Electro-Voice 100M

Name: Electro-Voice 100M
Brand: Electro-Voice

Two 100-watt amplifiers, eight channels of mixing, and a pair of eight-band graphic EQs in one box. The 100M did it all before "everything" was a selling point.

Overview

The 100M is a self-contained powered mixing console. It has eight input channels, dual 100-watt (8-ohm) internal power amplifiers, a pair of 8-band graphic equalizers, onboard reverb, phantom power, and a fluorescent bargraph meter section. It runs on 100, 120, 220, or 240 V AC at 50/60 Hz, so the same chassis could be sold into any market without a different power transformer. For a band hauling its own PA, that meant one box instead of three. Mixer, power amp, and EQ all share a single chassis and a single power supply.

The amplifier section is the spec that matters most. Each of the two internal amplifiers is rated at 100 watts into 8 ohms. The manual is blunt about what that means in practice: the total load on each amplifier must be no lower than 4 ohms, and 8 ohms is the recommended figure. It lists the acceptable combinations - one 8-ohm speaker, one 4-ohm speaker, two 8-ohm speakers, two 4-ohm speakers wired in series, four 16-ohm speakers, or any combination totalling 4 ohms or more. Running below the 4-ohm minimum, down to 2 ohms, may damage the amplifiers, and the manual says such damage is not covered by the warranty. That's a real constraint, not marketing hedging. Owners report the 100M is happiest driving a pair of the matching Electro-Voice 100S speakers, which the manual itself cites as the example 8-ohm load.

The equalizer section is where the 100M earns its keep. Each of the two graphic equalizers can boost or cut any of eight frequencies by 12 dB. The equalizers sit after the mixer section and are routed via the Power Amplifier Assign Mode switch, which determines whether the left and right EQs feed the stereo outputs or the monitor and mono outputs. The manual documents a useful trick: set the 63 Hz slider to +3 dB and the bass response of the 100S speaker system extends an additional 1/3 octave, down to a low-frequency cutoff of approximately 60 Hz. There's a trade-off, and the manual says so. That extra low-frequency boost puts more demand on the power amplifiers and may cause premature activation of the anti-clipping circuitry. In that case, use less boost.

The anti-clipping circuit changes how the amplifier behaves under stress. Each amplifier's output is monitored individually for clipping. When clipping is detected, the gain is automatically reduced just enough to keep the output clean. If the input signal rises further, gain drops further. The Maximum Power LEDs on the front panel indicate this protection circuitry engaging, not clipping itself. Occasional blinking is normal. Sustained illumination means the system is being overdriven, and once those indicators are on continuously the 100M will not get significantly louder no matter how far the volume controls travel. The manual's suggested cures are to turn the master down or add more power amplifiers and speakers.

The meter section uses a dual-channel fluorescent bargraph display. It's calibrated so that 0 VU corresponds to +4 dBu (1.23 V rms) at the stereo or monitor outputs, and +3 VU corresponds to the 100-watt (8-ohm) output from the internal amplifiers. Depending on the Mode switch position, the left and right bargraphs show either the main and monitor output levels, or the left and right stereo output levels. The meters read the output of the graphic equalizers, so what you see is post-EQ.

The input and output complement is extensive for a box this size. Phantom power is 48 V and switchable, with an LED confirming its presence at the XLR microphone inputs. The manual notes phantom powering is a compatible system, so dynamic microphones can be used alongside phantom-powered condensers without damage. The stereo and mono mixer outputs are at line level (+4 dBu, 1.23 V rms at 0 VU), unaffected by the graphic equalizers or the Mode switch. The mono output is a mix of left and right, affected by the Sub L and Sub R controls and adjusted by the Main control. The manual suggests it for feeding a house PA through a direct box or a high-impedance-to-low-impedance transformer. The monitor send output is +4 dBu nominal and isn't affected by the graphic equalizers regardless of Mode switch position. It can be used for recording or as a send to an external sound system.

The effects section has two send jacks. One is a high-level 1/4-inch phone jack at +4 dBu for studio-type line-level devices. The other is a low-level 1/4-inch jack at -16 dBu for guitar-type devices normally patched between an instrument and its amplifier. Both can be used simultaneously. The effects return accepts either level. The manual is emphatic that any Blend control on an external effects unit must be set to 100% or full effect, otherwise expect overall volume changes when the effects return control is varied. It also notes that most pedal-type effects lack this control, so using them with the 100M (or any other effects send/return system) isn't recommended. There's also an internal reverb system with its own level and EQ controls, plus a rear-panel footswitch jack for remote on/off using any standard footswitch that shorts the hot wire to ground.

The patching jacks on the rear are what separate the 100M from simpler powered mixers. Graphic EQ Out and Amp In jacks are normaled, so no patch cords are needed for normal operation. The EQ output jacks can be patched at any time without disrupting signal flow to the internal amplifiers. Inserting a plug into the Amp In jacks interrupts the signal from the graphic EQ section. The manual lists the possibilities: patching both internal amplifiers to one graphic EQ output, patching either graphic EQ output to external amplifiers, separating the internal amplifiers completely from the mixer circuitry, patching from the graphic EQ output directly to a tape recorder where the EQ effect is wanted, or patching in external equalizers. The Amp In jacks require line-level signals, with +8 dBu for amplifier clipping. All connections here should use shielded cable.

One detail that dates the 100M to the era of coiled guitar cables and questionable stage wiring: the manual warns in bold against using coiled guitar cables for speaker connections, calling them unreliable and noting they waste amplifier power. It recommends 18-gauge zip cord for most purposes, heavier 16- or 14-gauge wire for runs over 50 feet, and type SVT or SJ portable cordage for heavy-duty applications where gear is constantly put up and torn down. Shielded cable is neither necessary nor desirable for speaker connections.

The headphone jack is on the rear panel, monitoring the outputs of the internal power amplifiers, and is suitable for stereo phones with a rated impedance of 8 to 20,000 ohms. The AC mains fuse is a 3-A Slo-Blo, type MDL3. The manual warns that repeated fuse blowing is a sign of internal trouble that will only be aggravated by fitting a larger fuse.

The 100M comes from a period when Electro-Voice was building complete PA systems rather than just components. The 100S speaker system it was designed to pair with is the clearest evidence of that intent. The manual references the 100S repeatedly as the reference load, and the equalizer's bass-extension trick is specifically calibrated for that speaker.

For anyone considering one today, the practical questions are the usual ones for gear of this vintage: whether the power supply has been serviced, whether the graphic EQ sliders are clean and tracking properly, and whether the amplifier section has ever been run below its 4-ohm minimum. The manual's warnings about load impedance and fuse ratings aren't theoretical — they're the failure modes these units actually develop. The patching jacks and the assignable EQ architecture also mean the 100M rewards someone willing to read the manual, because the routing options aren't obvious from the front panel alone.