McIntosh MQ-101
A stereo equalizer with +17 dB of low-frequency boost on tap - room correction the way McIntosh did it in the 1970s.
Overview
The MQ-101 is a stereo equalizer from the era when McIntosh would sell you a two-piece tuner-preamp and a rack of glass-fronted separates. It exists to solve a problem every serious listener eventually runs into: the room, not the speakers, is what you're hearing. The front panel has three bands of control - low, mid, high - each with its own rotary switch, plus an input attenuator and a tape-monitor switch. That's it. No graphic display, no spectrum analyzer, no digital anything. Just a small metal box with a power transformer inside and a relay to switch the signal path.
The numbers are the interesting part. The low-frequency band offers 0 to +17 dB at 20 Hz in five discrete steps - 0, +6, +9, +13, and +17 dB in positions 1 through 5. That's a lot of bass lift, and it's boost-only, which tells you what McIntosh thought this box was for. It wasn't a cut-and-boost tone control in the conventional sense. It was a correction tool for speakers that rolled off early in a room that reinforced nothing. The mid band runs ±5 dB at 4000 Hz in five equal steps, and the high band runs ±4 dB at 20,000 Hz, also in five equal steps. Frequency response through the unit, with the low switch in position 1 and the mid and high switches in position 3 (flat), is specified at ±0.5 dB from 20 Hz to 20,000 Hz. That's a serious claim for a box with this much boost range, and it's the reason the MQ-101 has held a niche reputation among collectors rather than being dismissed as a period curiosity.
Power draw is 20 watts from a 120-volt, 50/60 Hz line. That's transformer-and-relay territory, not op-amp-and-wall-wart territory. It explains why the MQ-101 has the heft and the internal layout of a proper McIntosh component rather than the folded-steel-and-plastic feel of most consumer equalizers of the period.
Key Features
Five-Step Low-Frequency Boost to +17 dB at 20 Hz
The low band's five positions are calibrated at 0, +6, +9, +13, and +17 dB, all centered at 20 Hz. The step size is roughly 3 to 4 dB between positions. That's coarse, so the MQ-101 was never meant to be a precision instrument - it was meant to be set once and left alone. The +17 dB maximum is the headline figure. In practice it's enough to make a small sealed speaker in a dead room sound considerably larger, and enough to bottom out a woofer that can't take it. The switch is a rotary, not a pot, so settings are repeatable and there's no track wear to worry about.
Mid and High Bands at ±5 dB and ±4 dB
The mid band gives ±5 dB at 4000 Hz in five equal steps, and the high band gives ±4 dB at 20,000 Hz in five equal steps. Unlike the low band, these are cut-and-boost, which makes them useful for taming a bright tweeter or pulling down a peaky presence region. The asymmetry, ±5 in the mids and ±4 up top, is a small detail. The 4 kHz region is where the ear is most sensitive, so having the widest range there makes sense.
Flat Response When Defeated
With the low switch in position 1 (0 dB) and the mid and high switches in position 3 (center), the unit is specified at ±0.5 dB from 20 Hz to 20,000 Hz. An MQ-101 set to neutral is effectively transparent within half a decibel across the audio band. That separates it from the equalizers that earned the format its bad reputation - the ones that added noise and phase smear even when set flat.
Tape Monitor Switching and Input Attenuator
The front panel has a Tape Monitor switch and an Input Attenuator alongside the three frequency knobs. The tape-monitor function lets the MQ-101 sit in a tape loop and be switched in and out without repatching. The input attenuator gives some gain-matching flexibility when the equalizer is inserted between a preamp and a power amp. The signal path is switched by a relay, part 087-007. That's a more serious approach than a mechanical switch and one of the reasons these units still function decades later.
Transformer-Coupled Power Supply
The power transformer is part 159-092, and the unit draws 20 watts from a 120-volt, 50/60 Hz line. The power supply board carries a 200/200 µF, 150/100 V electrolytic (C104) and a pair of 220 µF, 16 V electrolytics (C103 and C106), plus a pair of silicon rectifiers and a 0.5-amp fuse. It's a linear supply with real iron in it, which explains why the MQ-101 weighs what it weighs and why it doesn't hum.
Component Quality and Serviceability
The signal-path capacitors are Mylar - 0.1 µF at 250 V for the input and output coupling positions, 0.22 µF and 0.47 µF at 250 V elsewhere in the circuit - with a handful of tantalum electrolytics in the 0.47 µF and 3.3 µF range. The chokes are 300 mH. McIntosh's own manual includes a replacement-parts list with part numbers and a direct line to the Customer Service Department in Binghamton, New York. The schematic notes document serial-number-dependent component changes. R63 and R64 are 47k in units below serial 1V445, for example, and a whole cluster of resistor and capacitor values differ in units below 3V164. That level of documentation is unusual, and it's a real asset for anyone servicing one today.
Historical Context
The MQ-101 belongs to the period when room equalization was a serious audiophile concern rather than a home-theater afterthought. Audio-Collection (p.332) laid out the case plainly: an equalizer could compensate for room conditions and for different speaker positions, and the power output of a bass speaker could vary over an 8-to-1 range - 9 dB - depending on where it sat in the room. That's the exact problem the MQ-101's +17 dB of low-frequency boost was built to address. The serial-number-dependent component changes, documented in its own service manual, also place it in the era when McIntosh was still hand-tuning production runs rather than freezing a design and running it unchanged for years.
Collectibility & Value
The MQ-101 sits in an odd spot in the McIntosh collector market. It's not a tuner, not a preamp, not a power amp. It's an accessory, and accessories don't command the same prices as the components they support. That said, it's a genuine McIntosh-built equalizer with a transformer power supply, a relay-switched signal path, and a documented schematic, which puts it well above the mass-market equalizers of the same era. The practical concerns are the usual ones for a unit this age: the electrolytics (C103, C104, C106) are the first suspects if it's noisy or weak, and the relay contacts can oxidize. The Mylar capacitors in the signal path are generally fine. Because the schematic notes distinguish between serial-number ranges, buyers should record the serial number before ordering parts - R63 and R64, for instance, are 47k only in units below 1V445.
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