Test Report on: Phase Linear 4000 Auto Correlation Pre-Amp.
Date: June 1975 £340.00 Ex VAT.
The Phase Linear 4000 is a high fidelity pre-amplifier of a more sophisticated type than usual.
The pre-amplifier can take its input signal from any one of five sources. The selected source can be one of two magnetic pick-up cartridges, an auxiliary, as with a radio tuner, a second radio tuner or a tape recorder. Provision is made for a second tape recorder so that recordings can be transferred from one to the other. The bass and treble controls for the left and right channels are separate, which seems odd. I can't imagine wanting different tone settings on the two sides. Both bass and treble controls are 11 position switches not the normal continuously variable type, and there is an additional switch for each which makes it work from the centre of the audio range or just control the extreme end, leaving the middle flat.
The most interesting feature of the amplifier is a noise suppression system using 'auto-correlation' technique.
This is as effective as the Dolby noise reduction system but different. The auto-correlation can be used with a tape recorder which is already fitted with a Dolby system and the overall noise reduction will be a cumulative effect.
The second most interesting feature is the inclusion of an S.Q. quadraphonic decoder, a joystick type balance control and the associated front and rear, left and right outputs.
Even this is not the end of the features. A third one is a volume expander which can undo the volume compression which often has to be used in the recording process to reduce signals of exceptional dynamic range to a relatively constant signal level suitable for recording.
The construction is of standard 19 inch rack format with a totally enclosed electronic box mounted behind a beautiful satin chrome front panel. All the knobs and switches are also satin finish and of large proportions giving a very solid but space age appearance.
The inside of this large box is very full of "works". There are a total of 14 glass fibre printed circuit boards which carry all the components including the front panel switches and the input and output sockets on the back. Two of the boards are "mother board" which carry edgeway connectors into which the other boards plug. This technique almost does away with conventional wiring.
Components are all of good quality and soldered joints are good. The input and output connectors are phono plugs; and two stereo jack sockets are provided on the front panel for additional outputs.
The noise reduction system and volume expansion unit, which we would particularly have liked to test fully, could only be given a qualitative test. Both these systems seemed to work very well.
|Parameter ||RESULT ||TEST CONDITIONS ||COMMENTS |
|Phono 1 ||1.1m VRMS ||Test signal a ||Expressed in dBm, the |
|Phono 2 ||1.1mV ||1KHz for an ||levels are 1.1mV = ~57dBm |
|Aux ||118mV ||output level of 0dBm. ||and 118mV = -16.3dBm |
|Tuner ||119mV ||Volume control at ||good sensitivity |
|Tape 2 ||116mV ||maximum. |
Noise Referred to iP
|Phono 1 ||-155dBm ||Wideband ||Good |
|Phono 2 ||-153dBm ||measurements |
|Aux ||-92dBm ||for one channel |
|Tuner ||-92dBm ||with 47Ka dummy source |
|Tape 2 ||-92dBm |
|Phono iP ||-19dB ||This is the amount of L.H. which ||Not at all good |
|Aux iP ||-41.5dB ||breaks into the R.H. and R.H. channel ||on phono. |
| || ||which gets in to the L.H. one |
|+10.0dB ||Boost Selector switch set |
| ||-15.5dB ||Cut to 2KHz and test at 20KHz |
| ||+3.7 dB ||Boost Selector switch set |
| ||-8dB ||Cut to 8Kh and test at 20KHz |
|+8.5dB ||Boost Select set to 150Hz ||Less range than |
| ||-7dB ||Cut and tested at 40Hz ||conventional tone controls |
| ||+4.5dB ||Boost Select set to 40Hz |
| ||-4.8dB ||Cut and tested at 40Hz |
|Square Wave || || ||Good and dean |
Output level at clipping
|9.7 VRMS (+22dBm) || ||Good |
|0.08% ||Phono 0dBm output level |
| ||0.14% ||Aux on 1KHz test sig. |
|20Hz to greater than 100KHz |
- far greater than necessary
Our Overall impression of this unit is favourable. The standard of construction is good and the performance is good in most respects. We regret not being able to test the star feature: the noise reduction system - maybe some other time. In this country and in the whole of Europe, an AC mains wire should be brown, blue and green/yellow. The Phase Linear has a mains wire of good quality but colour coded black, white and green. With a little common sense, it can be determined which wire goes Where, but guess work should not be necessary on something as important to safety as this.