audioguru Posted April 23, 2007 Report Share Posted April 23, 2007 Hi Bruce,The volume control in the FRS radio feeds its audio amp (the NJM2073 has a voltage gain of 100) which has an output for the speaker, or for the earphone and for your MC34119 mixer/amp. Quote Link to comment Share on other sites More sharing options...
CALAHAN Posted April 23, 2007 Author Report Share Posted April 23, 2007 O.K. so I was wrong and the headphone output which I am using is amplified. How do I fix my problem do you think?Maybe tonight I will snap an image of the internals of that headphone jack. I noticed when I was breadboarding it, the MC34119 circuit worked with the FRS on either pin of barrel of the jack I plugged in it. The jack does not look like the schematic. When pushing the jack in, both contacts move off of posts inside. Perhaps I have the output to the MC34119 linked off the wrong end of the jack. Thanks,Bruce Quote Link to comment Share on other sites More sharing options...
CALAHAN Posted April 25, 2007 Author Report Share Posted April 25, 2007 O.K. here is the jack. Right now I have the wire to the amplifier fed off the head of the jack. Perhaps I should have it attached to the shaft? and that is why I don't have volume control?Bruce Quote Link to comment Share on other sites More sharing options...
audioguru Posted April 25, 2007 Report Share Posted April 25, 2007 Your pic appears to be a completely different circuit than the FRS schematic you posted. Where is its NJR2073 audio power amplifier IC? Quote Link to comment Share on other sites More sharing options...
CALAHAN Posted April 25, 2007 Author Report Share Posted April 25, 2007 Audioguru,I have no idea where the amp is. The schematic I posted is off the FCC web page and is the original submitted drawing for this model radio. They do state that the production models may differ from the submitted drawing to some extent. Bruce Quote Link to comment Share on other sites More sharing options...
CALAHAN Posted April 27, 2007 Author Report Share Posted April 27, 2007 Audioguru,This issue was my error. I opened the comm back up, and I had the 10uf capacitor backwards which caused chaos with the batteries. After resolving this issue, the volume pot works, but there does seem to be some damage in the middle of the sweep which was my mistake also. Out of curiosity, will this amplifier schematic you provided work "as is" with 6 volts run into it instead of 4.5, as I will need to do it with my next build?And, is there any quick and simple way to knock the 6 volts down to 3 to power the sound effects? two sets of diodes perhaps instead of one, or a voltage split?Regards,Bruce Quote Link to comment Share on other sites More sharing options...
audioguru Posted April 27, 2007 Report Share Posted April 27, 2007 The MC34119 will get very hot with a 6V supply and an 8 ohm speaker. It will waste a lot of battery power. Use an LM386 amplifier IC instead.Connect four diodes in series to drop 6V down to 3.2V. Quote Link to comment Share on other sites More sharing options...
CALAHAN Posted April 27, 2007 Author Report Share Posted April 27, 2007 Can you give me a bit more on the diodes. You gave me the way to hook up two diodes earlier in this thread to get 3v from 4.5. So now I do this procedure twice using four diodes?Bruce Quote Link to comment Share on other sites More sharing options...
audioguru Posted April 27, 2007 Report Share Posted April 27, 2007 A silicon diode has about 0.7V across it. So four in series from 6V produces 3.2V.When the battery voltage drops to 4V then the output from the diodes will be only 1.2V. Quote Link to comment Share on other sites More sharing options...
CALAHAN Posted April 27, 2007 Author Report Share Posted April 27, 2007 I went shopping today and bought four Zener diodes like I used for this other build, and will test them out tonight or this weekend,.Thanks,Bruce Quote Link to comment Share on other sites More sharing options...
CALAHAN Posted May 1, 2007 Author Report Share Posted May 1, 2007 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 Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 1, 2007 Report Share Posted May 1, 2007 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. Quote Link to comment Share on other sites More sharing options...
CALAHAN Posted May 1, 2007 Author Report Share Posted May 1, 2007 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 Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 1, 2007 Report Share Posted May 1, 2007 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. Quote Link to comment Share on other sites More sharing options...
CALAHAN Posted May 1, 2007 Author Report Share Posted May 1, 2007 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 Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 1, 2007 Report Share Posted May 1, 2007 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. Quote Link to comment Share on other sites More sharing options...
CALAHAN Posted May 1, 2007 Author Report Share Posted May 1, 2007 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 Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 1, 2007 Report Share Posted May 1, 2007 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. Quote Link to comment Share on other sites More sharing options...
CALAHAN Posted May 1, 2007 Author Report Share Posted May 1, 2007 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 Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 1, 2007 Report Share Posted May 1, 2007 So I did O.K. then?Your selection of a 1M resistor is perfect. ;D Quote Link to comment Share on other sites More sharing options...
CALAHAN Posted May 8, 2007 Author Report Share Posted May 8, 2007 Audioguru,With this MC34119 circuit, can you tell me how to add (if possible) the proper components to boost the low end audio like what can be done with the LM386?Thanks,Bruce Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 8, 2007 Report Share Posted May 8, 2007 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. Quote Link to comment Share on other sites More sharing options...
CALAHAN Posted May 8, 2007 Author Report Share Posted May 8, 2007 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 Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 9, 2007 Report Share Posted May 9, 2007 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. Quote Link to comment Share on other sites More sharing options...
CALAHAN Posted May 9, 2007 Author Report Share Posted May 9, 2007 O.K. I do have some .022uf and .047uf capacitors, so I'll go that route.Thanks,Bruce Quote Link to comment Share on other sites More sharing options...
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