LDR1 & LDR6 Operating Manual – Rev 1
Tortuga Audio
Page: 1
Terminology
LDRx:
When features and operation are common to both the LDR1 and LDR6
reference will be made to the LDRx.
Overview
Passive Preamp:
The LDRx Passive Preamplifier is a unity gain (i.e. passive – no
amplification) attenuator.
The LDR6 has 6 selectable unbalanced RCA stereo line stage inputs and a single
unbalanced RCA stereo output.
The LDR1 has a single unbalanced RCA stereo line stage input and dual unbalanced
RCA stereo outputs.
The LDRx can be operated via the rotary encoder/pushbutton switch on the front
panel and via an infrared remote. Unless explicitly noted, either control has
identical functionality.
Why call it a “preamplifier” if it doesn’t amplify? It’s a matter of convention as much
as anything. Historically, a “preamp” is the device upstream of the amplifier which
allows for selecting the input source (CD, DAC, Phono etc.), adjusting volume, and in
some cases adjusting channel balance and tone control. Most preamplifiers also
provides some degree of active amplification or buffering between the source
device and the amplifier. A truly passive preamplifier neither amplifies nor buffers.
The LDRx Passive Preamplifier is passive in the truest sense. Perfectly manifested,
the perfect preamplifier does nothing to the audio signal other than to attenuate its
strength (i.e. control volume). No coloration. No added anything. And ideally,
nothing removed either. Getting out of the way to let the music through the way it
was recorded - the perfect preamp.
Audio Taper:
The LDRx is a stepped attenuator with 70 discrete steps between 0 db
and -60db where step 0 triggers full muting of the incoming signal. The LDRx
emulates a ~100k potentiometer using the conventional L-Pad configuration. The
audio taper of the LDRx is logarithmic as shown in the graphic below.
Note that approximately the last 10 dB of attenuation leading up to full volume
follow a more granular increments than the previous 50 dB. This feature smooths
out the incremental volume increases as you approach max volume where even a 1
dB steps can result in very noticeable increases in sound pressure levels.
