Power Supply for Homemade Synth Two Channel 555 timer and lm386

Thread Starter

Adam Monarch

Joined Mar 17, 2019
35
I am designing a two note synth using two channels...
Channel 1 = 555 timer in series with a lm386
Channel 2 = 555 timer in series with a lm386
I have built the circuit and it works with a separate 9 volt (variable) power supply for each channel rendering 0 amps on both power supplies.
What I will like to do is use one power supply for both channel 1 and channel 2.
I shared a node of vcc and ground for both channel 1 and channel 2.
I tried using a single variable dc power supply on both channels and I ended up measuring close to 1 amphere
on the amm meter on the variable dc supply and turned the voltage down before overloading the circuit.
Channel 1 and channel 2 have separate 8 ohm speaker outputs. I also hooked each output up to a mixer with headphones so I do not irritate the neighbors and disconnected the 8 ohm speakers. I continued to hook up my oscilloscope to measure the frequency of the waveform.
Can some please tell me the best solution for this problem.
Thanks
 
Last edited:

Audioguru

Joined Dec 20, 2007
11,251
Your LM386 amplifiers are probably oscillating at a high frequency which causes them to use a high supply current because they are missing the important RC Zobel networks at their outputs as shown on every circuit in the datasheet.

The input signal level is WAY TOO HIGH since the 555 output with a 9V supply is a squarewave that is 7.3V peak-to-peak but the maximum input to the LM386 for full output level is only 0.12V peak-to-peak. Add an attenuator to reduce the 7.3V to 0.12V.

How can your squarewave "buzzer" irritate the neighbours when an LM386 output when powered from only 9V and driving an 8 ohm speaker is only about 1W (0.5W for the fundamental frequency and another 0.5W for all the distortion harmonics).
 

Tonyr1084

Joined Sep 24, 2015
3,470
I have built the circuit and it works with a separate 9 volt (variable) power supply for each channel rendering 0 amps on both power supplies.
Nine volts with zero amps? What am I missing here? How can you have zero amps and have an amplifier that does something? Anything? The 9V batteries sitting in my stock closet are using zero amps. They're also doing nothing. So what am I missing here?
 

Thread Starter

Adam Monarch

Joined Mar 17, 2019
35
Nine volts with zero amps? What am I missing here? How can you have zero amps and have an amplifier that does something? Anything? The 9V batteries sitting in my stock closet are using zero amps. They're also doing nothing. So what am I missing here?
I was referring to the amphere readout on the variable dc power supply. The variable dc power supply has a voltage reading and an amphere reading. The amphere reading on the variable dc voltage supply usually reads 0 amps. If the variable dc power supply has a reading of 100mA
or more this indicates that there is something wrong with the circuit.
 

Thread Starter

Adam Monarch

Joined Mar 17, 2019
35
Your LM386 amplifiers are probably oscillating at a high frequency which causes them to use a high supply current because they are missing the important RC Zobel networks at their outputs as shown on every circuit in the datasheet.

The input signal level is WAY TOO HIGH since the 555 output with a 9V supply is a squarewave that is 7.3V peak-to-peak but the maximum input to the LM386 for full output level is only 0.12V peak-to-peak. Add an attenuator to reduce the 7.3V to 0.12V.

How can your squarewave "buzzer" irritate the neighbours when an LM386 output when powered from only 9V and driving an 8 ohm speaker is only about 1W (0.5W for the fundamental frequency and another 0.5W for all the distortion harmonics).
Your LM386 amplifiers are probably oscillating at a high frequency which causes them to use a high supply current because they are missing the important RC Zobel networks at their outputs as shown on every circuit in the datasheet.

The input signal level is WAY TOO HIGH since the 555 output with a 9V supply is a squarewave that is 7.3V peak-to-peak but the maximum input to the LM386 for full output level is only 0.12V peak-to-peak. Add an attenuator to reduce the 7.3V to 0.12V.

How can your squarewave "buzzer" irritate the neighbours when an LM386 output when powered from only 9V and driving an 8 ohm speaker is only about 1W (0.5W for the fundamental frequency and another 0.5W for all the distortion harmonics).
Thank you
 
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