Skip navigation

Recently Digitech has released a new version of the venerable FX 10 BiFet preamp, The FX10 was an updated design of the original DOD BiFet 410 Studio Preamp. The original 410 was designed as a preamp for acoustic guitars with piezo pickups. It has a very high input impedance with no foot switch so it was an always on device.


There is also an XLR ouput connector next to the standard output jack presumably to go direct to a mixer for SR or recording. The “BiFet” label is sometimes misinterpreted as there two or “bi” FET devices in the circuit. BiFET actually refers the type of op-amp used with an FET input and a bipolar transistor output. The combination of these two device types produces an op-amp with good high impedance input with the FET  and an improved bipolar output with low impedance and good current drive abilities. The tone control is a “tilt” type EQ that provides simultaneous treble boost/bass cut or bass boost/treble cut. It is a very effective type EQ  that gives subtle shifts in tone around the mid point from 10 to 2 o’clock on the knob. The same basic tilt EQ is used in quite a few DOD overdrive and distortion pedals.


Here is the schematic for the original 410 Studio Pre-amp. It is a simple single op-amp circuit easily built by a diyer.  I have included  a circuit snippet from the FX10 schematic for comparison. The FX10 is a more complicated circuit with FET switches incorporated. You could build it on a piece of perfboard, or if you have the abilities I have included a simple PCB layout below.



This is a great circuit for an always on buffer or to follow an over drive or distortion that needs some post EQ. Try this circuit after a standard cry baby wah to see how it can improve the sweep.


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: