Vox AC15CC1 "Custom Classic" Amplifier
A Look "Under the Hood"
2005 - 2010

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Introduced in 2005, the Vox AC15CC1 replaced the Vox AC15TB/TBX offered from 1995 to 2004. It was designed by then Vox lead engineer Steve Grindrod and manufactured for Vox by
the Sanecore Division of the International Audio Group of Shenzen China. The International Audio Group owned the Wharfedale brand, explaining the use of Wharfedale speakers during this period.

AC15CC1 Features
The AC15CC1 was a single channel, single input amp powered by two 12AX7 and two EL84 tubes. It included spring reverb, tremolo, and the traditional "Top Boost" tone control circuit.

The AC15CC1 had a box end steel chassis. The chassis was painted in semi-gloss black paint with silk screened control panel nomenclature. The chassis bolted to the amplifier cabinet with four large machine screws.

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. This allowed the AC15CC1 chassis to act as a heat sink for the tube sockets.

Printed Circuit Board Design
Most of the AC15CC1 circuitry was designed onto one main printed circuit board (PCB). This PCB included the power supply, preamp, tone control, reverb, tremolo and output amplifier circuits. Hand wired leads connected the main PCB to the tube sockets.

The rotary controls (Volume, Treble, Bass, Reverb, Tremolo Speed, Tremolo Depth and Master Volume) were mounted to a second PCB. The input, foot switch and speaker output jacks were mounted to three small PCBs. Multiple conductor cables interconnected the five boards.

Power Transformer
Vox produced four versions of the AC15CC1 chassis, each equipped with a power transformer that accommodated regional differences in mains AC voltage. The following chart details the part numbers of those power transformers.

Transformer P/N
Mains Voltage
100 VAC
United States
120 VAC
230 VAC
240 VAC

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. 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.

B+ Power Supply and the "SAG" Circuit
Prior to the 2005 introduction of the AC15CC1, the Vox AC-15 power supply always included a tube rectifier. The purpose of the tube rectifier was to convert the AC voltage from the B+ (HT) winding on the power transformer to DC.

While not directly in the audio signal path, the rectifier tube significantly affected the tone of the AC-15. When played at loud volumes, amps with rectifier tubes will exhibit a brief "sag" or dip in power supply voltage. These momentary sags in B+ voltage cause compression in the audio output of the amp. Many feel that this rectifier induced audio compression is an essential ingredient of Vox tone.

Vox hoped to design the AC15CC1 so that the street price of the amp might be less than $600. Such pricing would require trimming some costs. Part of the cost cutting involved the elimination of the tube rectifier. 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. He called the new design the "SAG" circuit.

The "SAG" circuit was simple in design. 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). When played at a high level, the SAG circuit caused the B+ voltage to drop, similar to the action of a tube rectifier.

DC Filament Heaters
The wires running between the 6.3 VAC filament tap on the power transformer and the tube sockets are typically twisted together. Twisting the filament wires cancels the electrical and magnetic fields eminating from the wires and reduces 60 hz hum in the audio output. 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.

Clever engineering solved this problem on the AC15CC1. A pair of diodes and a 0.22 uf capacitor were used to convert the filament voltage from 6.3 VAC to 6.3 VDC. The change to a DC filament supply eliminated the potential for filament induced hum in the audio output.

All Tube Signal Path
The AC15CC1 featured an all tube signal path. The signal from the input jack was preamplified by one half of V1a (12AX7). The classic "Top Boost" circuit (Bass and Treble controls) was powered by V1b. A second 12AX7 (V2), served as the phase inverter. Two EL84 output tubes (V3-V4) created the classic 15 watt Class A, NFB Vox AC-15 output stage.

Solid State Reverb and Tremolo Circuits
Both the reverb and tremolo circuits in the AC15CC1 were solid state.

The reverb drive signal was powered by a pair of NJM2147D integrated circuits. An M5201 integrated circuit powered the return signal from the three spring Belton 3EB3C1B short reverb pan.

The tremolo was powered by an MF2 integrated circuit.

The AC15CC1 had three fuses. FS4 was the main fuse and was located inside the AC receptacle. The 100 VAC version of the AC15C1 required a T1.6AL/250V, the 120 volt version required a T1.25AL 250V fuse, the 230 /240 volt versions required a T630mAL/250V. Two fuses were on the main circuit board. FS1 required a T250mAL/250v fuse for the B+ circuit. FS2 required a T6.3AL fuse to protect the heater filament (6.3V) circuit.


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Photos and editorial content courtesy Gary Hahlbeck, North Coast Music

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