Solis SO-7500 Stereo Bluetooth Vacuum Tube Audio System REVIEW

5 min readMay 22, 2018

I have been intrigued by the different speaker options out there that I’ve seen the past few years. I’ve had the opportunity to test out tiny waterproof speakers, enormous studio monitors, and everything in between. The thing is that even though all of these speakers are different sizes and have different features, they all pretty much have the same specs. Until recently, I’d never had the pleasure of testing out an audio system that is driven by a vacuum tube. That’s where the Solis SO-7500 Stereo Bluetooth Vacuum Tube Audio System comes in.


The Solis SO-7500 audio system is a unique item in the Bluetooth speaker space. For starters, it utilizes a vacuum tube/solid-state hybrid amplifier. The system features a high gloss black finish on both speakers and the amplifier. Each two-way bass reflex speaker takes up less than 6″ of shelf space and they deliver 2 x 12W (RMS). You have the option to connect audio sources through Bluetooth or RCA auxiliary inputs. The matching speakers feature a 3.5-inch polymer cone woofer and a 1.25-inch soft dome polymer tweeter for the best well-rounded sound possible.


  • Wireless: Bluetooth — v4.0 with aptX™ for high fidelity audio streaming
  • Inputs: 2 x Auxiliary input jacks (RCA)
  • System frequency response: 20Hz ~ 20kHz
  • 2 x 12AX7 vacuum tubes — 5000-hour life rating
  • Toroid transformer power supply
  • Power output: 2 x 12W RMS
  • Amplifier output impedance: 4 Ohms ~ 8 Ohms
  • HiFi 2-way bass reflex stereo speaker system
  • One 3.5-inch polymer woofer
  • One 1.25-inch soft dome tweeter
  • Removable fabric grille
  • 6-Ohms nominal impedance
  • Supplied accessories:
  • Two 6’ speaker cables pre-terminated with banana plugs
  • One 6’ stereo line-level RCA cable
  • One grounded power cable
  • Two cotton gloves
  • One soft brush
  • Dimensions:
  • Amplifier — 5.12” H x 9” W x 7.28” D
  • Speakers — 8.27” H x 7.28” W x 5.12” D
  • Power: AC120V 60Hz

User Experience

The SO-7500 audio system came packaged in a single box. The outside of the box had the name of the product printed on it with a nice image of the system. There weren’t many details of the product but the packaging was very nice. When you open the exterior box, you will find two interior cardboard boxes — one says ‘MAIN UNIT’ and the other reads ‘SPEAKERS’. The MAIN UNIT box contains not only the amplifier but also the accessories for the system. One of the accessories that come with the system is a set of white cotton gloves. I highly recommend that these be used when unpackaging and placing the speakers and amplifier. Since they have a high-gloss finish, fingerprints cling to them very easily.

If you are familiar with setting shelf speakers up, these will not be difficult for you at all. You simply connect the power to the amplifier and run the provided speaker cables to each of the speakers. That’s pretty much it. Once you have connected the system to itself, you then decided where your audio input will be coming from. The specs state that the system has two auxiliary inputs. As a point of clarification, the inputs are RCA (red/white) ports and not for a 3.5mm stereo mini cable, which I typically think of as the ‘aux’ port. Therefore, you have the option to connect something that is analog to this system using the provided RCA cables. The other option is to connect through Bluetooth, which is what I ended up doing. I actually connected to two different devices — my 2016 13-inch MacBook Pro and my iPhone 7.

Pairing was a different experience. The first time you power your speakers on in Bluetooth mode, they will be a discoverable device on your computer or mobile phone. I paired my iPhone 7 first. I was able to find ‘SO-7500’ in the Bluetooth menu quickly and it paired almost instantaneously. After about 30 minutes or so, I paused my music and manually disconnected from the speakers as I was leaving the room. About 45 minutes later, I reentered the room where the speakers were and my phone automatically re-connected to them. Now, all of that is pretty normal for Bluetooth speakers (in my experience). What wasn’t normal to me was how I had to go about connecting to my MacBook Pro after connecting to the phone. I had to ‘forget the device’ on my phone and cycle the power on the Solis amplifier in order for it to reenter pairing mode. Once it appeared on my Bluetooth menu though, my computer connected rather quickly. This is a little bit of a pain for a Bluetooth speaker, but I do recognize that many people might use this system for a more permanent installation with an analog device instead of connecting through Bluetooth.

As far as sound quality goes, I was actually pretty impressed with the crisp clarity that the SO-7500 system produced. I listened to several different types of music through them and found that the audio system really excelled with orchestral pieces like Rhapsody in Blue by George Gershwin. You could hear every detail of the piece and it was really awe-inspiring. I felt that there was a very nice depth of sound, but that the bass, while punchy, wasn’t booming. It’s a good bass sound, but if you want something that shakes the floor, this system doesn’t really do that.


I really enjoyed using the SO-7500 audio system from Solis. It was a different experience and I can definitely tell a difference between this vacuum tube-driven amplifier and modern speakers. It’s a high-quality sound no matter what type of input you use. With this type of high-quality system, I was surprised to find that there were more input options available for audio sources. That and the Bluetooth pairing issue I had were really my only complaints of this system and I think people who want to attach this system to a turntable will not be disappointed with the sound quality.

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Originally published at on May 22, 2018.




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