L-Pads (L refers to the shape of the network, the way the parts are connected to form the pad. Some also refer to the L as
meaning Loss or Losser Pad) are used to decrease the output level of a speaker.
One use for an L-Pad attenuator is to be able to crank your amp into power
tube distortion, and then reduce the power to the speaker to a comfortable level.
L-Pad attenuators, as noted in the picture below are rather simple devices, and you
can build one yourself. All you have to do is calculate the correct resistance for the
attenuation you want, then make sure you have the correct power rating on the resistor for the
amp you intend to use it with. You must ensure that you put in values that correspond to
the amps output impedance, so the total impedance will be calculated to be the same as the amp.
This is critical if you intend to dime your amp with heavy distortion (compressed signal, square wave).
An L-Pad is nothing more than 2 resistors, one in series (R1), and one in parallel (R2) with your speaker.
From amp output
Z = Your amp output and speaker impedance (very important).
A = The amount of attenuation you want in DB.
If you want to experiment with equalizing it, you can try different values of nonpolarized capacitors across R1 for a treble boost, different values of inductors for a bass boost, or a combination of both.
These are low impedances, so the values would be in the microfarads and 10's of millihenries.
You can make the L-Pad variable by substituting ganged rheostats for R1 and R2. Or, you can hand select
several resistors that will be switched in as sets for R1 and R2. Remember to ensure that you match the input impedance
of the L-Pad to the amplifier output impedance if you are going to dime the amp.