Cutting Edge CE1000M Class AB Mono Amplifier

Cutting Edge rates this amplifier at 1,000 watts into one ohm. The amplifier can be bridged with a second CE1000M to achieve 2,000 watts into a single two-ohm load.

Cosmetics
With class D amplifiers becoming the standard for big power, the high output CE1000M class AB measures a bit on the large side at 17.5" x 11.25" x 2.6". Visually, the sizeable heatsink looks like a model Stealth Bomber elaborated upon by a tattoo artist. In the center of the amp is a chrome, epoxy sticker that displays the Cutting Edge tribal logo. The uniquely shaped heatsink fins were designed to allow multiple CE1000M amplifiers to be stacked. In this configuration they have a rather impressive look.

Layout
The layout of this amp uses through-hole components. Internally, the CE1000M is clean; that is, the designers managed the circuit layout well without the use of messy jumper wires. There is a fan mounted in the PCB near the signal end of the amplifier. We could not figure out how it helps as there was no path for the air flow; it just blows through the board to the heatsink.

The class AB amplifier, which uses sixteen 130 watt Sanken bipolar power devices, employs 85* C capacitors that were used throughout, including critical power stages (see sidebar).

No inductors were included for the 12 volt power and, as the power supply is unregulated, no inductor was included there either. This amplifier uses no isolation between the power supply and the audio circuitry. Non-isolated amplifiers must use differential inputs to break the ground loop. This type of circuitry must have high common-mode rejection to reject supply switching noise and low frequency ripple that is generated by the power supply. We measured some distortion and noise introduced by this technique, especially into a 1-ohm load where the power supply current can exceed 120 amps (as seen in the power vs. distortion test). The graph "Distortion/Noise" shows this as well. Although this non-isolation/differential input technique increases distortion, it remained below 0.3% into 1 ohm, which should not be a problem when driving subs. This distortion level is lower than most class D amplifiers in this power class.

Audio input connections are standard RCA gold plated PCB mount connectors. There is also a buffered pair of line out RCA connectors allowing the amplifiers to be daisy-chained.

At the opposite end of the amplifier lie the power connections. These power and speaker connectors are made of heavy brass that is gold plated; an allen-keyed set screw to secures the wire tight. The hefty power connector can accommodate #4 gauge wire; the speaker connector can handle #8 gauge.

Preamp
The crossover in the CE1000M is switchable on or off in low-pass mode only. This limits the user to select from either low-pass or full-range configurations. The slope of the crossover is rather steep at 24 dB/Octave, a slope that is not necessarily undesirable. The crossover frequency is variable from 30-250 Hz, leaving this amplifier only open for use in midbass and sub-bass regions.

On the low side of things is the subsonic filter. This 18 dB/octave highpass filter is variable from 25-70Hz and allows the user to turn it on or off. We are always happy to see subsonic filters on bass amplifiers; delivering power below the cutoff frequency of any ported enclosure wastes power and can be destructive to the speaker. This subsonic also goes high enough in frequency to make for a nice bandpass setup for a midbass speaker.

Cutting Edge also supplies a remote gain control with the CE1000M amplifier. This control detents the gain setting of the amplifier, allowing the user to adjust the amplifier output 0 to -26dB from a remote location.

The CE1000M is bridgeable amplifier. Not by itself, but with a like amplifier. In other words, you can connect two amplifiers together to double the power. Bridging two amplifiers together can be difficult. When matching the gains, crossover points, subsonic filters and bass boost, you must be very precise. To simplify matters, Cutting Edge provides a parallel output for the slave amplifier so that all settings are made on the master amplifier only. Each amplifier can be initialized to their duty by selecting the master or slave position on each amp (one must be master and the other must be slave).

There is also a bass boost control in the preamp section. Centered around 45Hz, the boost has a range of 0-18dB. The Q is much lower (wide response curve) than we've seen in other amps, as indicated in the graph. This will likely produce a boomy sound when used. Some may prefer this sound, though.

Power Supply
The power supply uses ten 85 ampere MOSFETs. That's a lot of power handling capacity! The FETs are mounted on opposite sides of the PCB, with speaker traces routed across these high current traces, which should be avoided. We saw evidence of switching noise in the speaker output probably due to this layout technique. We tested the amplifier with input voltages as high as 20 volts in search of its over-voltage protection, but the amplifier did not shut down as expected. Most amplifiers are limited to voltages of 16-18VDC in case of voltage spikes in the system or alternator regulator failure. Since the power supply is unregulated, the amplifier continued to increase its power output at this high voltage. While we did not measure output power at this high battery voltage, we're sure the SPL competitors will exploit this.

Protection
The amplifier is protected by four internal ATO (automotive) 20 ampere fuses. As these fuses blew when we attempted to drive the amplifier to full power (1,220 watts), we replaced them with more appropriately sized 40 ampere fuses. After measuring the full power output, we placed the recommended 20 ampere fuses in place for the remaining tests. During the output short test, these fuses blew again. It was evident there was no short protection other than these fuses. Fuse blowing as a form of short protection might be acceptable, but they should be accessible externally. The heavy clipping used during SPL tests will likely cause these stock fuses to blow.

We also forced the amp into thermal protection. The amp recovered from this test without a hitch.

Manual
The manual is written fairly well. Although it clearly states in the introduction, "this manual is written for the experienced installer," the content provided is enough for those who have basic installation skills to do a decent job powering this unit up. All specifications, features, wiring and troubleshooting are covered in detail. The only difficulty was deciphering what images go with what instructions, as they are not all labeled correctly.

Performance
The CE1000M surpassed the factory's power specifications at all impedance levels. At 1 ohm, Cutting Edge rates this unit at 1,000 watts; our test revealed this amplifier to be slightly more powerful, producing 1,220 watts at 0.3% T.H.D with 14.4VDC supplied. Being Class AB, the CE1000M produced 1,000 watts over the audio bandwidth of 20-20kHz, unlike many of its Class D counterparts.

The slew rate, about 13 volts/uS was a bit slow for a full range amp. However, slow slew rates should not affect an amplifier's performance when used for bass, so you could safely ignore this number for subwoofer applications.

With regard to our reactive load test this amp passed with ease; it drove all of our nasty reactive loads without a hint of instability. While inductors in the speaker path are usually required to ensure stability, the lack of them in the CE1000M did not disrupt its performance.

The damping factor was better than 275 into a 4-ohm load. Into a 1-ohm load, the damping fell to just better than 60; still acceptable.

Signal-to-noise ratio (SNR) was good at 100dB, A-weighted just below clipping; and efficiency at full power into 2 ohms was 54%, about average for a class AB amp. At 1/3 power the efficiency fell to 30%, a bit lower than we like to see.

Idle current measured only 1.1 amps, very low for this power class. At low power, the amplifier should remain at a cool operating temperature.

Finally, the input sensitivity had a nice wide range, variable from 160 mV to 4.5 volts. The CE1000M should have no problem making full power with any source unit.

Listening Test
Because this amplifier is monaural, we conducted our listening tests on our subwoofer system only. We confirmed our electrical tests, indicating that this amp should introduce no sound of its own when driving such a system; thus no coloration or distortion could be detected. The bass response was solid and reasonably accurate. There was, however, a slightly noticeable turn-on thump and a turn-off thump.

Conclusion
The CE1000M is very powerful and is cleaner then its class D counterparts. With 1,220 watts of power, a variable subsonic filter, 24dB/Octave crossover, variable bass boost and remote level controller, this amp should meet the audio enthusiast's requirements.