MET-28 Audio Transformer Equivalent & Substitute Parts

Part Overview

The MET-28 is an active audio transformer manufactured by Tamura, designed for data and voice coupling applications. This through-hole component features a 1k:50 ohm impedance ratio with a 4.47:1 turns ratio and operates across the 300Hz to 100kHz frequency range. The part is RoHS Compliant and currently in active production status with 1192 pieces available in stock. Substitute parts are identified when equivalent electrical and mechanical specifications are required due to inventory constraints, design flexibility, or application-specific performance needs.

Key Parameters

Parameter	Value	Unit
Impedance - Primary	1k	Ohms
Impedance - Secondary	50	Ohms
Turns Ratio (Primary:Secondary)	4.47:1	Ratio
Frequency Range	300Hz ~ 100kHz	Hz
Frequency Response	±2dB	dB
DC Resistance - Primary	110	Ohm
DC Resistance - Secondary	8	Ohm
Power Level	50mW	mW
Mounting Type	Through Hole	-
Voltage Isolation	500VRMS @ 30 Seconds	VRMS
Operating Temperature	-20°C ~ 85°C	°C
RoHS Status	RoHS Compliant	-

Substitute Part Grouping Explanation

Substitution eligibility for the MET-28 is determined by the following critical parameters:

Primary Electrical Criteria:

Impedance matching: Primary impedance 1k ohms and secondary impedance 50 ohms
Turns ratio tolerance: 4.47:1 ±0.07 (acceptable variance within audio transformer specifications)
Frequency range: 300Hz to 100kHz minimum coverage
Frequency response: ±2dB flatness requirement
Power level: 50mW minimum rating

Mechanical Criteria:

Mounting type: Through Hole configuration
Termination style: PC Pin
Physical dimensions: Compatible footprint (approximately 10.4mm L × 7.87mm W × 11.8mm H seated)

Compliance Criteria:

RoHS compliance status (RoHS Compliant or ROHS3 Compliant acceptable)
Moisture Sensitivity Level: MSL 1 or Not Applicable

The SP-33 manufactured by Triad Magnetics meets all substitution criteria within these parameters.

Parameter Comparison

Parameter	MET-28 (Tamura)	SP-33 (Triad Magnetics)	Compatibility
Impedance - Primary (Ohms)	1k	1k	Equivalent
Impedance - Secondary (Ohms)	50	50	Equivalent
Turns Ratio (Primary:Secondary)	4.47:1	4.4:1	Compatible
DC Resistance - Primary (Ohm)	110	145	Acceptable Variance
DC Resistance - Secondary (Ohm)	8	8	Equivalent
Frequency Range (Hz)	300Hz ~ 100kHz	300Hz ~ 100kHz	Equivalent
Frequency Response (dB)	±2dB	±2dB	Equivalent
Power Level (mW)	50mW	50mW	Equivalent
Mounting Type	Through Hole	Through Hole	Equivalent
Voltage Isolation	500VRMS @ 30 Seconds	1000VRMS @ 1 Second	SP-33 Exceeds
Operating Temperature (°C)	-20°C ~ 85°C	-40°C ~ 85°C	SP-33 Exceeds
RoHS Status	RoHS Compliant	ROHS3 Compliant	Compatible
Termination Style	PC Pin	PC Pin	Equivalent
Size / Dimension (mm)	10.40 L × 7.87 W	10.41 L × 7.87 W	Equivalent
Height - Seated Max (mm)	11.80	11.80	Equivalent

Engineering Selection Recommendations

MET-28 (Tamura) Selection Criteria:

Primary choice when Tamura component qualification is required
Active production status with 1192 pieces in stock ensures supply continuity
RoHS Compliant certification meets standard environmental requirements
Specified isolation voltage of 500VRMS @ 30 Seconds is sufficient for standard audio coupling applications

SP-33 (Triad Magnetics) Selection Criteria:

Direct electrical substitute with turns ratio variance of 0.07:1 (1.6% deviation from MET-28)
Higher isolation voltage rating (1000VRMS @ 1 Second) provides additional safety margin
Extended operating temperature range (-40°C to 85°C) accommodates wider environmental conditions
ROHS3 Compliant status meets current regulatory requirements
Higher inventory availability (4431 pieces) supports rapid procurement
Primary DC resistance of 145 ohms (versus 110 ohms) results in 3.2% additional insertion loss, acceptable within ±2dB frequency response specification

Both parts are suitable for data and voice coupling applications within the specified frequency range. Selection between MET-28 and SP-33 depends on manufacturer qualification requirements, supply chain preferences, and environmental operating conditions.

Frequently Asked Questions (FAQ)

Q: Can SP-33 directly replace MET-28 in existing designs?

A: Yes. The SP-33 meets all critical electrical parameters: 1k/50 ohm impedance, 4.4:1 turns ratio (within acceptable tolerance of 4.47:1), identical frequency range and response, and equivalent mechanical footprint. Both components feature PC Pin termination and through-hole mounting.

Q: What is the significance of the turns ratio difference (4.47:1 vs 4.4:1)?

A: The 0.07:1 difference represents a 1.6% variance. This falls within standard audio transformer manufacturing tolerances and does not affect circuit performance within the ±2dB frequency response specification.

Q: How does the DC resistance difference affect circuit performance?

A: MET-28 primary DCR is 110 ohms; SP-33 is 145 ohms. This 35-ohm difference (3.2% increase) results in marginally higher insertion loss. Both transformers maintain the ±2dB frequency response specification across the 300Hz to 100kHz range.

Q: Are there packaging differences between MET-28 and SP-33?

A: MET-28 is supplied in Tube packaging; SP-33 is supplied in Bulk packaging. Both use identical PC Pin termination and through-hole mounting configuration with equivalent physical dimensions (10.4mm × 7.87mm × 11.8mm seated height).

Q: Which part has better environmental specifications?

A: SP-33 exceeds MET-28 in two areas: isolation voltage (1000VRMS vs 500VRMS) and operating temperature range (-40°C to 85°C vs -20°C to 85°C). Both are RoHS compliant.

Q: What is the Moisture Sensitivity Level difference?

A: MET-28 is rated MSL 1 (Unlimited); SP-33 is Not Applicable. Both ratings indicate minimal moisture sensitivity and do not restrict handling or storage procedures.

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