The Commander tube linestage preamplifier is a product that has been anticipated for 5 years and with the last 20 months in earnest design. The idea was to deliver a fully realized, very sophisticated, cosmetically seductive and revolutionary cutting edge new design. It uses a pair of dual triode 12BH7 tubes as a first gain stage. It has a second pair of 12BH7s used to flip polarity. This is unique to this design and is discussed further in the technical highlight notes below. There is 1 XLR input, 3 RCA inputsa home theater bypass and a tape loop. There are also 2 variable RCA outputs, 1 XLR output and a fixed RCA output. Technical highlights of the commander design are listed below for review. Sonically the Commander achieves levels of resolution and sense of "realness" combined with levels of timbre, harmonics, tonality and a naturalness heretofore unknown in high end preamplifiers. Music is rendered with a delicacy, transparency and resolution never before experienced . Without realizing it you sometimes find yourself experiencing, even music heard many times before, from a completely different and new perspective. Even music that you may have not liked in the past can be reinterpreted due to the newfound resolution. If you are looking to reproduce a personal, subjective, overpretty sound then you best look elsewhere. The Commander is not an "old school" vintage sounding tube preamplifier. It is the epitome of current state-of-the-art, cutting edge music reproduction. If you are looking to create the sense of an absolute real performance then the Commander is the preamplifier for you. The Commander is completely designed in house and as with all other Wells Audio products completely hand built in the USA. There are 3 Commander models, the Commander, Commander Level II and Commander Level III.
Frequency response +0/-0.1db from 2Hz to 20kHz
Noise -92 db, 35uv wide band
Total Harmonic Distortion (THD): at 1k or at 20k 1.5v out = .05%
Max Output = > 10v
Channel Separation = 82db at 1kHz
Input Impedance: 25k Ohms nominal
Output Impedance = 200 Ohms
Inputs: 3 pair RCA unbalanced, 1 pair XLR unbalanced, 1 pair Tape-in, 1 pair Home Theater Bypass RCAs unbalanced
Outputs: 2 pair variable RCAs unbalanced, 1 pair variable XLR unbalanced, 1 pair fixed output RCAs
Operating Voltage: 120V, 240V at 50 or 60Hz
Dimensions: Shipping weight 20 pounds
Remote Control Functions: Volume up/ down, mute, polarity flip, H/T, aux 2, aux 3, aux 4, XLR input
Uses one gain stage: a simple 12BH7A triode. Our goal is to create the classic triode sound, using one of the most linear triodes ever made. Linear in this case means minimal high-order harmonics, the kind that produce irritation and listener fatigue. What remains is a small amount of mainly 2nd order harmonic in the distortion spectrum. The result is pure triode tonality.
Includes a phase inverter stage for inverting signal polarity by means of a 12BH7 split-load triode. The split-load triode is the closest thing to an ideal phase-splitter. It consists of a single triode that produces virtually identical frequency response and harmonic products when identical loads are used at the plate and cathode. Unlike most other phase-splitters, the sound of the split-load triode does not change significantly when the polarity is flipped. It is virtually transparent in either polarity.
To operate as an ideal phase-splitter the split-load triode must see identical loads at the plate and cathode. This is done by adding a buffer stage at the plate and cathode of the phase-splitter stage.
The buffer is a tube/transistor hybrid design. The transistor is the same one used in all Wells Audio output stages: a high power PNP made by Toshiba. It does the work of supplying current to the load, while the tube presents a high impedance to the phase-splitter.
All of the above stages are direct-coupled. Only one coupling cap is used at the output of the audio circuit.
Filament Power Supply & Regulator
The filament supply consists of two LT3081 regulator IC’s, recently introduced by Linear Technology. This state-of-the-art IC uses a current source to produce a reference voltage. There are no zeners or band-gap references in this IC. The current source is buffered by a voltage amplifier IC, which isolates the reference voltage from changes in the output voltage or load current. By this means, the LT3081 achieves a new benchmark in low noise and stability.
Each of the two filament regulators are located adjacent to the audio stages they supply. This minimizes trace inductance, which reduces ringing and overshoot in a regulator.
Plate Power Supply and Regulator
The high-voltage plate supply follows a similar concept, but is fully discrete. The plate supply is divided into four discrete elements or stages.
The first element is the rectifier and filter. Two filter caps are daisy-chained through a resistor to reduce ripple and noise, so the succeeding stages work less to filter the AC line than to regulate load current changes.
The second element in the plate supply is a reference-voltage circuit. Instead of zeners, a trio of LED’s are supplied a constant current, causing the LED’s to drop a fixed voltage. This voltage is used to lock down the plate voltage in the succeeding stages of the plate supply. The LED’s are yellow, the quietest type.
The third element in the plate supply consists of a dual MOSFET capacitance multiplier circuit, one for each channel. This circuit works in conjunction with small, low ESR electrolytic capacitors to produce a virtual capacitor of enormous size. The multiplier circuit acts as a buffer to isolate the phase-splitter and buffer from the gain stage.
The fourth element in the plate supply consists of a dual bipolar transistor capacitance multiplier circuit, one for each channel. This circuit works in conjunction with film capacitors for the fastest possible response. The circuit acts as a buffer to isolate the gain stage from the phase-splitter and buffer stages.
All of the above power supply stages are configured in a daisy chain, such that each element acts as a filter and isolator for the succeeding stage.
Each of the capacitance multiplier circuits are located adjacent to the audio stages they supply. This minimizes trace inductance, which reduces ringing and overshoot in a regulator. The capacitors used in the multiplier circuits have been tuned for minimal resonance into the trace inductance. This allows the multiplier circuits to remain rock stable while supplying current to fast-changing transients in the audio circuit.
Commander II Level II
The Commander Level II improves upon the already impressive performance of the Commander with Bybee AC purifers and Rike Capacitors best cap, the copper foil polypropylene paper-in-oil, as the output coupling capacitors. The noise floor is dramatically lower, dynamics are now more explosive than ever, resolution, timbre, harmonics, tonality and color are all increased. Everything is taken to the next level. The entire system benefits dramatically.
Commander II Level III
The Commander II Level III is our ultimate expression at the absolute state-of-the-art in preamplifier design and performance. Improvements to the Level II include all Vishay “naked Z foil” resistors in the entire signal path, cryo’ed Furutech IEC, Cryo’ed Cardas input and output RCAs and XLRs, Cryo’ed tubes, all PCBs and wire have been cryogenically treated, Bybee AC purifiers on all 3 AC legs, Vishay “naked Z foil” resistors for the series resistors on the shunt style Khozmo attenuator, Wells Audio innovative “Volumeter” with choice of blue, white or green backlighting and a custom designed polished solid brass meter bezel. No expense has been spared for this “all out” assault on the absolute pinnacle of preamplier design. We guarantee this to be the best preamplifier you have ever heard.