Zapco ST-1B Review: A Budget Class AB Mono Amp for One Subwoofer
Updated: Oct 6
The Zapco ST-1B is a mono Class AB amplifier from Zapco's Studio-B (ST-B) series, rated at 200 W into 4 Ω and 300 W into 2 Ω. At an Indian MRP of ₹15,990 it undercuts every Studio-XM III mono amp by a wide margin, and it carries the same 4 Ω and 2 Ω ratings as the Class D ST-500XM III for less than half the price. It suits a single subwoofer in a hatchback, sedan or compact SUV, for buyers who want a simple, well-featured amp and can give it room to breathe. Our ST-1B store page has today's price.
The short version
Same 200 W (4 Ω) and 300 W (2 Ω) ratings as the ST-500XM III, at less than half its MRP.
Class AB, so expect more heat and current draw than a Class D amp of the same power; Zapco publishes no efficiency figure.
Low-pass crossover, subsonic filter, 0–180° phase, bass boost and RCA outputs for a second amp; the ST-BR remote is optional.
No verified owner reviews, and Zapco's own sources disagree on its signal-to-noise ratio.
Zapco ST-1B specifications
Specification | ST-1B |
|---|---|
Type | Mono Class AB amplifier, MOSFET power supply |
Power at 4 Ω | 1 x 200 W |
Power at 2 Ω | 1 x 300 W |
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 and manual: 97 dB) |
Frequency response | 15 Hz – 30 kHz ±1 dB (manual: 20 Hz – 20 kHz) |
Input sensitivity | 0.25 – 5 V (catalogue gain range: 0.2 – 4 V) |
Inputs and outputs | 2 x RCA in; 2 x RCA out |
Controls | Gain, low-pass crossover, subsonic filter, phase 0–180°, bass boost (0–12 dB) |
Remote | Optional ST-BR remote level control |
Chassis | Extruded aluminium |
Dimensions | 280 x 182 x 52 mm chassis (catalogue: 51 mm high); 310 mm overall length |
India MRP | ₹15,990 |
Figures come from Zapco's ST-1B product page, the ST-B Series owner's manual and the 2026 Indian catalogue. Zapco's page quotes more than 90 dB signal-to-noise while the catalogue and manual print 97 dB, so we show the more conservative figure. The manual's narrower 20 Hz – 20 kHz response makes little practical difference for a subwoofer. Crossover frequencies, the fuse rating and the warranty aren't published in these sources.
Class AB in a bass amp: what you gain and give up
A Class AB output stage keeps its transistors partly switched on all the time, which is why it runs warm and draws more current than a Class D design for the same output. Zapco doesn't publish an efficiency figure for the ST-1B. Class AB amps typically turn half to two-thirds of their input into output at full power, so as a rough estimate, not a Zapco figure, 300 W into 2 Ω could draw around 30–40 A. The Class D ST-500XM III, using Zapco's 85% efficiency figure, would need about 25 A for the same 300 W.
The classic argument for Class AB is low distortion at high frequencies, which matters little below 100 Hz, where a subwoofer works. What the ST-1B really offers is price. You pay for the saving in size, heat and current, and you give up the Class D amp's 1 Ω rating and strapping.
Subwoofers it suits
With one single-coil 4 Ω subwoofer, the ST-1B delivers 200 W. That suits JL's 8W3v3-4 (250 W) and the budget 10W0v3-4 and 12W0v3-4 (300 W each), which will work comfortably inside their ratings. An ST-1B with a 12W0v3-4 totals ₹34,480 at MRP, a sensible entry point to proper bass.
To use the 300 W rating, choose a dual 4 Ω sub and wire its coils in parallel for 2 Ω. JL's 10TW3-D4 and 12TW3-D4 are rated at 400 W, so 300 W leaves headroom, and they are designed for shallow spaces. Two single-coil 4 Ω subs in parallel also make 2 Ω, but each then gets only 150 W.
Inputs, outputs and building a system around it
Zapco lists RCA inputs and outputs but no speaker-level input. With a factory touchscreen head unit that has no RCA outputs you'll need a line output converter or a DSP in front of the amp; our article on the need for DSP in car audio systems explains why many installers go the DSP route. The RCA outputs pass the signal on to a second amp without splitting cables, which Zapco highlights as a feature of the Studio range.
That makes a two-amp system easy: the ST-1B on the sub and an ST-2B (2 x 65 W into 4 Ω, ₹10,990) on the front speakers, for ₹26,980 at MRP. The five-channel ST-5B costs ₹22,990 and on paper offers more: 4 x 70 W plus a sub channel of 250 W at 4 Ω or 400 W at 2 Ω. Two smaller amps are easier to place in a small boot and to upgrade one at a time; the ST-5B is cheaper and needs only one power run.
What owners and reviewers say about the Zapco ST-1B
When we checked in October 2026, we found no independent owner or press reviews of the ST-1B that we could verify, and a US retail listing we looked at showed no ratings. What is verifiable comes from Zapco itself: its product page and the ST-B Series owner's manual, which covers the ST-1B alongside the ST-2B, agree on the power ratings but differ on noise and bandwidth figures.
Zapco's catalogue pitches the Studio-B range as bringing the brand's sound quality and reliability to an everyday, affordable amplifier, and says plainly that it isn't built for competition. That is promotional copy, not a review. A DIYMobileAudio thread comparing the ST-B, ST-X and ST-X SQ series exists, but we couldn't access its content, so we can't report what it says. If you own an ST-1B, we'd welcome your feedback.
ST-1B vs ST-500XM III and JL JD500/1
The ST-500XM III is the obvious alternative: the same 200 W and 300 W ratings, but Class D with efficiency above 85%, a 400 W rating into 1 Ω, strapping, a bass boost with a movable centre frequency and a dash remote in the box, per our listing. It is also smaller, 225 x 160 mm against 310 x 182 mm, and costs ₹19,000 more at MRP. Unless you need 1 Ω or the smaller chassis, the ST-1B gives you the same usable power for much less.
JL's JD500/1 (₹35,990 MRP) is rated at 250 W into 4 Ω and 500 W into 2 Ω, a real step up in power for more than twice the price. For a single sub on a tight budget the ST-1B is the sensible choice; for a demanding 12-inch, the JD500/1 or Zapco's ST-1000XM III is the better tool.
Who it's for, and who should spend more
Choose the ST-1B if you want one subwoofer driven properly on a budget, have room for a 310 mm amp with space around it, and like straightforward controls.
Spend more if your subwoofer is rated well above 300 W, you want to run a 1 Ω load, your car's electrical system is marginal, or you want the reassurance of published owner reviews, which we couldn't find for this model.
Installation notes for Indian cars
Class AB amps need airflow. Mount the ST-1B with its fins exposed, not under carpet or pressed against the sub box, and avoid the hottest corner of the boot behind the rear glass; heat is the main enemy of any Class AB amp in an Indian summer. At 310 x 182 x 52 mm it may fit under some front seats, but measure before you decide.
For a 2 Ω setup drawing perhaps 30–40 A at full output, an 8 AWG cable such as Tchernov's 8 AWG power cable suits short runs, while long runs to the boot may justify heavier wire. Fuse ratings aren't in our data, so we follow the manual at install. Set the low-pass and subsonic filters to suit your sub and box, and set the gain with a test tone. VA3 Car Studio installs and tunes Zapco amps at our Ghaziabad studio.
Price and where to buy
The ST-1B has an MRP of ₹15,990 in the 2026 Indian catalogue. VA3 Car Studio often sells below MRP, so check the Zapco ST-1B product page for today's price. It is a genuine Zapco product, distributed in India by Supreme Audiotek Pvt. Ltd., New Delhi.
Bottom line
This is an honest, affordable mono amp: 200 W into 4 Ω or 300 W into 2 Ω, sensible bass controls and RCA outputs to grow a system. It runs warmer and draws more current than a Class D equivalent, lacks a 1 Ω rating, and has no verified owner feedback yet. For one 300 W-class sub, though, it delivers the same rated power as Zapco's own Class D entry model for less than half the money.
Zapco ST-1B FAQ
Is the Zapco ST-1B good enough for a 12-inch subwoofer?
Yes, for a 12-inch rated at roughly 300 W to 400 W. It gives a single 4 Ω JL 12W0v3-4 200 W, or a dual 4 Ω 12TW3-D4 wired to 2 Ω the full 300 W. Hungrier subs need a bigger amp.
Does the ST-1B have speaker-level inputs?
Zapco lists RCA inputs only, so a factory head unit without RCA outputs needs a line output converter or a DSP with speaker-level inputs in front of it. We can recommend the right interface for your car.
What is the difference between the ST-1B and the ST-500XM III?
Both are rated at 200 W into 4 Ω and 300 W into 2 Ω. The ST-500XM III is Class D, smaller and more efficient, adds a 1 Ω rating and strapping, and includes a dash remote (per our listing), but costs ₹19,000 more at MRP.
Buy the Zapco ST-1B in India
You can buy the Zapco ST-1B online from VA3 Car Studio with pan-India shipping. See more Zapco amplifiers, compare other mono amplifiers, or book amplifier installation in Ghaziabad.
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