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In an era dominated by FETs and IC-level integration, it’s easy to forget just how powerful a well-designed bipolar transistor can be. Yet for the analog engineer chasing ultra-low drift, tight matching, and reliable gain stability, bipolar junction transistors (BJTs) remain indispensable. Linear Systems carries forward the legacy of precision bipolar technology with a complete line of monolithic matched dual and single transistors  designed for low noise, high stability, and long-term reliability in demanding analog applications. Why Bipolar Transistors Still Matter Bipolar transistors offer high transconductance, low offset voltage, and predictable linearity —attributes that make them ideal for precision amplifiers, log converters, and differential front ends. While FETs dominate in high-impedance designs, BJTs remain the preferred choice when low noise at higher currents, tight matching, or excellent gain tracking  over temperature are essential. Linear Systems’ monolithic dual transistors combine those advantages with the consistency of devices fabricated on a single die. The Linear Systems Bipolar Lineup Each device family is built on a foundation of precision matching, temperature stability, and proven analog performance. Series Type Configuration Highlights / Applications IT120 / IT124 Series NPN Monolithic Dual Ultra-low drift, ideal for differential input stages LS310 Series NPN Monolithic Dual Tight beta matching for instrumentation and audio circuits LS318 NPN Monolithic Dual Log conformance for log and transimpedance amplifiers LS301 Series NPN Monolithic Dual High-voltage, super-beta design for precision high-voltage amplifiers LS3250 / LS3250S NPN Dual / Single High-speed switching with excellent gain stability LS3550 Series PNP Dual / Single Complementary to LS3250 series for push-pull amplifier design LS350 / IT130 Series PNP Monolithic Dual Tight matching and tracking for low-offset differential stages LS358 PNP Monolithic Dual Log-conformance PNP pair for current-mode and logarithmic circuits Each part is manufactured on Linear Systems’ precision analog processes to ensure gain, offset, and temperature characteristics remain tightly controlled —a vital advantage for applications where unmatched discretes simply can’t deliver. Monolithic Matching for Real-World Precision Unlike discrete matched pairs mounted side-by-side, Linear Systems’ monolithic dual transistors share the same silicon substrate , ensuring both devices track identically over time and temperature. This results in: Exceptional V_BE and beta matching  across the operating range Reduced thermal drift  and offset voltage Improved common-mode rejection  in differential circuits Long-term stability  ideal for metrology, medical, and instrumentation applications Whether you’re designing a precision current mirror, amplifier front end, or logarithmic converter, these transistors ensure your design behaves predictably across environmental extremes. Applications and Design Examples Linear Systems’ bipolar transistors appear anywhere analog accuracy matters: Instrumentation Amplifiers  – Tight beta matching minimizes offset and drift. Audio Circuits  – Complementary NPN/PNP pairs deliver low distortion and consistent tone. Logarithmic and Transimpedance Amplifiers  – LS318 and LS358 provide superior log conformity. High-Speed Switching  – LS3250S single devices handle rapid switching with excellent gain linearity. Precision Current Mirrors  – Matched pairs like the LS310 maintain balance and accuracy even under temperature cycling. For designers upgrading legacy systems or maintaining long-term platforms, Linear Systems’ bipolar families also serve as drop-in replacements  for many classic transistor types from Amelco, National, and Intersil. Designing with Confidence Choosing the right transistor pair often comes down to your application’s operating voltage, gain target, and thermal environment. Linear Systems offers both NPN and PNP duals  with complementary performance, making it straightforward to design push-pull amplifier stages  or balanced sensor inputs . A few design tips: Keep both transistors at the same thermal potential for best tracking. Match emitter resistances in differential applications. For ultra-low drift, pair complementary NPN and PNP devices from the same process family. Review each device’s datasheet for log conformity and beta matching specifications. Legacy of Precision — Built for the Future For over four decades, Linear Systems has specialized in high-performance discrete analog semiconductors —and their bipolar transistor line continues that legacy. As system voltages drop and performance margins tighten, these devices offer the unmatched consistency and analog fidelity  designers still rely on. If your circuit demands accuracy, low drift, and repeatable performance, Linear Systems’ matched bipolar transistors deliver a proven path to precision. Explore the full product line and datasheets: 🔗 linearsystems.com/bipolartransistors Request samples or technical support: 📧 info@linearsystems.com  | Sample Request Form

B1 Buffered Passive Preamp Few names in audio design inspire as much respect as Nelson Pass . For decades, Nelson has pushed the boundaries of amplifier and preamp design with simple, elegant circuits that deliver extraordinary sound quality. His work has shaped the way audiophiles, DIY builders, and even professional engineers think about high-end audio. One of his most enduring contributions is the B1 Buffer Preamp . At first glance, it looks deceptively simple: a unity-gain buffer with just a handful of components. But simplicity is part of the magic. The B1’s performance comes directly from the quality of the devices at its heart — JFETs , chosen for their unmatched noise and linearity characteristics. Why JFETs? JFETs are ideal for front-end and buffer applications because of their: High input impedance  – preventing loading on delicate audio sources. Low output impedance  – ensuring strong, stable drive into power amps. Low noise and excellent linearity  – crucial for preserving the subtle details in music. Nelson Pass has long relied on Linear Systems’ JFETs in this role. In the B1, the complementary pair of N-channel  and P-channel JFETs  provides transparency and neutrality — qualities that have made the circuit famous in the audio DIY community. Linear Systems Inside The classic B1 buffer used the 2SK170 and 2SJ74, but as those parts became scarce, Nelson and the DIY community turned to Linear Systems’ equivalents : LSK170  – N-channel JFET, ultra-low noise, high transconductance, widely used in audio and precision instrumentation. LSJ74  – P-channel complement, designed as a low-noise, high-performance match to the LSK170 . LSK389  – dual, monolithic version of the LSK170 , offering superb device matching and thermal tracking in a single package. By integrating these parts, the B1 achieves a combination of clarity, drive, and quiet backgrounds  that has made it a reference design for both commercial and DIY preamps. Design Philosophy: Simple but Brilliant The B1 isn’t about flashy complexity or an endless parts list. It’s about getting the fundamentals right. Nelson has often said that he prefers simple circuits with the best possible devices , and the B1 reflects that philosophy. With Linear Systems’ JFETs, the B1 offers: Musical transparency  – nothing added, nothing taken away. Reliability and stability  – thanks to tightly controlled device specifications. Enduring accessibility  – DIYers and builders around the world continue to build and enjoy this design. A Partnership Built on Trust Nelson Pass has been a longtime friend of Linear Systems , and his decision to use our JFETs reflects a deep trust in their performance and consistency. From phono stages to amplifiers to buffers like the B1, Linear Systems devices have become a staple in Pass designs. That legacy continues today, as both professional audio engineers and hobbyists choose LSK170 , LSJ74 , and LSK389  as drop-in solutions for their high-end audio projects. Learn More & Build It Yourself The full B1 Buffer schematic and project description are available directly from Nelson Pass at PassDIY – B1 Buffer. Whether you’re an audiophile, a designer, or a curious DIY builder, the B1 is a perfect example of how great devices make great circuits possible . At Linear Systems, we’re proud to see our JFETs featured at the core of such a beloved design. 🔗 View the schematic and project at PassDIY – B1 Buffer .

When designing circuits for test instrumentation , medical electronics , or any system where stable, low current is crucial, the choice of a current-regulating diode (CRD) can make all the difference. Linear Systems’ J500  and SST500  series provide engineers with reliable, tightly specified constant-current performance — even across wide voltage and temperature ranges — while simplifying circuit design. What is a Current Regulating Diode? A current-regulating diode (also called a constant current diode) is a two-terminal device that limits current to a fixed value, regardless of voltage fluctuations within its operating range. Internally, most CRDs use a JFET with the gate tied to the source. Once the device reaches saturation, the current remains steady over a wide voltage swing. This gives designers a simple, compact, and reliable current source  without additional circuitry. Key advantages: Reduced part count compared to op-amp or resistor-based current sources Stable performance across voltage changes Compact and easy to integrate in low-power and battery-driven designs The J500 & SST500 Series at a Glance Feature J500 Series SST500 Series Package TO-92 (through-hole), plus bare die SOT-23 (surface mount), plus bare die Current Range ~0.19 mA to 5.6 mA (nominal) ~0.19 mA to 5.6 mA (nominal) Operating Voltage Up to 50 V Up to 50 V Temperature Range −55 °C to +150 °C −55 °C to +150 °C Forward Capacitance ~2.2 pF (typical) ~1.5 pF (typical) 🔗 J500 Product Page 🔗 SST500 Product Page Why It Matters Tight, predictable performance  — essential for sensitive applications in medical instrumentation and precision test gear. Package flexibility  — TO-92 for prototyping and robust handling, SOT-23 for space-constrained SMT designs. High reliability  — Wide voltage and temperature ratings ensure stable performance even in harsh environments. Simplified design  — Drop-in constant current without biasing networks or active components. Application Examples Driving LEDs or photodiodes with a fixed current, even as supply voltage changes Providing a stable bias for RTDs, thermistors, or strain gauges Current sources in battery-powered medical devices Simplifying constant-current references in test and measurement equipment Choosing Between J500 & SST500 Prototyping / through-hole builds  → J500 (TO-92 package) Compact SMT designs  → SST500 (SOT-23 package, lower parasitics) Custom packaging or tighter screening  → Bare die options available directly from Linear Systems Final Thoughts Linear Systems’ J500 and SST500 current regulating diodes  deliver stable, predictable current regulation in easy-to-use packages. With options ranging from TO-92 to SOT-23 to bare die, and current levels spanning ~0.19 mA to 5.6 mA, these CRDs simplify circuit design while ensuring high performance across demanding applications. 📄 Explore datasheets on our Current Regulating Diodes page ✉️ Contact our applications team at support@linearsystems.com  for design guidance 📦 Request samples to evaluate the J500 and SST500 in your next design Prefer to speak with someone directly? Give us a call at (510) 490-9160 and our team will connect you with the right person.

< Back AEA Linear Systems Mar 17, 2023 AEA’s Ribbon Microphones & Linears’ JFETs AEA When John Kurlander sought to capture the vast array of sound for the Lord of the Rings movies, he turned to Wes Dooley and his ribbon microphones. And for years, when Wes needed ultra-low-noise semiconductors to build and amplify those microphones, he turned to Linear Systems, Inc. “Linear Systems has kept that tradition going of making parts that are competitive with the [discontinued Toshiba] SK170s and 389s,” Dooley said in a recent interview. “And that gives us the ability to make compact, high-performance audio products.” “We make the quietest ribbon mic in the world, the A440, and the higher SPL A840. Both of them use the [Linear Systems] LSK389, for the output drivers and their current supply,” Dooley said. Dooley's company, Audio Engineering Associates (AEA), also uses the LSK389 in front ends of its RPQ and RPQ 500 preamplifiers, which were designed for use with ribbon microphones. AEA's microphone business started with ribbon mics for classical music used as movie scores. “John Kurlander did all three Lord of the Rings using AEA mics on strings left and right almost as strong in the mix as the main orchestra mics,” Dooley said. “When you work with such people, one really learns to be of service.” AEA's customer list reads like a Who's Who of Grammy and Academy Award-winning recording engineers and artists. Among the many examples, sound engineer Michael Bishop, winner of eight Grammy awards, extensively uses AEA's A840 microphones and AEA preamps for his recordings. Shawn Murphy, who's worked on over 330 films and won an Academy award for Jurassic Park, also relies on AEA's preamps and microphones. One of the best parts of AEA's website is the long list of reviews and mentions by users . Dooley, a lifelong ribbon microphone enthusiast and developer, got into the business by repairing ribbon mics built by RCA during the golden age of radio. “We started servicing mics in '76 when RCA shut down making them,” he said. “Many of our favorite RCA designs were from the mid '30s, when a designer's foremost tool was listening to live music. Critical listening was the gold standard as acoustical measurements were cumbersome.” “We've adopted that approach, which is: musicality trumps metrics. The mic has to sound good to people in the music business,” Dooley said. “If it doesn't sound good, measurements don't matter. Once you have a mic that sounds good to people who have experienced ears, then measurements are very important, as they are the key to consistent production.” “So we first strive to make sure it sounds musical, and then we measure what it does,” Dooley said. “Because, as one of my mentors, Richard Heyser, said, if it measures well but doesn't sound right, then you're measuring the wrong things. Often you find you don't know what the right thing to measure is. Over time you discover what those metrics might be. Ultimately, it's a matter of how it sounds. Since we come from an acoustic music tradition, it's pretty simple: you put the mic in front of live music, and compare that live sound with the reproduction, to see how close it is.” Dooley told the story of working with legendary bluegrass fiddle player/violinist Richard Greene. Greene, along with his wife, a violinist with the LA Chamber Orchestra, recorded samples using over 20 microphones. “The next day, when they had 'fresh ears,' they listened to all the recordings and said the one made using our ribbon microphones was the best,” Dooley said. “And that's what we try for, for the musicians to experience that this is the closest they've ever heard to an actual performance.” Asked to comment for this article, Greene had high praise for Dooley and his microphones. “Silky, smooth, best violin sound I ever heard, Wes is amazing and his tech support and other free maintenance are over the top,” Greene wrote. “I will never have any use for any other mic on my violin. I have the AEA 440.” Dooley said this close interaction with artists drives how he builds microphones and preamps. “The whole thing,” he said, “is to build tools they need. That is the key to survival for a small business doing high-performance products.” The LSK389 “is a very good part for manufacturing,” Dooley said. AEA uses the “C” grade of the LSK389. “We started with the 'A' [grade], but then we realized it didn't make any difference for what we were doing,” he said. The LSK389 is graded by IDSS ; all three grades have the same ultra-low-noise characteristics. The Linear Systems LSK389 part used by AEA is an ultra-low-noise junction field effect transistor. Linear System Founder and CEO John H. Hall began working on a JFET similar to Toshiba's 2SK389 about the time that the Japanese company began to discontinue the device 10 years ago. “Toshiba kept its production process for the 389 secret, so we had to figure out on our own how to build something to the same specification, which was extremely difficult,” Hall said. Expertise brought to Linear Systems is based on processes and products Hall developed since 1962 at Amelco, Union Carbide, Intersil, and Micro Power Systems. Hall, a protégé of Silicon Valley legend Dr. Jean Hoerni, was the director of IC Development at Union Carbide, co-founder and vice president of R&D at Intersil, and founder/president of Micro Power Systems. Much of Linear Systems' current development work focuses on lower-noise JFETs. The production techniques Hall conceived to squeeze the last bit of noise out of the 389 led to development of another part, the LSK489. The LSK489 has less transconductance than the 389, and though this increases noise slightly, it makes the part easier to design into new circuits. “While the 389 is the perfect part for some users, such as Wes Dooley, who need the lowest noise levels in existence, we found that the high gate-to-drain capacitance of the 389 caused problems for some of our other customers,” Hall said. “Building a high transconductance part, such as the 389, formed part of the basis for providing ultra-low-noise levels, but the high input capacitance causes intermodulation distortion in some higher-frequency applications,” Hall said. “Since we had created some advanced processing techniques to make the 389, we decided to go back and look at creating a part with lower capacitance using the same processes.” Though Dooley's ribbon microphone and other devices take advantage of the 389's low noise level, other developers could tolerate a slightly higher noise level in a part that has much lower input capacitance due to a lower transconductance, Hall said. The lower capacitance and other features make the LSK489 a lower-noise, functional replacement for Linear Systems' LS840-series of JFETs, as well as the Siliconix U401-403 series. Dooley's precision ribbon microphones are perfect applications of the LSK389, Hall said. “Both ribbon microphones and JFETs are very difficult to design and build, but there's really no other way to achieve the level of performance needed than to do the work this way.” The circuit design work using the LSK389s was done for AEA by Fred Forssell of http://www.forsselltech.com . For more on Dooley's microphones, go to: http://www.ribbonmics.com Data sheets for the LSK389 and LSK489, the application notes for the LSK489, and a good paper on general JFET theory and use can be downloaded at: http://linearsystems.com .

< Back Headphone Amp Eval Board Introduction Linear Integrated Systems headphone amplifier evaluation board includes the following features: Stereo, single‐ended input and single‐ended output 400 mW output power into 100Ω Wide frequency response (10Hz‐200kHz; ‐1dB) Voltage gain 5 (14dB) Low distortion (THD+N is less than 1% at 10Hz‐20kHz at 5Vrms into 100Ω and less than 0.1% from 10 Hz to 20 kHz at 1Vrms into 100Ω load) Short‐circuit protection Pop reduction (slow start) circuit Defeatable cross‐feed circuit Volume control Overvoltage and reverse polarity power protection Audio input and output connections: left and right RCA phono jack inputs, ¼” stereo phone jack output External 9V–16V supply input External power supply connector: power jack, inside diameter 2.1mm, outside diameter 5.5mm Read More

The Linear Systems family of high speed DMOS switches is designed to handle a wide range of video, fast ATE, telecom and other analog switching applications. DMOS High Speed Switches The Linear Systems family of DMOS devices is designed to handle a wide range of video, fast ATE, telecom and other analog switching applications. These components are capable of ultrafast switching speeds (tr = 1 ns, tOFF = 3 ns) and excellent transient response. Thanks to reduced parasitic capacitances, our DMOS can handle wideband signals with high off-isolation and minimum crosstalk. SD/SST210 Series SD/SST210 SINGLE, HIGH SPEED N-CHANNEL LATERAL DMOS FET SWITCH Read More SD/SST211 Series SD211DE SINGLE, HIGH-SPEED N-CHANNEL LATERAL DMOS FET SWITCH Read More SD5000 Series SD5000 SERIES QUAD, HIGH SPEED N-CHANNEL, LATERAL DMOS FET SWITCH Read More