April 2017

McIntosh MP100 Phono Stage With Analog And Hi-Res Audio Digital Output Review
Andrew Harrison reviews McIntosh's first ever phono stage, complete with digital output.
Review By Andrew Harrison

  The McIntosh Laboratory has been around for almost 70 years, but it wasn't until late last year that it launched its first dedicated phono amplifier, the MP100. It's a phono stage that's well stocked with features for the category, with separate switchable inputs for moving-coil and moving magnet cartridges, balanced XLR outputs, plus a wide range of cartridge loads, accessible without the aid of a screwdriver directly from the front panel. However, for some users the star attraction may well be the built-in 24-bit/96kHz ADC, for making digital recordings of LPs.

A glance at the photo doesn't necessarily show the scale, but the MP100 is actually a midget McIntosh, not designed to stack with its usual pre and power amplifiers (nor indeed the similarly full width MT5 plug 'n' play turntable that McIntosh now sells). It could, however, sit on top of the company's bijou midi-width MXA70 music system, matching MB50 stream player and MHA100 headphone amp.

That small chassis would make it tricky for McIntosh to include a full suite of valves and a linear power supply, so the McIntosh Labs MP100 uses neither. Instead this advanced phono amplifier draws on many of today's consumer electronics tricks: surface-mount devices, compact switch-mode power supply, embedded ARM processor, digital converter, and USB ports inside and out. The McIntosh tradition of the very green front panel is fully maintained, with gothic black logo, polished metal knobs and mock lab handle cheeks. Once powered up, the MP100 stays fully lit with no dimming or blackout options.

McIntosh MP100 Details
The front has two ratcheted control knobs are mounted symmetrically to adjust moving-magnet capacitance loading (left) and moving-coil input impedance (right). These allow six options each, of 50, 100, 150, 200, 300 and 400 pF; and 25, 50, 100, 200, 400 and 1 kOhm. Voltage gain is fixed at 40dB for moving magnet and 60dB moving-coil.

Four soft-touch electronic buttons ranged between the rotary encoders offer, respectively, mono summing of stereo channels; switching between MM and MC inputs; a two-position 'digital output' selector with clip indicator; and unit standby switch.

The mirror-finish rear panel features one pair each of RCA/phono and XLR analogue outputs, two separate phono inputs for MM and MC cartridges (with earthing posts for each), plus three digital outputs – phono and TosLink S/PDIF, and a USB 2.0 Type B port. Power inlet is a modest two-pin 'figure 8', and thanks to the high-frequency power supply the unit will work from 100 to 240V without adjustment. A pair of 3.5 mm jacks can trigger remote standby and power-up with compatible components; regrettably there's no way to control cartridge loading remotely from the listening seat.

Electronic Design
At heart the McIntosh Labs MP100 is a chip-based phono amplifier, deriving active RIAA equalization through filters within the feedback loop of the initial non-inverting op-amps. A single large PCB fills most of the unit's footprint, with surface-mount devices from the cartridge-loading passive components at one end, to a 120MHz ARM Cortex-M8 microprocessor and 12MHz crystal clock at the other.

Other updates to the traditional phono stage are the digital converter and transmitter chips from Asahi Kasei, for direct digitization of the RIAA stage's analogue signal. Core A-to-D conversion is courtesy of an AKM AK55532VN, a 24-bit/768kHz ADC which here has been throttled back to 24-bit/96kHz-only operation. When queried why, Senior Electronic Design Engineer Ron Evans pointed to the just launched MP1100 which can operate at either 24-bit/96kHz or 24-bit/192kHz. (This is a full-width £9995 phono amplifier with two valves per channel, selectable non-RIAA curves, and rumble and scratch filters. The AKM converter chip incorporates four digital input filters, and McIntosh opted for one of two slow roll-off options 'to allow for a wider transient response'. The Mono switch sums (L+R) channels in the digital as well as analogue domain. A design error quickly came to light after I had made some recordings, as left and right channels were reversed on all digital outputs. McIntosh subsequently stated that the issue was limited and had been quickly corrected.

Driving the MP100 is a GlobalTech 5V switch mode power supply. A medical-grade rating might suggest quiet operation although its certification is related to general safety rather than specifically addressing spurious RFI generation. In use, the power supply had a low-level acoustic buzz just audible in a quiet room, which became louder whenever in standby mode. This was confirmed by McIntosh as normal for this product.

Sound Quality
On first audition the MP100 impresses with its fabulously low noise floor and squeaky clean sound. It has a well-lit tonal balance, adding sparkle and shine to give a modern, almost 'digital' definition to records. (That may not be quite what one expects from an analogue phono stage of course!)

In several ways the McIntosh Labs MP100 reminded me of a Linn Linto, both units are midi-size, fully electronic phono stages that leverage modern production techniques such as SMPS and SMD assembly. Like the Linn the MP100 has a tight, disciplined sound, damped enough to maintain a good sense of timing. Bass transients could be felt with controlled LF slam, for instance, but low-level detail, like the long tail of a reverberation, was typically robbed in the process. Through the MP100, live recordings were drier and the acoustic space was reduced, spotlighting the main foreground well enough but within a rather hollow supporting background.

Transparent and inviting would not be my description of the McIntosh. In tape-generation terms it seemed to be one stage removed, yet remained bright in its upper reaches, as noted by rather 'zingy' percussion and some over-reedy strings. Cymbals could sound tinselly, and overall I felt that treble was not given free expression, sounding all too often monotonic. While decent midband tonality could flesh out a colorful sound, it somehow seemed to gloss over the timbral richness of acoustic instruments. As instrumental passages built, strands would still remain separate but increased thickening pushed instruments together.

Soundstaging was potentially very wide, with solid images spaced left to right when playing simple jazz or string quartets, but stage depth was clearly foreshortened to leave a shallow, two dimensional effect. However, the substantial width was not matched by comparable height – the McIntosh Labs MP100 may be somewhat cinemascope side-to-side but it left a relatively narrow letterbox of sound through which to peer.

Recordings were made direct from Linn and Michell turntables to an Apple MacBook Pro with Sony Vegas Pro audio software. The setup is easy, just requiring a USB cable from the MP100 to any personal computer with DAW software installed (the free open-source Audacity is a good starting point to try digital transcription). The resulting 24-bit/96kHz-encoded AIFF files were quite close to the unit's original analogue sound (after correcting the stereo L/R channel reversal in software), although that is to say the recordings preserved the processed, almost CD-like nature of the sound of the MP100 phono stage.

Conclusions
McIntosh Laboratory had a good idea in combining an RIAA phono stage with a 24-bit PCM digital audio converter (ADC), as it makes a relative breeze of transcribing beloved records to a more convenient format. It also presents an opportunity to make informed decisions about the components and calibration of a turntable – I found myself making recordings of different decks to compare their sound signature easily, as well as comparing pressings and small geometry changes, for example.

However, the final product is difficult to recommend, principally because the core sound quality of the phono stage is not really faithful enough to make reliable archive recordings. And the power supply buzz alone was annoying enough to unplug the unit except when demanded.

After several weeks of listening and experimenting with ripped files I found its intrinsic analogue sound just too processed to warrant investment in ownership, or indeed the time required to archive vinyl to high-rate PCM. At best, when used solely as a phono amplifier, the McIntosh had the ability to make LPs sound like good CD replay from the best four-figure CD players. But vinyl discs can sound so much better, so why stop there?

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Specifications
Analog Outputs: Unbalanced RCA and balanced XLR
Analog Inputs: Two separate phono inputs for MM and MC cartridges with earthing posts for each
Digital Inputs: RCA coax S/PDIF, Optical TosLink and a USB 2.0 Type B port
Total Harmonic Distortion: 0.005%
Frequency Response: ±0.3dB from 20Hz to 20kHz
Maximum Volts Out (Balanced / Unbalanced): 16/8 V RMS
Input Impedance: 
  MC: 25, 50, 100, 200, 400 or 1,000 Ohms; 470pF
  MM: 50, 100, 150, 200, 300, 400pF; 47 kOhms
Phono Voltage Gain: MC 60dB, MM 40dB
Signal To Noise Ratio: MC 78dB, MM 80dB
Maximum Input Signal: MC 8mV, MM 80mV
Sensitivity: MC 1mV, MM 10mV
Rated Output: 2V Balanced, 1V Unbalanced
Output Impedance:  200 Ohms Balanced, 100 Ohms Unbalanced
Dimensions: 11.5" x 3.78" x 16.75" (WxHxD)
Weight: 8.6 lbs.
Price: $2000

Company Information
McIntosh Laboratory, Inc. 
2 Chambers Street 
Binghamton, NY 13903

Voice: (607) 723-3512
Fax: (607) 724-0549 
Website: www.McIntoshLabs.com