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Tube guitar preamplifier with IR-based cabinet simulation
The Shift Line Twin MkIIIS is the third revision of our tube guitar preamplifier which boasts a characterful sound, universal connectivity, and a compact enclosure.

The dynamic range has been expanded to achieve more maximum gain. As a result, it can go from its renowned clean sound into crunch and overdrive without external boosting. The cabinet simulation is based on the Impulse Response Convolution technology, which provides a realistic and detailed sound while preserving the character of the power amp, cabinet and microphone used to record the impulse. The device comes with two impulses recorded from the Fender Twin combo amplifier. The microSD card slot allows users to upload their own cabinet impulses.


  • IN is the signal source input.
  • THRU is a buffered output for the unprocessed signal split from the IN jack.
  • SEND/RETURN is a series effects loop for external processing. The SEND out can also be used as an additional output.
  • OUT is the main output designed to connect the preamplifier to a power amplifier (RETURN or POWER AMP IN on combo amplifiers, INPUT on power amplifiers).
  • AUX IN is an external audio input (the signal from the AUX IN is only heard through the PHONES output).
  • PHONES is a headphones output.
  • BALANCED OUT is a balanced output.
  • POWER IN is a power supply input. The power requirements are 12V DC 650mA.
  • MicroSD is a microSD card slot.
Shift Line Twin MkIIIS Connections
Shift Line Twin MkIIIS Controls


  1. GAIN controls input signal amplification. It can go from a crystal-clear sound all the way to a classic California-style overdrive.
  2. The BASS, MIDDLE and TREBLE knobs constitute a classic 3-band passive EQ with a mild frequency correction effect.
  3. MASTER controls the volume of the signal coming from the OUT jack.
  4. VOLUME controls the volume of the signal coming from the PHONES and BALANCED OUT jacks.
    The MASTER and VOLUME knobs work independently.
  5. The TOP switch controls the signal's high frequency harmonic content. The "+" position accentuates the highs and the attack. The "-" position provides a milder sound by cutting the high frequencies. The neutral position does not affect the signal in any way.
  6. The GNDswitch allows to override "ground loops" that can negatively affect the signal when using XLR connections. In the lower position of the switch, the preamp's "ground" is connected to the signal receiver's "ground". In the middle position, the "grounds" are disconnected. In the upper position, the "grounds" are connected and an additional filter is used to remove interference.
    The optimal setting of the GND switch is selected by ear: there should be a minimum amount of 50Hz hum and interference.
  7. The CAB switch selects one of the two built-in cabinet impulses recorded from a Fender Twin combo amplifier with two JBL D120F speakers:
    • The "A" position selects the impulse recorded by a LOMO 19A19 microphone placed 15cm away from the edge of the speaker's protective cap.
    • In the middle position, cabinet simulation is disengaged.
    • The "B" position selects the impulse recorded by a Sennheiser e609 microphone placed 25cm away from the center of the speaker.
    When using a microSD card, impulses are loaded from the corresponding folder on the card. The CAB switch affects the signal from the BALANCED OUT and the PHONES OUT but does not affect the signal from the main OUT.

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Loading impulses from a microSD card:

Before using a microSD card, make sure it is formatted to the FAT32 filesystem.

When the memory card is used for the first time, a "SL_IR" folder is automatically created on it. The folder contains two more folders ("A" and "B", corresponding to the CAB switch positions) in which the default impulses are stored. To use external impulses, replace the default ones with your own files. The supported impulse format is 24bit 48kHZ WAVE PCM1, uncompressed.

To restore the default impulse files, insert a blank microSD card into the device. This will create a "SL_IR" folder containing the default files. If no card is inserted, the built-in impulses are used.
  • Tube type: 12AX7
  • Memory card type: microSD
  • IR latency: 1,2ms
  • IN: 6,3mm, mono, unbalanced, -20dB, 1MOhm input impedance
  • THRU: 6,3mm, mono, unbalanced, -20dB, 1kOhm output impedance
  • SEND: 6,3mm, mono, unbalanced, -10dB, 1kOhm output impedance
  • RETURN: 6,3mm, mono, unbalanced, -10dB, 1MOhm input impedance
  • OUT: 6,3mm, mono, unbalanced, +20dB, 1kOhm output impedance
  • BALANCED OUT: XLR, mono, balanced, +10dB, 1kOhm output impedance
  • AUX: 3,5mm, stereo, unbalanced, 0dB, 10kOhm input impedance
  • PHONES: 3,5mm, stereo, unbalanced, +10dB, 10Ohm output impedance
  • POWER: 12V DC 650mA, negative tip, 2.1/5.5mm diameter. Phantom power of the balanced line (+48V) or battery power are insufficient for the preamp to operate on. If phantom power is turned on, it will not damage the device. Use a regulated PSU only.
  • Dimensions (LxWxH): 124x104x55mm (4.9x4.1x2.2")
  • Unit weight: 480g (1.06lb)
  • PSU weight: 120g (0.26lb)

Delivery set:

  • Twin MkIIIS preamplifier;
  • 12V DC 1000mA PSU with 4 changeable plugs;
  • User guide.
NOTE: microSD card is not included in the delivery set.

We constantly perfect our products and reserve the right to alter their appearance and specifications with no prior notification.

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