Vox AC100, AC50 MASTER SECTION

Generally speaking the position of each control knob will influence the effect of the other two. Our

advice is to set the three controls at their midpoint positions and start from there. Experimentation

is the key to finding your tone. For starters turning the Middle control down will make the sound

more “hollow” particularly with high gain (distorted) settings, as typified on many modern heavy

rock songs. Turning the Middle up will make the tone fuller, smoother and produce a more “sing-

ing” tone. Adjust Bass & Treble to suit.

The PRESENCE control is often found on other rock oriented guitar amps. It normally functions

in the feedback circuit of the power amp to gently boost the presence frequency range (around 2

to 3kHz). This achieves the purpose of making the sound more lively and attacking, and originally

was used to compensate for dead sounding rooms and auditoria. But of course, we at VOX like

to do things a little differently than other amp companies: our Presence circuit combines the

traditional active power amp feedback circuit with a passive circuit within Channel 2’s preamp

that not only focuses the Presence boost but, by turning the control down, will introduce a high

frequency cut filter that can be used to de-fuzz the preamp distortion, making it less aggressive

and sweeter.

11. REVERB

This control regulates the amount of the on-board spring reverberation required for Channel 2

only. Please remember that the reverb is controlled ON or OFF by the footswitch as well!

12. VOLUME

This control is set at the end of the Channel 2 preamp circuit, before it goes to the FX Loop,

Reverb, and Power Amp sections. As such it governs how loud the sound generated by the

Channel 2 electronics will be. Obviously, low settings of the control will mean the amp will be

pretty quiet, and higher settings will mean total mayhem has broken out! As the total sound level

is controlled by both the Gain and Volume controls (and the Output Master, but more on this later)

you will need to balance both the level and character of the sound with both these controls.

MASTER SECTION

This control is what is called a Post Phase Inverter Master Volume (PPIMV) and is so called

because it operates in the power amplifier circuit between the output of the phase inverter valve

and the input of the power output valves. A great deal of the sound of a valve guitar amplifier is

actually generated by the phase inverter valve and therefore by using this type of design much of

the true power amp characteristics are retained when you use this type of Master Volume. I.e. it

keeps much of the true valve sound even at low levels of volume. In simple terms this control

regulates the actual power output produced by the power amplifier, so at lower levels it is akin to

playing through a low power valve amp. Another benefit of this type of circuit and control (as

mentioned in the introduction) is that the DI circuit is connected between the phase inverter valve

and the Output Master Volume. This not only gives the DI the tone of the power amp, but the DI

and power output control are totally independent.

The standby switch is used to a) turn the amplifier on or off for short durations such as breaks

when you do not want to go through the required warm up period, and b) it is used to alleviate

strain on the amp’s output valves when you are powering up from cold i.e. when warming up the

amp.

Historically the operation of the Standby switch is actually converse from its On & Off markings.

Standby OFF means that the amp is switched INTO Standby and the amplifier is not operating,

and Standby ON means the amp IS working. The Green LED indicator above the Standby switch

will illuminate when the amplifier is ON.