Craig Anderton published a design many years ago for a frequency booster project that was based on a circuit that first appeared in Electronotes, as I recall. It’s a nice little EQ boost but it is not formatted properly for guitar pedal use. It is powered by two 9v batteries and needs some minor redesign to allow use with a single 9v or standard power supply.
The schematic at the top of the article is my modified version of the original frequency booster design. A bias supply and a few other essential components have been added to adapt the circuit to 9v power. This is a simpler adaptation than the updated version that later appeared in Do-it-yourself projects for Guitarists.
Please note that you must drive this eq circuit with a low impedance, such as an opamp output or a buffer of some sort. If you use a dual opamp, one section can be used for the buffer and the other for the equalizer.
I suggest a starting value of 0.047uF for C1 and C2, but you should select the values depending on what frequency you want to modify, and the 100k resistor on the circuit output can be made a volume control if you need to trim back the output. Enjoy!
This circuit arrangement looks at a glance like the HI band of the Studer 169 EQ. I’ve breadboarded that and liked what I heard on some briefing tests.
Thanks for presenting.
My guitarist has been using one of these I built for him – it replaced an MXR Kerry King eq on his pedalboard as his main lead boost. I have it wired with a 3-way switch, cap values to boost at approx 400 Hz, 600 hz and 900 Hz. Great little circuit 🙂
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Which transistor would you recommend as the FET op-amp?
Thanks!
Anders, the TL071 will do the job.
regards, Jack
Thanks. Ah, an IC! Forgive me my ignorance…
I am building this. So, do I only connect legs number 2, 3 and 6 of the TL071?
Also, pin 7 of the TL071 goes to 9v and pin4 goes to ground.
regards, Jack
not working for me. just generates sin wave signal. if C1 and C2 is disconected, then working as clean preamp
You must drive it from a low impedance source. See the next to last paragraph.
regards, Jack
For some reason when i have it on 9 volts it makes some weird noise but when i unplug 9v it acts like a preamp like “runce” said.