Audioguru,
I created an amp with the LM386 as you stated. It seems to work fine. I used a schematic you drew up on another thread from last year. However, after looking at this 6v powered new FRS I am using, there is a LM386 clearly marked as such in use on the circuit board already. What would happen if I connected the sound effects circuit to the input of the onboard LM386? Sound effect out to a .22 uf capacitor, then the relevant resistor (I used a 1 meg ohm this time to keep the effect from distorting) then to the input pin of the IC on the FRS. Would it work? I assume I would be bypassing the onboard digital FRS volume control with this also.
Bruce
I created an amp with the LM386 as you stated. It seems to work fine. I used a schematic you drew up on another thread from last year. However, after looking at this 6v powered new FRS I am using, there is a LM386 clearly marked as such in use on the circuit board already. What would happen if I connected the sound effects circuit to the input of the onboard LM386? Sound effect out to a .22 uf capacitor, then the relevant resistor (I used a 1 meg ohm this time to keep the effect from distorting) then to the input pin of the IC on the FRS. Would it work? I assume I would be bypassing the onboard digital FRS volume control with this also.
Bruce
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You added a 1M mixing resistor in series with a 0.22uF DC-blocking capacitor from the output of the effects circuit which is fine. I think the effects circuit must have a resistor from its output to the supply to simulate its speaker.
The FRS volume control might not be able to adjust the volume of the effects.
The FRS volume control might not be able to adjust the volume of the effects.
I am creating a second FRS communicator. I am using the same toy hacked sound effects circuit as specified earlier - (I have a few of them of course, the first FRS works fine but the batteries go fast).
I wired the + speaker output to a 10 ohm reistor then to the - output as you had me do before. The negative speaker is then fed to the .22, then the 1m resistor then the LM386. The resistor was the only value I could find that would keep the LM386 from distorting the speaker. Generally the LM386 schematics show to us a 10k, but that created nothing but distortion. I did not add the capacitor between 1 and 8 either so it is minimal volume.
If I were to tap into the FRS onboard LM386, I would not need volume control for the sound effects. Should I try it?
Bruce
I wired the + speaker output to a 10 ohm reistor then to the - output as you had me do before. The negative speaker is then fed to the .22, then the 1m resistor then the LM386. The resistor was the only value I could find that would keep the LM386 from distorting the speaker. Generally the LM386 schematics show to us a 10k, but that created nothing but distortion. I did not add the capacitor between 1 and 8 either so it is minimal volume.
If I were to tap into the FRS onboard LM386, I would not need volume control for the sound effects. Should I try it?
Bruce
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You can add a volume control to the output of the effects circuit if you want. Then the slider of the volume control can feed a 100k attenuation/mixing resistor that connects to the input of the LM386 amp.
I don't need a volume control I just want to amplify the sound effects based on the value of the resistor, and since this FRS already has an onboard LM386, perhaps I could tap into that and in effect feed both of these circuits into one speaker like the last build I did. Why shoudl I build a new LM386 amp, when there is already one there for me to use right? Would this work?
Bruce
Bruce
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I don't know the new FRS radio circuit.
It might need to have a mixing resistor added in series with its volume control. It might be difficult to cut the circuit to add the resistor.
Maybe you can just feed the effects through its own volume control then connect it directly to the LM386, but then the FRS volume control will also affect its volume.
It might need to have a mixing resistor added in series with its volume control. It might be difficult to cut the circuit to add the resistor.
Maybe you can just feed the effects through its own volume control then connect it directly to the LM386, but then the FRS volume control will also affect its volume.
Audioguru,
Oh yes, I see, and also, the amplification would not work with the FRS turned off. O.K. scratch that idea.
Do you think I could run an LED off of the power pin of the onboard LM386, which I need to turn on when the FRS is turned on?
And, do you see any issues with me having to use the 1m resistor in this LM386 curcuit that I built for the sound effects? 1m is a long way from 10k, but it was the only one that I found that kept the unit from distorting.
Bruce
Oh yes, I see, and also, the amplification would not work with the FRS turned off. O.K. scratch that idea.
Do you think I could run an LED off of the power pin of the onboard LM386, which I need to turn on when the FRS is turned on?
And, do you see any issues with me having to use the 1m resistor in this LM386 curcuit that I built for the sound effects? 1m is a long way from 10k, but it was the only one that I found that kept the unit from distorting.
Bruce
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An LED needs to have a properly calculated current limiting resistor in series with it. It will drain a small battery quickly.
The LM386 has a 50k resistor at its input to ground inside the IC.
The 1M resistor makes a voltage divider with the 50k resistance, attenuating the 3v p-p signal from the effects circuit to 150mV p-p. Then the LM386 amplifies it 20 times to 3V.
The LM386 has a 50k resistor at its input to ground inside the IC.
The 1M resistor makes a voltage divider with the 50k resistance, attenuating the 3v p-p signal from the effects circuit to 150mV p-p. Then the LM386 amplifies it 20 times to 3V.
You stated:
"The LM386 has a 50k resistor at its input to ground inside the IC.
The 1M resistor makes a voltage divider with the 50k resistance, attenuating the 3v p-p signal from the effects circuit to 150mV p-p. Then the LM386 amplifies it 20 times to 3V."
So I did O.K. then?
As fro the LED, I'll put the tester on the power leg of the LM386 and find the voltage and then put in a resistor as specified on one of those LED web sites to match the required LED's forward voltage.
Bruce
"The LM386 has a 50k resistor at its input to ground inside the IC.
The 1M resistor makes a voltage divider with the 50k resistance, attenuating the 3v p-p signal from the effects circuit to 150mV p-p. Then the LM386 amplifies it 20 times to 3V."
So I did O.K. then?
As fro the LED, I'll put the tester on the power leg of the LM386 and find the voltage and then put in a resistor as specified on one of those LED web sites to match the required LED's forward voltage.
Bruce
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Your selection of a 1M resistor is perfect. ;DCALAHAN said:
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Hi Bruce,
It is easy to boost the bass frequencies foe an MC34119 amplifier simply like the LM386 amp does it.
This modification has a voltage gain of 1 at high frequencire and a voltage gain of nearly 12k/3.3k= 3.6 at low frequencies.
Bass boost works only if the sound source has bass frequencies and if the speaker can produce bass frequencies.
It is easy to boost the bass frequencies foe an MC34119 amplifier simply like the LM386 amp does it.
This modification has a voltage gain of 1 at high frequencire and a voltage gain of nearly 12k/3.3k= 3.6 at low frequencies.
Bass boost works only if the sound source has bass frequencies and if the speaker can produce bass frequencies.
Audioguru,
You threw in a few wrenches on me here. I see the original 3.3k resistor is changed to a 12k and an extra 4.7k is added with a "68nf" - what is that a capacitor? Do I have to use an nf capacitor, becuase those have to be ordered. I looked and see a 68nf is the same as a .068uf. Again, not commonly found. What happens if I use a .047uf?
I'll have to see if I can dig up those values of resistor.
The speaker may not like low frequencies, but I'll try it.
Thanks,
Bruce
You threw in a few wrenches on me here. I see the original 3.3k resistor is changed to a 12k and an extra 4.7k is added with a "68nf" - what is that a capacitor? Do I have to use an nf capacitor, becuase those have to be ordered. I looked and see a 68nf is the same as a .068uf. Again, not commonly found. What happens if I use a .047uf?
I'll have to see if I can dig up those values of resistor.
The speaker may not like low frequencies, but I'll try it.
Thanks,
Bruce
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audioguru2
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The 68nF is a 0.068uF capacitor which is a standard value for a metalized plastic film type with a 5% and 10% tolerance.
If you use 47nF instead then the boost peak will occur at about 62Hz where the input capacitor is cutting the very low frequencies and your tiny speaker can't produce 60Hz anyway.
47nF plus 22nF in parallel equals 69nF which will work fine to replace the 68nF capacitor. Two 33nF capacitors in parallel equal 66nF which will also work well.
If you use 47nF instead then the boost peak will occur at about 62Hz where the input capacitor is cutting the very low frequencies and your tiny speaker can't produce 60Hz anyway.
47nF plus 22nF in parallel equals 69nF which will work fine to replace the 68nF capacitor. Two 33nF capacitors in parallel equal 66nF which will also work well.
Audioguru,
I have a problem with my first communicator build which we used that MC34119 amp in. Something is sucking the batteries of power even when it is turned off. I'll leave it on the desk after using the sound effects for a few days, and the batteries are dying. Any ideas?
Bruce
I have a problem with my first communicator build which we used that MC34119 amp in. Something is sucking the batteries of power even when it is turned off. I'll leave it on the desk after using the sound effects for a few days, and the batteries are dying. Any ideas?
Bruce
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Then I guess the MC34119 amplifier is still bring powered by the battery when the radio and the sound effects circuit are turned off.CALAHAN said:
The MC34119 amplifier should receive its power after the on-off switch.
The FRS radio obviousley has an off/on switch, but the sound effects chip does not. On the original toy it came in there was no on/off switch, the sound effect is activated when a diaphram switch is hit wich completes the circuit - but it is momentary. You hit it once and the sound effect plays through to it's end, and then resets when the diaphram is hit again. Holding the switch closed causes the sound effect to play in a continual loop. I guess that meas the original toy circuit is always hot.
Bruce
Bruce
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A transistor with a coupling capacitor can perform the momentary function of the sound effect's diaphram switch to start it playing then it will shut itself off.
You need to find out exactly what the diaphram switch does. It might make an input go high or go low.
You need to find out exactly what the diaphram switch does. It might make an input go high or go low.
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