LSK170A - Low Noise N-Channel JFET, 40V | Linear Systems
MPN: LSK170A β Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $1.79 | $1.79 |
| 10 | $1.61 | $16.10 |
| 100 | $1.34 | $134.00 |
| 500 | $1.12 | $560.00 |
| 1,000 | $0.94 | $940.00 |
Drop-in alternatives for LSK170A β same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Quick Comparison Tool β Select alternative parts for side-by-side comparison:
LSK170B
β Drop-In β οΈ εζ°εΎ ιͺθ―π Reference alternative (not in catalog)
LSK170C
β Drop-In β οΈ εζ°εΎ ιͺθ―π Reference alternative (not in catalog)
LSK170D
β Drop-In β οΈ εζ°εΎ ιͺθ―π Reference alternative (not in catalog)
IF170
β Drop-Inπ Reference alternative (not in catalog)
LSK170A Maximum Ratings & Electrical Characteristics
| Device Type | N-Channel JFET Amplifier |
| Configuration | Single |
| Drain-Source Voltage (VDS) | 40 V |
| Continuous Drain Current (ID) | 10 mA |
| Power Dissipation (PD) | 400 mW |
| IDSS Range (Grade A) | 2.6 mA to 6.5 mA (VDS = 10 V) |
| Noise Performance | Ultra-low noise (audio-grade) |
| Input Capacitance | Low capacitance |
| Input Impedance | High input impedance |
| Transfer Characteristic | Uniquely linear VGS transfer function |
| Replacement For | Toshiba 2SK170 (pin-for-pin) |
| Package | SOT-23-3 (3L), surface mount |
| Mounting Type | Surface Mount |
| RoHS Status | RoHS Compliant |
| Grade Options | A / B / C / D (IDSS bins) |
LSK170A Pin Configuration
| Pin 1 | D β Drain |
| Pin 2 | S β Source |
| Pin 3 | G β Gate |
Safe Operating Area (SOA) & Thermal Characteristics
No official SOA curve available for this component. Always operate within absolute maximum ratings specified in the datasheet. Ensure adequate cooling and derate as needed.
Typical Applications
LSK170A is suitable for 6 applications: Microphone / Phono Preamplifier Front End, Acoustic and Vibration Sensor Buffers, Instrumentation Front Ends, Medical and Biopotential Signal Acquisition, DIY Hi-Fi Amplifier Input and Cascode Stages, High-Impedance Active Filters and Mixers.
Microphone / Phono Preamplifier Front End
The LSK170A is the canonical input device for ultra-low-noise microphone and phono preamplifier front ends. Its ultra-low input-referred voltage noise, combined with low junction capacitance and high input impedance, keeps the noise floor below the signal when the source is a moving-coil cartridge or a low-sensitivity dynamic microphone capsule. A typical circuit biases the JFET at 2-4 mA drain current with a source resistor or current source, feeding an active load or a BJT second stage for additional gain. Because grade A IDSS spans 2.6-6.5 mA, select source resistance for the measured device, or order matched pairs. The 40 V BVDSS gives ample headroom for high transient program content without gate-clipping artifacts.
Recommended
Acoustic and Vibration Sensor Buffers
Piezoelectric acoustic, hydrophone, and vibration sensors present extremely high source impedance and microvolt-level signals. Placing an LSK170A source follower directly at the transducer converts this high impedance to a low-impedance drive without adding measurable noise, thanks to the device's low input gate current and audio-band noise density. The low input capacitance matters here: it forms a capacitive divider with the sensor capacitance, and the LSK170A's small Ciss preserves signal amplitude at the gate node. Bias the follower at 1-3 mA; the 400 mW dissipation limit is far from reached at these currents, so thermal design is trivial even in the compact SOT-23-3 footprint.
Recommended
Instrumentation Front Ends
In test and measurement instrumentation, the LSK170A serves as a low-noise input buffer or as the amplifying element in discrete instrumentation front ends where op-amp input noise would dominate. The uniquely linear VGS transfer function documented in the Linear Systems datasheet keeps distortion low across large input swings, while high BVDSS (40 V) tolerates input overrange transients better than low-voltage CMOS alternatives. Common topologies include cascoded JFET input stages with source degeneration for improved linearity and a bipolar second stage for voltage gain. Select grade A for 2-4 mA bias points; grades B-D suit higher-current, lower-output-impedance designs on the same PCB footprint.
Recommended
Medical and Biopotential Signal Acquisition
ECG, EEG, and other biopotential front ends demand picoampere-level input currents and microvolt noise floors - exactly the LSK170A's strengths as a high input impedance, ultra-low-noise JFET. The device's Electronics Notes-documented positioning for the medical market reflects its use in electrode buffers and differential input pairs where DC drift and 1/f noise corrupt weak physiological signals. Bias each input device below 2 mA to minimize power and noise bandwidth, and use matched LSK170/LSJ74 pairs to control offset in differential stages. The SOT-23-3 package keeps the buffer small enough to mount on wearable or cable-mounted electrode assemblies.
Recommended
DIY Hi-Fi Amplifier Input and Cascode Stages
The enthusiast audio community widely uses genuine LSK170A parts in DIY amplifier input stages, phono equalizers, and JFET cascodes - projects such as popular first-watt-style F6 builds specify matched LSJ74/LSK170 pairs from the diyAudio Store. The LSK170A replaced the discontinued Toshiba 2SK170 in these designs without PCB changes thanks to pin-for-pin compatibility. Builders should match devices (VGS at operating current) or buy factory-matched pairs, since forum reports show counterfeit 2SK170s cannot be paralleled or matched reliably. Grade A (2.6-6.5 mA IDSS) matches the classic 2SK170GR bias window used in most schematics.
Recommended
High-Impedance Active Filters and Mixers
Studio mixing consoles, EQ modules, and active filter networks benefit from the LSK170A as a buffer or gain element where source impedance is high and coloration must be negligible. The linear transfer function supports low THD through large program swings, and the low capacitance preserves frequency response accuracy in Sallen-Key and state-variable filter topologies. In console channel strips, a source-follower buffer built on the LSK170A isolates fader and EQ networks from the preceding gain stage. The 40 V rating comfortably covers bipolar audio rails (Β±15 V), and grade selection lets designers standardize one footprint across multiple bias-current requirements.
Recommended
Recommended Products Summary
Engineering reference data for LSK170A β comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | LSK170B | LSK170C | LSK170D | IF170 |
|---|---|---|---|---|---|
| Package | SOT-23-3 | SOT-23-3 - same | SOT-23-3 - same | SOT-23-3 - same | SOT-23-3 (verify option) - same footprint |
| Brand | Linear Integrated Systems | Linear Integrated Systems | Linear Integrated Systems | Linear Integrated Systems | InterFET |
| IDSS Range | 2.6 - 6.5 mA | ~4 - 8 mA (higher bin) | ~6 - 12 mA (higher bin) | ~8 - 20 mA (highest bin) | [DATA_NEEDED] |
| VDS Rating | 40 V | 40 V | 40 V | 40 V | [DATA_NEEDED] |
| Max Drain Current | 10 mA | 10 mA | 10 mA | 10 mA | [DATA_NEEDED] |
| Power Dissipation | 400 mW | 400 mW | 400 mW | 400 mW | [DATA_NEEDED] |
| Noise Class | Ultra-low noise (audio-grade) | Ultra-low noise - same die | Ultra-low noise - same die | Ultra-low noise - same die | Comparable (vendor comparison data online) |
| Replaces Toshiba 2SK170 | Yes (pin-for-pin) | Yes (pin-for-pin) | Yes (pin-for-pin) | Yes (pin-for-pin) | Yes (marketed cross for 2SK170/LSK170) |
Key Differentiators
- Lowest IDSS bin for low-bias, low-noise designs (vs LSK170D)
- Direct 2SK170 replacement from a current, active manufacturer (vs IF170)
- Tighter initial grading versus generic substitutes (vs 2SK170 (gray market))
Design Notes
Grade selection is the most common mistake. Grade A IDSS spans 2.6-6.5 mA; if your self-bias design assumed a 2SK170GR device, grade A is the right bin, but the spread still means a fixed source resistor yields different drain currents part-to-part. Always size the source resistor around the measured midpoint of your purchased batch, or specify factory-matched pairs. Also verify pinout before drop-in substitution: some SOT-23 JFETs place the gate on pin 1, whereas the LSK170A uses D-S-G.
Keep the gate trace short and guard it with ground for high-impedance nodes - the JFET's high input impedance means board leakage and stray capacitance dominate performance if layout is sloppy. Place a 100 nF ceramic decoupling capacitor within 2 mm of the drain supply connection. In the SOT-23-3 package, the tab (pin 2, source) can double as a thermal relief but at 400 mW maximum dissipation, no heatsinking is required for normal audio bias currents of 1-5 mA.
For lowest noise, bias the LSK170A at a substantial fraction of IDSS (typically 1-3 mA for grade A) where transconductance is highest; noise scales inversely with gm. Avoid paralleling unmatched devices: forum-documented tests show genuine LSK170A parts parallel cleanly when matched, but mis-binned or counterfeit 2SK170s do not. For differential input stages, buy Linear Systems factory-matched LSK170/LSJ74 pairs instead of hand-matching from mixed batches.
Compliance Information
Distributor listing states RoHS compliant for the LSK170A SOT-23 3L RoHS part. REACH, halogen-free, and conflict-minerals status not stated in provided data.
