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MTX muscle from a TH Series amp

If you're addicted to great sound, then you know that MTX has been building great amps for decades. Their TH90.4 amp mixes the latest advancements in amp technology with MTX know-how to bring you strong, clean power that you can rely on — day in and day out. This TH Series 4-channel amp delivers 60 watts RMS per channel to your front and rear speakers, with some cool features that'll make your life a little easier.

TH90.4 control panel

Flexibility and reliability

MTX designs their amps for reliability. All internal wiring is as short as possible, for the purest reproduction with low noise. An anodized aluminum heat sink pulls the heat right out of this amp, so it'll keep on rockin' even when you push your system hard. You can bridge the amp to 2-channel operation to drive two subs with 180 watts each, and you can use the built-in frequency filters to tailor the amp to the job at hand, whether it's powering speakers or subs.

Product Highlights:

  • 60 watts RMS x 4 at 4 ohms (90 watts RMS x 4 at 2 ohms)
  • 180 watts RMS x 2 bridged output at 4 ohms (4-ohm stable in bridged mode)
  • PWM MOSFET switching power supply
  • Intelligent Surface Mount Technology for cleaner sound and greater reliability
  • variable high-pass/low-pass crossovers (40-400 Hz at 12 dB/octave)
  • preamp and speaker-level inputs
  • 4-gauge power and ground leads recommended — wiring and hardware not included with amplifier
  • fuse rating: 30A x 2
  • 14"W x 2-1/16"H x 7-1/8"D
  • warranty: 5 years (free repair or replacement for 2 years; prorated replacement for years 3 through 5)
  • Our 60-day money-back guarantee

My system has plenty of power. Who needs an amp?

You might think you don't need an amp because you have a 400-watt system in your car, or because your new stereo puts out 50 watts a channel. But those are peak wattage ratings, which may boil down to 15 or 20 watts per channel, using the more realistic RMS rating. An amp sends your speakers the power they need to deliver your music with clarity and impact, whether you're using factory speakers or high-performance components. And low-frequency reproduction requires lots of power, so an amp is an absolute must if you're adding a sub to your system.

MTX TH90.4 Reviews

Hands-on research

What's in the box?

Download owner's manual

  • 4-Channel amplifier with two 30A ATO fuses installed in the bottom
  • 2 Spare 30A ATO fuses
  • Two 12" Speaker-level input harnesses
  • 2.5mm Allen wrench
  • 3mm Allen wrench
  • 4 Self-tapping screws (M4 x 20mm)
  • 4 Flat washers
  • Owner's Manual (En/ Fr/ Sp/ Po)

Product Research



Overview: The MTX TH90.4 is a 4-channel, Class-AB amplifier. It has anodized aluminum heatsinks to dissipate heat generated by the amplifier. The amp produces 60 watts RMS x 4 at 4 ohms, and 90 watts RMS x 4 at 2 ohms.

Bridgeable: The front and rear channels of the amp are independently bridgeable. The bridged output is 180 watts x 2 at 4 ohms.

Protection Circuits: The TH90.4 provides protection against overheating and electrical short circuits.

Gain: The amp's independent front and rear rotary gain controls are continuously variable from 100mV to 6V to match the output of the source unit.

Crossovers: The built-in front and rear crossovers can be independently set to high-pass, full-range, or low-pass operation via a 3-way switch. If set to high-pass or low-pass, the cutoff frequency can be set between 40Hz and 400Hz.


Line Level Input/Output: The line-level signals from the source unit are input using two pairs of stereo RCA inputs. The amp does not offer a line-level output.

Speaker-level Inputs: If the source unit lacks RCA outputs, such as a factory head unit, you can connect the amplifier via speaker-level inputs. Two plug-in 2-channel input harnesses are included with the amp, which can be spliced to the head unit's speaker wires.

Power Terminals: The TH90.4 features set screw terminals for power, ground and remote turn-on. The power and ground terminals will accommodate up to 4 AWG wire, while the remote turn-on terminal will accept up to 8 AWG wire. The set screws can be loosened or tightened with the supplied Allen wrenches. MTX recommends the use of 4 AWG power and ground wires with the TH90.4.

Speaker Connections: The amplifier is equipped with set screw terminals for the speaker outputs. The terminals will accommodate up to 8 AWG wires, and can be loosened or tightened with the supplied Allen wrench.


5 Year Warranty Terms: This product carries a 5-Year Prorated Warranty with the following terms:

  • Years 1-2: Products found to be defective in materials or workmanship during the first two years will be, at Mitek's option, repaired or replaced by Mitek at no charge. The warranty period does not renew, but continues on from the original date of purchase.
  • Years 3-5: The purchase price of an item which becomes defective after the first two years and prior to the end of the warranty period will be prorated and credited toward the purchase of a new MTX product. The amount of proration is determined by dividing the original purchase price by the number of months in the warranty period (60), then multiplying the result by the number of months remaining in the warranty period.

Our Product Research Team

At Crutchfield, you'll get detailed, accurate information that's hard to find elsewhere. That's because we have our own in-house Product Research team. They verify what’s in the box, check the owner's manual, and record dimensions, features and specs. We stay on top of new products and technologies to help people make informed choices.