making an LPB1 a Treble booster

[KevinPA]

ok so first of all, I'm new to DIYing pedals and I'm about to embark on my first project with this

I read this very handy breakdown of an LPB1 schematic on beavisaudio.com check the link http://www.beavisaudio.com/techpages/HIW/hiw1.gif

It says I can turn it into a treble booster by simply changing the values of the C1 capacitor (which in the schematic is 0.1uf) and the R2 resistor (which is 43kOhms). Seems easy enough for a first project. It's a very cheap pedal and I already have one.

Is it a bit more complex than that? If not, does anyone know what I should change the values to to get a treble boost without getting any volume loss?

Again, I'm new to DIY, electronics, soldering and electrical engineering so layman's terms would be much appreciated


Thanks

[jonfoote]

nope, it is that simple

the cap and resistor make a high pass filter, effectively reducing (but not entirely cutting) the amount of bass going into the circuit. changing these so the cut off frequency is higher will mean more treble coming out the other end as you turn up the volume of the LBP.

[Tonemonger]

See if you can find a schematic for an EH Screaming Tree - It's the same.
I made one about 20 years ago at a slightly lower freq. and it still gets regular use.
There's just something "organic" about some 1 and 2 transistor circuits.
Have fun !

[Mark Hammer]

Not so fast.

A "treble booster" may, or may NOT also imply a "bass cutter".  Some folks feel that having a bass rolloff that starts up high, and continues at 6db/octave down towards DC is a treble booster.  And yes, it DOES make the treble the most obvious part of thesignal.

Others would say that a treble booster is precisely that: something that leaves everything below a certain frequency untouched, and merely increases everything above a certain frequency.

The two are, and sound, different.

The Beavis audio document correctly identifies the input and output caps as places where the amount of bass content can be adjusted.  However, making those caps lower in value gets us the first type of treble booster and not the second.

If you wanted the 2nd type, then the easiest way to accomplish that is to use the AC bypass cap and make the cap value small.  For example, if you look at the Alembic Stratoblaster - http://www.generalguitargadgets.com/pdf/ggg_sbb_sc_i.pdf - you will see a 10uf cap in series with the Gain control.  That 10uf cap provides an "express lane" for AC, going to ground.  When the Gain pot is at maximum resistance, it is a more direct route for the AC to go through the 12k fixed resistor.  make the 50k resistance smaller than 12, and all of a sudden, the audio finds an easier path.

WHICH audio?  Good question.  the portion of the audio spectrum that has the "easier" path to ground is dictated by the value of that electrolytic cap.  In this instance, a 10uf value assures that any gain will be applied to the entire signal.  If, however, you make that cap smaller in value, then whatever additional gain is produced is only applied to signal somewhat higher up. 

Assuming that the normal rules apply, for each halving of the cap value, the frequency where the gain begins to be applied moves up by an octave.  So, if 10uf gave us a corner frequency of 20hz, the 5uf would get us 40hz, 2u5 would get us 80hz, 1u1 would get us 160hz, and .505uf would get us a treble boost starting around 320hz.

Note that in this instance there is no impact on the content below that corner frequency, merely boost applied to what is above it.