IGS Audio Double Triode Limiter

The Double Triode Limiter (DTL) is an expanded version of the Double Triode microphone preamp.
The design was upgraded with a opto-limiter. The limiter is based on classic solutions used in the 60's and 70's. The component in charge of compression is a IGS Audio custom designed photocell. It consists of a electroluminescent panel and a photo resistor. This panel illuminates the photo resistor which reduces the audio path amplification. Limitation of the amplification is directly proportional to the light intensity in the photocell. The limiter threshold is indicated by a diode labeled “Limit” on the front panel.

Audio path of the preamp is a 2-steped tube amplifier with individual drive of both steps. The saturation of the first step is dependent on the input signal (with possibility to use Pad -20dB). The saturation of the second step is dependent on the Output regulator. Inputs and outputs are balanced with Sowter and Edcor (USA) transformers. The anode voltage is close to 300V DC.

For each of the channels Gain, Output and Limiter threshold can be regulated smoothly. The featured switches are: +48V, Mic/HiZ, Phase, Pad -20dB. Hiz inputs are located on the front panel. The meters show output signal level.