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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4.1 ★★★★★
Based on 8 reviews
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D. Smith
Lexington, US
★★★★★ 5
Hands down, the BEST handheld frother I've ever used!
Color: Black
Hands down, the BEST handheld frother I've ever used! I got the black one, but any color will have the same results. Over the past 12 years or so, I've used so many different handheld frothers and they've ALL fallen short of expectations for quality, longevity, power, features, and usability. I've used everything from cheap, $15 models to $50+ models and everything in-between. Some with fancy attachments for various types of mixing, frothing, beating, whipping, etc. Some with rechargeable batteries, some without. Some AC powered, some with fixed whisks, some with detachable/replaceable whisks, some with stands, etc. NONE have been spectacular. Most broke within 6 months and got tossed. ALL were major disappointments in the end, including the "revered" Zulay models of which I tried several. I finally found this Maestri House branded, variable speed frother with detachable / replaceable whisks and got one to try. I was literally on Cloud Nine the first time I turned it on. Like, WOW! Not only was it FAST on the highest speed, but it was powerful enough to churn right through milk, eggs, cream, etc, without bogging down like many others. This thing makes milk froth like a milkshake and Matcha Lattes like nothing else I've ever experienced. I used to have to sift my Matcha, then whisk it in hot water, then froth milk and then blend them together to make the perfect latte. and if the milk was cold (my preference), pre-whisking in hot water was a must to avoid lumps. However, with THIS frother? I literally pour my milk into a tall tumbler, drop in un-sifted Matcha powder, and spin up the Maestri House frother at first on a medium low speed to get it mixed, then jump straight to the highest speed to really whip that milk and match up. After about 30-45 seconds, I've got the thickest, richest, smoothest, most aerated latte around. And NO LUMPS at all!!! What a time and dish saver! And cleaning? I just run it under hot running water to get the shaft cleaned and then spin it up in a dish with hot running water for a few moments, then spin it on high for a few seconds in the air to dry it off instantly. Now, I'll be honest here, too. The specs say it can go months on a charge, using it for a couple minutes a couple times daily. Well, I guess it could do that and still spin. But I use it FULL SPEED, churning hard for at least a minute a couple times per day. After about 2 weeks, I can start to notice a speed reduction so I just plug it back in on the charger. All things considered, this is still better than all the other handheld frothers I've used over the years. After using the heck out of this thing for the past 7 months, I've even decided to start selling these in our Japanese gift shop. The manufacturer is has been very responsive both in customer support (I called them about an issue I thought I was having, and they called me back with a couple hours even though I didn't leave voicemail when they didn't answer right away) and in reseller support. I have to give these guys an A+ for responsiveness and quick resolution when problems might arise. HIGHLY recommended!!
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Reviewed in the United States on October 17, 2025
H
Verified Purchase
Hawaii Keith
Alexandria, US
★★★★★ 5
Great Addition!
Color: Black
Why did you pick this product vs others?: I just started a powdered drink routine recently and was having a difficult time mixing it with water. I would consistently end up with small nuggets of mix making it unenjoyable to drink. I knew I needed a mixer and was glad I found this device when I did. It works perfectly! I like the fact that it comes with its own stand and included two mixing heads. It is solid, well-designed, and you can feel the quality when you pick it up. The variable speed of the mixer is perfect for ensuring that everything is blended well. I haven’t used it to “froth” anything yet, at least not on purpose, but I accidentally found out that it can do that well. This is a great addition to our kitchen and is very easy to wash after use. So far…no issues. Highly recommend for those of you looking for the right tool to make sure those protein mixes aren’t full of unmixed nuggets.  
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Reviewed in the United States on June 21, 2025
S
Verified Purchase
Suzi blue
Los Angeles, US
★★★★★ 4
Low foam
Color: Black
Love this frother. It is great quality and the turn speed is amazing. My only issue is this. It comes w 2 wands and they are both singles. The single is great for stirring things up. It does not make a lot of froth and for some things it’s perfect but sometimes I like a lot of froth and I wish it either came w a single and a double or you could purchase a double separately to intermix. I don’t want to buy a whole other unit just for the double. I wrote to them bc the double frother they sell doesn’t look as good as this one but sometimes a girl needs a lot of foam and sometimes th stirring is perfect.
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Reviewed in the United States on February 20, 2026
H
Verified Purchase
Hanna
Belleville, US
★★★★★ 5
Still The Best Frother Ever!
Color: Black
I love how it is easy to use, how it holds a charge, and how much power it has. I've only charged it once since I got it & I've been using it on a daily basis!!! Though it isn't a long time, I'm happy with it so far! I definitely will recommend it to anyone looking for a great frother. If you are looking for one, look no further! You won't be disappointed! I've read some comments where they found it to be too strong that their drink spilled everywhere. But for me I have not had any incident of spilling over. I have used it both for my coffee and my matcha tea and it worked great without any spilling over. You just have to start with the lowest power and ensure that you have a large enough container to have a room for your frothing. My sister tried to use it recently during her visit to make us matcha tea. However, she experienced spillage all over the cup, because she had used a small cup. Otherwise, she liked it very much and said she will get one when her battery operated one stops working... Another thing I like about the product was the customer service that I had received. When I got my first order which came quickly, it wasn't working after having charged it over 24 hours. It was not turning on at all. I returned it and ordered a replacement which I received within a day or two. This time after charging it for the recommended amount of time, I was a bit skeptical when I turned it on. However, I was pleasantly surprised that it worked like it was supposed to and it has been working ever since having charged it only once so far. I may come back and give an update depending on how it does after 6 months of use, so keep in tune... I don't know if there is a way to write a new entry as a follow up to the old entry, so I'm going to add my follow up comment over here. May 23, 2025 - I love my frother more than I can say in words. It's functionality has not changed a bit from the time I have purchased it. It charge lasts several weeks to few months before I charge it again and the power is still the same. Recently I decided to buy another one for my office use. I like the white color and so tried it but that one wouldn't even turn on. And then I got a gray one to have a different color. That one was much weaker than the black one I own. Then I replaced it with another gray one within few days. I tried it and it was exactly the same as the one I already replaced. So then I decided to go with a black one again hoping that it would be the same as the one I have. The black one did much better than the gray ones in the strength or power of the frother. However, it is weaker than the one I already have been using since last August. While I am not very happy with the quality being inconsistent in all of the ones I have tried including the recent pictures of the black one, I have decided to keep the black one because it is relatively better than the gray ones I tried. What I don't understand is why there is inconsistency in the quality of the same product by the same maker. I am beginning to wonder if the black one I purchased in Augusta last year was anomaly of a quality and a good way. Maybe I lucked out on my older black frother, but I'm unsure if quality is going to get better if I were to order another one. I have a sister who is a pro in making coffee drinks and she was the reason I had ordered this frother to begin with. She uses a battery operated one at this time and I have been thinking about getting her one like mine. While I am still skeptical, I am going to give it a shot and order her one sometime soon. If it doesn't work, I guess we will return it back. But one thing that I am grateful is that I have been able to return every one of those that I have tried recently with no issues. I hope that I don't have to return my most recent purchase in black. I was not even able to review the new purchase because of the item being the same color which is crazy.
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Reviewed in the United States on September 8, 2024
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Verified Purchase
R. Cordosi
Charlottesville, US
★★★★★ 5
Outstanding Frother!
Color: Space Gray
Exceptional! This frother is in another league compared to the cheapo push button frothers. The motor is smooth, quiet and powerful. This has an intuitive thumb dial on top that operates smoothly with a wide range of smooth speed adjustment. It’s gentle enough to froth a little bit of milk for a macchiato and powerful enough to scramble 3 eggs. The head is removable for easy cleaning. It’s also rechargeable. I charged this the day I bought it on April first. I use it at least twice a day. It’s September 26th today and I have yet to recharge it and it’s not showing any signs of needing a charge. One minor quibble is that they give you 2 of the same frother heads. They are built so well, that I don’t imagine it ever wearing out. It would have been nice to get a whisk or something different. Not a deal breaker at all though.
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Reviewed in the United States on September 26, 2025

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