GlassWare Audio Design
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Headphone Amplifier Kits
Headphones and headphone amplifiers
Ah, headphones: either you love them or you hate them. I love them. I like not hearing noise from refrigerators, air conditioners, barking dogs, the subwoofers of rude neighbors, cars, trucks, and especially loud minibikes and motorcycles. Moreover, I like hearing normally unfamiliar and uncharted musical events: the floorboards creaking beneath the 300-pound jazz bass player, the hall’s reverberation, the guitarist’s fingerprints across the strings, the vocalist’s gasps for air, the recording engineer’s clumsy edits, the sheet music’s repeated turnings during every classical performance, George Harrison’s thick-fingered flubs, the mechanical articulation on a saxophone, the pianist’s humming—well, strike that last one item—in other words, the hundred diminutive sonic artifacts harbored by recordings but seldom heard. Some are annoying, others are embarrassing, others still are transporting, but all reveal a hidden world unmapped by even the finest loudspeakers.
What’s wrong with loudspeakers? A loudspeaker’s crossovers and massive diaphragms smear the sonic minutia, rolling over the barely audible information, washing away the recording’s sonic fingerprints, like a blurry photograph that truthfully reveals a dress’s color, but not its texture. Here is a simple experiment: visit a music store and listen to the sonic signature of each type of cymbal displayed; then go home and listen to your loudspeakers. What happened to that obvious and marked difference in timbre? Now listen to the same recordings with high-quality headphones. Can you hear more of the distinctions in size, brand, and composition of cymbals? (Yes, I know that CDs make this test much harder than LPs or tape did.)
To subtract further, the little that the loudspeaker can faithfully reproduce pours into a sonic coffin known as your listening room. Parallel walls, floor, and ceiling reverberate unevenly, stressing some frequencies, but attenuating others. I imagine that even the air between a loudspeaker and your ears subtracts from what the ear could hear directly against the loudspeaker; being no more than a mixture of gasses, how could we expect it to hold a precise imprint for very long before its natural sponginess smears the finest details? Here is an additional experiment: sit in the front row of a concert hall and listen to the amazing brightness, if not downright harshness of many of the orchestra’s instruments. Then move to the rear of the hall and sit in an untaken seat and listen to the soft, murky sound, where many discrete violins meld into one fat, large violin.
Verily, headphones circumnavigate so many sonic snares that it is amazing that more are not ardent headphone listeners.
Ah, headphones: either you love them or you hate them. I love them. I like not hearing noise from refrigerators, air conditioners, barking dogs, the subwoofers of rude neighbors, cars, trucks, and especially loud minibikes and motorcycles. Moreover, I like hearing normally unfamiliar and uncharted musical events: the floorboards creaking beneath the 300-pound jazz bass player, the hall’s reverberation, the guitarist’s fingerprints across the strings, the vocalist’s gasps for air, the recording engineer’s clumsy edits, the sheet music’s repeated turnings during every classical performance, George Harrison’s thick-fingered flubs, the mechanical articulation on a saxophone, the pianist’s humming—well, strike that last one item—in other words, the hundred diminutive sonic artifacts harbored by recordings but seldom heard. Some are annoying, others are embarrassing, others still are transporting, but all reveal a hidden world unmapped by even the finest loudspeakers.
What’s wrong with loudspeakers? A loudspeaker’s crossovers and massive diaphragms smear the sonic minutia, rolling over the barely audible information, washing away the recording’s sonic fingerprints, like a blurry photograph that truthfully reveals a dress’s color, but not its texture. Here is a simple experiment: visit a music store and listen to the sonic signature of each type of cymbal displayed; then go home and listen to your loudspeakers. What happened to that obvious and marked difference in timbre? Now listen to the same recordings with high-quality headphones. Can you hear more of the distinctions in size, brand, and composition of cymbals? (Yes, I know that CDs make this test much harder than LPs or tape did.)
To subtract further, the little that the loudspeaker can faithfully reproduce pours into a sonic coffin known as your listening room. Parallel walls, floor, and ceiling reverberate unevenly, stressing some frequencies, but attenuating others. I imagine that even the air between a loudspeaker and your ears subtracts from what the ear could hear directly against the loudspeaker; being no more than a mixture of gasses, how could we expect it to hold a precise imprint for very long before its natural sponginess smears the finest details? Here is an additional experiment: sit in the front row of a concert hall and listen to the amazing brightness, if not downright harshness of many of the orchestra’s instruments. Then move to the rear of the hall and sit in an untaken seat and listen to the soft, murky sound, where many discrete violins meld into one fat, large violin.
Verily, headphones circumnavigate so many sonic snares that it is amazing that more are not ardent headphone listeners.
 The Triadtron solid-state buffer offers no gain, but does deliver high current into low-impedance lows, such as 16-ohm (and above) headphones. Many standalone DACs and CD players put out over 2V of peak output signal, which is plenty loud for most low-impedance headphones. The Triadtron PCB hold two unity-gain power buffers. The PCB requires a monopolar power-supply voltage from 12Vdc to 24Vdc, with even 48Vdc possible. If you are like me, you own many orphaned switcher power supplies from now dead or superseded electronics. $24.00 |
 Due to popular demand, the SRPP+ is back, minus the power supplies. The new PCB is 6in by 5in and, like all GlassWare PCBs, is crazy overbuilt, with extra thick double-sided PCB material and heavy 2-ounce copper traces. Each channel gets its own large power supply RC filter, whose voltage rating can be a low 250Vdc, perfect for high idle current applications, such as headphone amplifiers; or, 400Vdc, perfect for line-amplifier use. The SRPP+ PCB holds pads for two sets of output coupling capacitors. All in all, it's a fun little board and I can imagine many different audio applications, from the input stage of single-ended amplifiers to headphone amplifiers for high-impedance cans, such as those offered by Beyer and Sennheiser. $29.00 |
 12Vac SRPP HPA holds two hybrid SRPP headphone amplifiers. The output stage is actually a small power amplifier in its own right (a Zen single-ended amplifier). It consists of one MOSFET that is loaded by a constant-current source, which is made up of an LM317P voltage regulator configured as a constant-current source. A two-resistor negative feedback loop sets a gain of 1 (unity) for the inverting output power amplifier. Each channel sees a 200mA idle current flow, which is enough to deliver 3Vpk of output voltage into 16-ohm headphones and twice that into 32-ohm drivers. Of course, it can also easily drive 300-ohm headphones. $29.00 |
