Audio T Verdict
The Musical Fidelity M6si500 is a 500-watt-per-channel integrated amplifier built around a separate pre-amplifier and two bridged mono power-amplifier sections.
It provides one balanced XLR input, four RCA line inputs, a switchable home-theatre bypass, tape-monitor facilities, a fixed recording output and a volume-controlled pre-output.
This is a specialised high-power analogue amplifier. It has no phono stage, built-in DAC, network streaming or headphone socket, and its bridged speaker outputs require more careful system matching than conventional grounded amplifier terminals.
Musical Fidelity M6si500 Integrated Amplifier
The Musical Fidelity M6si500 is the current manufacturer name for the amplifier also described as the M6 500i and M6si 500.
It combines a dedicated pre-amplifier with four internal power-amplifier circuits bridged into two 500-watt mono channels.
The design is intended for systems requiring substantial voltage, current and dynamic headroom while retaining source selection and volume control within a single chassis.
Current Model Name: M6si500
Musical Fidelity's current product page uses M6si500. Earlier literature and the Audio T listing use variations including M6 500i and M6si 500; these names refer to the same amplifier family.
The Audio T description also contains “M6500i”, which is a typographical error rather than a separate model.
Directly Supported Sources
- Balanced analogue sources through stereo XLR
- CD players, DACs and streamers with RCA line outputs
- Tuners, tape decks and other line-level sources
- Home-cinema processors with controlled front-channel outputs
- Passive loudspeakers compatible with bridged amplification
Requires Additional Equipment
- Every turntable requires a suitable external phono stage
- Digital sources require a DAC with analogue output
- Network playback requires a separate streamer
- Headphones require a separate headphone amplifier
- Ground-referenced speaker-level accessories require compatibility checks
500 Watts per Channel
Musical Fidelity rates the M6si500 at 500 watts per channel into 8 ohms, equivalent to 27dBW.
The manufacturer specifies a maximum output voltage of 64V RMS at the onset of clipping, 100 amps peak current and a damping factor greater than 250.
Musical Fidelity also describes the current capability as 200 amps peak to peak. These are two ways of expressing the same symmetrical current swing rather than two separate output ratings.
Although the amplifier has substantial reserves, loudspeaker compatibility must still account for impedance behaviour, grounding, sensitivity, room size and intended listening level.
Bridged Dual-Mono Architecture
Four internal power amplifiers are bridged in pairs to create two independent 500-watt mono channels.
Each channel has its own heatsink, mains transformer and six pairs of output devices. The pre-amplifier is separately arranged and receives its own power-supply winding.
Musical Fidelity uses 12 bipolar power transistors per channel and keeps the input sockets close to the main pre-amplifier board to shorten the internal signal path.
Important Bridged-Output Warning
Both the red and black speaker terminals carry an active signal. Neither terminal is at conventional ground potential and neither must be connected to earth, chassis ground or another channel.
Check compatibility before using electrostatic loudspeakers, speaker-level active-subwoofer inputs, switching boxes, common-ground accessories, bi-amplification or any non-standard speaker arrangement.
An incorrect grounded connection can short part of the bridged amplifier and cause damage.
Heavy-Duty Speaker Terminals
Each channel provides two pairs of heavy-duty 4mm binding posts, allowing compatible loudspeakers to be connected or bi-wired without stacking two cables on one terminal.
The terminals are not independently switched Speaker A and Speaker B outputs. They belong to the same amplifier channel and remain subject to the bridged-output warning.
Maintain correct loudspeaker polarity, switch off the amplifier before changing cables and ensure that no loose conductor strands can contact another terminal or the chassis.
Balanced XLR Input
One stereo balanced XLR input accepts a source fitted with compatible left and right balanced outputs.
The documented pin arrangement is pin 1 ground or shield, pin 2 normal polarity and pin 3 inverted polarity.
Balanced connection can be useful over longer cable runs or where the source and system environment benefit from balanced noise rejection. RCA remains appropriate for conventional unbalanced sources.
Four RCA Line Inputs
Four unbalanced stereo RCA inputs are labelled CD, Tuner, AUX/HT and Tape.
These labels are provided for convenience. Any suitable line-level source can use any input configured for normal operation.
The input specification sometimes uses the phrase “RCA/phono connectors”. In this context, phono describes the physical RCA connector and does not indicate a turntable phono stage.
No Built-In Phono Stage
A turntable cannot normally be connected directly to the M6si500 because the amplifier does not provide moving-magnet or moving-coil gain and RIAA equalisation.
Connect the turntable to a suitable external phono stage, then connect the phono stage's line-level output to one of the M6si500 inputs.
A turntable with a built-in phono stage can connect directly when its output is set to Line rather than Phono.
Switchable Home-Theatre Bypass
The rear AUX/HT selector changes the AUX input between normal line-level operation and a fixed-gain home-theatre bypass.
In AUX mode, level is controlled by the M6si500. In HT mode, its volume circuit is bypassed so the connected home-cinema processor controls the front left and right channels.
Home-Theatre Bypass Safety
Never connect a conventional fixed-output CD player, streamer or DAC while the input is set to HT. The connected device must provide a properly configured volume-controlled output.
Reduce the processor volume before initial setup. An uncontrolled input can produce extremely high sound levels and may damage loudspeakers or hearing.
Precision Digital Volume Control
The M6si500 uses a digitally controlled analogue volume network with laser-trimmed substrate resistors.
The front display shows the selected level in 0.5dB steps, helping the left and right channels track consistently at low listening levels.
If the stored level is unusually high when the amplifier is switched on, the control automatically reduces it to help protect the loudspeakers.
Tape Input, Record Output and Monitoring
The Tape input operates as a normal line input and is accompanied by a fixed Tape Record output.
The selected source is routed to the recording output independently of the amplifier volume. A compatible three-head tape deck can be monitored using the front-panel Tape Monitor function.
Because the Tape output is fixed, any connected headphone amplifier or recording device must provide its own appropriate level control where required.
Variable Pre-Amplifier Output
The stereo RCA Pre Out follows the M6si500 volume control and can feed a compatible external power amplifier, bi-amplified system or active subwoofer.
The pre-output is full range rather than a filtered subwoofer channel. The subwoofer must therefore provide its own crossover, phase and level controls.
Musical Fidelity specifically recommends the volume-controlled Pre Out rather than a potentially grounded speaker-level connection when adding an active subwoofer.
No Built-In Digital Audio or Streaming
The M6si500 is an analogue amplifier. It has no USB audio, coaxial, optical, HDMI, Bluetooth, Wi-Fi or network-streaming input.
A digital source must provide its own analogue output or connect through an external DAC. Network playback requires a separate streamer.
There is also no headphone socket. A separate headphone amplifier can use the fixed Tape output and must provide its own volume control.
Remote Control
The supplied remote controls amplifier power, input selection, volume and mute.
It also contains controls for compatible Musical Fidelity CD players, allowing an M6-series source and the amplifier to share one handset.
The infrared receiver requires a reasonably clear line of sight and can be affected by strong sunlight, fluorescent lighting and some infrared security equipment.
Power and Installation Requirements
The manufacturer specifies approximately 0.25W in standby, 150W when switched on with no signal and up to 2,000W at full output.
The amplifier must connect to an appropriately rated, earthed mains supply. Any extension, mains conditioner or power-distribution product must be capable of supporting its potential demand.
Ventilation openings above and below the chassis must remain clear. Do not enclose the amplifier in furniture where heat cannot escape.
At 30kg, the M6si500 requires a stable support and careful handling. Two-person lifting is sensible when placing or moving the amplifier.
Black or Silver Finish
The M6si500 is available with a black or silver fascia, subject to current stock and availability.
Both finishes use the same amplifier architecture, connections and technical specification, so the choice is cosmetic.
Key Features
- 500 watts per channel into 8 ohms
- Bridged dual-mono power-amplifier architecture
- Separate pre-amplifier section
- Individual transformer and heatsink for each channel
- 12 bipolar power transistors per channel
- 100A peak and 200A peak-to-peak current capability
- Precision volume control with 0.5dB display steps
- One stereo balanced XLR input
- Four stereo RCA line inputs
- Switchable fixed-gain home-theatre bypass
- Tape-monitor loop and fixed recording output
- Volume-controlled stereo pre-output
- Two pairs of heavy-duty speaker terminals per channel
- Black or silver finish
Frequently Asked Questions
Are the M6 500i and M6si500 different amplifiers?
They are naming variations used for the same amplifier family. Musical Fidelity's current product page uses M6si500.
How powerful is the M6si500?
Musical Fidelity rates it at 500 watts per channel into 8 ohms, with 100A peak current capability.
Does it have a phono stage?
No. The reference to RCA or phono connectors describes the socket type. A turntable requires a suitable external phono stage unless it already provides a line-level output.
Does it have digital inputs or streaming?
No. It is an analogue amplifier with balanced XLR and unbalanced RCA inputs. Digital and network sources require a DAC or streamer with analogue output.
Can it be used with any loudspeaker?
Its power and current reserves suit many demanding loudspeakers, but electrical, grounding and room compatibility must still be checked. The bridged outputs make this particularly important.
Why must the speaker terminals not be grounded?
Both terminals carry an active signal because each channel is bridged. Grounding either terminal can short part of the amplifier and cause damage.
Can I use a speaker-level subwoofer input?
Only after the subwoofer manufacturer confirms compatibility with fully bridged, non-ground-referenced outputs. The safer normal connection is the volume-controlled RCA Pre Out.
What does HT mode do?
It bypasses the M6si500 volume control for the AUX input, allowing a home-cinema processor to set the level. Never use HT mode with an uncontrolled fixed-output source.
What is the difference between Tape Out and Pre Out?
Tape Out is fixed and intended for recording or monitoring. Pre Out follows the amplifier volume and is suitable for a compatible power amplifier or active subwoofer.
Does it need special ventilation?
It requires substantial open airflow above and below the chassis. It should not be enclosed in furniture where heat can accumulate.
Why Buy From Audio T?
- High-power amplifier and loudspeaker compatibility advice
- Bridged-output grounding and connection checks
- Balanced and unbalanced source matching
- Home-theatre bypass setup guidance
- Phono-stage, DAC and streamer selection
- Active-subwoofer and pre-output advice
- In-store demonstrations through participating branches
- Part-exchange options on suitable equipment
- Delivery and installation planning for a 30kg amplifier
- Ongoing system setup and servicing support
Contact your local Audio T store
to arrange a demonstration and confirm loudspeaker, mains, furniture and source compatibility before ordering.