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It has become widely known that the output transformers in the Dynaco ST-70 and MK-3 are among the best ever made - easily better than the infamous Marantz 8B or any of the Macs. Used Dynaco Mark-3's, readily found for a few hundred dollars, can serve as the foundation of a truly reference tube amplifier capable of uncompromising musical performance. The fact that even simple upgrades in either the amplifier or power supply can provide significant improvement is testimony to their potential. We have realized this potential for nearly 20 years and have developed "no compromise" design that takes advantage of the transformers by addressing the limits in both the original driver amplifier and power supply. Although they are independent, each contribute to the final result. Please Note : Although our power amplifier modules have been used successfully in many other power amplifiers (including the highly acclaimed Sonic Frontiers units), they have been optimized both electrically and physically for Dynaco amplifiers. Accordingly, please consult us to discuss other specific amplifier applications. |
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The PWB-1A and ASM-1A (unassembled or assembled for the Mark-3) is a precision vacuum tube differential amplifier driver stage system. An all triode design it uses a cascode differential amplifier topology supported by a unique active current source at the cathodes. The cathodes effectively "see" a 3M resistor and "share" 99.996% of the current resulting in unparalleled phase inversion accuracy. A key factor in its performance is the totally direct coupled topology (except high quality output capacitor), that results in exceptional stability, low noise, and wide bandwidth. Open loop frequency response extends from 1Hz to 90 KHz!. This results in an ultra stable design that is both conditionally and unconditionally stable (no spurious instabilities when driving the output stage). This stability has another benefit - it is very tolerant of a wide range of tube parameters - you may substitute nearly any 9 pin miniature twin triode such as the 6N1P, 6922, 6DJ8, 7308, 6CG7, and others. This proprietary driver technology has evolved over many years of designing, building, testing, and auditioning both traditional and unorthodox circuit topologies. It provides an unprecedented degree of musical information, neither sterile nor subjectively warm while retaining dynamic contrasts and resolution. Subtle variations can be easily realized with the quick substitution of tube types and output capacitors. The module incorporates our proprietary Wide Bandwidth / Low Impedance (Z) HV-B+ regulator to insure that the purity and musicality of our audio amplifier is preserved and not modulated by power supply voicing. Our regulator has been extensively developed, tested, and auditioned to be completely "inert" sonically. You may want to review our white paper on the "Audibility of Power Supplies" for an in depth discussion of the significance of the power supply in the overall performance of the amplifier. Equally important, its noise level is so low that you can easily operate the your amplifier open loop (without feedback) without any trace of noise or hum. It can easily be incorporated into nearly any DIY amplifier project using a PP or PP parallel output configuration. It has been used successfully in many other power amplifiers (including the highly acclaimed Sonic Frontiers units). Please feel free to consult us for other specific amplifier applications. The board is exactly the same size as the original Dynaco 6AN8 driver board so that no extra holes need to be drilled or cut - simply remove the old board and "drop" it in. The MK-3 premium drive module is available in blank board, kit (blank board with all components), or fully assembled & tested versions. Additionally, for those choosing to purchase the unassembled board, we will offer our "Semi-Pac" that is a complete package of all of the required semiconductors (diodes, IC's, transistors). ORDERING INFORMATION Blank Board Pair, MK-3 Driver Amp : P/N PWB-1A = $80 / pair Semi-Pac Pair, MK-3 Driver Board : P/N SEMI-1A = $35 / pair Full Kit (Board & All Components w/o Tubes): P/N KIT-1A = $395 / pair Assembled Board (Includes All Components w/o Tubes) : P/N ASM-1A = $470 / pair Driver Tube Option, 4 Premium 6922 Dual Triodes (OPT-V-4) = $64 |
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The PWB-M3P (unassembled) and ASM-M3P (assembled) is a complete power supply and Wide Bandwidth / Low Z regulation system specifically designed to support the Dynaco Mark-3 power amplifier. It includes HV rectification to support the entire amplifier and three regulators (Plate HV supply, Screen Grid HV supply, and Bias Supply) to maintain a consistent and near infinite current supply for the Output Stage(s). Also included is a Complete Bias Supply - rectification, filtering, zener diode regulation, and adjustment potentiometers. The adjustment potentiometers and test points are conveniently placed to appear at the front of the amplifier to simplify setting the bias. Our Plate and Screen Grid regulators are our proprietary Hi-Speed Low-Z designs that are the result of extensive development and refinement. They are "Audibly Inert" allowing the audio circuitry to "speak" with its own clear voice. Typical "cookbook" HV regulators have an uneven impedance curve (adding the same signature voice) and ring terribly upon high frequency transients (resulting in harshness). Our regulators have been optimized not only for Low Impedance (Z) but maintain that impedance consistently from DC to 1MHz. More importantly, the circuitry is damped optimally so that there is absolutely no ringing under any circumstances. The result is a completely inert power supply that neither adds nor subtracts from the amplifier circuit but delivers instantaneously the current required. For a more thorough discussion, please refer to our white paper "The Audibility of Power Supplies". With stable regulation, after you turn on your amplifier, the operation of the output stage bias quickly reaches and maintains the desired operating point and will continue over the full lifetime of the tubes. The benefit is "set & forget" biasing (90 days) and significantly extended tube life (since bias currents do not drift unknowingly upward). In addition, your amplifier will sound the same, day to day, over the full lifetime of the output tubes. Installation is very easy - the PWB / ASM -M3P module is designed to physically "Drop In" to the bottom of the MK-3 chassis (on 1" standoffs) using existing holes - no drilling cutting or hanging appendages. All the connections from the power transformer, "Quad" filter capacitor, and other power supply connections terminate on the module - its easier that the building the original MK-3. The MK-3 premium drive module is available in blank board, kit (blank board with all components), or fully assembled & tested versions. Additionally, for those choosing to purchase the unassembled board, we will offer our "Semi-Pac" that is a complete package of all of the required semiconductors (diodes, IC's, transistors). ORDERING INFORMATION Blank Board Pair, MK-3 Pwr / Reg : P/N PWB-M3P = $89 Semi-Pac, MK-3 Pwr / Reg : P/N SEMI-M3P = $122 Premium Semi-Pac, MK-3 Pwr/Reg: P/N PSEMI-MP3 = $137 Full Kit (Board & All Components): P/N KIT-M3P = $395 Assembled Bd. Pair, MK-3 Pwr / Reg : P/N ASM-M3P = $475 |
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