The two keys to the quality audio this device produces are the fact that it is a tube type amplifier. The tube creates a "richness" to the voice that cannot be explained but you know when you hear it. The other key is the "Big Bottom" feature. This feature really enhances the lower frequencies which is especially good for baritones. These units are not inexpensive to repair.These units ARE worth every penny. I have multiples as back ups Only because my current unit failed and I was without it for days waiting on Audio Rehab to repair it. It is once again fully functional and back in service and way better than it was before. I have yet to find a preamp that matches what the APHEX Channel can do. The APHEX units are in limited supply and most of the listings you see are for APHEX units that are not working/for parts. Understand that most of these units are 10 plus years old and have likely never been serviced. Even though the repair shop is certified to repair them, just like the preamps themselves, parts are in very limited supply. If you want to hear a difference in the quality sound the APHEX produces, follow (copy and paste) the link below to a demonstration recording comparing the difference between just a Presonus audio interface, a Presonus audio interface in conjunction with a Presonus Studio Channel preamp, and finally, the Presonus interface with the APHEX. This item is in the category "Musical Instruments & Gear\Pro Audio Equipment\Preamps & Channel Strips". The seller is "clone43068" and is located in this country: US. This item can be shipped to United States.