model 424 & model 428 Full-Balanced Portable Headphone Amp.

For the First 50 units only at the Special Price 180,000JPY ->150,000JPY
(model428 was sold out)

model424 (Balanced Out XLR 4pin type) 180,000JPY ->150,000JPY

model428 (Balanced Out Pentaconn type) 180,000JPY

All the products by Mass-Kobo are made to order.

The price is only for the orders shipping overseas.
All the orders must be prepaid. (The production will begin after the payment.)

Import duties and shipping costs are not included.
You may be obligated to pay VAT to receive goods.

The first shipment is at the September.

To pay by PayPal, you need to add 5% of the total amount.
Pyapal account :


Reservation status 20.April.2019 12:00

model No. Under consideration Number of reservations Accept orders Total
model424 0 0 22 22
model428 0 0 50 50

Under consideration = I am considering purchasing
Number of reservations = Waiting for deposit
Accept orders = Paid


The new two models of amplifiers use the balanced circuit of model 404 which is one of the most popular models.

The input terminal uses Pentaconn manufactured by Nippon Dicks Co., Ltd. with high reliability.
The balanced output terminal is XLR in model 424, and Pentaconn in model 428.
The size of the body is smaller than 404, for the number of power-supplying batteries is down to 4 instead of 6.

No cable is used between the internal substrates, and all the connecters are gold-plated.
The sound quality is clearly improved.

These amplifiers are equipped with a mode change-over switch that enables you to connect both balanced and unbalanced output players.

Both models are equipped with the same output gain-changing switch as the one used in model 406, our flagship model.
Now you can listen to all types of headphones and earphones, with both dynamic and balanced-armature drivers properly with a single amplifier.

It can be used for about 4 hours with alkaline AA batteries.
(It varies depending on battery condition and type)

It can also be powered by connecting a power bank to the micro USB terminal.
(There is no charge function, digital input / output function)

*Balanced output of model 424, model 428 is not compatible with unbalanced headphones and earphones.
Unbalanced headphones or earphones connected to the balanced output with or without adapters may cause the amplifier to malfunction.
NEVER connect them to the balanced output.
Please use 3.5 mm unbalanced output for unbalanced headphone or earphones.

<Specifications> (Batt. 6V or USB 5V)

Model: Full-Balanced Portable Stereo headphone amplifier
Input: φ4.4 TRRS x 1 (balanced or unbalanced)
Output: model424 XLR-4Pin model428 4.4 TRRS (balanced) , φ3.5 TRS (unbalanced)
Maximum Input Level: +16dBm (balanced), +10dBm (unbalanced)
Maximum Output Level (P-P): 7 V (balanced), 3.5V (unbalanced) (with 32Ω loaded, 1kHz, THD+N 0.5%)
           (RMS): 2.3V (balanced) , 1.2 V (unbalanced) (with 32Ω loaded, 1kHz, THD+N 0.5%)
Maximum Output without Distortion: 165mW (balanced), 45mW (unbalanced) (with 32Ω load, 1kHz, THD+N 0.5%)
Frequency Characteristics: 20Hz - 20kHz (-1dB)
Noise Level: Less than 40μV (in the minimum volume position, 32Ω loaded) Less than 150μV (in the maximum volume position, 32Ω loaded)
Power Supply: AA Alkaline or rechargeable battery x 4
External Power Supply: Micro USB +5v
Consumption Current: 0.19A (battery 6V, No signal) 0.21A (rechargeable battery, 4.8V No signal) 0.21A (USB 5V, No signal)
           0.28A (battery 6V, 1/8 Output) 0.32 A(rechargeable battery, 4.8V, 1/8 output) 0.31A(USB 5V, 1/8 Output)
           0.49A (battery 6V, Maximum Output) 0.61A (rechargeable battery), 4.8V, Maximum Output) 0.58A (USB 5V, Maximum Output)
Size: 97mmW x 132mmD x 40mmH (not include protrusions)
Weight: model424 445g (with batteries), 387g (without batteries)
    model428 440g (with batteries), 382g (without batteries)