CMI 100W Lead & Bass Amp
TEST ON: CMI 100W Lead & Bass Amp
DATE Sept 1975
PRICE £127.57 Ex VAT.
The CMI 100 watt lead and bass amplifier is one of the many competing in the popular 100 watt market. However, this solid-state amplifier is designed to simulate some of the characteristics of valve designs and consequently gives a sound which is somewhere between the undistorted transistor amplifier sound and the warmer "valve sound". This should satisfy many people who would like a "valve sound" but are not prepared to accept the reliability problems associated with valve equipment.
The facilities provided include two input channels, each with its own volume control; one set of tone controls comprising bass, middle, treble and brightness; a master volume; on-off switch and pilot light and a speaker impedance selector. A useful extra is an effects socket which can be used to take the signal to an external effects unit, such as an echo chamber, and re-introduce the processed signal back into the amplifier.
Another useful feature is the speaker impedance selector switch, which permits full power to be driven into 4, 8 or 16 ohm speaker systems. With most amplifiers, only the lowest impedance loads receive full power and higher impedances receive reduced power.
The unit has low profile styling with a case heavily constructed in wood and covered in dark blue rexine. All the corners are protected by moulded caps. A carrying handle is placed in the centre of the top and deep feet have been fitted, which will clear the depth of a handle, so that several amplifiers can be stacked.
The electronics are all mounted in a cadmium plated steel chassis. The front edge of this is the control panel and the back edge carries a very large heat sink for the two output transistors. The whole chassis is very easily removed from the outer case, giving good access to the spaciously laid-out interior.
The larger components are mounted directly to the chassis but all the small components, including the control parts, are mounted on a single glass fibre printed circuit board. The workmanship is neat; the soldered joints are good and all the components are of good quality.
|Power Output||125W||for 10% distortion at 1KHz.|
|Distortion (total harmonic)||4%||@ 100W output 1 KHz.||At high outputs the distortion|
|0.7%||@ 10W||is mainly 2nd harmonic,|
|1.8%||@ 1W||rather like a valve amplifier|
|Sensitivity||4.4 mV. r.m.s.||input A for 100W out @ 1 KHz.||More than adequate|
|7.5 mV. r.m.s.||input B Vols at max|
|3.5 mV. r.m.s.||input A + B tone controls central|
|Tone Control Range||13.6dB.||Bass @ 50Hz.||Not very wide range.|
|7dB.||Middle @ 500Hz.||particularly middle|
|14dB.||Treble @ 10KHz.||and brightness.|
|7.5dB.||Brightness @ 10KHz.|
|Noise||—64.8dB.||Vols at min compared with 100 watts.||Fair but could be be better.|
|-46dB.||Vols at max|
|Master Vol. at max and tone controls central|
|Effects Socket Level||440 mV.||Equivalent to running the amplifier at 100 Watts||Approx -4dBm. level|
|Capacitive load test||OK||28% overshoot with 2 uF and 8 ohm load.|
|Open Circuit OP||OK|
|Short Circuit OP||OK||2 minute short||Worked when short was removed.|
This CMI product is well made, modern and does not have any obvious "bad habits". The high level of distortion compared with most transistor amplifiers is intentional, and similar in character to that from valve amplifiers; at least at high level. Another valve characteristic is that, when the output is overdriven, the peaks of the wave form become gently "flattened", rather than sharply clipped; as would normally happen in a transistor amplifier. This is all part of getting the "valve" sound. Attention has been given to practical details such as recessing the front panel and protecting box corners. The same care has been extended to the whole mechanical design and the result of this should be good reliability.
The background noise level and the ranges of two of the tone contro/scan only be described as fair, but in all other aspects the desired performance is achieved.
The amplifier comes complete with a water resistant cover and represents good value for money; particularly for those who want the robustness of solid-state but a valve sound.
Review by Bruce Gibbs
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