2SJ74-BL - P-Channel Low-Noise Audio JFET | Toshiba
MPN: 2SJ74-BL β Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $4.9 | $4.90 |
| 10 | $4.41 | $44.10 |
| 100 | $3.92 | $392.00 |
| 500 | $3.43 | $1,715.00 |
| 1,000 | $2.94 | $2,940.00 |
2SJ74-BL Overview
A JFET (junction field-effect transistor) is a voltage-controlled semiconductor device in which current flows through a channel whose conductivity is modulated by the gate-source junction, which is reverse-biased and therefore draws virtually zero gate current. Within the semiconductor hierarchy, the 2SJ74-BL belongs to small-signal transistors, specifically depletion-mode JFETs, and occupies the same niche in audio front-ends that vacuum tube triodes once held: extremely low voltage noise combined with high input impedance.
Key differentiating features include Toshiba's optimized geometry for low noise in the audio band (20 Hz to 20 kHz), tight Idss grading (6-12 mA for BL), and a transconductance characteristic that suits source-follower and common-source first stages. According to the Toshiba datasheet, the device is explicitly recommended for the first stages of EQ amplifiers and MC (moving-coil) head amplifiers, where input-referred noise dominates total system performance.
Technically, the 2SJ74 uses a lateral P-channel diffused structure. Because gate current is picoampere-level, the input impedance is extremely high, allowing direct connection to high-impedance sources such as moving-coil step-up transformer secondaries or piezo/ceramic cartridges. Its complement, the N-channel 2SK170, is routinely paired with it in push-pull and folded-cascode circuits.
Typical applications include MC/ MM phono preamplifier input stages, microphone preamplifiers, EQ amplifier front ends, and low-noise active loads or constant-current sources in high-end discrete audio design.
A key design consideration is Idss spread: even within the BL bin, Idss varies from 6 mA to 12 mA, so biasing should use source degeneration resistors or local feedback rather than assuming a fixed value. Verify authenticity carefully, as the market carries many counterfeit parts.
This page synthesizes distributor availability data, grading-bin comparisons, drop-in alternatives including the Linear Systems LSJ74, and practical design guidance not found in the manufacturer datasheet alone.
Drop-in alternatives for 2SJ74-BL β same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Variants in this series
Same-series models that are drop-in compatible with 2SJ74-BL (same form factor and footprint) β differing in Package, Transistor Type, Mounting Type, Configuration, Channel Type.
Quick Comparison Tool β Select alternative parts for side-by-side comparison:
2SJ74-GR
β Drop-Inβ In Stock
Contact for price
View Datasheet β2SJ74-GR/BL
β Drop-Inβ In Stock
$1.55 / Unit
View Datasheet βLSJ74BL
β Drop-Inπ Reference alternative (not in catalog)
LSJ74
β Drop-Inπ Reference alternative (not in catalog)
2SJ74-BL Maximum Ratings & Electrical Characteristics
| Transistor Type | P-Channel JFET (depletion mode) |
| Drain-Source Breakdown Voltage (VGDS) | -25 V |
| Drain-Source Current (IDSS), BL grade | 6 mA to 12 mA |
| Total Power Dissipation (PD) | 400 mW |
| Package | TO-92 (Toshiba 2-5F1A, SC-43), 3-pin |
| Mounting Type | Through-Hole |
| Number of Units in IC | 1 |
| Channel Type | P |
| Applications | Low noise audio amplifier, first stages of EQ amplifiers and MC head amplifiers |
2SJ74-BL Pin Configuration
| Pin 1 | S β Source |
| Pin 2 | G β Gate (control terminal, reverse-biased junction) |
| Pin 3 | D β Drain |
Typical Applications
2SJ74-BL is suitable for 6 applications: MC Phono Head Amplifier Input Stage, RIAA EQ Amplifier First Stage, Microphone Preamplifier Front End, JFET Constant-Current Source / Active Load, High-Impedance Instrumentation Buffer, Legacy and High-End Audio Repair / Restoration.
MC Phono Head Amplifier Input Stage
Moving-coil cartridges output only tens of microvolts at high source impedance, so the first active device determines the entire signal-to-noise ratio. The 2SJ74-BL fits this role because its Toshiba-optimized geometry delivers very low input-referred voltage noise in the audio band, and its near-zero gate current eliminates bias-current noise into the cartridge. Used in a common-source or cascode configuration with the BL grade's 6-12 mA Idss providing high transconductance, the device achieves head-amplifier performance per the datasheet's explicit recommendation for 'first stages of MC head amplifiers.' The trade-off is the -25 V breakdown limit, so supplies should stay near +/-15 V, and pairs should be matched for differential inputs.
Recommended
RIAA EQ Amplifier First Stage
EQ (RIAA correction) amplifiers demand a first stage that combines low noise with sufficient headroom and gain for the subsequent passive equalization network. The 2SJ74-BL is explicitly recommended in the Toshiba datasheet for 'first stages of EQ amplifiers.' Its depletion-mode behavior allows simple self-bias with a source resistor, and the BL Idss range (6-12 mA) supports low-value source resistors, minimizing excess thermal noise contribution. Because the RIAA network follows directly, the JFET's high output impedance should be buffered or the drain load kept high for gain. Designers should verify per-device Idss, since the bin spans a 2:1 spread, and consider matched-pair sourcing for stereo channel consistency.
Recommended
Microphone Preamplifier Front End
Condenser and ribbon microphones present high source impedance and microvolt-level signals, exactly the regime where the 2SJ74-BL's voltage-controlled, high-input-impedance JFET input excels. Gate leakage is negligible, so no significant bias current flows into the microphone, preserving low-frequency response and avoiding shot noise. In a source-follower or gain stage biased around several milliamps, the BL grade offers the highest transconductance available in the 2SJ74 family, reducing input-referred noise. The -25 V VGDS rating suits 48 V phantom-powered designs only with proper voltage-dropping networks. For battery-powered field recorders, the 2SJ74-GR variant trades some transconductance for lower standing current.
Recommended
JFET Constant-Current Source / Active Load
A JFET with gate tied to source forms a simple two-terminal constant-current source at its Idss, and the 2SJ74-BL's 6-12 mA BL grading makes it ideal as an active load or tail current source in discrete audio stages. The high output impedance of the JFET load dramatically increases gain and power-supply rejection of the mirrored stage compared with a resistor load. Because Idss falls with temperature (negative temperature coefficient), the circuit is inherently self-stabilizing - a key advantage over BJT current sources needing compensation. Select devices measured at the desired current, or add a source resistor to trim the current down from Idss for precise tail currents.
Recommended
High-Impedance Instrumentation Buffer
Measurement and instrumentation circuits probing piezo sensors, electret capsules, pH probes or high-value pickups need an input stage with gigaohm-level input impedance and minimal added noise. The 2SJ74-BL's reverse-biased gate junction draws picoampere-level current, so it loads such sources negligibly, while its low voltage noise keeps small signals resolvable. Wired as a source follower biased at several milliamps (BL grade), it drives cables or the next gain stage with unity gain and low distortion. Designers must respect the -25 V maximum and provide input overvoltage clamping, since the gate junction is fragile. A complementary 2SK170 follower forms a push-pull buffer for even lower output impedance.
Recommended
Legacy and High-End Audio Repair / Restoration
Vintage Japanese audio equipment from the 1970s-1990s - Accuphase, Denon, Yamaha and similar flagship units - frequently uses 2SK170/2SJ74 JFET pairs in phono and line stages. For restoration, the 2SJ74-BL offers the original manufacturer's device with authentic noise and transconductance behavior. Where genuine Toshiba stock is unavailable, the Linear Systems LSJ74BL is a validated direct replacement with the same TO-92 footprint and grading philosophy, as stated by Linear Systems on its product page. When substituting, measure Idss of new devices and trim source resistors so the restored stage's operating point matches the service manual, since grading bins alone do not guarantee identical bias.
Recommended
Recommended Products Summary
Engineering reference data for 2SJ74-BL β comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | 2SJ74-GR | 2SJ74-GR/BL | LSJ74BL | LSJ74 |
|---|---|---|---|---|---|
| Package | TO-92 (2-5F1A, SC-43) | TO-92 (2-5F1A, SC-43) - same | TO-92 (2-5F1A, SC-43) - same | TO-92 - same | TO-92 - same |
| Brand | Toshiba | Toshiba | Toshiba | Linear Systems | Linear Systems |
| Polarity | P-Channel JFET | P-Channel JFET | P-Channel JFET | P-Channel JFET | P-Channel JFET |
| Drop-in Replacement Status | Reference device | Yes (lower Idss bin, bias check needed) | Yes (grading spread check needed) | Yes - stated direct replacement by manufacturer | Yes - stated direct replacement by manufacturer |
| Primary Application | Low-noise audio first stages (EQ, MC head amp) | Low-noise audio, lower-current bias | Low-noise audio, flexible bias | Ultra-low-noise audio/acoustic applications | Ultra-low-noise audio/acoustic applications |
Key Differentiators
- Highest Idss grading in the 2SJ74 family (vs 2SJ74-GR)
- Validated cross-brand drop-in exists (vs LSJ74BL)
- Purpose-built audio noise optimization (vs LSJ74)
Design Notes
Do not assume a fixed Idss: the BL bin spans 6-12 mA, a 2:1 spread. Always self-bias with a source resistor rather than relying on a nominal value, and measure devices (or buy matched pairs) for differential and current-source duties. Additionally, the 2SJ74 is among the most counterfeited audio semiconductors - community reports describe unlabeled TO-92 pieces resold as genuine. Purchase only from authorized distributors such as Mouser, and sanity-check measured Idss and transconductance against datasheet expectations on receipt.
Respect the 400 mW total power dissipation and -25 V VGDS limits. Estimated: at a 15 V rail and 10 mA standing current, a common-source stage dissipates roughly 150 mW in the device (VDS x ID), safely inside the limit, but a cascode or active-load stage with high VDS could approach it - compute VDSxID for your actual operating point and derate above 25 C ambient per the datasheet derating curve. Keep supply rails near +/-15 V or below to preserve breakdown margin for signal swing and transients.
Keep the gate node physically short and guard it with ground ring/flood on high-impedance inputs (phono, piezo) to minimize leakage and hum pickup. Use metal-film or better resistors in the gate network to limit excess thermal noise, and avoid carbon composition parts in the source bias path. Because the TO-92 is through-hole, lead dress matters in hand-built audio: keep gate leads away from the power supply wiring and twist heater/supply pairs to reduce induced noise into the sub-microvolt input stage.
For lowest input-referred noise, bias toward the upper part of the BL Idss range where transconductance (and hence equivalent input noise voltage, roughly inversely related to gm) is best; estimated benefit is meaningful because voltage noise scales approximately with 1/sqrt(gm). For stereo symmetry, match VGS at the target current across channels to within a few tens of millivolts. If a source follower drives cable capacitance, check for ringing and add a small gate-stop or output series resistor as needed.
Compliance Information
Mouser listing references 'X34 Pb' in the part description, suggesting a lead-related classification; full RoHS/REACH status must be confirmed on the current Toshiba/Mouser product page before use in new RoHS-restricted designs.
