BENSON: Preamp, Mojo Vero Layout (with 1m bass pot mod)

The Benson Preamp is pretty popular, but 2M pots are hard to find.  This is a modded vero layout using a 1M bass pot.  To make this change and keep the same frequency response, resistances are halved, capacitance is doubled.  Note that the Drive pot value also had to be halved.

I'll add a regular size layout with normal 1/4 resistor later - just felt like a larger layout for this one.

BENSON PREAMP - MOJO VERO LAYOUT

BENSON PREAMP - MODDED SCHEMATIC

As you can see, the response is nearly identical between the stock and modded values.  This will change a little using stock cap and resistor values, but it will still be pretty close.

BENSON PREAMP - VIDEO DEMO

BENSON: Preamp, Dylan159 Modded

This is a modded Benson Preamp by Dylan159 on Freestompboxes.  Dylan has taken the original and simplified it but has retained the overall character.  Quite a detailed explanation via the link above, including a schematic, LTSPICE model traces, audio and his vero layout.   What a solid effort.

For me, this is useful, as it has a standard pot value for the bass control, rather than a hard to find B2M pot.

BENSON PREAMP - MODDED - VERO LAYOUT

note: pin 1 volume to ground

BENSON: Preamp

One of my older vero layouts for the Benson Preamp that I posted on Guitar FX layouts forum a while back - updated due to the bass and treble outer lugs being the wrong way around...

I have previously posted the point-to-point version, but I forgot to post the vero layout at the time.  I never actually boxed this one up, as I prefer the Fairfield Barbershop as far as JFET overdrives go.

It's a JFET adaptation of a Benson amplifier pre-amp.  Treble is a basic cap to ground situation - like a guitar tone control, and bass is cut, with the pot bypassing a small capacitor that limits how much bass can pass.

BENSON PREAMP - VERO LAYOUT

This is a JFET version of one of the Benson amps, which is I think why the pedal doesn't really have a proper name.

It's hard to find a B2M pot for the bass control, but you can use a dual B1M pot and gang the two sides together to reach 2M.  Check the Pedal PCB 'Son of Ben' build docs to see how.   

Or you can change somme values and use a 1M pot instead, see this post for values.

Like any pedal using J201 FETs, make sure you get proper ones, or it just won't work very well (I naively tried cheap J201 FETs once - it sounded awful).   

There's a thread on Freestompboxes where Mr Benson jumps in with advice too.  Nice guy...   note: the schematic on freestompboxes has a 330pf cap listed instead of the 250pf cap on the Pedal PCB schematic.  The 250pf value was supplied by Benson.

BENSON PREAMP - POINT TO POINT LAYOUT