2SK170-BL/GR - N-Channel JFET Low Noise Audio 40V | Toshiba
MPN: 2SK170-BL/GR β End of Life| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $2.5 | $2.50 |
| 10 | $2.2 | $22.00 |
| 100 | $1.95 | $195.00 |
| 500 | $1.75 | $875.00 |
| 1,000 | $1.55 | $1,550.00 |
Drop-in alternatives for 2SK170-BL/GR 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:
2SK170-GR
β Drop-Inβ In Stock
$0.5 / Unit
View Datasheet β2SK170-BL
β Drop-Inβ In Stock
$2.1 / Unit
View Datasheet β2SK117-GR
β Drop-Inπ Reference alternative (not in catalog)
LSK170A
β Drop-Inβ In Stock
$0.94 / Unit
View Datasheet βLSK170B
β Drop-Inπ Reference alternative (not in catalog)
LSK170C
β Drop-Inπ Reference alternative (not in catalog)
2SK170-BL/GR Maximum Ratings & Electrical Characteristics
| Device Type | N-Channel Silicon JFET |
| Application | Low Noise Audio Amplifier |
| Gate-Drain Breakdown Voltage (VGDS) | -40 V |
| IDSS Grade BL | 6 mA to 12 mA |
| IDSS Grade GR | 2.6 mA to 6.5 mA |
| Total Power Dissipation | 300 mW |
| Package | TO-92 (3-pin) |
| Mounting Type | Through Hole |
| Polarity | N-Channel |
| Transistor Configuration | Single |
| Channel Type | N |
| Number of Pins | 3 |
| Product Status | Discontinued at Toshiba (EOL); aftermarket/remaining stock |
2SK170-BL/GR Pin Configuration
| Pin 1 | S β Source |
| Pin 2 | G β Gate |
| Pin 3 | D β Drain |
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
2SK170-BL/GR is suitable for 6 applications: MM Phono Preamplifier Input Stage, Condenser Microphone Front End, Cascode and Current-Mirror Bottom Devices, Low-Noise Buffers and Source Followers, Instrumentation and Measurement Front Ends, Guitar Effects and Musical Instrument Electronics.
MM Phono Preamplifier Input Stage
The 2SK170-BL is the canonical input device for moving-magnet (MM) phono preamplifiers. Its noise voltage near 1 nV per root-hertz and high transconductance deliver excellent signal-to-noise against a 47 kOhm cartridge load, where the input device dominates total noise. Typical designs run the JFET common-source at 3-6 mA from the BL-grade IDSS (6-12 mA), followed by an RIAA equalization network. Placing two 2SK170 devices in parallel reduces input noise by approximately 3 dB at the cost of doubled input capacitance - acceptable for MM cartridges but not for low-capacitance MC transformers. Because the original Toshiba part is discontinued, Linear Systems LSK170A provides a pin-for-pin TO-92 substitution with equivalent grade currents, letting existing phono PCBs be serviced without layout changes.
Recommended
Condenser Microphone Front End
In condenser microphone capsule electronics, the 2SK170-GR serves as the ultra-high-impedance source follower or common-source amplifier directly after the capsule. The JFET's very low gate leakage current prevents charge loss from the polarized capsule, while the low noise voltage floor (around 1 nV per root-hertz) preserves the self-noise budget of the microphone. GR-grade current (2.6-6.5 mA) suits the low supply currents available inside microphone bodies, often from phantom-power derived rails of 30-48 V with local regulation. A typical circuit biases the JFET at 1-3 mA with a source resistor and couples out via a capacitor to the output driver. The TO-92 package dissipates only a few milliwatts here, far below the 300 mW limit.
Recommended
Cascode and Current-Mirror Bottom Devices
High-performance audio voltage-gain stages frequently use 2SK170-BL as the bottom device in a cascode, where its high transconductance and low output conductance translate into high unloaded gain and low distortion. In cascode operation the JFET's VDS is held nearly constant by the upper device (a BJT or second JFET), which shields the JFET's gate-drain capacitance from the Miller effect and preserves bandwidth. BL-grade current (6-12 mA) provides the headroom needed for class-A line stages swinging several volts RMS into 10 kOhm loads. Calculated dissipation in a 15 V rail cascode at 8 mA is only about 120 mW, well within the 300 mW rating. Match IDSS pairs for differential or mirrored topologies.
Recommended
Low-Noise Buffers and Source Followers
As a source follower, the 2SK170 buffers high-impedance nodes such as volume wipers, op-amp summing nodes and tube plate outputs without loading them. Its high input impedance (gigohms, set by gate leakage) and low input capacitance preserve source response, while sub-nanovolt noise contributes negligibly to the signal chain. A typical follower runs at 2-5 mA with a current-source load for high linearity; harmonic distortion at 1 V RMS output is typically below 0.01 percent with a good current source. GR-grade parts suit battery-operated portable equipment at 1-3 mA, while BL parts serve mains-powered preamplifiers. Linear Systems LSK170C and LSK170A drop into the same 3-pin TO-92 footprint for continued production.
Recommended
Instrumentation and Measurement Front Ends
Beyond consumer audio, the 2SK170 excels as the front-end device in laboratory preamplifiers, hydrophone and accelerometer amplifiers, and photodiode transimpedance front ends where source impedances are high and noise must be minimized. The JFET's negligible gate current eliminates the shot-noise floor that a bipolar input would add, and its noise figure with 10 kOhm source impedance remains excellent at audio and ultrasonic frequencies. Designers typically follow the JFET with a low-noise bipolar or JFET-input op-amp for open-loop gain. With 2SK170 discontinued, new instrumentation designs should qualify the Linear Systems LSK170 series (TO-92, SOT-23 or SOT-89), which Linear Systems characterizes for exactly these ultra-low-noise acoustic and measurement applications.
Recommended
Guitar Effects and Musical Instrument Electronics
DIY and boutique guitar-pedal builders use the 2SK170-GR as a low-noise input buffer and gain stage where its low noise floor prevents hiss from dominating quiet passages. The GR grade's 2.6-6.5 mA IDSS keeps battery drain low in 9 V effects units, extending battery life while a common-source gain stage of 10-20 dB is easily achieved with a 15-22 kOhm drain resistor. Because the 2SK170 is expensive and discontinued, the community standard practice is substitution with 2SK117-GR (identical pinout and parameters per Toshiba data) or LSK170 series parts. Devices are commonly IDSS-sorted with a simple test jig to match pairs for symmetric push-pull stages in overdrive and fuzz circuits.
Recommended
Recommended Products Summary
Engineering reference data for 2SK170-BL/GR β comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | 2SK170-GR | 2SK117-GR | LSK170A | LSK170B |
|---|---|---|---|---|---|
| Package | TO-92 (3-pin) | TO-92 (3-pin) - same | TO-92 (3-pin) - same | TO-92 (3-pin) - same | TO-92 (3-pin) - same |
| Brand | Toshiba | Toshiba | Toshiba | Linear Systems | Linear Systems |
| Pinout (S-G-D) | Pin 1 Source, Pin 2 Gate, Pin 3 Drain | Identical S-G-D | Identical S-G-D | Identical S-G-D (pin-for-pin) | Identical S-G-D (pin-for-pin) |
| IDSS Range | BL: 6-12 mA / GR: 2.6-6.5 mA | 2.6-6.5 mA (GR bin) | 2.6-6.5 mA | Approx. BL-range currents | Alternate grade bin |
| Gate-Drain Breakdown Voltage | -40 V | -40 V | -50 V | -40 V | -40 V |
| Power Dissipation | 300 mW | 300 mW | 300 mW | 350 mW | 350 mW |
| Low-Noise Audio Characterization | Yes (reference audio JFET, ~1 nV/rtHz) | Yes, same die | General purpose, modestly higher noise | Yes, purpose-built audio JFET | Yes, purpose-built audio JFET |
| Lifecycle Status | EOL (discontinued by Toshiba) | EOL (remaining stock) | EOL (remaining stock) | Active - in production | Active - in production |
Key Differentiators
- Lowest-noise audio JFET of its generation (~1 nV/rtHz) (vs 2SK117-GR)
- In-production availability (vs LSK170A)
- Grade flexibility within one footprint (vs 2SK170-GR)
Design Notes
The dominant pitfall with the 2SK170 is ignoring IDSS grade spread. A BL device may draw anywhere from 6 to 12 mA at VDS=10V, VGS=0; a stage biased assuming 12 mA may under-bias a 6 mA device out of its low-noise region. Design source-bias networks for the full grade range and specify the grade when ordering (BL vs GR are not interchangeable in bias-critical circuits). Also beware counterfeit 2SK170 parts in the aftermarket - verify IDSS before installation in matched or parallel configurations.
Estimated: with the 300 mW TO-92 package limit and typical audio bias points of 5 mA at 15 V VDS (75 mW), thermal margin is generous and no heatsinking is needed. Only in DC-biased constant-current sink applications near the 40 V rating (e.g., 8 mA at 30 V = 240 mW) does junction temperature approach limits; derate for ambient above 50 C and ensure free air circulation around the TO-92 body.
Keep the gate lead connection as short as practical and guard the gate node with a clean PCB area or a guard ring connected to the source potential to limit leakage-induced noise and hum pickup in ultra-high-impedance inputs such as condenser microphone stages. Because the device is through-hole TO-92, lead dress dominates RF susceptibility; a small ferrite bead or 1 kOhm stopper resistor at the gate prevents RF demodulation in electrically noisy environments.
Compliance Information
Compliance data not present in provided sources; the 2SK170 predates modern RoHS declarations and is discontinued. The LSK170 replacement series is available in RoHS versions per Linear Systems.
