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Need assistance outlining earphone speaker circuit

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Need assistance outlining earphone speaker circuit

Postby Garhurd Jung » Fri Aug 04, 2017 9:36 am

I need to outline an earphone speaker circuit. We are told the impedance of the earphones and the base voltage they require and furthermore the voltage source. In the wake of inquiring about I have discovered that the LM386N-4 is a prevalent decision. (an example from datasheet LM386N-4 - https://www.icrfq.com/part/2377557-LM386N_4.html ). I've seen many circuit graphs yet what I don't comprehend is the means by which to pick the voltage increase required for the speaker.

I initially believed that you would need to know the info sound flag voltage and when you increased that by the pick up that would need to give the base voltage required by the earphones, yet it gives the idea that what is important is the present which I don't get.

Also, would you say you are ready to plan such a circuit without thinking about the sound information flag? In the event that you do need to think about it what is it you have to think about it and why?

I would greatly appreciate any help as I am very lost.
Thanks in advance!
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Re: Need assistance outlining earphone speaker circuit

Postby Charlie Schultz » Fri Aug 04, 2017 9:58 am

Hi Garhurd and welcome to the forum.

Can we clarify a couple things? First, the LM384 is a power (voltage) amplifier and it will provide the power increase needed for the earphones (typical application circuit from the datasheet below).

And by "sound information flag", I think you mean the input (pickup) signal?

Capture.PNG
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Re: Need assistance outlining earphone speaker circuit

Postby Garhurd Jung » Fri Aug 04, 2017 12:54 pm

Hello Charlie, thanks for the welcome and clear me the speaker circuit.

Yeah, I mean input signal and now I got my point.

Thanks, thanks a lot.
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Re: Need assistance outlining earphone speaker circuit

Postby Chad Schmidt » Fri Aug 04, 2017 1:07 pm

Hello Garhard,

Here's a link a thread that shows a circuit schematic I used recently and have been happy with.

viewtopic.php?f=4&t=3976&start=20#p38858

If you search for Jenkins Headphone Amplifier, you should find a report (I think this was a student thesis) that discusses the design tradeoffs and process.

That same linked thread also shows a schematic for a stereo circuit by Vellman. There is also some documentation on this circuit you may be able to find with a web search.

Hope this helps!
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Re: Need assistance outlining earphone speaker circuit

Postby David King » Fri Aug 04, 2017 2:51 pm

I hate the LM386, it's specs were garbage when it came out in the 1970s. We've gone through dozens if not hundreds of evolutions of "pocket sound" since then and there's no reason not to look for a better alternative or simply buy something off the shelf, or as a kit to get this job done. I'd look through some of ST's offerings here: http://www.st.com/en/audio-ics/headphon ... fiers.html
I'm sure TI also has some great options. There are some good legacy chips from the 1980s and 1990s that would serve well albeit use way more current than the latest generation. Most of the modern packages are designed as SMT only and will undoubtedly pose an issue for a one-off implementation but I'm sure there are ways around that.
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Re: Need assistance outlining earphone speaker circuit

Postby Beate Ritzert » Fri Aug 04, 2017 4:23 pm

Before i would talk on circuits i would do a "rule of thumb" design.

which impedance does the speaker have (the variance may be huge)? What is the maximum current (or power) needed to deliver? From that follows the necessary voltage output swing, and that - of course with some margin - will define the operation voltage of the device. Power should be less a problem than output impedance.

And then design from the last stage backward voltage source means small output impedance which might mean Op-Amp (well check if it can deliver the power), or a source resp. emitter follower stage. Maybe even a valve. The rest follows: which amplification is needed for Your signal? Maybe You need some NFB to improve linearity and to reduce the output impedance? Do You have enough open loop gain for this?

And then it is time to chose the technology for the implementation.
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Re: Need assistance outlining earphone speaker circuit

Postby David King » Fri Aug 04, 2017 5:27 pm

Beate,
Agreed! In this case choosing a headphone that matches up well with the instrument. Headphones/earphones suitable for bass might be a very different choice from ones for guitar or uke etc.
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Re: Need assistance outlining earphone speaker circuit

Postby Rodger Knox » Fri Aug 04, 2017 5:47 pm

David King wrote: Most of the modern packages are designed as SMT only and will undoubtedly pose an issue for a one-off implementation but I'm sure there are ways around that.


You can always design and etch your own board and solder on all the SMT components. It's not easy, but it can be done.
IMGP3482.JPG

This is one of the MIMF preamps designed by Vlad Arlean, the board is 2" x 1 1/2".
A man hears what he wants to hear, and disreguards the rest. Paul Simon
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