Jeff Rowland Conductor Phono Stage Preamplifier
The Conductor Phono Preamplifier was designed for the discriminating music listener to provide the highest quality playback of a wide variety of modern and vintage phonograph records. A versatile feature set permits the use of this preamplifier in any high-quality audio system.
The Conductor can be Ordered with One to Four Active Cartridge Inputs
Inputs 1,2, and 3 are dedicated for Moving Coil (MC) cartridges and Input 4 is dedicated only for Moving Magnet (MM) or High Output Moving Coil (HOMC) cartridge types. For example, this feature allows the use of phono turntables with multiple tonearms, each with a particular tonearm/cartridge combination optimized for the user’s unique preference or quality. Since each input preamplifier circuitry is independent from one another, each input can be optimized with regards to gain, loading and other parameters which will be explained later in this manual. Additionally, this feature allows input switching to occur at a higher “line-level signal” instead of switching at the microvolt signal level of a phono cartridge where signal degradation is more likely to occur. In whatever input configuration the Conductor is ordered, machined cover plates are installed over the unused inputs for an uncluttered rear panel look.
Both balanced (XLR) and unbalanced (RCA) interconnect options are provided for all MC inputs and main outputs. Only RCA input jacks are provided for the MM input option, however, all inputs and outputs are transformer-coupled for noise elimination and galvanic isolation. There is no gain difference between any paired balanced or unbalanced input or output.
The Conductor Incorporates Custom Made Input Transformers for All Inputs
These unique transformers, co-developed between Lundahl and JRDG, are wound with high purity copper wire sourced from Cardas Audio and specifically designed with a low turns ratio to ensure minimum copper losses and extremely low noise in conjunction with the active low noise circuitry directly following the transformers. A very low turns ratio was chosen to ensure the highest signal bandwidth possible since a higher turns ratio would limit bandwidth. A transformer cartridge interface prevents the input current of the first stage active circuitry from flowing through the connected phono cartridge coils, thus preventing the micro-magnetization of the connected cartridge. The active circuitry can thus have a defined and constant low impedance dc Current path, providing stable operating parameters independent of different connected cartridge types. The transformer also provides the ideal “coil to coil” balanced, ground isolated interface between the phono cartridge and active circuitry, offering an extremely high common-mode rejection of common-mode noise present on the unshielded tone-arm and interconnect wiring. Additional differential-mode noise filtering is also provided which prevents intermodulation distortion in the first gain stages of the amplification circuitry due to RF and EMI ingress. The transformer cartridge interface is provided with both XLR and RCA input connector types.
The Conductor can be ordered with two different types of input transformer core materials, standard or high-grade amorphous type.
Phono cartridge loading is performed by individual thin-film resistors inserted on the input transformer secondary with precision relays, selected by rear panel mounted toggle switches for easy switching. This loading resistor position allows maximum cartridge signal energization of the transformer primary without electrical energy being consumed by a direct connected load resistor. Fourteen individual loading values can be selected by choosing a particular switch combination listed in the Conductor Cartridge Loading Chart for Moving Coil Cartridges.
For each selected input, fully balanced, low noise, high gain, solid-state circuitry provides the necessary gain and equalization. The signal is maintained and amplified differentially to preserve a high common-mode noise rejection and provides excellent immunity from overload. All signal amplification is provided with a total of three wide-band, flat gain stages, optimized to maintain all distortion and noise products less than 100 dB below operating signal level throughout the full audio bandwidth. Equalization to conform to the RIAA standard and additional EQ curves are provided via hand-selected capacitors and 0.1 % thin-film resistors.
An optional handheld wired remote control box can be plugged into the rear panel of the Conductor to provide different equalization curves for playback of selected vintage recordings.
A two-pole (12 dB/octave) maximally flat high-pass filter is incorporated into the signal path for filtering out undesirable low-frequency turntable rumble signals. An internal switch is provided to insert an additional filter, which working in conjunction with the two-pole filter, provides an additional attenuation greater than 40 dB at 10 Hertz, a common tone-arm resonance frequency. The composite effect of these filters will have a minimal result on the audio pass-band with less than 3 dB of attenuation at 20 Hertz.
Any MC input can be modified for higher gain for use with low output phono cartridges. An additional 6 dB of gain is available. The gain increase is accomplished by connecting the input transformer primary windings in parallel for a higher turns ratio over standard. This allows extra gain without a significant increase of overall noise. A soldered jumper provides this change without compromising signal integrity.
Front panel pushbuttons provide selection of Input, Mute, Standby, Mono and Left minus Right functions. Functional definitions of these buttons will be covered in the Operation Manual.
The Conductor can be powered with two different external power supplies. For users that own the optional JRDG Model PSU power supply, the Conductor can be plugged into one of the unused PSU auxiliary DC outputs. The Model PPS-1 DC Power Supply can also be used to power the Conductor via its DC output connector. Both power supply options provide a fully regulated, low noise direct current power source for the Conductor and are designed to be switched on and off via the CONDUCTOR front panel Standby push button.
All of the active circuitry is elastomerically mounted within a chassis machined from a solid block of aircraft-grade 6061 bar stock aluminum, providing resonance control and shielding from external radio frequency interference. Each input amplifier/equalizer and output circuits are configured as individual “modules”, which can be exchanged, updated or modified as needed. All circuitry is strategically placed for the smallest possible “loop area”, utilizing precision 0.1% thin-film surface mount (SMD) componentry on four-layer circuit boards for the lowest possible noise, distortion and field interaction. Individual low-noise regulators independently power each input, output and filter sections, which, together with low noise external power supplies, eliminate all forms of noise from any source.
Both models of external power supplies assure quiet, reliable operation on all worldwide mains voltages.
To assist the break-in of all internal circuitry, an Inverse RIAA Network board is included with the Conductor. This device is installed between any line-level output such as a tuner or CD player and any active input of the Conductor. The line-level source signal is attenuated and pre-equalized such that it can be safely used to break-in the Conductor circuitry in much less time than simply playing phonograph records.
Gain: 42 dB MM, 52 dB High Output MC, 68 dB MC, 74dB Low Output MC
Max. Output Level: 16 V rms, balanced outputs
RIAA conformance. +/- 0.1dB, 30 Hz – 80kHz
S/N Ratio: 68 dB, ref. 0.5 mV@1 kHz, unweighted
THD: 0.0015%. 30 Hz – 20 kHz
CMRR: 110 dB, 20 Hz – 20kHz