I was incredibly fortunate not so long ago to be invited to beta test a new Hypex based Class D amplifier from KJF Audio (of Pensil speaker kit fame). I believe I was one of the first people in the world other than Stefan to hear it as well. I have been intrigued by Class D for some time and the various options out there so this was a great opportunity to hear a decent one in action.
Full disclosure - I was sent the beta unit, had it for 3 or 4 weeks and then sent it on to the next tester. No money changed hands either way although I will, when funds permit, be buying one
. Note also I write these reviews for no other reason than hifi is a hobby and I like words so I tend to write them for kit I demo from time to time on the off-chance someone is interested.
My system; analogue front end - Custom one off ARB TT and arm with Rega Ania for stereo and a Leak 2001 Transcription Unit with AT MONO3/LP for mono both feeding a Cyrus Phono Signature. Digital front end - Topping D50s fed by a Raspberry Pi 4 with Roon and HQPlayer all powered by an ifi iUSB3.0, preamp - Khozmo Acoustics Passive Pre, usual power amp - Baldwin HiFi 405C. Speakers - Rega RX3 with a BK Electronics XLS200 sub. Van Damme interconnects and Atlas speaker cables.
I have a set demo track list I always use as follows and then I meander off listening to whatever. My music taste cover just about every genre under the sun so I try to cover as much as possible in a track list which means I won't get evicted for squatting when in a dealers!
Sophie Zelmani - Oh Dear
Agnes Obel - Cameras Rolling
A Man Called Adam - Easter Song (Cafe del Mar mix)
Tony de Vit - Are You All Ready
Miles Davis - So What
Ray Lamontagne - Barfly
Alison Krauss - Down To The River To Pray
The sublime Ms Zelmani. I adore this album and the first track has moved me to tears before. Her haunting voice has a slight reverb in parts and there’s a mighty bass line that, whilst restrained, moves organs in the right system. However it is easy to have the bass overblown at the expense of the guitar and vocals. The SA-01 is ruthlessly revealing though teasing every last detail and every last drop of emotion from Sophie's voice. I don't usually like ultra revealing systems though but this is different of which I will explain more in a bit.
On to Agnes Obel then. A new artist to me but I’ve been listening to her album a lot (Myopia) and had listened to my current system for an hour or so before leaving to calibrate my hearing so know it well. Again ruthless detail and in I could hear more texture to Agnes’s voice in parts and more space between the different elements that make up the track but still. The first track actually breaks into a duet and only on a sorted system can you really hear the male vocal contributing.
Ah Easter Song, my chill out track of choice and has been since I first heard it on Cafe del Mar vol Dos all those years ago. There is a long repeating bass note during the build up at the start of the track. An ok system will deliver it as a nice chunky lump of monotone bass woomph but a really good system will show just how much the bassline modulates and fades in and out. The SA-01 is in the really really good category here. There is also a harp that can be a bit bright, particularly when juxtaposed over the bassline but again, whilst the SA-01 is ruthless in putting out what's on the track it has an unerring delicacy as well. The other aspect of this track I have been trying to reproduce is one I heard in the demo room at Moorgate Acoustics when listening to a pair of Spendor D7 fed by a Sugden A21SE - just a particular note was as holographic as I have ever heard - floated in a part of the room no speaker has the right to project sound and was quite magical. I didn't quite get this with the SA-01 and have been chasing it it with various amp / speaker combos but it did a fine job of at least resolving the note in question if not quite left it floating in the air.
The legend that is TdV and perhaps his seminal hard house anthem next - Are You All Ready? A track I have heard hundreds of times in clubs, have mixed into my own sets dozens of times and have heard my friends mix dozens more. A track I know intimately. And yet, I now realise just how much more there is to the production. A little leading edge to one of the bass loops, a 'swing' to the hoover that is more staccato on lesser amps and countless little cheeky noises and effects chucked in. I find a good well produced house track is a great system check as there is so much to them that just gets lost on a good club system. Get up close and personal though and the detail is revealed. Pace is important as well, a good hard house track should drive along at a constant yet unrelenting tempo such that you cannot but nod your head and tap your foot in time. Doesn't necessarily have to be at a massively high BPM but it does need to be totally metronomic and the SA-01 passed this test with flying colours. It had an iron grip on the bass beat and didn't deviate or hesitate although the repetition was bang on.
Let’s see what Miles could bring to the party. At last I was getting excited. The double bass at the start of So What has so much texture and timbre. I could visual the size of the instrument given the energy the notes were giving out. And a double bass should sound like this, you should get an impression of the string tension and just what a powerful instrument it is. There should be real attack to the leading edge of the note. And then, being a traditional Blue Note recording the instruments should all be clearly and definably in their own space. Drums to the left, piano to the right with the double bass next to it and the sax and trumpet in the middle. And this is what you get with the SA-01 - the perfect 60's jazz soundstage. Nothing more and nothing less. Oh, and the timing - just perfect. Again more on this shortly.
Ray Lamontagne. His control of his voice at the beginning of Barfly had a real sense of restraint and he almost breathes the words out and the SA-01 presented this far better than anything I’ve heard before. Again there are some powerful bass notes but these need to be properly controlled so as not to become bloomy and again the SA-01 grips the speakers and doesn't let them stray.
Finally Ms Alison Krauss. My favourite female vocalists and one of the best there is. I have seen her sign Down to the River live, solo and A Cappello. The recorded track she has a gospel choir supporting her, starting softly but growing louder. They harmonise beautifully and on my current system it comes across as a really well sorted choir but with the SA-01 I can pick out individual voices and follow them through the harmonies - something I simply haven't been able to do before. Again - that ruthless attention to the very finest of details that I don't usually like.
So to wrap up - why do I like the laser like focus on detail of the SA-01. Simply because it is the only amp I have heard, at any price (and I've heard some high end Naim through some high end speakers, have enjoyed ownership of 25W of pure Class A loveliness of a Sugden A21L etc) that combines this ruthlessness with pure musicality. You want to sit back and let the music wash over you, you can. Want to get lost in the detail, you can. Want to just enjoy the finest audio reproduction you've ever heard? This is the amp to do it.
However, the kicker for me is the timing this thing brings to any genre. Hard house needs a certain tempo and the SA-01 is metronomic totally nailing the chugging beats. Softly miked vocals require an amp that can be delicate and let the vocals and emotion flows and again that's what you get. Ditto the timing nuances required by classical, jazz, indy rock, metal, rock n roll, country etc - it's as if the amp resets its internal clock to suit the music being played. It's unerring at first, then jaw dropping and then you realise just what really well sorted, really well thought out Class D can do. It has truly come of age in the KJF amp.
Finally a note on the construction. Personally I wouldn't mind if it looked like something you'd more usually leave lying in a skip if you saw it poking out but luckily the case is very fetching. Very similar dimensions to the standard Cyrus shoebox but very pronounced curves to the corners and I really like the walnut finish. It matches the sides to my Khozmo pre just beautifully. The current production run of them have an aluminium faceplate though and not wood but also look the business.
So in summary - I have already made it clear I want one and I will be buying one, no question at all and I will sorely missed the amp when I had to pass it on to the next tester. If Class D is tempting you then would recommend a listen
EDIT - If anyone is interested in a 'proper' review this is what Hifi World think of it https://kjfaudio.com/wp-content/uploads/2021/03/HiFi-World-April-21.pdf
Full disclosure - I was sent the beta unit, had it for 3 or 4 weeks and then sent it on to the next tester. No money changed hands either way although I will, when funds permit, be buying one
. Note also I write these reviews for no other reason than hifi is a hobby and I like words so I tend to write them for kit I demo from time to time on the off-chance someone is interested.My system; analogue front end - Custom one off ARB TT and arm with Rega Ania for stereo and a Leak 2001 Transcription Unit with AT MONO3/LP for mono both feeding a Cyrus Phono Signature. Digital front end - Topping D50s fed by a Raspberry Pi 4 with Roon and HQPlayer all powered by an ifi iUSB3.0, preamp - Khozmo Acoustics Passive Pre, usual power amp - Baldwin HiFi 405C. Speakers - Rega RX3 with a BK Electronics XLS200 sub. Van Damme interconnects and Atlas speaker cables.
I have a set demo track list I always use as follows and then I meander off listening to whatever. My music taste cover just about every genre under the sun so I try to cover as much as possible in a track list which means I won't get evicted for squatting when in a dealers!
Sophie Zelmani - Oh Dear
Agnes Obel - Cameras Rolling
A Man Called Adam - Easter Song (Cafe del Mar mix)
Tony de Vit - Are You All Ready
Miles Davis - So What
Ray Lamontagne - Barfly
Alison Krauss - Down To The River To Pray
The sublime Ms Zelmani. I adore this album and the first track has moved me to tears before. Her haunting voice has a slight reverb in parts and there’s a mighty bass line that, whilst restrained, moves organs in the right system. However it is easy to have the bass overblown at the expense of the guitar and vocals. The SA-01 is ruthlessly revealing though teasing every last detail and every last drop of emotion from Sophie's voice. I don't usually like ultra revealing systems though but this is different of which I will explain more in a bit.
On to Agnes Obel then. A new artist to me but I’ve been listening to her album a lot (Myopia) and had listened to my current system for an hour or so before leaving to calibrate my hearing so know it well. Again ruthless detail and in I could hear more texture to Agnes’s voice in parts and more space between the different elements that make up the track but still. The first track actually breaks into a duet and only on a sorted system can you really hear the male vocal contributing.
Ah Easter Song, my chill out track of choice and has been since I first heard it on Cafe del Mar vol Dos all those years ago. There is a long repeating bass note during the build up at the start of the track. An ok system will deliver it as a nice chunky lump of monotone bass woomph but a really good system will show just how much the bassline modulates and fades in and out. The SA-01 is in the really really good category here. There is also a harp that can be a bit bright, particularly when juxtaposed over the bassline but again, whilst the SA-01 is ruthless in putting out what's on the track it has an unerring delicacy as well. The other aspect of this track I have been trying to reproduce is one I heard in the demo room at Moorgate Acoustics when listening to a pair of Spendor D7 fed by a Sugden A21SE - just a particular note was as holographic as I have ever heard - floated in a part of the room no speaker has the right to project sound and was quite magical. I didn't quite get this with the SA-01 and have been chasing it it with various amp / speaker combos but it did a fine job of at least resolving the note in question if not quite left it floating in the air.
The legend that is TdV and perhaps his seminal hard house anthem next - Are You All Ready? A track I have heard hundreds of times in clubs, have mixed into my own sets dozens of times and have heard my friends mix dozens more. A track I know intimately. And yet, I now realise just how much more there is to the production. A little leading edge to one of the bass loops, a 'swing' to the hoover that is more staccato on lesser amps and countless little cheeky noises and effects chucked in. I find a good well produced house track is a great system check as there is so much to them that just gets lost on a good club system. Get up close and personal though and the detail is revealed. Pace is important as well, a good hard house track should drive along at a constant yet unrelenting tempo such that you cannot but nod your head and tap your foot in time. Doesn't necessarily have to be at a massively high BPM but it does need to be totally metronomic and the SA-01 passed this test with flying colours. It had an iron grip on the bass beat and didn't deviate or hesitate although the repetition was bang on.
Let’s see what Miles could bring to the party. At last I was getting excited. The double bass at the start of So What has so much texture and timbre. I could visual the size of the instrument given the energy the notes were giving out. And a double bass should sound like this, you should get an impression of the string tension and just what a powerful instrument it is. There should be real attack to the leading edge of the note. And then, being a traditional Blue Note recording the instruments should all be clearly and definably in their own space. Drums to the left, piano to the right with the double bass next to it and the sax and trumpet in the middle. And this is what you get with the SA-01 - the perfect 60's jazz soundstage. Nothing more and nothing less. Oh, and the timing - just perfect. Again more on this shortly.
Ray Lamontagne. His control of his voice at the beginning of Barfly had a real sense of restraint and he almost breathes the words out and the SA-01 presented this far better than anything I’ve heard before. Again there are some powerful bass notes but these need to be properly controlled so as not to become bloomy and again the SA-01 grips the speakers and doesn't let them stray.
Finally Ms Alison Krauss. My favourite female vocalists and one of the best there is. I have seen her sign Down to the River live, solo and A Cappello. The recorded track she has a gospel choir supporting her, starting softly but growing louder. They harmonise beautifully and on my current system it comes across as a really well sorted choir but with the SA-01 I can pick out individual voices and follow them through the harmonies - something I simply haven't been able to do before. Again - that ruthless attention to the very finest of details that I don't usually like.
So to wrap up - why do I like the laser like focus on detail of the SA-01. Simply because it is the only amp I have heard, at any price (and I've heard some high end Naim through some high end speakers, have enjoyed ownership of 25W of pure Class A loveliness of a Sugden A21L etc) that combines this ruthlessness with pure musicality. You want to sit back and let the music wash over you, you can. Want to get lost in the detail, you can. Want to just enjoy the finest audio reproduction you've ever heard? This is the amp to do it.
However, the kicker for me is the timing this thing brings to any genre. Hard house needs a certain tempo and the SA-01 is metronomic totally nailing the chugging beats. Softly miked vocals require an amp that can be delicate and let the vocals and emotion flows and again that's what you get. Ditto the timing nuances required by classical, jazz, indy rock, metal, rock n roll, country etc - it's as if the amp resets its internal clock to suit the music being played. It's unerring at first, then jaw dropping and then you realise just what really well sorted, really well thought out Class D can do. It has truly come of age in the KJF amp.
Finally a note on the construction. Personally I wouldn't mind if it looked like something you'd more usually leave lying in a skip if you saw it poking out but luckily the case is very fetching. Very similar dimensions to the standard Cyrus shoebox but very pronounced curves to the corners and I really like the walnut finish. It matches the sides to my Khozmo pre just beautifully. The current production run of them have an aluminium faceplate though and not wood but also look the business.
So in summary - I have already made it clear I want one and I will be buying one, no question at all and I will sorely missed the amp when I had to pass it on to the next tester. If Class D is tempting you then would recommend a listen
EDIT - If anyone is interested in a 'proper' review this is what Hifi World think of it https://kjfaudio.com/wp-content/uploads/2021/03/HiFi-World-April-21.pdf
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