Zapco ST-104D SQ III Amp 4-Channel Class D Compact Amplifier 4x100w RMS
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The Zapco ST-104D SQ III is a compact 4-channel Class D full range amplifier rated at 4 x 100W RMS at 4 ohms and 4 x 150W RMS at 2 ohms. With RCA and speaker level inputs, it suits upgrades to factory or aftermarket head units where space is limited. It is part of Zapco's ST-III range.
Key specifications
- Model: ST-104D SQ III
- Channels: 4, full range, Class D
- Power @ 4 ohms: 4 x 100W RMS
- Power @ 2 ohms: 4 x 150W RMS
- Bridged @ 4 ohms: 2 x 300W RMS
- Inputs: RCA and speaker level
- Input sensitivity: 0.35v to 9v (Low)
- Frequency response: 15Hz – 30kHz ±1dB
- Signal to noise ratio: >90dB
- THD @ rated power: <0.5%
- THD + Noise: <0.1%
- Net dimensions: 124(W) x 50(H) x 213(L) mm
- Overall dimensions: 124(W) x 50(H) x 254(L) mm
ST-104D SQ III — 4-channel Class D compact amplifier
The ST-III series introduced Zapco's Studio brushed aluminium finned chassis. If you need a 4-channel Class AB option, the Zapco ST-4B is also available.
- 4-channel, full range, Class D
- RCA and speaker level inputs
- Variable input gain control
- Variable electronic crossover
- Variable bass boost control
- Power @ 4Ω: 4 x 100W RMS
- THD @ rated power: <0.5%
- Power @ 2Ω: 4 x 150W RMS
- Power bridged @ 4Ω: 2 x 300W RMS
- Signal to noise ratio: >90dB
- THD + Noise: <0.1%
- Frequency response: 15Hz to 30kHz ±1dB
- Input sensitivity: 0.35v to 9v (Low)
- Net dimensions: 124(W) x 50(H) x 213(L) mm
- Overall dimensions: 124(W) x 50(H) x 254(L) mm
Explore the full range in Zapco Amplifiers.
Specification
| Type | 4-Ch., Class-D |
|---|---|
| S/N Ratio | > 90dB |
| THD | < 0.1% |
| Frequency Response | 15Hz - 30KHz |
| Amp. Power (@ 14.4V) | 4 x 100W (4Ω), 4 x 150W (2Ω), 2 x 300 (4Ω/Bridged) |
| Filter Mode | Low-Pass / High-Pass |
| Filter Freq. Range | 30Hz - 3KHz |
| Input Impedance | 10KΩ (Low), 50Ω (High) |
| Low Input Voltage | 0.25-6V |
| High Input Voltage | 0.6-15V (High) |
| Working Voltage | 9-16V |
| Fuse Rating | 40A |
| Net Dimensions (mm) | 214(L) x 124(W) x 50(H) |
| Overall Dimensions (mm) | 254(L) x 124(W) x 50(H) |
What's Included
- Zapco ST-104D SQ III
Zapco
About the Zapco ST-104D SQ III
From our tech experts at CEN
The Zapco ST-104D SQ III is a compact 4-channel Class D full range amplifier from Zapco's ST-III series, rated at 4 x 100W RMS at 4 ohms or 4 x 150W RMS at 2 ohms. Its brushed aluminium finned chassis measures 124 x 50 x 213 mm net. Both RCA and speaker level inputs allow connection to factory or aftermarket head units.
Who it suits
This suits drivers upgrading door or component speakers who are short on space. The variable crossover and bass boost give useful flexibility for full range setups. Those wanting Class AB performance may prefer the Zapco ST-4B.
Our tech experts advise
Check the 124 x 50 x 213 mm net dimensions against your mounting location before ordering. Speaker level inputs remove the need for RCA outputs on your head unit. Bridged, the amp delivers 2 x 300W RMS at 4 ohms across two channels. Installation is priced per vehicle — see our Nottingham fitting service for details.
Explore the full Zapco range at CEN, with fast UK dispatch and expert advice from our Nottingham team. Shop all Zapco
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Have it Fitted By Our Team
Our team fits car audio, stereos, dash cams and vehicle security at our workshop in Beeston, Nottingham. Tell us your vehicle and we'll confirm the parts and a fitted price.
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Tell us your vehicle
Make, model and year, and what you'd like fitted.
- 2
We confirm the parts
Fascia, wiring and interfaces checked for your car, with a fitted price.
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Bring it to our Beeston workshop and we do the rest.
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Frequently Asked Questions
Q: How do I choose the right amplifier for my speakers or subwoofer?
A: Match the amplifier's RMS output per channel to the RMS handling of your speakers or subwoofer at the same impedance. The Specification tab lists the power figures. If in doubt, contact CEN with your setup and we will recommend a match.
Q: What wiring do I need to install this amplifier?
A: You will need an amplifier wiring kit sized to the amplifier's power draw, typically including power and earth cable, a fuse, RCA leads and a remote wire. CEN stocks complete wiring kits, and the amplifier's fuse rating is the guide to the cable gauge required.
Q: What class of amplifier is this and does it matter?
A: Class D amplifiers are compact and efficient, ideal for subwoofers and modern installs. Class AB designs are traditionally favoured for outright sound quality on mid and high frequencies. The class is listed in the Specification tab where provided.
Q: Will an amplifier work with my factory head unit?
A: Yes, in most cases. If your head unit has no RCA outputs you will need a line output converter to feed the amplifier a clean signal. CEN stocks line output converters and can advise the right one for your vehicle.
Q: Can CEN install this amplifier?
A: Yes. CEN offers professional amplifier installation from our Nottingham premises, including secure mounting, wiring and setup. Contact us to book.
Q: Can the ST-104D SQ III connect to a factory head unit?
A: Yes. It has both RCA and speaker level inputs, so it can take a signal from a factory head unit without RCA outputs.
Q: How much power does the ST-104D SQ III produce?
A: It is rated at 4 x 100 watts RMS at 4 ohms, 4 x 150 watts RMS at 2 ohms, or 2 x 300 watts RMS bridged at 4 ohms.
Q: How big is the ST-104D SQ III?
A: The net dimensions are 124mm wide, 50mm high and 213mm long, or 254mm long overall.
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