Fifty-two dollars, thirty watts, and a room that smells faintly of warm metal
I have a rule about amplifiers that arrive in padded envelopes: lower your expectations, then lower them again, and only then open the bag. So when the “PASS A3 Single-ended Class A Power Amplifier Kit / Amplifier Board 30W+30W” landed on my bench for fifty-two dollars — eBay cheerfully offering to let me pay in four Klarna installments of $11.25, which remains the funniest thing about this entire project — I assumed I was buying a souvenir. Two bare green rectangles from Foshan. A “reference to famous PASS A3 circuit,” as the listing puts it, with the immortal reassurance: “if Welding is correct, connect power Will can works.”
The welding was correct. And it does can works. Rather alarmingly well, in fact, which is the only reason we’re still talking.
Fair warning before the good part: the boards are the cheap bit. Everything they demand afterward — a serious toroid, an obscene bank of filter capacitance, heatsinks the size of radiators, a chassis that stabilizes around 52°C and makes guests ask if something is broken — turns fifty-two dollars into roughly six hundred plus. The build guide at tubemaze.biz lays out exactly what that costs and why, and you should read it before you click Buy It Now rather than after, as I did. That’s the last practical sentence in this review. From here on it’s just listening.
The first ten seconds
What you notice is not detail, not bass, not soundstage. It’s ease. There’s no sense of an electrical device working at anything. Voices simply arrive, already formed, without the faint halo of grain and hurry that most solid-state amplifiers wear like cheap cologne — the thing you don’t hear until it’s gone and then can’t unhear ever again. Put on a close-miked female vocal and the sound is liquid in a way that has nothing to do with softness. It isn’t syrup added. It’s hash removed.
My wife walked through the room during the first session, stopped, and said “something’s different.” She has never once said that about a piece of equipment, including several that cost more than a month rent in NYC. That’s the kind of difference this is: not an audiophile difference, a room difference.
The midrange is the whole event
Everything this circuit is famous for lives between roughly 200Hz and 4kHz, and it lives there like a tenant who has no plans to move. The midrange is dense, faintly warm, and physically present in the room in a way that makes the speakers feel unbolted from the floor and pushed backward through the wall. Cellos have wood in them — you hear the box, not just the string. Brass has spit and rasp without turning into a hearing test. Massed strings, which normally congeal into one bright smear, separate into a crowd of individual instruments that happen to be playing together.
Piano is where I kept losing the plot. On most amplifiers a piano note is three events: struck, sustained, gone. Here it’s one continuous line, the hammer’s impact melting into the body of the note and the note thinning into air with nothing chopped off the end. I sat through the entirety of a Bill Evans record I’ve heard four hundred times and heard the sustain pedal working — not as an effect, as a physical mechanism a man was operating with his foot.
Acoustic guitar gets the same treatment. The pick attack is there, but attached to a body resonance rather than floating in front of it as a separate percussive click. Fingers squeak on strings. Someone’s chair creaks in the third bar. Small stuff, but it’s the small stuff that makes you believe the rest.
Space
Holographic is a word that should be retired, so let me be specific. Images here have depth and mass, not just left-right position — a singer occupies a volume of air with a front and a back to her, and you could walk around her if the laws of physics were more accommodating. The soundstage extends behind the speaker plane much further than the price suggests it has any right to, and — more unusually — it stays organized when the music gets busy. Big orchestral tuttis don’t collapse into a wall; the back of the hall stays at the back of the hall. The air in soundstage is not as good as in a good tube amp, but not much is.
Reverb tails are the tell. On lesser amplifiers they get truncated, snipped off by something in the circuit that decides low-level information isn’t worth the trouble. Here they thin out and leave, gradually, the way sound actually does in a room. Live recordings gain an unnerving amount of venue. On one small-club recording I could hear the ceiling.
The top end, and an honest disagreement
This is where the design shows its hand. The treble is sweet, unfailingly civilized, and just slightly rounded. Cymbals shimmer rather than splash. The very last sliver of leading-edge bite on a triangle or a hard-struck snare rim is politely withheld, as though the amplifier considered it and decided against.
Some listeners call this rolled off. I hear a designer choosing, deliberately, to be wrong in this direction rather than the other one, and having listened to a great many amplifiers err in the other direction, I find I agree with him. After a week I stopped noticing. After a month, switching back to a big, brightly lit, feedback-heavy amplifier felt like someone had turned on the fluorescents in a candlelit room. There is no fatigue here. None. I have fallen asleep in the listening chair twice, which I choose to interpret as a compliment.
Bass, and the polite man backing out of a room
Bass is tuneful, textured, and finite. Notes have pitch — you can follow a walking bass line as a melody, which is rarer than it should be, and double bass sounds like a wooden object being plucked rather than a generic low-frequency event. Kick drums land with real weight.
What you don’t get is iron grip: that sense of a giant hand clamped around the woofer, holding it still. And when you push past this amplifier’s comfort zone it doesn’t clip so much as gently, apologetically compress — the whole presentation drawing inward, everything getting quieter and smaller at once, like a polite man backing out of a room he’s realized he shouldn’t be in. There’s no hardness, no glare, no grit. Just less music, and a clear hint that you should turn it down.
Which is the whole story in one sentence: this thing has no bad-sounding mode. It has a wonderful mode and a smaller version of the wonderful mode.
What it wants
Efficient speakers — 90dB and up. This is not a suggestion, it’s the whole relationship.
An easy, honest load. Punishing low-impedance towers will flatten it and you’ll blame the amp unfairly.
Music with a midrange at its center: voices, strings, jazz, small ensembles, anything with a human being in it.
Air around the chassis, and a listener who doesn’t mind heat – the amp is sitting around 125F (50 C).
Patience. It sounds mediocre cold and glorious after forty minutes.
Final verdict
Judged as a $52 purchase this is preposterous value, and judged honestly it’s the cheapest component in a $600 amplifier that will out-sing most $2,000 commercial designs on midrange truth, texture, and spatial realism while losing to them on grip and sheer volume. If you own efficient speakers and listen to music with people in it, build it — you’ll stop shopping for amplifiers for a very long time. If you need to fill a large room with a large orchestra at a large volume, look elsewhere and be happier.
My absolute pleasure, Nelson. Thank you on behalf of the entire audio community for designing such legendary amplifiers and so generously sharing your designs with us all.
Fifty-two dollars, thirty watts, and a room that smells faintly of warm metal
I have a rule about amplifiers that arrive in padded envelopes: lower your expectations, then lower them again, and only then open the bag. So when the “PASS A3 Single-ended Class A Power Amplifier Kit / Amplifier Board 30W+30W” landed on my bench for fifty-two dollars — eBay cheerfully offering to let me pay in four Klarna installments of $11.25, which remains the funniest thing about this entire project — I assumed I was buying a souvenir. Two bare green rectangles from Foshan. A “reference to famous PASS A3 circuit,” as the listing puts it, with the immortal reassurance: “if Welding is correct, connect power Will can works.”
The welding was correct. And it does can works. Rather alarmingly well, in fact, which is the only reason we’re still talking.
Fair warning before the good part: the boards are the cheap bit. Everything they demand afterward — a serious toroid, an obscene bank of filter capacitance, heatsinks the size of radiators, a chassis that stabilizes around 52°C and makes guests ask if something is broken — turns fifty-two dollars into roughly six hundred plus. The build guide at tubemaze.biz lays out exactly what that costs and why, and you should read it before you click Buy It Now rather than after, as I did. That’s the last practical sentence in this review. From here on it’s just listening.
The first ten seconds
What you notice is not detail, not bass, not soundstage. It’s ease. There’s no sense of an electrical device working at anything. Voices simply arrive, already formed, without the faint halo of grain and hurry that most solid-state amplifiers wear like cheap cologne — the thing you don’t hear until it’s gone and then can’t unhear ever again. Put on a close-miked female vocal and the sound is liquid in a way that has nothing to do with softness. It isn’t syrup added. It’s hash removed.
My wife walked through the room during the first session, stopped, and said “something’s different.” She has never once said that about a piece of equipment, including several that cost more than a month rent in NYC. That’s the kind of difference this is: not an audiophile difference, a room difference.
The midrange is the whole event
Everything this circuit is famous for lives between roughly 200Hz and 4kHz, and it lives there like a tenant who has no plans to move. The midrange is dense, faintly warm, and physically present in the room in a way that makes the speakers feel unbolted from the floor and pushed backward through the wall. Cellos have wood in them — you hear the box, not just the string. Brass has spit and rasp without turning into a hearing test. Massed strings, which normally congeal into one bright smear, separate into a crowd of individual instruments that happen to be playing together.
Piano is where I kept losing the plot. On most amplifiers a piano note is three events: struck, sustained, gone. Here it’s one continuous line, the hammer’s impact melting into the body of the note and the note thinning into air with nothing chopped off the end. I sat through the entirety of a Bill Evans record I’ve heard four hundred times and heard the sustain pedal working — not as an effect, as a physical mechanism a man was operating with his foot.
Acoustic guitar gets the same treatment. The pick attack is there, but attached to a body resonance rather than floating in front of it as a separate percussive click. Fingers squeak on strings. Someone’s chair creaks in the third bar. Small stuff, but it’s the small stuff that makes you believe the rest.
Space
Holographic is a word that should be retired, so let me be specific. Images here have depth and mass, not just left-right position — a singer occupies a volume of air with a front and a back to her, and you could walk around her if the laws of physics were more accommodating. The soundstage extends behind the speaker plane much further than the price suggests it has any right to, and — more unusually — it stays organized when the music gets busy. Big orchestral tuttis don’t collapse into a wall; the back of the hall stays at the back of the hall. The air in soundstage is not as good as in a good tube amp, but not much is.
Reverb tails are the tell. On lesser amplifiers they get truncated, snipped off by something in the circuit that decides low-level information isn’t worth the trouble. Here they thin out and leave, gradually, the way sound actually does in a room. Live recordings gain an unnerving amount of venue. On one small-club recording I could hear the ceiling.
The top end, and an honest disagreement
This is where the design shows its hand. The treble is sweet, unfailingly civilized, and just slightly rounded. Cymbals shimmer rather than splash. The very last sliver of leading-edge bite on a triangle or a hard-struck snare rim is politely withheld, as though the amplifier considered it and decided against.
Some listeners call this rolled off. I hear a designer choosing, deliberately, to be wrong in this direction rather than the other one, and having listened to a great many amplifiers err in the other direction, I find I agree with him. After a week I stopped noticing. After a month, switching back to a big, brightly lit, feedback-heavy amplifier felt like someone had turned on the fluorescents in a candlelit room. There is no fatigue here. None. I have fallen asleep in the listening chair twice, which I choose to interpret as a compliment.
Bass, and the polite man backing out of a room
Bass is tuneful, textured, and finite. Notes have pitch — you can follow a walking bass line as a melody, which is rarer than it should be, and double bass sounds like a wooden object being plucked rather than a generic low-frequency event. Kick drums land with real weight.
What you don’t get is iron grip: that sense of a giant hand clamped around the woofer, holding it still. And when you push past this amplifier’s comfort zone it doesn’t clip so much as gently, apologetically compress — the whole presentation drawing inward, everything getting quieter and smaller at once, like a polite man backing out of a room he’s realized he shouldn’t be in. There’s no hardness, no glare, no grit. Just less music, and a clear hint that you should turn it down.
Which is the whole story in one sentence: this thing has no bad-sounding mode. It has a wonderful mode and a smaller version of the wonderful mode.
What it wants
Final verdict
Judged as a $52 purchase this is preposterous value, and judged honestly it’s the cheapest component in a $600 amplifier that will out-sing most $2,000 commercial designs on midrange truth, texture, and spatial realism while losing to them on grip and sheer volume. If you own efficient speakers and listen to music with people in it, build it — you’ll stop shopping for amplifiers for a very long time. If you need to fill a large room with a large orchestra at a large volume, look elsewhere and be happier.
I’m keeping mine. Running it… In winter.
Thanks very much for the high praise, comments like these help keep me inspired at the ripe old age of 75…
😉
My absolute pleasure, Nelson. Thank you on behalf of the entire audio community for designing such legendary amplifiers and so generously sharing your designs with us all.