Specifications



Aretha MKII has proven to be a very popular preamplifier, hand built to the finest standards, using the venerable 6SL7 triode, one of the best octal preamp tubes available.
We chose this tube due to its high gain factor and classic sound, which allowed us to design this circuit with just two tubes per channel, yet giving the listener unparalleled tone quality and listening pleasure.
There are literally 1000's of NOS 6SL7's available, allowing the user to try out many different brands with varying carachteristics of this classic preamp tube, also known as tube rolling, which can have a positive effect to the overall sound of this preamp.
Aretha is shipped with a quad set of factory new matched 6SL7's, or, we can use client supplied 6SL7's.
Please note, it will take time for these factory new 6SL7's to settle in and mellow, generally about 50-100hrs.


Circuit:
Aretha MKII is a Baxandall tone control preamplifier in a classic cathode follower circuit with a tube output buffer. The tone controls allow the user to adjust for not-so-perfect recordings and to compensate for room acoustics. With the tone controls in the cut/center position, there is no influence to the signal. See below graph for tone control range.
If the Tone Defeat option is chosen, the Baxandall circuit is completely bypassed, resulting in a classisc line preamp.

Care was taken in this design to keep the circuit as straightforward as possible to avoid manipulating the signal more than is strictly necessary. The result is this outstanding tone control preamplifier.


Power Supply:
We have completely re designed the high volatge B+ power supply, using a far superior MOSFET based circuit, resulting in a more stable and extremely low noise B+!
The regulated DC filament supply is based on the excellent LD1085 voltage regulator.

The power transformer is our own design and custom made for us, low noise toroidal unit.

A 120V/240VAC 60/50Hz selector switch on the rear panel allows Aretha MKII to be used anywhere in the world.


Components:
Only high quality components are used in the construction of Aretha MKII. Low-noise Vishay +/-1% variation metal film resistors are used throughout the signal circuit with high quality Panasonic metal oxide resistors in the power supply circuit. WIMA film and Wurth electrolytic capacitors are used throughout. Coupling capacitors are Mundorf MCap EVO series.

The volume and balance controls are high precision 59 step attenuator, made up with 1% SMT metal film resistors with a range of -60dB to 0dB. It's body is CNC machined aluminum.

The printed circuit boards are designed in house , manufactured to FR4-TG standards, and are double-layer with full ground planes on both sides to ensure complete screening of the circuits.

RCA sockets are gold plated and mounted directly onto their dedicated printed circuit board, which also carries the selector switch keeping wiring within the preamp to an absolute minimum. The selector switch is connected via a stainless steel shaft and supported by a miniature ball bearing running through the front panel to the selector knob.

Tubes are factory new quad set of matched  6SL7's or NOS 6SL7's depending on availabillity of factory new tubes.

General specs:
Main preamplifier gain with tone controls centered - 12dB (x4)
Frequency response is  20Hz to 30KHz, +/-0.1dB
Output impedance, 625 OHMS; Input impedance 1M
Tone controls, boost and cut of 12dB
Power consumption: 34W
Chassis size: 14.5"W x 13"D x 7"H
Weight: 12lb