Deutsche Version
About the EMT equalizer amplifiers
Frequency response of EMT eq amp's
The frequency responses of all EMT eq amp's are reduced in the lower range at 30Hz to avoid distortions caused by the tone arm resonances. Although you will find an adjustment potentiometer, it is not thought to adjust the frequency limit to adjust the linearity.
The frequency response in the treble range differs between the eq amp's. While it reaches up to about 80kHz at the EMT 155 it is limited down to about 22kHz for the EMT 153 and the eq amp' in the units EMT 938, 948 and 950. The reason for that is to avoid disturbing inductions when the unit was used near to AM broadcastings.
Is it possible to extend the frequency range?
It is possible to extend the frequency range in certain limits by replacing of different componentes. But it is recommended to do that by skilled persons. By the way: It may be interesting that one of the reasons for creating the F2 boards (for EMT 948 and EMT 950) was the research for extending the frequency range. But the F2 boards have also the advantages of a better x-talk, less distortion and lower noise.
Can the sound be improved by replacement of the operation amp's?
This question is often asked for the boards 7 950 038 and 7 950 039. When these boards had been developed the operational amplifier 741 was state of the art and is also today still not out of date. Nevertheless today there are operational amp's with shorter slew rates, higher frequency limits and lower noise. But they can't replace the 741 1:1 as most of them need a compensation which is not provided in the layout. If the compensation is passed on the circuit may start oscillating. As the oscillation frequency may be in an inaudible range you may not recognize it acoustically. But together with the audio frequency there will be audible distortions.
Also in this case I'd like to refer to the F2 boards which are equipped with operational amplifiers with much better data than the 741.