The ST-X Series. Class A/B and D Amplifiers.





The Studio-X line of amplifiers from Zapco was designed specifically for today’s car audio market. The Studio-X compact chassis makes it an easy fit in any car and even in motorcycle fairings.

The square, low profile chassis also means it will be easy to trim out for a great looking installation so your system will look as awesome as it sounds. And speaking of sound...This is a Zapco amplifier and sound is what it’s all about. These are Class A/B Zapco amplifiers.

The Studio-X have the same high quality caps, op-amps, and bi-polar outputs that made the C2K and Reference series amps the industry standard for sound quality. 

Reliability? Zapco defines reliability. It’s not at all unusual to see Zapco amps moved from car to car and from generation to generation. Zapco Amps produced in the ‘90 are still being traded and bought on the internet by sound quality fans world wide. The Studio-x will be no different.


These amps are built to last. See the Studio-X amps at a dealer today.

Studio-X Amplifiers with DSP

The new ST-6X DSP and ST4X DSP for 2021are now shipping. Power of these new units remains at 100 RMS/Channel @4Ω for the 6X DSP and 65W RMS/Channel @4Ω for the 4X DSP, like the earlier models. But almost everything else about them is new and improved. 


First the chassis: The new ST-DSP amps are the first to get the new Studio brushed aluminum finned chassis with thermal controlled fan cooling, to play hard all day long without shutting down. Both the new units have improved high speed (96kHz) digital signal processing for 8 channels to provide processed channels for an extra bass amp with the 6X DSP and for two external amps with the 4X DSP. 

Both units have analog input level controls with clip lights for the most accurate input gain setting possible. Both units have Inputs for optical inputs Digital SPDIF signals. Both units have a Zapco Comm Port to accept the optional Zapco HD-BT module for hi-definition AptX Bluetooth music streaming.

There are six full range amplifiers in the Studio-X series and all are Class A/B and all use

bi-polar output devices for the smoothest possible sound. And, all are packed with all those features you want. Common features of the ST-X amplifiers include variable HP/LP/ Full Range electronic crossovers, variable bass boost, variable gain by channel pair, speaker level input, heavy duty positive lock terminal blocks and preamp outputs to daisy chain out to the next amp in your system without having to add more RCA cables. And the most important feature shared by all the ST-X amps is the legendary Zapco sound quality, developed with over 40 years of experience.


The ST-2X is the 2-Channel ST-X amplifier with 50 Watts RMS/Channel and less than 0.05% THD + noise. With a chassis only 15.4 cm x 16 cm x 5.2 cm, it provides great Zapco sound and all the ST-X features in a chassis that fits unobtrusively in the smallest of cars. In fact, this amp is the choice for Class A/B sound quality in motorcycles and other power sports vehicles and other limited space vehicles. The ST-2X is now available with a lot of SQ upgrades, check out the new ST-2X SQ.


The ST-4X II is the 4-Channel ST-X amp and it’s also rated at 50W RMS/Channel. This amp has been out for about a year and is by far the fastest selling amp we have ever made. With 320 watts RMS, the versatility of the bridgeable 4-channel platform, and all the ST-X features, the ST-4X II is an excellent balance of power, sound performance, and price.


Studio-X Class A/B Full Range Amplifiers

Bass, Bass, Bass.... and more bass.



Bass is only a small part of most any musical pieces, but it is what sets the mood for everything else. And, although everyone wants bass, everyone’s needs for bass are not the same. In the Studio-X line we have six Class D, mono bass amplifiers, ranging from 500 Watts RMS to 2,000 watts RMS.  And if that is not enough for you... all the Studio-XM amps can be strapped together to a single voice coil, so you can always double you power by just buying another of the same model amp. 


All the ST-XM Class D bass amps are 1Ω stable as necessary in today’s market. However, we also see a strong need to provide power to a 2Ω load in the medium power ranges for the sound quality fanatic in all if us. The 2Ω load, is a more efficient use of current and is better for sound quality. The ST-850XM and the ST-1350XM were both designed to have maximum efficiency and produce over 70% of their power into a 2Ω load with 600W RMS and 970W RMS respectively. With RMS powers of 500W, 850W, 1,000W, 1350W, 1650W, and 2,000W, and the ability to strap together, the ST-XM amps cover just about any need you might have from 500watts to 4,000 watts.


Here is what all the new ST-XM amps share:


Remote Dash Control - All the ST-X amps come with a remote so you can change the bass output as needed instantly.

Input Sensitivity (Gain) Control - Sets sensitivity anywhere 200mV to over 5 volts.

Mono Bridge Out and Bridge In - These allow the bridging of two amplifiers together (Strapping). When the Bridge Out RCA from the main amp is connected to the Bridge RCA In of the slave amp, the main (out) amp will take priority for control. At that point you will make all adjustments at the main amp only and they will be duplicated in the slave amp.

Low Pass Crossover - Intended only as bass amplifiers, all the ST-XM amps have a full time low pass crossover variable from 40 to 180Hz.

Sub Sonic (HP) Filter - Reproducing frequencies below those you want to hear wastes amplifier power. The Sub Sonic filter helps save that energy for the frequencies you do want to hear. More importantly, trying to reproduce frequencies below the range of the woofer can quickly destroy your woofer. This is especially important for ported enclosures. i.e. If your enclosure is ported 40Hz then you should set you Sub Sonic to 40 Hz to protect your  

subwoofer investment.

Bass Boost Control - All the ST-XM amplifiers have a variable bass boost. You can vary the amount of the bass boost from 0dB to 12dB as needed for your particular installation.

Bass Frequency Control - Fact: No two cars are the same. The bass response of a woofer will be different in every car you put it in, so a bass boost at 50Hz can be great for one car but useless in another. The ST-X Bass  Frequency control allows you to set the bass boost at any frequency from 30Hz to 80Hz, so you can set it precisely to match your music in your car.

Phase Control - Facing you bass enclosure to the front will sound different than facing it to the rear. In either case, changing the phase of the woofers will also make a difference. The problem is you won’t know which is best until the system is installed. Then you can listen each way to see which way the bass sounds best. The phase control on the  ST-XM amps lets you adjust the phase of the signal right at the amp. In addition the ST-XM phase control is variable from 0° to 180° so you can dial in exactly the phase relationship that works best in your car.


Studio-XM Class D Bass Amplifiers 

For 2015 we have done something truly unique with the ST-4X II, we have taken this top seller and tweaked it to create two more ST-4X versions with targeted performance goals tailored for two groups of consumers whose musical tastes run in specific directions.


First, we have created the ST-4X SQ for the customer who appreciates the finer points of the music and wants to invest a little extra for a more “live” sound. We did this by upgrading the caps and op-amps and making few other changes. The SQ version will have a more open sound and a more precise sound stage. We also used Tiffany style panel mount RCA connectors on the ST-4SQ for a solid signal transfer.

Then, for the Rock, Country, and Hip-Hop fans, and anyone else who wants the bottom end “loud ‘n clear”, we designed The ST-4X P. P for Power! For the ST-4XP we have boosted the supply voltage, used higher voltage output devices and upgraded the  supporting components to get a 60% increase in RMS power to 80 Watts/Ch. @ 4Ω and 120 Watts RMS /Ch. @ 2Ω. That’s 480 Watts RMS of Class A/B power in a chassis that is only 28.2 cm x 16 cm x 5.2 cm.

The ST-5X is the All-In-One Studio amp. The ST-5X mates the ST-4X P with 80W/Ch. x 4 @ 4 Ω to a bass amp with 200 Watts RMS @ 4Ω. This is truly a powerhouse in a compact chassis. Like the other ST-X amps the ST-5X is Class A/B even on the bass end, so you get tight solid  bass. You can bridge this amp at 4Ω and get 300W RMS x 2 and 300Watts x 1. The ST-5X has an input mode switch so you can use six channels of input, or only four, or even just two channels and get all 5 channels of output. So if you only have a stereo head unit you can still drive front and rear speakers plus a subwoofer. Altogether, a lot of punch in not a lot of space. Of course the ST-5X doesn’t have the has the next amp already built in.


ST-2000XM Panel
ST-850XM Inside
ST-2000XM Terminals

The Zapco ST-X Series DSP Amplifiers

The Zapco ST-X Series Amplifiers

The Zapco ST-X Series SQ Amplifiers