M7BT vs M7PLUS 48V: Which Desktop Amplifier Fits You?

TRASAM is a 17-year Hi-Fi manufacturer based in Guangzhou, building amplifiers, DACs and speakers in our own 1,500 m² factory. The M7BT and M7PLUS 48V are the two compact desktop amplifiers in that range, and they share a chassis, a power platform and an amplifier stage. They are not two versions of the same product, though — they are built for two different systems.

This article lays out the real differences so you can pick once.

What the two models share

• TI TPA3255 Class D amplifier platform
• 48 V supply: 115 W x 2 into 8 ohms with distortion below 1%, maximum 150 W x 2 into 8 ohms with distortion below 10%
• Bluetooth 6.0 wireless input
• 136 x 36 x 144 mm chassis — allow up to 166 mm of depth including speaker terminals and the control knob
• Fanless operation, suited to nearfield desktop listening

Power figures apply to the 48 V version under the specified test conditions. They are not interchangeable with 36 V SKUs, and they should not be read as a claim about any other supply voltage.

Where they differ

M7BT is the analog-first choice

The M7BT assumes you already own a DAC. It gives you RCA and XLR inputs for a DAC, streamer, CD player or preamp, Bluetooth 6.0 for casual wireless listening from a phone or tablet, and speaker outputs for passive bookshelf speakers. That is the whole product, deliberately.

The feature that decides it for many buyers is the full-range RCA LINE OUT. That output lets the M7BT act as the hub of a larger system: feed a separate power amplifier, feed powered speakers, or feed an active subwoofer while the speaker outputs drive your main pair. If you are building outward — a subwoofer today, a second zone later — the M7BT is the model that gives you somewhere to go.

What it does not have is a USB input, a headphone jack or a display. If you have no DAC and no plan to buy one, the M7BT will not solve that for you.

M7PLUS is the complete desktop system

The M7PLUS adds the digital half. USB-C connects a computer, optical and coaxial connect a TV or digital player, RCA and XLR take analog sources, and Bluetooth 6.0 handles phones and tablets. The USB input accepts PCM up to 24-bit/192 kHz and DSD128; optical and coaxial accept up to 24-bit/192 kHz, with actual capability depending on the source device and software.

It also adds a 3.5 mm headphone output, with the power-amplifier output stopping when headphones are inserted. For a desk where the same chair is used for speakers during the day and headphones at night, that single jack removes an entire extra box.

The 1.3-inch OLED display, tone control and remote are conveniences, and worth being honest about: they are the reason the M7PLUS costs $100 more once you have accounted for the digital board. The headphone output is the reason most people choose it.

What the M7PLUS does not have is the RCA LINE OUT. If you specifically need a line-level feed to an external power amplifier or a subwoofer, the M7BT is the correct model.

What 48 V actually changes

A Class D amplifier’s output power is limited by its supply rail. Raising the rail raises the maximum voltage swing, and with it the power available into a given load. That is the entire reason 48 V versions exist, and it is also why the number cannot be separated from the load and the distortion threshold attached to it.

Read the specification the way it is written. 115 W x 2 into 8 ohms is quoted at distortion below 1% — a condition you can listen at. 150 W x 2 into 8 ohms is quoted at distortion below 10%, which is a headroom figure rather than an everyday operating point. Nobody listens at 10% distortion; the number tells you how much transient headroom the supply can supply on peaks.

Two consequences follow. First, a 4 ohm speaker will draw more current than an 8 ohm speaker at the same voltage, so heat and supply behaviour change even though the published figure is for 8 ohms. Second, the practical difference between 36 V and 48 V shows up mainly on dynamic peaks and on less sensitive speakers, not on the average level of a quietly mixed recording.

Desktop placement and heat

A 36 mm tall fanless chassis with a 48 V supply is designed to be sat on a desk with air around it, not stacked under a turntable or pushed against a wall. Leave the top clear, keep a few centimetres of space at the sides, and do not cover the vents if you add feet or a stand.

Both models are fanless, which matters more than it sounds in a nearfield system: a small fan at 40 cm is audible between tracks in a way that it is not from across a room. That is the tradeoff the chassis height represents.

Pairing a source: where the two models separate

If you choose the M7BT, the source is your decision. A two-converter desktop DAC such as the LP2 gives you XLR preamp outputs that match the M7BT’s balanced input, which is the cleanest way to run the pair. A four-converter unit such as the HD200 adds a 4.4 mm balanced headphone output, so the headphone listening happens at the DAC and the speaker listening happens at the amplifier.

If you choose the M7PLUS, you already have the DAC, the headphone stage and the amplifier in one box, and the question becomes whether to spend the saved money on speakers. In most desktop systems it should be.

Bluetooth 6.0 in practice

Both models accept Bluetooth, and it is worth being clear about what that input is for. It is the input you use when a guest wants to play something from a phone, or when you are listening to a podcast while working. It is not the input to build a critical listening system around, because the codec and the transmitting device’s stack determine the result before the amplifier sees a signal.

Which one to buy

• You already own a DAC or streamer with RCA or XLR outputs, and you want to drive passive speakers. M7BT.
• You want to add a subwoofer or an external power amplifier later. M7BT, because of the line output.
• You want one box on the desk: computer in, speakers and headphones out. M7PLUS.
• You watch TV or films from a digital source and want the amplifier to take an optical feed. M7PLUS.
• You listen mostly at night on headphones but want speakers available. M7PLUS.

The $100 gap is not a quality gap. Both models use the same amplifier platform and the same 48 V supply, and both are rated identically into 8 ohms. The gap buys inputs, a headphone jack and a display — or it does not, depending on what is already sitting on your desk.

FAQ

Can the M7BT accept a USB connection from a computer?

No. The M7BT has RCA and XLR analog inputs plus Bluetooth 6.0. A computer needs a DAC between it and the M7BT, or you use Bluetooth.

Does the M7PLUS have a subwoofer output?

No. The M7PLUS drives passive speakers and headphones. If you need a line-level output for a subwoofer or an external power amplifier, choose the M7BT, which has a full-range RCA LINE OUT.

Will either model drive difficult speakers?

Both are rated at 115 W x 2 into 8 ohms from a 48 V supply. Whether that is enough depends on your speakers’ sensitivity, your listening distance and how loud you listen — not on the amplifier’s price.

Can I connect a turntable directly?

Not without a phono stage. Both models take line-level analog signals; a turntable needs a phono preamplifier between it and the amplifier.

Is the headphone output on the M7PLUS a separate amplifier?

It is a dedicated headphone output, and inserting headphones stops the speaker output according to the product specification. That behaviour is what makes it usable as a night-time listening path without unplugging speakers.

Do I need the 48 V version?

The 48 V version is the one rated at the figures above. Do not assume 36 V specifications carry over.

Can I use the M7PLUS as a preamp?

It has analog inputs, a volume control and a headphone stage, but no dedicated line-level output. For a line-level feed to another amplifier, the M7BT is the appropriate model.