Kari Nevalainen has posted a review of the A Sound Concertina integrated amplifier at Innerworld Audio. His conclusions:
“A Sound’s Concertina is a petit and, given its size, unusually uncompromising integrated 10W PP tube amplifier. All of its stages are designed independently of others and their performance optimized separately. Its compact size will attract those who wish a tube amp to companion their desk computer. However, Concertina’s technical and sonic virtues would go astray if it were used for playing mp3 files via a cheap dac and through modest super-store loudspeakers. Against this background, it is not a sin but a merit that the Concertina lacks a headphone amp. On the other hand, for high-end computer listening the Concertina fits perfectly.”
You can read the full review here.