Smart Research SSL01/7 Channel Input Amplifier

High performance Mic and Line Amplifiers, Channel Switching and Buffers. Upgrade for SSL-E and -G series* Channel Modules. Easy to fit card.

The Input Card contains a significant part of the circuitry in each console channel module, and can therefore greatly influence overall module performance. Mic, line and insert return inputs and selector switching; channel fader selector switching; phase reverse circuitry and buffers feeding the record bus outputs all reside on this card. Operationally, our mic-amp offers 16; 4dB gain steps from +4dB to +64dB; and silent phantom power switching (the output mutes to avoid thumps). The card is easy to install by soldering a two wire link, and can be swapped back with no changes to the module. The measurements for the card appear on the following page, and to date (perhaps more importantly), all the opinions expressed to us by users have been favourable (most being surprised at a quite audible difference). The design philosophy has been to incorporate every factor that may yield beneficial performance; (detailed below) and score as highly as possible in each; the most crucial being the sound of the final circuitry. The design has been the result of some five years of research, a process that included surveying every op-amp and switch I.C currently available, with the final devices chosen through auditioning those short listed.

Subjective but potentially audible factors include the use of DC-servo amplifiers in all circuits to avoid electrolytic capacitors. Transformerless input. Removal of all wiring in gain critical areas of circuit. Mic amp gain is remote controlled, also allowing control from existing mic gain controls. Use of fet/transistor hybrid 'Butler' input op-amps. These are latest generation devices, and tend toward even harmonic distortion components. Total symmetry to minimise phase error in all balanced circuits. Use of latest generation electronic switches to reduce switch-on impedance and hence minimise switch colouration.

Measurable factors include: Noise floor. Distortion. Slew rate/frequency response. Headroom. Common Mode Rejection Ratio. Switch 'off' isolation.

We believe that the most significant factors affecting the audible performance in this case are slew rate, and switch 'off' isolation. The older NE5534 op-amp used in the existing channel has a quoted slew rate of 6v/µs with 22pf compensation; which can be further degraded by capacitors added to the feedback path to improve stability. The op-amp we use is unity gain stable, needing no compensation capacitors, and has a slew rate of 22v/µs; an almost four-fold improvement. With regard to the existing electronic switches, if signal transients approach within 5 volts of clipping they can break through the J-fets used. These devices also exhibit significant on-impedance. Both of these factors do not apply to the analogue switches used in our design. Examine the following figures yourself, and if you would be interested to hear the difference, please call us.

The following figures compare the Smart Research 01/7 Channel input amplifier to the original input card measured at Metropolis Audio (Australia). Note that these figures are not necessarily guaranteed for other situations. All figures are measured 22Hz-22KHz RMS at the channel insert send; for 3 gain or frequency settings as indicated in the graphs as 1,2 and 3.