Zapco ST-5B Review: One Class AB Amp for Four Speakers and a Subwoofer
Updated: Oct 6
The Zapco ST-5B is a five-channel Class AB amplifier from Zapco's Studio-B (ST-B) series, rated at 4 x 70 W plus 1 x 250 W into 4 Ω, or 4 x 100 W plus 1 x 400 W into 2 Ω. One chassis can run front and rear speakers and a subwoofer, which is why it suits buyers who want a complete system without stacking amplifiers in a small boot. Its Indian MRP of ₹22,990 is the highest in the ST-B range but well below JL's JD700/5 and RD900/5. See the current offer on our ST-5B store page.
What you need to know
Four channels of 70 W into 4 Ω for door speakers, plus a sub channel of 250 W (4 Ω) or 400 W (2 Ω), from one amplifier.
Zapco's page lists RCA and OEM speaker-level inputs, so it can work with a factory touchscreen.
No subsonic filter on Zapco's spec sheet (the catalogue lists one), so we plan without it.
No verified reviews, and the ST-B owner's manual we found online doesn't cover this model.
Zapco ST-5B specifications
Specification | ST-5B |
|---|---|
Type | 5-channel Class AB amplifier, MOSFET power supply |
Power at 4 Ω | 4 x 70 W + 1 x 250 W |
Power at 2 Ω | 4 x 100 W + 1 x 400 W |
Bridged | 2 x 180 W (4 Ω) + 1 x 400 W (2 Ω) |
Minimum load | 2 Ω stereo, 4 Ω bridged |
Rating conditions (catalogue) | 14.4 V, under 1% THD |
THD at rated power | Less than 0.2% |
Signal-to-noise ratio | More than 90 dB (catalogue: more than 97 dB) |
Channel separation | More than 45 dB |
Frequency response | 15 Hz – 30 kHz ±1 dB |
Input sensitivity | 0.25 – 5 V (catalogue gain range: 0.2 – 4 V) |
Inputs | RCA (six, per the catalogue) and OEM speaker-level |
Crossover | Variable full / low-pass / high-pass |
Bass boost | Variable, 0–12 dB |
Subsonic filter | Not listed by Zapco (the catalogue and our listing show one) |
Remote | Optional ST-BR remote level control |
Dimensions | 351 x 182 x 52 mm chassis (catalogue: 51 mm high); 381 mm overall length |
India MRP | ₹22,990 |
Figures are from Zapco's ST-5B product page and the 2026 Indian catalogue, with the catalogue's figure in brackets where they differ; the optional remote is from our store listing. Where the two disagree on features, we follow Zapco's page. Neither source gives crossover frequencies, a fuse rating or warranty terms.
Where a five-channel amp makes sense
A typical upgrade in a hatchback or compact SUV covers front speakers, rear speakers and a subwoofer. Doing that with separate amps means two or three chassis, several power runs and extra signal cables. The ST-5B puts all five channels in one 381 mm box with one power cable, one ground and one remote turn-on lead, which simplifies both the install and the boot layout.
The trade-off is flexibility. One amp is a single point of failure, the sub channel tops out at 250 W or 400 W, and more power for one part of the system later means adding a second amplifier or replacing this one. For many daily drivers, that is a fair exchange for one tidy installation.
Planning the channels
The four main channels deliver 70 W each into 4 Ω, a good match for JL's C2-650 component set up front (60 W RMS, 15–100 W recommended) and C1-650x coaxials at the back (50 W RMS, 10–75 W recommended). Set the main channels to high-pass so the doors leave the deep bass to the sub.
The sub channel gives 250 W into 4 Ω, which suits a single-coil JL 12W0v3-4 or 10W0v3-4 (300 W each). Wire a dual 4 Ω sub such as the 10TW3-D4 to 2 Ω, and the channel's 400 W matches the sub's 400 W rating exactly. Zapco's bridged rating also lets the four main channels become two 180 W channels into 4 Ω, with the sub channel unchanged, but that suits only front speakers rated for the power; a 60 W set like the C2-650 is better off on the stereo channels.
The subsonic filter question
Zapco's product page lists no subsonic filter for the ST-5B, although the 2026 catalogue and our own listing include one in its controls. We go by Zapco's page and plan as if there isn't one. That matters if you want a ported subwoofer box, because a subsonic filter keeps the cone from moving too far below the port's tuning. A sealed enclosure is the safe default here; if you prefer ported, ask us to check the unit's controls before you commit.
Reviews of the Zapco ST-5B: the honest picture
Independent reviews of the ST-5B are absent: when we checked in October 2026 we found no owner, retailer or press feedback we could verify. The ST-B owner's manual circulating online covers other ST-B models but not this one, so the specifications rest on Zapco's product page and the Indian catalogue, which disagree on the subsonic filter, the signal-to-noise figure and the input description.
A DIYMobileAudio thread comparing the ST-B, ST-X and ST-X SQ series exists, but its content wasn't accessible to us, so we can't relay any opinions from it. Zapco's description of the Studio-B line as reliable, affordable everyday amplifiers rather than competition gear is the manufacturer's own promotion. If you run an ST-5B, tell us how it's working for you.
ST-5B vs separate ST-B amps, JL five-channels and the HB 46 II 4A
An ST-2B for the front plus an ST-1B for the sub costs ₹26,980 at MRP, ₹3,990 more than the ST-5B, and gives you two fewer channels and a 300 W rather than 400 W sub channel at 2 Ω. The separates win on flexibility, and the ST-1B's subsonic filter appears on both Zapco's page and in the catalogue.
JL's JD700/5 (₹69,990) is rated at 75 W x 4 plus 180 W x 1 into 4 Ω, and the RD900/5 (₹79,990) at 70 W x 4 into 4 Ω plus 500 W x 1 into 2 Ω. The ST-5B roughly matches their main channels and, against the JD700/5, has the stronger sub channel (400 W against 300 W at 2 Ω) at around a third of the price. Both JL amps are Class D, so they run cooler and draw less current for the same output, and the RD900/5 offers more sub power at 2 Ω.
Zapco's HB 46 II 4A costs a similar ₹21,990 but takes a different approach: a 4-channel Class AB amp with a 6-channel DSP, Bluetooth streaming and high-level inputs, rated at 4 x 23 W into 4 Ω. Choose it if tuning matters more than power; choose the ST-5B for three times the power per channel plus a sub channel.
Who should choose it
It suits a complete first system in a hatchback, sedan or compact SUV: four door speakers and one sealed subwoofer, fed from a factory or aftermarket head unit, at a price that leaves money for speakers and installation.
Look elsewhere if you want a ported sub with a confirmed subsonic filter, DSP tuning for time alignment, or more than 400 W for the sub. And note that we found no verified owner feedback on this model.
Installation notes for Indian cars
At 381 mm long and 182 mm wide, the ST-5B is a boot amp in most cars: on a side panel, the back of the rear seat or a false floor, fixed firmly enough for rough roads. Five Class AB channels in one chassis will run warm, so leave space around the fins and keep it away from the rear glass.
Zapco publishes no efficiency figure, but as a rough estimate a Class AB amp of this size driven flat out on every channel at 4 Ω could draw around 55–75 A; normal listening draws far less. A 4 AWG run such as Tchernov's 4 AWG power cable covers most installs. Zapco publishes no fuse rating in the sources we have, so size the main fuse near the battery to protect the cable; we confirm the amplifier's own fusing at install. Route speaker wires through proper door grommets, tap the factory wiring neatly if you use the speaker-level inputs, and set the gains with a test tone. VA3 Car Studio in Ghaziabad installs complete systems like this.
Price and where to buy
The ST-5B carries an MRP of ₹22,990 in the 2026 Indian catalogue, and we often sell it for less; current pricing is on our Zapco ST-5B product page. Every unit is genuine Zapco stock from the brand's Indian distributor, Supreme Audiotek Pvt. Ltd., New Delhi.
Verdict
This is the simplest way to power a full system with one Zapco amp: 70 W per channel for four door speakers, a sub channel that matches a 400 W dual-coil sub at 2 Ω, and speaker-level inputs for factory head units. The subsonic filter missing from Zapco's spec sheet, the lack of a model-specific manual online and the absence of reviews are real gaps. For a sealed-box daily-driver system, though, it is strong value at its MRP.
Zapco ST-5B FAQ
Does the Zapco ST-5B have a subsonic filter?
Zapco's own product page doesn't list one, although the 2026 catalogue and our listing do, so we plan as if it has none. Pair it with a sealed subwoofer box, or ask us to check the controls if you want a ported one.
Can the ST-5B run my whole system from a factory head unit?
Zapco lists OEM speaker-level inputs alongside RCA inputs, so it can take its signal from a factory head unit. The four main channels drive the door speakers and the fifth drives the subwoofer.
Which subwoofer suits the ST-5B's sub channel?
A single 4 Ω sub rated at around 250–300 W, such as JL's 12W0v3-4, makes good use of the channel's 250 W at 4 Ω. For more output, a dual 4 Ω sub wired to 2 Ω, such as the 10TW3-D4, gets 400 W, which matches its 400 W rating.
Buy the Zapco ST-5B in India
Check the Zapco ST-5B price in India, browse more Zapco amplifiers or compare all car amplifiers in India. Want it fitted properly? Book amplifier installation at our Ghaziabad studio.
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