Audio Projects

Audio Express BT170 Amplifier Review

Added: 2-May-2025
Updated: 5-May-2025

Like most audio cheapskates, I'm always looking for that sweet spot of high fidelity at a price where I don't feel like I've overpaid. I guess Grandma was right when she said I've got long pockets but short arms. Anyway, I thought my search had ended back in 2014 with an upgraded version of the Lepai Tripath TA2020 Class D amplifier. I've been using that with a separate Logitech Bluetooth adapter to provide connectivity with wireless devices. Recently I've noticed several inexpensive amps hitting the market with built-in Bluetooth, and while the existing setup works fine, the thought of having one fewer component adding to cable clutter is a good incentive to upgrade. Besides, the scratchy volume pot was starting to laugh at DeoxIT... so the search was on to find a suitable replacement for my now-ageing Lepai.

There are a ton of Class D amps on the market now, but separate bass and treble controls are also important to me. I spotted this tiny Audio Express BT170 amplifier with these features for just $23 USD, and with lots of favorable reviews I couldn't not check it out. Somewhere in the specs I read that the amp has a 90% efficiency rating and assumed it had to be a Class D design. It wasn't until the teardown after it arrived that I was able to look up the specs and see that it is actually a Class A/B amp. As the saying goes though, the proof is in the pudding... and I was pleasantly surprised by the results.

I listened to it first with the ubiquitous stock 4558 Op Amp (preamp) IC before removing it (and destroying it in the process - there goes 3 cents... so I guess in this case the "KIA" marking on the chip stands for killed in action). I replaced it with a socketed, pin-compatible equivalent (OPA2134PA). That improved the sound quality a fair amount. This amplifier is only rated at 7 Watts per channel, but as a near-field listener, this is perfectly adequate for my desktop setup with sound clarity being the priority over sheer power... and this device delivers!

The bass and treble knobs are in the expected positions and the boost/cut levels and rollover frequencies seem intentional and good. Sound seems to barely touch clipping levels when the volume is maxxed, which is also good. The case stays cool to the touch when in use, so heat dissipation is no issue. There is pretty much no hum or hiss with no input signal, which is great. There seems to be noise suppression when turning it on, but there is a pop sound every time it is powered off. It doesn't seem to be loud or harsh enough to damage the speakers, so I can probably live it.

As far as Bluetooth connectivity goes, I've found it to be somewhat hit-or-miss. It stays connected to my home PC or phone, but won't maintain a steady connection with my Lenovo work laptop for more than a few seconds before dropping the connection. At first I thought it might have been caused by signal attenuation inside the shielded enclosure, but the problem persisted even after removing the shell with the laptop less than three feet away. I also switched off the Logitech BT adapter to eliminate it as a possible source of interference. Not a huge deal, I'll just continue using the external Bluetooth adapter through the line-in RCA jacks.

The footprint is tiny! At 4⅞" x 3¾" x 1¾" (WxDxH) before rubber feet were added, it's even smaller than the Lepai and tucks away neatly under the monitor. The bidirectional LED behind the volume ring is red when connected to aux (line-in), blinks blue when ready for Bluetooth pairing and solid blue when paired. Like so many of these inexpensive electronic devices with LEDs, there doesn't seem to be any diffuser in the epoxy, so at certain viewing angles it can be hard on the eyes - that's why I bent the legs back a bit while it was disassembled. The tradeoff being that the light is a bit dimmer now, but to me it looks perfect because it's bright enough to discern which mode it's in without being unnecessarily conspiquous.

In summary, I'm happy with this unit. There will always be compromises when transitioning to new hardware and I would have liked a tone defeat button and a pop-suppressing relay, but honestly, at this this price point I really can't complain. I'll be keeping this amp for a while! I was not paid or otherwise compensated for this review.

Below are photos of the internal board and components, along with captions for notable hardware or modifications that were made: