Building a Guitar Amplifier (VOX AC30 Style)

The original AC30 has a tremolo built in. This replica was built on this circuit part is omitted. However, this amplifier has two different precursors are present.

 

In preamp 1 (normal channel) there is an EF86, or equivalent, tube for use. VOX also built a variant with this tube at the time. The sound (tone) can be found here, this circuit is also from VOX be taken over, influenced with a controller or switched off (bypass) become. A volume control (volume) is of course also for this channel exists.

 

Preamp 2 (top boost channel) essentially corresponds to a common current VOX precursor. Here there is a tone control for bass and one for Treble. There is a switch to switch from cool to hot. As for the normal channel, there is of course a volume control here too (volume).

 

The two pre-stage signals are added and an impedance converter (1/2 ECC83). The available afterwards „low resistance“ Guitar signal then goes to the main volume control (master volume).
Before that, there are two connectors accessible on the back available. Effect devices can be connected here (send, return). For further sound influence, there is a cut control in front of the power amplifier available.

 

The power amplifier consists of the classic VOX circuit with 4 EL84 units tubes. The quiescent current through the tubes is set lower (The individual cathode resistors have a value of 180 ohms, in the original 270 ohms). Thus, the tubes are protected and the heat development reduced.

 

There is a GZ34S for rectifying the anode voltages, or equivalents, tube. All transformers or chokes are original parts of the Hammond company.

 

The front panel is engraved and made of acrylic (two-tone, black/white). The design is modeled after an „Original AC30“. The speaker is a Celestion G12 Vintage 30.

 

 

The housing consists of 19mm thick 3-layer wood panels and wood profile strips. The speakers were covered with VOX-style diamond brown fabric. Tolex Taurus Vanilla was chosen as the case coating material and Keder Medium Black - 3.1 x 8.5 mm was chosen as the decorative strip (piping). All fittings (corners, handles, ..) are held in the VOX style.

 

I documented the entire construction process in great detail and even recorded it in a book (50 sheets, photo book in German).