From chasetone:

In the 1960s and 1970s, Echoplex tape echo delay units evolved from tube based designs into solid-state designs. Notably, the EP3 model was a solid-state model and had a few variations and revisions to the circuit. A select number of EP-3 models are highly sought after by musicians for their unique musical tone.

Famous musicians of the era and later realized having the EP-3 in their signal altered their tone, even when the echo was bypassed. An internal secret preamp was at work here, boosting and fattening the signal, along with a slight phase shift that alters mid and high frequency harmonic content providing a transparent warm boost – a truly secret preamp boost in the arsenal of the great guitarists of yesteryear!

But not all vintage EP-3s boosted, some dropped in signal due to the wrong TIS58 JFETs, and some were mediocre in tone being a different circuit revision. So, over a decade ago I did something about it! The Chase Tone® Secret Preamp™ Effects Pedal uses fine-tuned circuit components to ensure proper results. It is currently the only authentic replica of the most sought-after, musically transparent signal-boosting Echoplex units.

Features:

• AUTOMATIC Vintage EP3 22V+ POWER!
• (NEVER APPLY VOLTAGE HIGHER THAN 9VDC! Internal circuitry will automatically ramp 9VDC to 26VDC and then regulate and filter at 22VDC Vintage EP3 Power! )
• VOLUME CONTROL- Wired just like an original EP3 for Amazing Versatility!
• Vintage 1970s JFET cherry picked to cream-of-the-crop specs.
• Orange Drop 225P Film & Foil Polyester capacitors for the original, distinctive-yet-transparent tone.
• Professional Low-Noise PCB DESIGN: 

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This preamp is in excellent condition, no apparent scratches or scuffs, and comes in the original box. This pedal has been thoroughly inspected and tested by our expert tech.