DoBlue SLASH4 Review: This Tiny Gadget Breathed New Life into My Speakers

Slash4 – Hi Res Hybrid Bluetooth Receiver for Car & Home Audio

Slash4 - Hi Res Hybrid Bluetooth Receiver for Car & Home Audio







What We Dig

  • Great Build Quality
  • Smooth, Detailed, Sound
  • Easy To Use

What To Think About

  • Could use a little more depth and separation

Can this tiny device transform your music? Find out in our DoBlue Slash4 review – you might be surprised by the results.


The Slash4 Hi Res Hybrid Bluetooth Receiver/USB DAC, which comes from a small company in Korea, targets a specific need: bringing high-quality wireless audio to car stereos and home audio systems. Many audio systems, especially those in the car, lack the latest CD-quality (hi-res) Bluetooth codecs and hi-res DAC chips, so this new USB dongle aims to improve sound by providing this tech.

Its small, unassuming design is intended to integrate seamlessly into your existing setup, adding modern connectivity without drawing too much attention to itself. Like its sister device, the Slash6, which I reviewed last May and enjoyed a lot (remarkable sound!), the Slash4 packs a lot of functionality in a compact form. However, the Slash4 is even smaller, providing an intriguing dimension of added portability. Let’s see if I like the new Slash Bluetooth DAC as much as the old one!


At $89.99, the Slash4 is at the upper end of the price range for compact Bluetooth receivers. This price point might be considered a bit premium compared to some of the $20-$30 Bluetooth Adapters you’ll see on Amazon. However, its emphasis on high-resolution audio codec support targets users who demand a better-than-standard wireless listening experience. It also adds digital output and USB DAC functionality, something you don’t see in most BT dongles for the car.

What’s in the Box

Do SLASH4 Review

Cable(3.5mm to 3.5mm), User’s Manual, Optical Cable

DoBlue SLASH4 Review: Build & Design

The Slash4 keeps things simple with its discreet black form factor. It’s solidly built, and a single button on the side handles most operations. A single multi-color LED on the top provides status and codec information. This minimalist approach means it won’t look out of place in most car or home audio setups. It also means that the operation is pretty simple; as soon as you power it up, it goes into pairing mode. Then, you put your source device in pairing mode and select Slash4 from the list of available devices.

More importantly, the Slash4 offers versatile connection options: a 3.5mm aux/headphone jack for connection to home receivers and wired headphones, plus that jack doubles as optical digital output for the potential of the highest quality sound. At the end of the day, it looks like your typical USB Dongle DAC because that’s basically what the Slash4 is.

Key Features

  • Advanced Noise Isolation blocks power noise for pristine audio
  • Bluetooth Codec delivers high-quality sound without noise (LDAC, aptX-Adaptive, and aptX-HD)
  • Cutting-edge DAC Technology (ESS Quad DAC ES9219)
  • Ultra-Low Noise Operation minimizes background noise
  • Smart Connectivity automatically connects to the last-used smartphone
  • Optical output enhances the audio experience by connecting digitally to an audio processor or amplifier.

DoBlue SLASH4 Review: Features

The Slash4’s most significant selling point is its focus on high-resolution Bluetooth codecs like aptX HD, aptX LL, and LDAC. These promise improved audio quality compared to the standard Bluetooth (SBC) most devices of this type rely on. Another big bonus is its hybrid nature—even though the manufacturer promotes it heavily as an in-car solution, it can also transmit pristine Bluetooth audio to headphones, stereo amps, or powered speakers, vastly increasing its use cases. You can also use it as a USB DAC for your laptop.

To utilize the Slash4, your vehicle will need a USB-A connection and an AUX input jack, which many new cars lack. In my case, I had to borrow my son’s older Civic to test it out because neither of my vehicles (both 2022 models) had an AUX jack. In addition, many newer cars have USB-C connections, so you’ll need a USB-C to USB-A adapter (or a USB-A charger that will fit in the 12V plug), in that case.

For home use, you’ll probably need a 3.5mm to RCA adapter to connect to most speaker systems and amps (and wish to take advantage of the internal Quad DAC). Still, if your device has a 3.5mm aux port or Toslink optical input, then you can most likely use the cables that come in the box (if they’re long enough). Of course, if you use it as a USB DAC, you can plug it directly into a laptop using the built-in USB connector.

DoBlue SLASH4 Review: Sound

When paired with compatible devices and used with high-bitrate streaming services like Tidal, the Slash4 delivers a noticeable jump in sound quality over standard Bluetooth dongles (just like the Slash6 I reviewed before). You get more detail, more transparent highs, and a more engaging listening experience. However, your connected speakers or car audio system will still significantly affect the final sound quality.

When I used it in the car, I was pretty impressed by the clarity and low noise floor of the Slash4 compared to similar devices I have used. Most of those units were quite noisy and sounded like an AM radio. With the Slash4, when I used the aptX and LDAC BT codecs on my phone (especially LDAC), the USB dongle sounded much better than the car’s built-in Bluetooth connection.

Regarding home use, I tried it with the Cambridge Audio AXR100 Stereo Reciever ($599), which has its own Bluetooth connection, allowing me to do some A-B testing. This time around, the difference between the built-in BT connection and the Slash4 wasn’t as pronounced, despite the fact the AXR100 uses a low-bitrate SBC audio codec.

Listening to Steely Dan’s “Babylon Sisters,” both the integral (SBC) and Slash4 Bluetooth (LDAC-Optimized for Audio) sounded pretty good. While the Slash4 dongle had a bit more detail and sounded a bit more natural or fleshed out than the AXR100’s Bluetooth, I found the latter had a larger scale and more depth.

In other words, when I listened to the Slash4, the resolution was better than that of the AXR100’s Bluetooth receiver, so the vocals/instrumentation sounded a little more sweet and organic. That said, at the same time, the presentation sounded a little more constricted, with less space between the elements of the mix—a little less “airy,” if you will.

At the end of the day, both sounded pretty good, so if you’re device already has a Bluetooth receiver, the small change in sound may not justify the cost.

However, if your Powered Speakers or Stereo Amp doesn’t have Bluetooth, this Bluetooth receiver is a quick and easy way to add a great-sounding wireless connection to your setup.

Do SLASH4 Review: Verdict

Do SLASH4 Review

The Slash4 Hi Res Hybrid Bluetooth Receiver delivers on its promise of bringing older audio setups into the modern wireless audio age. Its support for high-resolution Bluetooth codecs makes it stand out if you crave better-than-basic wireless sound quality. While the most dedicated audiophiles will still want a wired solution, the Slash4 offers impressive wireless performance, and its versatile design makes it a compelling option for a wide range of users.

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