster" pedal family

I've recently been exploring some of Electro-harmonix early pedals... The LPB-1, the Screaming Bird & the Mole. They are really simple circuits & fall into the family of Boosters - all using a transistor for amplification.
The component values determine if the circuit boost all frequencies, bass or treble.

The LPB-1 boosts all frequencies, cutting nothing out.
R1 & R2 can be 430K & 43K respectively.
The transistor is a 2N5088 on my vintage example but you could also use a 2N5133 or BC239
if building your own.
 The Screaming Bird boosts treble.

The LPB-1 and the Screaming bird pretty much are the same circuit apart from
two capacitors (C1 & C2). The first part of the circuit (C1 & R2) work like a high pass filter.
Increasing the value of C1 should let in more bass. If you decrease it, more treble should appear.
With 0.1uF, most of the input signal goes through. In the case of the screaming bird, EHX have indeed reduced C1 to introduce more treble.

The Mole has a slightly different design even though one can see a family resemblance to the LPB-1.

EHX added two caps (C3 & C4) and again changed the value of C1 & C2 (the coupling caps).
R2 & C3 form a passive Low Pass RC (Resistor-Cap) filter .
R3 & C4 do the same. We have two LP filters ... before & after amplification.

+ Electro harmonix time line
+ My LPB-1

1 comment:

  1. Thank you for sharing this information, Its has help me to know more about Music Bass Booster