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Q: Which pins drive the speaker?

Pins 5 (VO1) and 8 (VO2) - speaker connects directly between them. The outputs swing 180° out of phase around mid-rail, so the speaker sees double the single-ended swing and needs no coupling capacitor or snubber.

Q: What is the CD pin for?

Mute and power-down control. Logic high (>2.0V) on pin 1 mutes the amp with over 70dB attenuation in under 2µs and drops current to 65µA. Low (<0.8V) or floating enables normal operation.

Q: Do I need both FC1 and FC2 capacitors?

For line-powered or noisy supplies, yes. C1 (1µF on FC1) handles high-frequency ripple; C2 (5µF on FC2) dominates where mains hum lives. A clean battery supply can leave FC2 open, but a line-powered speakerphone needs both.

Q: What supply voltage should I use?

3–6V covers most speakerphone designs; the chip accepts 2.0–16V. Output power is specified at 6V/32Ω (250mW). Below 3V the swing shrinks noticeably; above 12V there's no benefit for voice audio.

Q: Can the MC34119 drive headphones?

Yes - headphones are a natural load. The 8–100Ω load range covers 32Ω headphones directly. Drive them from VO1/VO2 with no coupling caps, or series resistors if you want a volume divider.

Q: Why is my output so quiet?

Check gain resistors first, then the bypass cap, then the CD pin. A wrong Rf/Ri ratio pins gain near 0dB; a missing 100µF bypass starves the output stage; a floating CD pin mutes intermittently.

Q: How much gain can I set?

Up to 46dB in the voice band, set by Rf/Ri on Amp #1. Above 46dB, bandwidth rolls off inside the 300Hz–3.4kHz band and stability tightens. For handsets, 20–40dB is the practical range.

Q: Is the MC34119 still a good choice for a new speakerphone?

Yes - it's the purpose-built part for the job. The differential output, CD mute, and 2.0V floor are exactly what a battery-powered hands-free circuit needs, and UTC keeps it in production. For louder audio, the TDA2822 family is the alternative.

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MC34119 Pinout, Specifications & Common Mistakes | ICMASS

2026/8/25 14:33:56

MC34119 Pinout, Specifications & Common Mistakes | ICMASS

The MC34119 is an 8-pin low-power audio amplifier for speakerphone circuits, in SOP-8 or DIP-8. It drives a speaker differentially (VO1/VO2), runs from 2.0V to 16V, and has a chip-disable (CD) pin for mute.

This page covers the pin functions, key specs, the typical circuit, and the mistakes that come up in real builds — most of them around the mute pin and the filter capacitors.

MC34119 Pinout and Pin Functions

Pin	Name	Type	Function
1	CD / Mute	Digital input	Chip disable: logic low (<0.8V) = enabled; high (>2.0V) = muted. Floating reads as low. 90kΩ input impedance.
2	FC2	Filter cap	Low-frequency supply filter; 5µF to ground for 52dB ripple rejection. Can be left open on clean supplies.
3	FC1	Filter / alt input	High-frequency filter and analog ground reference; 1µF to ground. Can serve as an alternate input.
4	V_IN	Analog input	Amplifier input. External cap and resistor set the low-frequency roll-off and input impedance; feedback resistor connects here.
5	VO1	Output	Differential output 1; DC level (V_CC−0.7V)/2.
6	V_CC	Power	Supply, 2.0V–16V. Decouple near the pin.
7	GND	Ground	Circuit ground.
8	VO2	Output	Differential output 2; equal amplitude, 180° out of phase with VO1.

Pin layout: pins 1–4 on the left (control, filter, input), pins 5–8 on the right (outputs, supply, ground). The differential outputs on 5 and 8 are the two pins that matter for the speaker hookup.

Key Specifications

Parameter	Value
Supply Voltage	2.0V–16V (abs max 18V)
Output Power	>250mW @ 6V / 32Ω, THD<10%
Quiescent Current	2.7mA typ; 65µA muted
Open-Loop Gain (Amp #1)	80dB typ
Closed-Loop Gain	Set by R_f/R_i; up to 46dB voice band
Load Impedance	8Ω–100Ω
Mute Attenuation	>70dB (CD pin)
Mute Turn-Off / Turn-On	<2µs / 12–15ms
Power Supply Rejection	52dB typ (1µF FC1 + 5µF FC2)
Operating Temperature	−20°C to +70°C

Typical Application Circuit

Circuit: electret mic into VIN (pin 4), 1µF on FC1 and 5µF on FC2 for the 52dB supply rejection, speaker straight across VO1 and VO2 — no coupling capacitor. Pull CD high to mute (70dB, 65µA standby).

PCB Layout Tips

Decouple VCC at the pin. A 100µF electrolytic plus 0.1µF ceramic right at pin 6 keeps supply ripple out of the audio path — the amp's own PSRR depends on the external filter caps, not on internal magic.

Keep FC1/FC2 caps close to the chip. Both filter pins feed the internal amplifiers; long traces pick up hum that the caps are supposed to reject. Route them to the ground plane with short, direct connections.

Ground the CD pin deliberately. If mute isn't used, tie pin 1 to ground — not to VCC and not floating. A floating CD input at 90kΩ picks up noise and mutes intermittently.

Speaker wires short and twisted. The differential outputs reject common-mode noise, but a speaker lead run across the board next to the supply still couples clicks into the input.

Common Mistakes When Using MC34119

1. Leaving the CD pin floating. It reads as logic low (enabled), but noise couples into the 90kΩ input and mutes the amp erratically. Tie it to ground when unused.

2. Skipping or downsizing the FC2 capacitor. Without the 5µF on pin 2, the 52dB ripple rejection drops to whatever the bare pin provides — line-powered speakerphones hum. The capacitor is the difference between clean audio and a hum box.

3. Wrong gain resistors. The closed-loop gain is R_f/R_i; a wrong ratio pins the output near silence. Verify the resistor values against the datasheet example before blaming the chip.

4. Expecting 6V power from a 3.3V rail. The 250mW figure is specified at VCC=6V; at 3.3V the differential swing drops and output halves. Design the speaker and volume expectation around the actual rail.

5. Treating the 12–15ms unmute delay as a fault. Coming out of mute ramps up over 12–15ms by design; a slow "wake up" is normal behavior, not a bad part.

6. No bypass capacitor on VCC. The amp handles small signals and drives a speaker from the same rail — without a bulk bypass, the output stage drags the rail down and the input stage clips.

Frequently Asked Questions

Q1: Which pins drive the speaker?

A: Pins 5 (VO1) and 8 (VO2) — speaker connects directly between them. The outputs swing 180° out of phase around mid-rail, so the speaker sees double the single-ended swing and needs no coupling capacitor or snubber.

Q2: What is the CD pin for?

A: Mute and power-down control. Logic high (>2.0V) on pin 1 mutes the amp with over 70dB attenuation in under 2µs and drops current to 65µA. Low (<0.8V) or floating enables normal operation.

Q3: Do I need both FC1 and FC2 capacitors?

A: For line-powered or noisy supplies, yes. C1 (1µF on FC1) handles high-frequency ripple; C2 (5µF on FC2) dominates where mains hum lives. A clean battery supply can leave FC2 open, but a line-powered speakerphone needs both.

Q4: What supply voltage should I use?

A: 3–6V covers most speakerphone designs; the chip accepts 2.0–16V. Output power is specified at 6V/32Ω (250mW). Below 3V the swing shrinks noticeably; above 12V there's no benefit for voice audio, just more heat.

Q5: Can the MC34119 drive headphones?

A: Yes — headphones are a natural load. The 8–100Ω load range covers 32Ω headphones directly. Drive them from VO1/VO2 with no coupling caps, or series resistors if you want a volume divider.

Q6: Why is my output so quiet?

A: Check gain resistors first, then the bypass cap, then the CD pin. A wrong R_f/R_i ratio pins gain near 0dB; a missing 100µF bypass starves the output stage; a floating CD pin mutes intermittently.

Q7: How much gain can I set?

A: Up to 46dB in the voice band, set by R_f/R_i on Amp #1. Above 46dB, bandwidth rolls off inside the 300Hz–3.4kHz band and stability tightens. For handsets, 20–40dB is the practical range.

Q8: Is the MC34119 still a good choice for a new speakerphone?

A: Yes — it's the purpose-built part for the job. The differential output, CD mute, and 2.0V floor are exactly what a battery-powered hands-free circuit needs, and UTC keeps it in production. For louder audio instead of voice, the TDA2822 family is the alternative.