The sound amplifier - the pre-amp is built and working - well I can say ! (pics)

The sound amplifier - the pre-amp is built and working - well I can say ! (pics)

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Thread: The sound amplifier - the pre-amp is built and working - well I can say ! (pics)

  1. #1
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    The sound amplifier - the pre-amp is built and working - well I can say ! (pics)

    Actually, the pre-amp is the easy part - well, perhaps more accurate, less difficult. Here's the pre-amp on the breadboard. I'm using a power supply right now so I can vary the voltage from 3.0 volts down to 2.0 volts - it works all through the voltage range!

    This is a test stage; I don't have the volume control on and it's not operating from a battery - which could introduce problems - battery operation that is. And the round thingy on the left is the mic; it likely won't be plugged into the board, but maybe.



    And if you haven't seen "testing" on an oscilloscope, here ya go,



    You'd recognize it anywhere, right?

    Also on the board is the dual constant current source - WOW - did that thing ever work! That's the part near the center of the board. I had to leave a gap for the frequency shaping circuit (to the left) and the power amp will go on the right. The dual constant current source holds the current to a 7.7% change for a 50% change in operating voltage. My simulator said it would vary 8.8% That is phenomenal agreement between all simulation and an actual built circuit - Yeah, yeah, I'm braggin' a bit

    Still a long way to go. I'll build the power amp next so I can get an idea where I am. It will be challenging to build, it's complex, complicated, and everything is interdependent. If one thing is not right, it makes everything else wrong too - very hard to troubleshoot.

    Even if all goes well with that, I may have to have so much volume for my BIL to be helped by it that it produces acoustic coupling. That's were the sound finds its way back into the mic. You've probably heard a squeal when someone is using a mic - that's caused by acoustic coupling. Can be hard to deal with, but I have a plan B and C already just in case,

    OK, back to work. Well not quite, this is range day after all.
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    Quote Originally Posted by Tangle View Post
    Actually, the pre-amp is the easy part - well, perhaps more accurate, less difficult. Here's the pre-amp on the breadboard. I'm using a power supply right now so I can vary the voltage from 3.0 volts down to 2.0 volts - it works all through the voltage range!

    This is a test stage; I don't have the volume control on and it's not operating from a battery - which could introduce problems - battery operation that is. And the round thingy on the left is the mic; it likely won't be plugged into the board, but maybe.



    And if you haven't seen "testing" on an oscilloscope, here ya go,



    You'd recognize it anywhere, right?

    Also on the board is the dual constant current source - WOW - did that thing ever work! That's the part near the center of the board. I had to leave a gap for the frequency shaping circuit (to the left) and the power amp will go on the right. The dual constant current source holds the current to a 7.7% change for a 50% change in operating voltage. My simulator said it would vary 8.8% That is phenomenal agreement between all simulation and an actual built circuit - Yeah, yeah, I'm braggin' a bit

    Still a long way to go. I'll build the power amp next so I can get an idea where I am. It will be challenging to build, it's complex, complicated, and everything is interdependent. If one thing is not right, it makes everything else wrong too - very hard to troubleshoot.

    Even if all goes well with that, I may have to have so much volume for my BIL to be helped by it that it produces acoustic coupling. That's were the sound finds its way back into the mic. You've probably heard a squeal when someone is using a mic - that's caused by acoustic coupling. Can be hard to deal with, but I have a plan B and C already just in case,

    OK, back to work. Well not quite, this is range day after all.
    I would rather use the phrase "If one thing is not right, it makes everything else wrong too - very hard to figure where to make the improvement"!!!!

    Great job. I am doing a similar one now just for fun. I will give you an update in a couple of days.

    How far away are you trying to pick and amplify a reasonable sound? 10 meter or so?
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    I built this back in 1974 if I remember correctly. Mine pushed 375 watts per channel RMS it was so over-engineered. I had it paired with a Dynaco pre-amp and a Thorens turntable and ESS speakers.



    It was not portable though.

    Your BIL will be very grateful!
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    Quote Originally Posted by Rock and Glock View Post
    I built this back in 1974 if I remember correctly. Mine pushed 375 watts per channel RMS it was so over-engineered. I had it paired with a Dynaco pre-amp and a Thorens turntable and ESS speakers.



    It was not portable though.

    Your BIL will be very grateful!
    Ahhh, the good old days of Heathkit!!! I'm think I'm gonna cry - those were some good times.

    I guess he could deal with a long extension cord - might be a bit loud though

    It's hard to believe there was such a market for building it yourself electronics. My uncle (in law) built a Heathkit color TV! I used to love to gaze through their catalog. Sadly, those days of "pick out a kit and build it" are gone.
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    Quote Originally Posted by Osprey View Post
    I would rather use the phrase "If one thing is not right, it makes everything else wrong too - very hard to figure where to make the improvement"!!!!

    Great job. I am doing a similar one now just for fun. I will give you an update in a couple of days.

    How far away are you trying to pick and amplify a reasonable sound? 10 meter or so?
    It's not about improvement, well not yet, it's about getting it to work in the first place

    Ten meters might be bit long, I'd be happy with 5 feet without feedback - assuming it helps him hear of course.
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    Quote Originally Posted by Tangle View Post
    It's not about improvement, well not yet, it's about getting it to work in the first place

    Ten meters might be bit long, I'd be happy with 5 feet without feedback - assuming it helps him hear of course.
    BTW, nice O-scope. I have an Hitachi V252 and a Hantek DSO1510
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    Quote Originally Posted by Tangle View Post
    Ahhh, the good old days of Heathkit!!! I'm think I'm gonna cry - those were some good times.

    I guess he could deal with a long extension cord - might be a bit loud though

    It's hard to believe there was such a market for building it yourself electronics. My uncle (in law) built a Heathkit color TV! I used to love to gaze through their catalog. Sadly, those days of "pick out a kit and build it" are gone.
    My Dad kept a Heathkit catalog around also. He taught me how to build my own "variable AC/DC power supply" when I was 14. We also shoped at "Allied", Radio Shack (before they went south), and several other "electronic's catalog's". I grew up in Dallas, & being there were several aircraft/aerospace facilities in D/FW area, there were several "junkyard's" in said area that bought antiquated/mothballed equipment from them, & resold to public for 15 cents @#. We used to go to them on Saturday mourning's, & search for "neat stuff"! The "good'ol days"! IF ever that phrase was appropriate, it's for sure that time!!!! (50's-early 70's) Now, it's cheap junk from "you know where", & people have "no clue OR even care to learn" what makes things tick!
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    A bit later, i.e. after the Heathkit era, I started writing articles for magazines. They were published under my real name which you will see is Ron - and your welcome to call me Ron in posts etc. My board name, Tangle, is my dog's name, one of the best friends I've ever had. She's been gone some years now but I still think of her often.

    Anyway before I start to cry, One of the first articles I wrote was how to build a horn that plays the cavalry tune "Charge". This was in the day of integrated circuits and way before microcontrollers were available.

    The tune consists of three notes played at different times, etc. I used one generator and three counter/dividers to synthesize the three notes so, one, it could never get out of tune, and two I could change the pitch and the notes would still be true. Well, enough, here's the magazine - old as the hills as they say.



    The table of contents reveals the author:



    And the circuit - oh, if you build this, add 0.1 uF capacitors across the power and ground terminals of each IC. Those got left off. And I would add that I could do every bit of that with one 8 pin microcontroller today - my how things have changed!



    I have to tell this story. After this article was published, I got a letter from Senator Barry Goldwater asking me to build one for him. I did, sent it to him and received a check in the mail for my quoted price! me.

    And here's one I won't drag you through the details of, but it's an article about how to create a single board computer dial a telephone number. It was a requested article as a programming tutorial.



    And my project made the cover on this one!



    Ahhh, the memories of the good old days - actually those were my young days.
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    Brings back a lot of memories.I worked in consumer electronics for 45 years before retiring 3 yrs ago.I serviced tv's starting w/b&w up thru LED 4ks,stereos,VCRs,DVD players and even smart phones.Used a lot of scopes,Tektronics,B&K,Hitachi,and Sencores.I have not tried to service ANY electronic item since retirement except for changing the charge port on my son's Galaxy S7 phone about 2 years ago.This reminded me why I retired.
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    I did the circuit I showed you earlier on a breadboard. It works pretty good. I did not measure the gain yet. I was about to but when I hooked up the o-scope ground to gnd and touched a jumper wire from the microphone I was getting in a pretty good AM signal!

    That is what I love about electronics, just fun to see what happens.

    The sound amplifier - the pre-amp is built and working - well I can say ! (pics)-asamp.jpg
    Last edited by Osprey; January 31st, 2020 at 06:52 PM.
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    @Osprey , Couple of questions if I may:

    What is the power supply voltage?

    What was the peak-to-peak output voltage?

    What was the load it was driving?

    How much current from the power supply?
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    Quote Originally Posted by Tangle View Post
    @Osprey , Couple of questions if I may:

    What is the power supply voltage?

    What was the peak-to-peak output voltage?

    What was the load it was driving?

    How much current from the power supply?
    I am using a 3.7V/380mAh Lipo. The load was a set of earphones.

    Peak to peak was varied from 680mv p-p to 980mv p-p.

    I used a 1Khz audio tone from a speaker that was 10 inches away.

    The output from microphone (on the board) was about 10 to 30 mv p-p.

    I did not measure the current yet. The Lipo battery does better than a AAA would.

    I am going to hook it to one of my power supplies today so I can adjust the input current.

    I might also put in resistor for a load instead of the earbuds.

    I am replacing the 1M ohm feedback resistors with 560k or 680k. I am getting way too much humming. No popping though :)

    I don't know why I did not use my waveform generator. I will use that when I play around with it today.

    My initial test was just a functional test anyway. I was not trying to get 100 percent accurate data. I will this weekend.

    I am glad I stumbled on this thread. I do at least one or two projects a month.


    The sound amplifier - the pre-amp is built and working - well I can say ! (pics)-aasampwaveform1.jpg
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