User Manual

RackPack: Premium Mic Pre

Triple Stage Preamp

The preamplifier circuitry of the Premium Mic Pre is composed of three

stages: a transformer, a discrete differential amplifier stage and an in-

strument preamplifier all contribute (in different shares) to the main

amplification. The three stage setup firstly ensures a load distribution

that minimizes the risk of overloads. Secondly, each stage can be op-

timally configured through select components and sophisticated cir-

cuits – a decisive advantage over single IC circuitries where the main

amplification is achieved by just one stage.

In addition, the potentiometer (as the control element of the differential

amplifier stage) only has to cover a range of approximately 68 dB while

the maximum amplification is at around 80 dB. In practice this means

that even very high amplification values are still outside of the extreme

control range positions – which are critical for any potentiometer.

Stage 1 – The Input Transformer

Inherent part of the Premium Mic Pre design are the input and output

transformers of the High Performance Series by Lundahl. These trans-

formers are lavishly handcrafted. They replace common input and

output balancing stages. These classic components offer a very high

sound quality and common mode rejection but they are also very reli-

able and provide connections and signals of superior quality.

Lundahl transformers have a very high reputation in terms of manu-

facturing quality and the resulting longevity as we have seen proven

impressively throughout many years of experience.

In any microphone preamplifier the input transformer is of special rel-

evance as it is an integral part of the preamp circuitry: it contributes

to the main amplification through a passive and permanent boost of,

in this case, 6 dB. The advantage of passive amplification over active

amplification is that it does not add any noise. A second advantage of

integrating this passive amplification is a signal processing that is, as a

matter of principle, lower in overdrive and noise throughout all follow-

ing stages simply because the rest of the electronic circuit is charged

with 6 dB less at any setting of the amplification.

In addition, transformers ensure a galvanic isolation, preventing any

disturbing or damaging voltages from being carried in any of the two

directions. Electromagnetic, high frequency or digital interference has

no more influence. Problems with humming e. g. in a live environment

that have been caused by differences in the potentials between the

stage and the FOH do not occur. >

Technology

Triple Stage Preamp, Stage 1 – The Input Transformer