SKU: 22399511801

Universal Buffer

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Description

Universal BufferThe Universal Buffer is a two channel (stereo) buffer, which can be configured to provide any of the following functions: Single ended (unbalanced, RCA) to differential (balanced, XLR) conversion. Differential (balanced, XLR) to single ended (unbalanced, RCA) conversion. Straight through buffer (single ended to single ended or differential to differential). Signal inverter. Can be configured with gain by adding two resistors. By adding a volume

The Universal Buffer is a two-channel (stereo) buffer, which can be configured to provide any of the following functions:

  • Single-ended (unbalanced, RCA) to differential (balanced, XLR) conversion.
  • Differential (balanced, XLR) to single-ended (unbalanced, RCA) conversion.
  • Straight-through buffer (single-ended to single-ended or differential to differential).
  • Signal inverter.
  • Can be configured with gain by adding two resistors.

By adding a volume control and input selector, multiple Universal Buffer boards can be configured as a full-featured preamplifier with support for both balanced and unbalanced sources and loads.

Technical Documentation

  • Specifications
  • Circuit Topology
  • Performance Graphs
  • The full set of specifications for the Universal Buffer are tabulated below.

    Parameter Value Notes
    Number of Channels 2
    Power Supply Voltage ±2.5 – ±17 V
    Quiescent Power Supply Current

    50 mA

    65 mA

    Nominal

    Maximum

    THD

    < 0.00001 %

    (-140 dB)

    2.0 V RMS
    THD+N

    < 0.00025 %

    (< -112 dB)

    2.0 V RMS
    THD+N

    < 0.00025 %

    (< -112 dB)

    +27.5 dBu
    IMD: SMPTE 60 Hz + 7 kHz @ 4:1 -107 dB 2.0 V RMS
    IMD: DFD 18 kHz + 19 kHz @ 1:1 -119 dB 2.0 V RMS
    IMD: DFD 917 Hz + 5.5 kHz @ 1:1 -109 dB 200 mV RMS
    Multi-Tone IMD Residual < -148 dB Ref.: 2.0 V RMS AP 32-tone, 2.0 V RMS
    Gain 0 dB (1.0×) Can be increased by resistor option.
    Gain Flatness ±0.1 dB 20 Hz - 20 kHz
    Bandwidth DC – 280 kHz 100 mV RMS, -3 dB
    Slew Rate 2.4 V/µs 100 kΩ || 220 pF load
    Total Integrated Noise and Residual Mains Hum 1.7 µV RMS 20 Hz - 20 kHz, A-weighted
    Total Integrated Noise and Residual Mains Hum 2.1 µV RMS 20 Hz - 20 kHz, Unweighted
    Dynamic Range (AES17) 137 dB 1 kHz
    Channel Separation > 125 dB 20 Hz - 20 kHz
    Common-Mode Rejection Ratio > 65 dB 20 Hz - 20 kHz
    Input Impedance 48 kΩ
    Output Impedance < 0.1 Ω
    PCB footprint 60 × 65 mm
    Fully assembled dimensions

    60 × 65 × 15 mm

    30 g

    (W × D × H)

     

    All parameters are measured at a power supply voltage of ±15 V, 100 kΩ load impedance, and differential input/output, unless otherwise noted.

    Sound Quality

    I designed the Universal Buffer to be sonically transparent and firmly believe I have achieved that goal. I generally prefer precise amplifiers as they render the source material naturally, without any colouration, and offer a spacious and realistic sound stage.

  • The Universal Buffer features a balanced differential input. This input can accept both differential (balanced) signals and, by jumper configuration, single-ended (unbalanced) signals. The Universal Buffer provides both a balanced differential output and a single-ended (unbalanced) output. In addition, it can be configured to provide gain and/or signal inversion. 

    A simplified block diagram of one channel of the Universal Buffer is shown below.

  • Measuring the -140 dB THD of the Universal Buffer is a significant challenge, in particular as the analyzer section of the Audio Precision APx525 analyzer is only good to -125 dB and its source to -112 dB. Thus, I use a precision oscillator with a THD below -140 dB and a notch filter to attenuate the fundamental frequency. The resulting measurement of the distortion residual is shown below. As shown, the third harmonic is just below -140 dB at 2 V RMS output voltage.

    The graph below shows the THD+N vs output level. The Universal Buffer delivers just over +27 dBu (differential) at the onset of clipping. With single-ended input, the maximum clean output is 6 dB lower. Note that the sharp jumps (aside from when the buffer clips) are caused by range switching in the APx525. The THD+N vs output power plots mostly show the THD+N floor of the measurement system.

    The Universal Buffer can be operated at a power supply voltage of ±2.5 to ±17 V. The absolute maximum supply voltage is ±18 V. The power supply should be regulated for the best performance. 

    Naturally, the maximum clean output voltage provided by the Universal Buffer depends on the applied supply voltage. The relationship is shown in the graph below.

    The THD+N versus frequency measurement below basically shows the noise floor of my APx525 audio analyzer.

    Siegfried Linkwitz argues that the 1 kHz + 5.5 kHz intermodulation distortion (IMD) measurement is one of the measurements which is more indicative of the perceived sound quality. He bases this argument on the fact that IMD products in this measurement fall in the frequency range where the ear is the most sensitive (see the Fletcher-Munson curves for more detail). I think this argument carries a good amount of weight, so I measured the Universal Buffer accordingly. The measurement is shown below. Note that due to a limitation in the IMD source of the APx525, the frequencies used must be an integer multiple of each other. Thus, I measured at 917 Hz (5500/6) + 5.5 kHz. The result is shown below. 

    The more conventional IMD measurements are shown below. The two plots show the SMPTE (60 Hz + 7 kHz @ 4:1) IMD and DFD (18 kHz + 19 kHz @ 1:1) IMD, respectively. Poor SMPTE IMD is often indicative of thermal issues or power supply issues in a circuit. The 18k+19k IMD is indicative of the loop gain available in the buffer near the end of the audible spectrum, which can be telling of the sound quality. The Universal Buffer provides exemplary performance on both of these measurements.

    Audio Precision has developed a multi-tone test signal, which contains 32 tones from 15 Hz to 20 kHz, logarithmically spaced in frequency. This test signal sounds a bit like an out-of-tune pipe organ. It is basically the closest I can get to music with a deterministic test signal. Thus, I argue that this multi-tone signal should be used in an IMD test for the best correlation between measurements and perceived sound quality. I run this test at 2.0 V RMS (which is also the 0 dB reference in the plot). Note that even the tallest IMD components are more than 147 dB below line level. This is likely why the Universal Buffer sounds transparent. This measurement shows that it does not add anything (or at least extremely little) to the source signal. Also note that the output is completely free of mains-related hum or noise.

    The plot below shows the residual mains hum and noise of the Universal Buffer when powered by a regulated power supply. The result shows the buffer outputs only minimal mains-related signal components (which are most likely from the test setup).

    As the Universal Buffer is a stereo circuit, I measured the channel separation. As shown below, the channel separation is truly exemplary, measuring nearly 140 dB midband.

    When used with a differential source, the Universal Buffer provides rejection of any signals imposed equally on both wires in the differential signal pair. Common sources of such common-mode noise includes mains hum. As shown below, the Universal Buffer provides more than 85 dB of CMRR at the mains frequency.

    For completeness, the amplitude response and gain variation are shown below.

    Transient Response Measurements

    One of the many applications of the Universal Buffer is as the output stage in a preamplifier. Thus, the Universal Buffer should be able to drive the capacitance of the interconnect cable connecting the Universal Buffer to the power amp or load. This cable capacitance tends to measure roughly 33-50 pF/m. Thus, as shown below, the Universal Buffer is capable of driving over 100 m of interconnect cable cleanly.

    The measurements below show the transient response of the Universal Buffer for increasing load capacitance. On its single-ended output, the Universal Buffer drives 10 nF cleanly and 22 nF with controlled overshoot. Even at higher load capacitances, the Universal Buffer remains stable.

    The measurements for the differential output are shown below. As shown, the Universal Buffer can drive 4.7 nF cleanly on the differential output and even drive 10 nF with controlled overshoot.

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SKU: 22399511801

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4.3 ★★★★★
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❈ Elizabeth ❈ | Breakawayreads
Battle Creek, US
★★★★★ 5
Fallen Angels, fae, vampires, oh my!
Format: Kindle
Rating: 4.5 | Spice: 2 (but a good slow-burn) • Main Characters: Huntyr and Wolf • I couldn’t wait to read this book; there was so much hype about it! And there was no doubt why. I fell in love with the characters and the plot itself. This book is mainly plot driven more than friction driven but it’s easy to follow along with. The characters are fun, easily understood. The main setting is at an academy where both the main characters are going through trials and building strength for the final test, The Transcendent. There are fantastic side characters as well. I loved the camaraderie between Huntyr and her friends. But we don’t like Lanson. 😆 We do have some plot twists that come into play throughout the book. Secrets and betrayal to be seen. I did adore Wolf and Huntyr’s relationship. It was a classic slow burn trope. They didn’t hit it off fast, but in time their feelings grew. I loved their banter, so sexy. Wolf is your next book boyfriend; Huntyr is your next vampire assassin independent bad-a*s female. Themes include loyalty, trust, self-discovery, a true slow burn romance. Side note: book ends on a angsty cliffhanger! • Emily, thank you for writing this awesome novel and I cannot wait to devour Book 2, Blood So Brutal! 😍 • Happy reading, my lovelies! xo
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Reviewed in the United States on January 21, 2024
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MelsABookworm
Alexandria, US
★★★★★ 4
“My heart bows to you and you only, Huntress.”
Format: Kindle
3.5 🌟 This book popped up in my KU recommended reading suggestions and the synopsis sounded like what I was in the mood for. I'm so glad I took a chance on it. I went into this knowing absolutely nothing about it and ended up really liking it. I love when this happens. The main characters are likeable and I easily found myself rooting for them. There is a mystery element to each of their backstories that I enjoyed watching unfold and can't wait to get more of. Wolf, in particular, has me fixated. Love him. I found this to be an entertaining, addictive read with a plot that moves along at a good pace. It reads so easily I found myself very reluctant to put it down. Lots of twists and turns and the angst is there. A good set up for the next book to come, for sure. My issues with this book....the dialogue feels a bit juvenile at times and there is a repetitive over use of a particular word phrasing that I found myself giving the ole eye-roll to. There are, without a doubt, some pretty cliche moments that gave me a bit of the cringe. I think this could've certainly 100% benefited from more depth regarding the world building. Perhaps the world building was sacrificed to keep the pacing quick? Just a guess. Also, the lack of consistency of character for the FMC was really evident and so she feels quite illogical at times. Overall, this was a fun and enjoyable read that hit the spot well enough for me. That ending certainly has me impatiently pining for book 2!
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Reviewed in the United States on June 18, 2024
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Amazon Customer
Port Orchard, US
★★★★★ 3
Interesting take on the genre
Format: Kindle
True rating: 3.25 ⭐️ I enjoyed the fresh take on the genre. The best way I could describe the setting and world is an apocalyptic dystopian version of Farie where vampires, fae, and angles struggle to survive in what is left of the world. It was definitely interesting throwing the academy/hunger games aspect into this world as well. Even though I guessed the final reveal early on in the book, I kept hoping I was wrong, and it would take a surprising turn. While the "plot twists" were a bit predictable to me, I still enjoyed the ride this book took me on. Another downfall for me was the plot holes in the world building... I.E. if society has fallen and the world is in the aftermath of war, how are there trains running around the world? Just to take young adults to the trials to get into the golden city? How is the train maintained, the tracks clear, etc? However, I did enjoy the FMC & MMC and thought they were fleshed out nicely. I also enjoyed the side characters but wish some were developed more like Ashalin (sp?). I do find myself rooting for the MCs to succeed and find happiness together, which is obviously an important aspect for romantasy. Overall, was this an earth-shattering, mind-bending, terrific piece of literature? No. But was it the worst thing I've read this year? Also, no. This book has, to me, the bones of a great read & just needs a bit more to push it from an alright book to a great book. Overall ratings: Plot- 3.5⭐️ World building 3⭐️ Spice 2.5 🌶🌶 Main characters 4 ⭐️ Supporting characters 3.5⭐️
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Reviewed in the United States on May 12, 2024
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Irene zamora
Charlottesville, US
★★★★★ 5
great book
Format: Kindle
I am really excited to meet the author at the book retreat this month. I really enjoyed this world that she built and most of the female main character Huntress is so awesome. She goes through a lot in this book and the ending; wow! I wouldn't have even guessed. I highly recommend everyone to read this book. I have been so lucky this year that almost all the books I have read have been, so far, 5 out 5 stars.
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Reviewed in the United States on June 2, 2026
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Anastasia Goygova
Chelsea, US
★★★★★ 4
Fallen for the Fallen Angel – A Guilty Pleasure Worth Every Page
Format: Kindle
There’s something deeply irresistible about a dark academia or trial-based setting, a brooding and arrogant fallen angel, and a fierce heroine with enough sass to go toe-to-toe with him. Wings So Wicked is exactly that kind of book—and I devoured it in just a couple of days. To be fair, the plot isn’t groundbreaking. If you’re looking for something fresh and innovative in terms of storyline, this might not be it. But if your reader heart beats faster at the mere mention of enemies-to-lovers, jealousy-fueled banter, magical trials, betrayals, and forbidden tension—you’ll feel right at home. It’s like catnip for those of us with this particular weakness. The chemistry between the leads could have used a slightly slower burn to make the tension sizzle longer, but I still found myself completely invested in their dynamic. There are moments and phrases that feel a bit cheesy or underdeveloped, but honestly? I didn’t care. The vibes were exactly what I wanted. This book isn’t trying to reinvent the genre—it’s here to give readers like me what we crave: high-stakes magical drama, angsty romance, and the thrill of watching a badass girl and her brooding counterpart clash and spark. If that sounds like your kind of story, Wings So Wicked will hit the mark. Here’s hoping Book 2 turns up the heat and keeps the magic alive.
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Reviewed in the United States on May 20, 2025

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