Case No. 7) Ming Da MC300-AA 300B Amplifier 
We performed a Basic Upgrade and Modification on this Ming Da MC300-AA amplifier. When it was new, the amplifier delivered satisfactory performance and gave it's owner the best bang for the buck given it's modest price point. However, the amplifier's performance deteriorated quickly when the modest internal components began to fail under its rather aggressive design. The Basic Upgrade and Modification was necessary to ensure longevity and continual safe operation of the amplifier.  Click to Enlarge Here is a comprehensive list of what we performed in order to bring the amplifier back to its original specification, using "non-exotic" consumer grade parts which were made in USA or Canada. Installed Soft Start circuitry to eliminate start up stress and noise Added driver stage decoupling noise filter capacitor to the circuit which greatly reduced noise and improved S/N Ratio Biasing circuit: Replaced factory capacitors which were under-rated causing leakage and "ballooning" (self expanding like a balloon) Biasing resistor: Replaced factory 10W resistors which were under-rated, with 25W ceramic resistors. The original resistors were under-rated by a huge margin and were burning up due to excessive heat. We replaced 2 defective diode bridge which were burned up due to excessive heat. We reduced the input sensitivity from 0.2 to 0.4V which dramatically reduced noise and improved S/N ratio. Heater Voltage: The filament voltage for the tubes were 20% above tolerance limits ! We adjusted the filament voltage to a proper 5.0 V, and also changed the filter E-Cap from 10000uf to 27000uf. We installed / changed the filament voltage from AC to DC. We removed and properly remounted certain components which were improperly "glued" to the chassis. This is a manufacturing shortcut which must be rectified as it posed a safety hazard to consumers. We replaced the internal wirings of certain signal paths with Teflon coated silver wiring. We replaced low quality components at certain crucial signal paths with higher quality components.
The upgraded / modified amplifier was bench tested to exceed original factory specification. We believe that simply replacing your amplifier with exotic parts without correcting the inherent weakness in its design, will do nothing to improve its sonic performance. Inadequate areas of the circuitry must be corrected in accordance with the fundamental principles of electronics, otherwise the money spent on exotic component upgrades will completely wasted. Total Cost of Upgrade/Modificatoin : $ 450 dollars including parts Turnaround Time: 7 days | 
