However, the connections to the tube sockets on the AC15CC1 passed through copper traces on a circuit board, making a twisted pair filament connection impossible.Ĭlever engineering solved this problem on the AC15CC1. Twisting the filament wires cancels the electrical and magnetic fields eminating from the wires and reduces 60 hz hum in the audio output. The wires running between the 6.3 VAC filament tap on the power transformer and the tube sockets are typically twisted together. When played at a high level, the SAG circuit caused the B+ voltage to drop, similar to the action of a tube rectifier. Rather than using a traditional diode bridge in the B+ circuit, the SAG circuit utilized a special center tapped B+ winding in the power transformer, two 82 ohm 5 watt resistors (R72 & R73) and two IN4007 silicon diodes (D5 & D6). He called the new design the "SAG" circuit. Vox lead engineer Steve Grindrod redesigned the AC15CC1 power supply to include a new solid state B+ supply that simulated the performance of a tube rectifier. Part of the cost cutting involved the elimination of the tube rectifier. Such pricing would require trimming some costs. Vox hoped to design the AC15CC1 so that the street price of the amp might be less than $600. Many feel that this rectifier induced audio compression is an essential ingredient of Vox tone. These momentary sags in B+ voltage cause compression in the audio output of the amp. When played at loud volumes, amps with rectifier tubes will exhibit a brief "sag" or dip in power supply voltage. While not directly in the audio signal path, the rectifier tube significantly affected the tone of the AC-15. The purpose of the tube rectifier was to convert the AC voltage from the B+ (HT) winding on the power transformer to DC. Prior to the 2005 introduction of the AC15CC1, the Vox AC-15 power supply always included a tube rectifier. In additional to a center tapped B+ (HT or high voltage) winding and filament heater winding, the AC15CC1 power transformer included an additional secondary winding to supply the solid state reverb and tremolo circuits. While the primary winding of the AC15CC1 power transformer varied to accommodate regional mains voltages, all four of the transformers listed above had identical secondary windings. The following chart details the part numbers of those power transformers. Vox produced four versions of the AC15CC1 chassis, each equipped with a power transformer that accommodated regional differences in mains AC voltage. Multiple conductor cables interconnected the five boards.
The input, foot switch and speaker output jacks were mounted to three small PCBs. The rotary controls (Volume, Treble, Bass, Reverb, Tremolo Speed, Tremolo Depth and Master Volume) were mounted to a second PCB. Hand wired leads connected the main PCB to the tube sockets. This PCB included the power supply, preamp, tone control, reverb, tremolo and output amplifier circuits. Most of the AC15CC1 circuitry was designed onto one main printed circuit board (PCB). This allowed the AC15CC1 chassis to act as a heat sink for the tube sockets. While the tube sockets of the AC15TB/TBX models that preceded the AC15CC1 were mounted directly to the fiberglass printed circuit boards, the tube sockets for the AC15CC1 were mounted to the steel chassis. The chassis bolted to the amplifier cabinet with four large machine screws. The chassis was painted in semi-gloss black paint with silk screened control panel nomenclature. It included spring reverb, tremolo, and the traditional "Top Boost" tone control circuit. The AC15CC1 was a single channel, single input amp powered by two 12AX7 and two EL84 tubes. The International Audio Group owned the Wharfedale brand, explaining the use of Wharfedale speakers during this period. The Sanecore Division of the International Audio Group of Shenzen China.
0 kommentar(er)
