Koch ATR-4502 Overview.

The ATR4502 is the first 2 x 45W stereo or 1 x 90W mono 19” rack mount power-amp for guitar on the market that offers real vintage tube tone in combination with only 1U of height and 5.5 kilos of weight.

So, might you be looking for a rack mount tube power amp and you do not want to drag a 2U (or more) high, 15 kg (or more) weighing heavy tank around, the ATR4502 is what you need. The ATR4502 houses two power amps that are similar to the ones in the Jupiter combo amps, which are already famous for their authentic tube sound.

The ATR4502 can be used either in stereo or mono mode, without having a stereo / mono (bridged) selector switch. Just plug your speaker or speaker cabinets into the stereo or mono speaker output jacks, and the ATR4502 automatically switches to either stereo or mono operation. Beside two Volume controls (one for each channel), the ATR4502 offers two voicing switches per channel for boosting Presence and Depth frequencies.

Further feautures of the ATR4502 include input level selectors (-10/0dBV), two speaker output jacks per channel, two thermal controlled cooling fans, short circuit protected outputs and overheat protection circuits with overload indicators on the front panel. The ATR4502 offers unique, totally analogue, full class-A circuitry for the best dynamic response and tone, and is designed to deliver maximum guitar sound quality in a small and light-weight 19” housing. The ATR 4502 will drive any speaker cabinet with an impedance between 4 and 16 Ohms in the stereo mode, and between 8 and 16 Ohms in the mono mode, with only minor differences in output power.

The ATR4502 teams up perfectly with the Pedaltone-II tube floor pre-amp. The ATR4502 for example can be combined with a 19” effects unit in a small 2U rack housing, while the Pedaltone-II can be combined with floor effects like a wah-wah pedal and a volume pedal on a pedal board. One guitar cable between them, and an endless world of sounds palets and colorings will open for you.

Koch ATR-4502 Specifications.

  • Hybride guitar power-amp
  • 2 x 12AX7-tube (1 for each channel)
  • ATR (Authentic Tube Response)
  • Mono- and stereo-output
  • Voicing-switches: Presence and Depth
  • Volume-pot for each channel
  • Power mono: 90 W (8 Ohm), 70 W (16 Ohm)
  • Power stereo: 2 x 50 W (4 Ohm), 2 x 45 W (8 Ohm),
    2 x 35 W (16 Ohm)
  • Automatic stereo/mono-switching
  • 2 mono-inputs 
  • Input level selectors: -10 dBV en 0 dBV
  • Short circuit protected outputs
  • 2 themically regulated fans (60 C)
  • Overheat protection circuits with overload indicators
  • 19 inch rack-mounted, 1U high
  • Weight: 5.5 kg