Guitar Practice Accompaniment Drummer

A close look at this circuit would show its apparent similarity with the last project. In fact it is a mixture of the project number four and three. It should be a welcome relief to all those amateur guitarists who have so far been at the mercy of their  drummer for their practice. This low cost device does many tricks that its expensive big brother automatic drummer does. It produces a bass drum sound on any every beat and can provide a woodblock sound on any of the two different beats in a bar. These beats may be adjusted to be simultaneous or separated depending upon the positions of potentio-meters R1,R5 and R8. the circuit diagram is given in figure 5. Here transistor Q1 provides the basic timing pulses which are coupled through R20 and C7 to the base of a two transistor Twin-T oscillator whose feedback components are so chosen as to give the sound of a bass drum, when shocked into oscillations. The pulse on R1 is also utilized as in last project to deposit charges on capacitors C2 and C3 through isolating diodes D1 and D3. When available, capacitors C2 and C3 should be of the low leakage tantalum type. The amplitudes of charges across C2 and C3 increase with every successive pulse from the clock generator. At some point during the voltage build up Q2 and Q3 fire, either simultaneously or independently and rapidly discharges C2 and C3 respectively.the 

Guitar Practice Accompaniment Drummer

circuit diagram

resulting pulses that appear across R7 and R10 are then coupled to the base  of the woodblock oscillator through isolating diodes D2 and D4. potentiometers R5 and R8 can be varied independently so that frequency dividers Q2 and Q3 fire at different rates to produce a wide variety of syncopated rhythms. The two Twin-T oscillators are almost identical in operation consisting of one common emitter and one emitter follower circuits. Presets R19 and R29 are so adjusted that with no pulse applied to these transistors there is no continuous oscillation. A slight shock like that given from a pulse should be sufficient to cause its oscillation which should then decay naturally. By varying the value of components in Twin-T oscillators shown below each transistor pair other instruments may be imitated. The balance potentiometer adjusts the balance between the sounds of the bass drum and the woodblock. The output should be fed into the auxiliary amplifier.