Fosi Audio M03 200 Watt TPA3255 Subwoofer Amplifier Mini Mono Channel Audio Power Amp for Home Theater Full-Frequency and SUB Bass Switchable with 32V/5A Power Supply

This little beast powers a JBL 3635 (18" passive theater subwoofer) with dynamics and authority for 2.1 channel music playback.I should also say I've become a little bit of a snob with audiophile gear over the years and I was not expecting much at all- my procurement of the M03 and the JBL 3635 was more so a fun way to add a subwoofer to my system cheaply to experiment with my room a little bit but it ended up being a keeper!The Sub Frequency knob allowed for seamless blending of subwoofer with main speakers (I assume this is some form of Low Pass Filter) and both this and volume knob provide a tactile click when turned to dial in each 1-2 clicks at a time, allowing for more precise adjustments. To integrate into my system perfectly, I have the volume knob at 4:00 and the Sub. Freq. at around 11:00. Meaning there's a touch of "gas" to spare for my situation with optimal sound with my 99 db sensitivity subwoofer.This little unit is solidly build in all aluminum construction and can easily be tucked behind main 2 channel amplifier or other devices on an audio rack if desired. I don't LOVE the look personally but its so discrete and easy to hide its not even an issue (I prefer silver faced gear with minimal branding like Schiit audio). When I acquired my passive subwoofer, I was a little concerned as to how I was going to power it in an aesthetically acceptable fashion (initially considering a Crown professional amplifier with 1000wpc bridged, but an uglier option) and this solved that problem with ease. Packaging is also quite nice for a sub-$100 unit.I'm unsure if this amplifier truly reaches specs in terms of output but it has performed exceptionally well for me, creating the ability to shake the entire house if pushed.This is a great little amplifier before factoring price into the equation. Once you do add price in, this is a top-tier subwoofer amplifier that is extremely capable. I would even consider building a passive subwoofer and using this instead of a plate amplifier just due to its value to performance ratio.If you have a passive subwoofer that needs power, this ought to do the trick! 10/10. Worth every penny.

UPDATE: The TAPE out hookup I mentioned below worked great for levels, but TAPE out is, by design, not controlled by the volume knob on my Pioneer receiver, so I had to constantly adjust two knobs, one under my desk at the sub, so not ideal. The solution? I just added a $25 preamp before the FOSI to have excellent subwoofer levels from the Pioneer subwoofer output, plenty of signal now at half volume or less on both the preamp and the FOSI main amp. The preamp is also a simple and excellent little device.https://www.amazon.com/dp/B0945RFJ6Z?ref=ppx_yo2ov_dt_b_fed_asin_titleI went with this preamp instead of some units, like the FOSI preamp, because it does NOT do any RIAA equalization that I did not want to add to the mix.I bought this FOSI to get my 24 year old KLH subwoofer running again.I am very pleased.I was able to remove the plate amp assembly and leave the SW box sealed on the back as it has always been, by the plastic box that had housed the circuitry.I might mount the FOSI in this plastic recess, but for now it sits atop the SW cabinet and if its rubber feet keep it from walking off I will just leave it there for ease of reaching the controls.This tiny powerhouse is driving the 8" KLH speaker to make better sounds and deep vibrations, than it has for years. Gone are the occasional deep pop and rattle sounds that I had thought might mean the speaker cone itself had deteriorated. It turns out the old cone is just fine. The KLH built in amp had apparently been slowly cooking its circuit board for a long time before it gave up completely last week.It looks like a bulging cap and some burned resistors... maybe I will fix that board someday.One word of warning. I was driving the old KLH ASW 100 powered subwoofer with an RCA Y-cable from the low level sub output RCA jack of a 20 year old Pioneer home theater amp. It turns out that the signal level on that jack is too low to get more than just a faint response from this FOSI, even turned up to the max.So don't assume this will be a direct replacement if you have that kind of subwoofer hookup.I ended up driving this FOSI with a dual RCA cable from the tape record outputs of the Pioneer, and I am getting loud, clear and rumbling bass from the FOSI at only about four clicks of the volume knob. The FOSI volume and freq cutoff controls have a nice, subtle, detent feel.