The Amdek Tuning Amp is an accurate, crystal controlled, reference device which can be assembled with the minimum of technical difficulty.

★ 220, 440, 880Hz outputs
★ Internal amplifier
★ Headphone output
★ Battery operated
★ Pre-assembled circuit board
★ Complete kit with detailed instructions

Accurate tuning to some form of known reference is essential in music, be it for musicians playing together or one person multitracking.

Amdek's Tuning Amp is a handy little unit which can provide precise, crystal controlled, frequencies of 220, 440 and 880Hz. The tones go through an amplifier and are then output to the internal speaker, or headphones, if required.

An input, via a standard jack, allows instruments, such as guitar or keyboards, to be connected and tuned audibly. Switching off the tuning note allows the device to become a small practice amplifier.

The Kit

The Tuning Amp is supplied in a bubble pack, complete with all the parts necessary for construction. Tools required are: a 15-30W soldering iron, wirestrippers/cutter; crosshead screwdriver and a small pair of pointed nose pliers. All the connecting wire and solder required is supplied in the kit.

Parts should be laid out on a clear surface and checked off against the list in the assembly manual. Once this has been done assembly of the unit can be started.

The first steps involve connecting wires to the controls and socket. Three leads are cut to length, stripped, tinned and then attached to the Volume control. Another four leads are prepared and attached to the headphone jack. A further six leads are prepared and attached to the Mode select switch. A white lead is also cut, stripped and soldered to the -Ve terminal of the speaker (Steps 1-5). The PP3 battery snap connector and LED leads are then stripped and tinned.

PCB preparation is next. During the flow-soldering process used in manufacturer of the PCB, the eyelet holes have been partially filled with solder. However, more solder should be applied, where necessary, to make a raised dome on each eyelet. This helps make a clean joint where wires are attached.

All the wires, when prepared, can now be connected to the board, as shown in the assembly manual. Also connect the purple wire from the headphone jack to the +ve terminal of the speaker. This completes all the soldering iron work (Steps 6-9).

The LED holder should be inserted and the speaker grille clipped in place. After slipping the locking ring over the LED, the LED can be clipped in place and locked with the ring. Mount the headphone jack next with a toothed washer, plain washer and nut.

After the detention key stud has been broken off the Volume pot it can be mounted, along with the Mode select switch into the case. Secure using washers and nuts (Steps 10-15).

The speaker should be placed inside the case on the grille and the small piece of sponge pushed into the PCB opposite. Inserting the PCB into the case, and locking with the nuts and washers on the DC and input sockets, retains the speaker. When this has been done the clear insulation sheet can be added to the bottom plate to protect the circuitry from shorts on the solder side.

To prevent the case from slipping, when used on a smooth surface, stick the rubber pad onto the other side of the bottom plate and using four M3 x 10mm screws attach the plate to the Case.

Once a PP3 battery has been inserted and the rubber battery cover fitted the two control knobs can be pushed on to the pots to finish the unit (Steps 16-22).

The Circuit

The circuit diagram of the Tuner Amp is shown in Figure 1.

Input signals are pre-amplified by the circuitry around Q1 and Q2. This amplifier has a frequency response characteristic most suited to the electric guitar. Signals from this pre-amp are mixed with tones from the crystal oscillator IC1, via the Volume control, and then sent to the audio amplifier, NJM386N Output from the amplifier goes to the internal speaker unless headphones are connected via the jack socket.

The four way Mode select switch makes the unit operational and selects: Amplifier, 220, 440 or 880Hz.

Operation

The unit worked first time and produced a pure tone on each frequency setting. With an instrument connected the amplifier produced a clear sound, adequate for quiet practice and headphone use.

Should you have any problems contact the Roland 'Hot-line' at the UK factory. (Contact Details).

Modifications

One modification which Amdek suggest is to disconnect the pre-amplifier, by removing R25 and C16 and linking R23 to C15, to provide a flatter frequency response ranging from 100Hz to 250kHz.

E&MM's special offer price for the Amdek Tuning Amp Kit is £35.75 inc. VAT and P&P. Please order as: Amdek TAK-100.