2SK170-BL/J74-BL - N-Ch JFET 40V Low Noise Audio | Toshiba
MPN: 2SK170-BL/J74-BL β End of Life| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $2.95 | $2.95 |
| 10 | $2.65 | $26.50 |
| 100 | $2.3 | $230.00 |
| 500 | $2 | $1,000.00 |
| 1,000 | $1.8 | $1,800.00 |
Drop-in alternatives for 2SK170-BL/J74-BL 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 β2SK117-GR
β Drop-In β οΈ εζ°εΎ ιͺθ―π 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)
2SK170-BL/J74-BL Maximum Ratings & Electrical Characteristics
| Transistor Type | N-Channel JFET (Junction FET) |
| Drain-Source Voltage (Vdss) | 40 V |
| Continuous Drain Current (Id) | 0.02 A (20 mA) |
| Idss Grade BL | 6 mA to 12 mA |
| Configuration | Single (N-channel); listed with P-channel companion 2SJ74-BL |
| Package | TO-92 (3-Pin) |
| Mounting Type | Through Hole |
| Application | Low Noise Audio Amplifier |
| Polarity | N-Channel |
2SK170-BL/J74-BL 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/J74-BL is suitable for 6 applications: Phono Preamplifier Input Stages, Microphone and Instrument Preamplifiers, Discrete Op-Amp Front Ends, Class-A Constant Current Sources, Guitar Effects and Instrument Input Buffers, Hybrid Tube/Solid-State Audio Circuits.
Phono Preamplifier Input Stages
The 2SK170-BL is the canonical choice for moving-magnet and moving-coil phono stages because its very low input-referred voltage noise and low 1/f corner preserve the tiny cartridge signals. The BL grade Idss of 6 mA to 12 mA provides high transconductance for adequate open-loop gain in a single discrete stage. Designers commonly parallel two or three devices to halve voltage noise for MC cartridges, accepting higher input capacitance that must be budgeted against cartridge loading. Bias with a source resistor and gate-leak network sized for the BL Idss spread, and measure Idss to pair matched devices.
Recommended
Microphone and Instrument Preamplifiers
Condenser microphone front ends and high-impedance instrument buffers benefit from the 2SK170-BL combination of very high input impedance, negligible gate leakage, and low noise, which keeps the source impedance from degrading signal-to-noise ratio. A JFET input also avoids the bias-current pops that bipolar inputs can exhibit with dynamic sources. With a 40 V drain-source rating, the device operates comfortably from 24 V to 48 V rails used in professional audio. The BL grade provides enough transconductance for single-stage gains exceeding 20 dB with a drain load resistor, and sourcemaster degeneration can be added for linearity.
Recommended
Discrete Op-Amp Front Ends
In discrete op-amp and line-stage designs, the 2SK170-BL pairs with the 2SJ74-BL P-channel complement to form JFET input differential pairs with ultra-low offset drift and no input bias current through the feedback network. Matching Idss within a few milliamps between the N and P devices minimizes input offset and second-harmonic distortion. The 40 V rating supports high-voltage class-A stages without cascoding in most audio designs, and the TO-92 package allows hand-matching and thermal coupling of paired devices on a small adapter or PCB island for stable differential performance.
Recommended
Class-A Constant Current Sources
The 2SK170-BL serves as a self-biased JFET current source (current regulator diode configuration with gate tied to source through a resistor) in tube and solid-state class-A circuits. Its BL Idss of 6 mA to 12 mA is directly useful as a current-sink value for preamp tubes and driver stages, and the device's low output conductance provides a high small-signal impedance that improves stage linearity and PSRR. Because Idss varies unit to unit within the grade, selecting devices by measured Idss allows precise current setting, and cascoding two JFETs multiplies output impedance for demanding applications.
Recommended
Guitar Effects and Instrument Input Buffers
JFET input buffers built on the 2SK170-BL provide the high input impedance (megohm-class) that preserves the tone of passive magnetic guitar pickups, which lose highs when loaded below a few hundred kilohms. The device's low noise keeps the buffer transparent, and its 40 V rating permits operation from standard 9 V to 24 V pedal supplies with wide headroom. Simple source-follower configurations achieve near-unity gain with excellent linearity at small signal levels, and the through-hole TO-92 package suits point-to-point and eyelet-board construction common in boutique effects pedals.
Recommended
Hybrid Tube/Solid-State Audio Circuits
In hybrid designs where JFETs buffer or bias vacuum tubes, the 2SK170-BL's 40 V rating, low noise, and BL-grade current range make it ideal as a cathode-follower assist, plate-load current source, or grid-leak replacement. A JFET source follower driving a tube stage lowers output impedance without adding transistor coloration, and JFET current sources in the plate circuit raise effective load impedance dramatically, boosting gain and linearity. Matched pairs of 2SK170-BL devices ensure symmetric push-pull bias, and the part remains the audiophile community's default recommendation for these low-level hybrid functions.
Recommended
Recommended Products Summary
Engineering reference data for 2SK170-BL/J74-BL 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 Integrated Systems | Linear Integrated Systems |
| Drain-Source Voltage | 40 V | 40 V | 50 V | 40 V | 40 V |
| Idss Grade Range | 6 mA to 12 mA (BL) | approx. 2.6 mA to 6.5 mA (GR) | GR band (lower than BL) | grade A band - select sub-range | grade B band closest to 6-12 mA |
| Polarity | N-Channel | N-Channel | N-Channel | N-Channel | N-Channel |
| Noise Class | Ultra-low noise (audio) | Ultra-low noise (audio) | Low noise | Ultra-low noise - direct replacement | Ultra-low noise - direct replacement |
| Lifecycle Status | EOL (discontinued) | EOL (discontinued) | EOL | Active | Active |
| Mounting Type | Through Hole | Through Hole | Through Hole | Through Hole (TO-92; SOT-23/SOT-89 variants) | Through Hole (TO-92; SOT-23/SOT-89 variants) |
| Continuous Drain Current | 20 mA | 20 mA | [DATA_NEEDED] | [DATA_NEEDED] | [DATA_NEEDED] |
Key Differentiators
- Highest Idss grade in the 2SK170 family (vs 2SK170-GR)
- Benchmark low-noise audio characterization (vs 2SK117-GR)
- Active-production continuity via drop-in equivalent (vs LSK170B)
Design Notes
Idss grading is the single biggest pitfall with the 2SK170-BL. The BL grade spans 6 mA to 12 mA - a 2:1 spread - so a fixed-bias design built around a 12 mA device will mis-bias a 6 mA device. Measure actual Idss (gate tied to source, drain at design voltage) before installing, and sort devices into sub-ranges. For differential pairs, match within 1-2 mA. Note also that counterfeits are common in the aftermarket because the part is discontinued; verify markings and Idss against datasheet behavior.
The TO-92 through-hole package is mechanically robust but thermally limited. Keep drain resistor power dissipation within the package's rated limit with margin at maximum ambient. For matched pairs, solder devices close together or thermally couple them (heatshrink or common clip) to minimize differential drift. The Linear Systems LSK170 shares the Toshiba TO-92 pinout (S-G-D), so existing footprints accept the drop-in replacement without board changes - but re-verify pinout against the datasheet outline before first production run.
With the very high input impedance of a JFET gate, gate-leak resistor value and input node leakage dominate noise and offset performance. Use film or quality ceramic gate resistors and clean, guard-ring PCB areas for phono-stage inputs. When paralleling multiple 2SK170-BL devices to reduce voltage noise for MC cartridges, insert small individual gate-stopper resistors or match devices carefully to avoid parasitic oscillation at VHF caused by uneven current sharing among paralleled gates.
Compliance Information
Compliance data not present in the provided web sources; the Toshiba 2SK170 predates RoHS and is discontinued. The Linear Systems LSK170 replacement is advertised as RoHS-compliant TO-92.
