Amdek Metronome Kit
Build and modify this accurate timing reference unit
The Amdek Metronome is an accurate reference device which can be assembled and modified with the minimum of technical difficulty.
A timing reference is essential when recording a piece of music, to help the musician keep each of the constituent parts in sync.
The Amdek Metronome can provide this reference with an accurate 40-208 beat range. Six timing patterns are provided which cause a downbeat 'chime' to occur on the 2nd, 3rd, 4th, 5th or 6th beat. This can help to establish 3/4, 4/4 or even 5/4 rhythms. Down beat is indicated with a red LED while beats are indicated by a green.
The Metronome is supplied in a bubble pack, complete with all the parts necessary for its construction. Tools required to do this are: a 15-30W soldering iron; wirestrippers/cutter; crosshead screwdrivers 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. Three leads are cut to length, stripped, tinned and then attached to the Tempo control. Another seven leads are prepared and attached to the beat selector switch. A further two leads are prepared and connected to the volume control, along with the leads from piezo-electric buzzer (Steps 1-4).
Power connections are made next by cutting, stripping and tinning the PP3 battery snap connector and a length of wire, which are then attached to the on/off switch. The two LEDs have leads already attached, but are prepared by twisting their black leads together before being tinned.
PCB preparation is next. During the flow-soldering process used in manufacture 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 when wires are attached.
All the wires, when prepared, can now be connected to the board, as shown in the assembly manual. This completes all the soldering-iron work (Steps 5-8).
The slide control and power switch are mounted on a small subchassis using four M2 x 3mm screws — a miniature crosspoint screwdriver is required here. Amdek suggest that the dust cover for the slider is stuck on top of the screws but it appears to be better to attach it first, then put the screws in.
Two holders for the LEDs are clipped into place and the LEDs inserted — not forgetting to put the locking rings over the LEDs first. The locking ring can now be used to secure the assembly.
After the detention key stud has been broken off the Tempo pot it can be mounted on the case and secured using a nut and washer. The beat selector slide switch can also be attached after sticking the dust cover to the inside of the case. Two M2.6x4 screws are used.
Another two screws are used to fix the subchassis to the casing. The ones supplied, however, are M3 x 10 countersunk which seems to be a mistake, since, not only are these too long but the holes in the case are not countersunk. This results in an untidy appearance not usually found in Amdek products. To rectify this you should either carefully countersink-drill the casing or use suitable pan head screws.
The piezo-electric buzzer is attached to the casing using a double sided adhesive pad. It should be placed so that the hole in the buzzer aligns with the one in the casing.
All the knobs can now be fitted, aligning the Tempo knob with the letter 'E' in EMK-100. Once a battery has been inserted the unit can be tested. (Steps 9-17).
The beat rate is set by two pre-sets on the board which will have to be set for accurate operation. VR1 adjusts the lowest beat frequency and VR2 the range. To calibrate the unit set the tempo rate to 180 on the dial and select a beat of 3. Using a watch or timer count the number of downbeats in 60 secs and adjust VR2 for 60 or one each second. Then set Tempo rate to 60, beat to 0 and repeat the process using VR1. Since the pre sets are interactive adjustment will have to be continuously repeated until accurate calibration results. An accuracy of ±3% can be obtained in this manner.
When calibrated the unit can be finished by fitting the PCB into the case using a piece of sponge to insulate it from the controls. An insulation sheet stuck to the base panel also prevents any shorts on the solder side. Once the rubber pad has been attached to base the case can be screwed together (Steps 18-20).
A circuit diagram for the Metronome is shown in Figure 1.
The main clock is based around IC1, a 555 timer. The supply to this chip is provided by the series-pass regulator Q5, D5, R22 and C11. This makes the timing essentially independent of battery voltage levels and temperature changes. Timing is set by the tempo pot, VR2 and VR1 which allow C9 to charge up to the discharge threshold.
The output at pin 3 drives the green LED via Q5, the beat voice via C7 and the down beat counter, IC2, via Q4. This counter is a ring counter with 8 outputs, each output going high on a clock pulse. The reset of the counter is set by the beat slider switch. The Q1 output, pin 1, provides the downbeat signal which drives the red LED via Q7 and the 'chime' voice via C5.
The 'beat' voice is based around Q1, and the 'chime' voice is generated by two CMOS gates and buffered by Q2. These are mixed via D1 and D2 and fed to the piezo buzzer, driven by two CMOS invertors, the level being adjusted by the slider pot.
Some modifications which can be made are listed below. These should be carried out with care and may effect any guarantee supplied by Amdek.
Mod 1. To change the pitch of the 'chime' voice, C4 can be replaced. A lower value will produce a higher pitch and higher value will produce a lower pitch.
Mod 2. To change the decay rate of the 'chime', R8 can be replaced. A lower value will shorten the sound and a higher value will lengthen it.
Mod 3. A 5 V positive going clock pulse approx 35mS in length is preset at pin 14 of IC2. This could be connected to a jack socket, fitted by drilling a hole in the case, allowing the metronome to become a master clock to drive a sequencer, arpeggiator or rhythm machine — and therefore allowing accurate tempos to be set.
E&MM's special offer price for the Amdek Metronome Kit is £28.00 inc. VAT and P&P. Please order as: Amdek EMK-100.
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