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Need help! Preamp or amp circuit

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by cyberquest, Jan 12, 2010.

  1. cyberquest

    cyberquest New Member

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    Hi all

    Enclosed is a diagram to a circuit I'm testing.


    The red square is the part of that curcuit I need help on.
    I need a amp or preamp that will in increase the out put tone comimg out on pin 16 to the TIP31 out the speaker.But the single is to waek for the mic to pick it up between 0-25ft away. I need a amp or preamp where i could control the gain ,if i need to. Maybe a circuit base on a 386 op amp or a 741 op amp might work.I need someone to help me who knows what will work for increasing the single out the speaker for the mic to pick it up a the distance i stated.The mic is either a electret mic or a magnetic mic they sell them in Radio shack .

    PS Don't have experience in amplifier ciruits.



    Jameco Electronics Electromechanical: JAMECO VALUEPRO: ECM-60PC-R
    THIS IS THE MIC I'M USING.
     

    Attached Files:

    Last edited: Jan 12, 2010
  2. cyberquest

    cyberquest New Member

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    Can someone on this forum with experience and back ground in Preamp and amp circuit design. Help!
     
  3. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The TIP31 has an input of about 4.5V peak and has an output of about 3.7V peak.
    The 2.5" speaker has a power output of about 0.86W. If it is in a proper enclosure and is fed a frequency that is high enough for it to produce loudly then a microphone can easily hear it only 25 feet away. Do not expect the tiny speaker to produce low frequency sounds.

    Maybe your microphone preamp is not designed correctly.
    What is the "receiver"?

    EDIT:
    Are the tones DTMF telephone touch-tones? They are not a crude powerful square-wave, they are a sine-wave at a fairly low output level so the single transistor is no good.
    If you post the part number of the IC then we can see its output level and how much current it has.
     
    Last edited: Jan 13, 2010
  4. dave

    Dave New Member

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  5. cyberquest

    cyberquest New Member

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    audioguru. Thanks for reponding.

    Yes they are DTMF tones key, phone, ect.

    Here's the part 5089

    http://www.national.com/ds/TP/TP5089.pdf#page=1

    So is there a preamp or amp circuit that you can draw for me that will work in this circuit, connected between pin 16 and the speaker. will I need the TIP31. This is what i had available. This is way I used it.
    I know that the speaker puts out only 0.86 watts because of the size I don't want to use a bigger speaker for more wattage.
    I want to keep it small this is way i went with the 2'' speaker.

    Also is there a preamp that will work for the microphone that i posted can you post a circuit that will work for the MIC.

    audioguru. You state don't expect the tiny speaker to produce low frequency sounds.
    Right! This speaker can't produce Any frequency below 320Hz, but this will help me in my project there is ambient noise at these lower frequencies and I don't want to pick-up them up anyway.This will give me a cleaner single.

    Some specs on this speaker i'm using.
    NOMINAL INPUT Power w O.25
    Input Power Max 0.5
    Output spl dB 86

    Receiver is a decoder. So. A preamps ouput will be connect to the decoders input.
     
  6. audioguru

    audioguru Well-Known Member Most Helpful Member

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    If the supply voltage is 10V and the TIP31 feeds an 8 ohm speaker then its typical input resistance is far too low to be driven from a TP5089 IC and it will not be properly biased. The output now is nothing but low volume distortion. You need to use a power amplifier IC. With a 10V supply the max amplifier output into an 8 ohm speaker is only 0.6W so your tiny speaker will be overloaded and will not be loud.

    There are hundreds of preamps for electret mics on the internet and most are the same. Post your preamp circuit and the receiver circuit.
     
  7. cyberquest

    cyberquest New Member

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    The receiver and decoder were tie together.
    I want to made them independent units using a 9V battery for each unit and by using a voltage regulator to drop the voltage for the 5V for each uint that powers the circuits ICs.

    I don't have a Power amp for the speaker or a Preamp for the mic I just show a Block diagram for mic. This is why i came to this forum to get help with a workable schematic for the mic side on the receiver uint. And for the power amp for speaker on the generator uint.


    enclosed is the receiver side.

    I don't understand what you stated in your last post about the TIP31 Feeding into the speaker.

    can you supply me with a circuit for the mic on the receiver side and a power amp for the generator side this is what i need i would appreciate this.

    Like i said I don't have alot experience in these amps. PLease help.

    This is all the info I have on these two uints the two diagrams.
     

    Attached Files:

  8. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The speaker needs a power amplifier IC, not a TIP31 transistor.
    Here is a power amplifier and a mic preamp:
     

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  9. cyberquest

    cyberquest New Member

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    I have some questions about the two Amplifiers.

    1.Why use the TDA2822M dual Power amp are you using one of the amps for feedback Please Explain! If you may. So i could understand this circuit.
    Power amp.
    2. Is this a workable circuit "meaning"' will it function (as is) if I connect the ouput of the DTMF Generator circuit to the input of the Power Amp. Not alot of experience in audio circuits so i wouldn't beable to modify the circuit.
    3. I assume the gain is variable controlled throught the POT at pin 7, what is the total gain for this circuit.
    4.What is the output wattage throught the speaker when the Pot is at zero gain and at maximum gain by turning the pot.
    5>Do I need to use a 10k rotary POT or can i use a 15 turn 10k trimmer POT.
    6. Do I use 5% carbon or 1% metal film resistors in Audio circuits.
    7.Capacitors C3,C1 are electrolytic, what are the rest of them mylar, ceramic, or other. What kind are best to use in audio circuits.
    8. Do I need to add any parts if so what parts would i need to add and there values before I conect the Power amp to the output on pin 16 on the Generator circuit, Or is it ready to be connected to the generators Output just the way you have it.

    (I do know not to ADD TIP31 back into the circuit. This will not be used.)


    A few questions on the Mics Preamp circuit.

    1. The Preamplifiers Output will be connected to the decoders Input do I need to take out any of the parts I have connected to the decodes Input. If not. I just connect the Preamps output to the decodes Input. As is. correct!

    2.What is the gain for the Preamp 20, 100, 200, or above that.

    3. Way did you use the TL071 instead of say 386 0r 741, and is there a big difference in functions.

    Thanks for the Amplifiers Please reply to all the questions so I will understand the amps this way I don't hook it up incorrectly.
     
    Last edited: Jan 15, 2010
  10. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The TDA2022M amplifier I show is a working power amplifier with an output power almost 5 times the power of an LM386 amplifier because it uses two amplifiers in a bridge so the voltage swing across the speaker is doubled.

    The pot is a volume control. The datasheet for the TDA2822M shows that the gain is 95.

    The output power depends on the supply voltage. With a 6V supply the minimum power is zero and the max power barely clipping is 0.9W into 8 ohms.

    Use a single turn logarithmic (audio taper) volume control or a single turn trim pot.

    5% carbon film resistors are fine.

    The input coupling capacitor should be 220nF/5%/63V film type. Film capacitors are good for coupling low power audio.
    C2, C4 and C5 can be ceramic type.

    it is ready to be connected.

    Simply connect them together.

    The max gain of the opamp is 1+ (470k/2.2k)= 215. The 470k pot is the gain control.

    The TL071 is a low noise audio opamp. It is available everywhere, is inexpensive and works very well as a preamp.
    The LM386 is a noisy power amp.
    The 741 is 42 years old and has very poor audio performance because it is noisy and has poor high frequency response.
     
  11. cyberquest

    cyberquest New Member

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    This helped!


    audioguru.
    Can you recommend any elementary to intermediate tutorials, books, video's , wedsites, schematic circuit building, in learning more about audio electronics.You may have some soruces that i don't know of, that could help me out in knowing more on about audio electronics.

    Thanks
     
  12. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The book called "The Art Of Electronics" is available online.

    There are many guitar "fuzz" circuits that use 45 year old parts to produce distortion that I avoid.
     
  13. cyberquest

    cyberquest New Member

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    audioguru


    I was looking to add a mono phone jack for an earbud to listen to the sound- tones as well, but I gotten stuck on where to connect the jack to the output of the decoder IC.
    Would i connect this jack to any of Q1-Q4 output pins on the decoder or to the input of the decoder so the single is not interupted when the single gos to the input of the BCD driver then connect to the 7-segment display.

    What would be the best way to add a jack to the decoder output where i can read and listen to the tones, and what added parts would I need other then the jack for this to work. a simple diagram would help for that connection, If you can.

    Any addditional help would be is greatly appreciated.


    Thanks
     
    Last edited: Jan 16, 2010
  14. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The tone is at the output of the preamp opamp but the opamp is not powerful enough to drive an earphone. Use an LM386 power amplifier with its own volume control to drive the earphone. The output of the preamp will feed the volume control of the LM386 amplifier.

    The outputs of the decoder are just a DC level change when a valid touch-tone is decoded.
     
  15. cyberquest

    cyberquest New Member

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    audioguru

    Can i add an audio plug with lead wires connected to the TLO71 Preamps Mic input that you post.

    I want to test the sound coming from a handheld portable radio headphones jack, would I just take a mono or stereo plug add a wire to the plug then on the other end of the wire connect one lead to the Mics input and the other lead wire to ground,but in-keeping the Mic connected to the preamps input,but switching the Mic off when the inputs Plug is connected to the portable radios earjack.



    Also I enclosed a circuit I designed. try to anyway, for post 13. Let me know if this will work for what i posted in post 12,and as you suggested i do in post 13. This is the first audio circuit i designed. Will it work for mono or stereo I might need another stage for stereo headphone. Please let me know or advise if you suggest if the vulues need to be changeD or what needs to be add to the circuit.

    cyberquest
     

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    Last edited: Jan 19, 2010
  16. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Your mono LM386 earphones amplifier will not work because its ground pin4 is not connected to ground. You might as well connect pin2 also to ground. Use two amplifiers for stereo.
    The 100nF input capacitor causes a low frequency cutoff at 193Hz so there will be no bass frequencies.
    If your earphones are 8 ohms then the 100uf output capacitor causes a low frequency cutoff at 200Hz so bass frequencies will again be reduced.

    There is no "next stage". The preamp drives both the earphones amplifier and the decoder.

    The output of a radio is about 27 times to 100 times too loud to feed the mic preamp. Use a switch to feed either the mic preamp to the volume control of the LM386 or the radio.
     
  17. cyberquest

    cyberquest New Member

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    audioguru

    Thank for the advice.

    Ok. What size capacitor can i use and what capacitor size do you think will get those lower bass frequecies for the input capacitor, and not have to change the 10k pot.
    And what size capacitor can i use to replace the 1OOuf, if my earphone are 8,16 ohms and still rececive those lower bass frequencies.

    Right! there is no next stage, but there is the decoder and the driver for the 7-segment display. I just stated next stage as a reference.But thanks for pointing that out.

    As for pin2 and pin4 the ground sign indicates there at ground. correct! don't i need the .01 coupling capacitors for noise. But please correct me if I'm wrong on that. but I do see your point that they should be directly to its ground state. would i still need to install those caps yes or no and where. Please advise.


    I'm not understanding the last paragragh in your post how do i feed the plug coming out of the radio's earjack into the preamp by using a switch then to either the preamp to the volume control of the 386 or the radio. Can you show me this in a simple diagram so i can visualize what you mean so i can understand this better.
     
    Last edited: Jan 19, 2010
  18. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Think of a cutoff frequency (half-power) then use a simple calculation, don't guess wrongly.

    Same as above.
    Since you have two RC cutoffs then double the calculated values of both capacitors so that when combined, their total cutoff frequency is what you want.

    With pin2 and pin4 connected directly to ground then the two capacitors do nothing because they are shorted.

    The toggle of the two-way switch is at the volume control. the switch selects either the output of the mic preamp or the jack for the radio.
     
  19. cyberquest

    cyberquest New Member

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    audioguru


    I'm still having trouble calculating for the input cap and the output cap in the 386 amp circuit.
    I was using a cutoff frequency calculator on the internet because I just don't understand the equation for this. Can you show me an example how i get the right capacitors for the input and output. I'm stuck on this. i Never used audio circuits before. Help!


    Help!

    I still don't have a clue on how i get the Mics input on the TL071 Preamp to switch to the Jack to the radio form the 386 amp, i do know what a two way switch its a ON-ON SPDT switch or a ON-OFF-ON DPDT switch.

    And what did you mean by toggle.In post 17

    Did you mean toggle switch. if you did, got it. That just came to me.
     
    Last edited: Jan 22, 2010
  20. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The calculation for the cutoff frequencies is simple as I show here.

    The switch does not switch the microphone. It switches either the output of the mic preamp or the jack from the radio to the volume control at the input of the amplifier IC.
     

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  21. cyberquest

    cyberquest New Member

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    audioguru.

    By using the equation as you given or using a cut-off fq calculator the out come is the same. So, By me using the calculator will give me the same results.

    The calculation for the cut-off Fq for the input Power amp would be is 72.34Hz for the 10k resistor and a 0.22mf capacitor on the input. I see that you rounded it off to 73Hz. Why!

    Ok.Here's my another problem i still have. How do I calculate for the output of the RC Fq on the LM386 without changing the cut-off fq for the input.

    Also, the most important factor is what frequency do I to use for the input and the output so the decoder detects the DTMF FQs But also the LM386 detects the FM/AM bands on the radio.

    How do i choose the right cut-off Frequency for the input and ouput for the 386.I would need to know cut-off Fqs fisrt to calculate for the cut-off points.Ay suggestions on this.

    PS can you give me a more simpler example of the RC equation break it down into a more elementary example so i could understand the equation better.
     
    Last edited: Jan 22, 2010

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