WTF is a Logarithmic Overdrive?

Help!I'maRock!

Help!I'maRock!

Mediocringly Derivative
lumberjack.jpg


LUMBERJACK

Congratulations on your purchase of the LUMBERJACK, the revolutionary new log overdriver by ELECTRO-HARMONIX. The distortion character of the LUMBERJACK changes depending on your playing dynamics, ranging from a powerful clean boost to subtle torn-speaker overdrive to gritty distortion. The LUMBERJACK is housed in a durable, compact die-cast chassis, and includes true-bypass switching to keep your bypassed tone intact.

- CONTROLS -

BOOST Knob – This knob controls the volume of your input signal. It can be used to boost a quiet guitar, to achieve more distortion, or, when set to higher settings, allows your natural guitar tone to blend with the overdriven signal.

LOG FACTOR Knob – This knob controls the amount of logarithmic distortion created by the LUMBERJACK. As you turn LOG FACTOR clockwise, overdrive distortion increases.

VOL Knob – Sets the output level of the LUMBERJACK.

FOOTSWITCH and LED – The Footswitch selects whether the LUMBERJACK is engaged or in true bypass mode. When the effect is engaged, the LED is lit.

INPUT Jack – This ¼” jack is the audio input for the LUMBERJACK. The input impedance is 1M Ohm.

AMP Jack – This ¼” jack is the audio output from the LUMBERJACK. The output impedance is 100 Ohm.

9V Power Jack – Plug the output of the supplied AC adapter into the 9V power jack located at the top of the LUMBERJACK. The LUMBERJACK requires 100mA at 9VDC with a center negative plug. The LUMBERJACK accepts Boss/Ibanez style AC Adapters.
 
I'm guessing it uses a log amp which provides a non-linear feedback loop for the amp circuit.

I'm not sure what this mans for the sound. Weird.
 
My guess is that they just used an audio taper pot for the gain (Log Boost) instead of a linear taper pot.
 
With potentiometers, linear vs. logarithmic taper has to do with how we hear sound. What is mathematically linear in terms of current doesn't sound linear. In other words, to our ears, half the current is not half the volume. Logarithmic taper compensates for this by reducing current in a non-linear way so that "5" sounds half as loud as "10".

Perhaps this boosts the input signal in a logarithmic fashion so that hitting the strings harder has a more pronounced distortion effect. That could potentially (pun intended) be cool. It would also fit the ad copy description.

Or it could just be another fun/funky EHX dirt box. :)
 
Oh, I see now.

By putting a diode in the feedback loop of the circuit, the current in the feedback loop varies exponentially (a.k.a. no linearly) with the applied voltage.

So, dig in a little bit more gets you a whole LOT more via the circuit feedback loop and, presumably, more dirt.

That's why they describer it as, "Depending on your dynamic level, its response ranges from powerful clean boost to subtle torn-speaker to gritty distortion."
 
My guess is that its an OD w/ a knob (log knobby) to dial in a diode to square the waveform and add distortion to the OD.
 
USian Pie said:
I think the idea is to accentuate it.

On a scale of 1-10, if you hit the strings at a "3", the distortion reacts as a "3". If you hit the strings at an "8", a logarithmic distortion might react more like a "15".
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so they cloned the BOSS Dyna Drive?
 
Help!I'maRock! said:
But doesn't any decent distortion pedal do this?
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My basic understanding is that from a 'techie' perspective, w/ OD the amount signal amplification is input amplitude (signal level) dependent...the whole touch sensitivity aspect. Distortion applies amplification to the input signal irrespective of input levels.
 
USian Pie said:
Perhaps this boosts the input signal in a logarithmic fashion so that hitting the strings harder has a more pronounced distortion effect. That could potentially (pun intended) be cool. It would also fit the ad copy description.
Click to expand...

You type faster than I.

That's the concept behind a log amp.

Help!I'maRock! said:
But doesn't any decent distortion pedal do this?
Click to expand...

It's not so much the direct input level that drives the amplifier circuit in the pedal into distortion - that's only part of it.
The feedback loop in an amplifier circuit plays a large part in balancing out the circuit.

Using a log amp gives you dynamic control over the current in the feedback loop. So, this pedal follows the dynamics of your playing.


The diode at the top of this circuit diagram is they key. (the triangle thingy with the line at the point)

LogAmp.png
 
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