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 Post subject: Amp Circuits
PostPosted: Mon Mar 09, 2009 7:55 am 
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I'm looking for a simple portable (i.e battery powered) amp circuit to build. Obviously there are a lot around the net, including the ubiquitous headphone amp.

This is also interesting, a battery powered mic amp.

I've also considered just buying a mixer, but the one that has a price tag in my range is a bit too limited for my needs. MFOS has some cool looking projects, but probably over my head at this point.

I only need a single channel for the stuff I'm doing, I may initially modify the Cmoy amp as a first project.

Anyway, just wanted to start a thread for any other input people have.

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 Post subject: Re: Amp Circuits
PostPosted: Mon Mar 09, 2009 10:47 am 
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Actually, let's step back a phase:

What do you want to do? Perhaps that's a better question to ask.

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 Post subject: Re: Amp Circuits
PostPosted: Mon Mar 09, 2009 10:54 am 
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uptownmaker wrote:
Actually, let's step back a phase:

What do you want to do? Perhaps that's a better question to ask.


1. Amplify contact mics to be audible (which is why I started looking at that mic amp circuit).
2. Amplify other noise making circuits to be more audible.

And ultimately

3. Mix multiple sources so they can be played together (and perhaps recorded).

Obviously portability is variable across those goals.

Edit: And of course the unstated, but probably the most important goal, learns some new stuff along the way. ;)

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 Post subject: Re: Amp Circuits
PostPosted: Mon Mar 09, 2009 11:23 am 
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1 is going to depend on teh type of mic used, but a generic mic preamp should be fine. keep in mind you may have phantom power needs.

2 is going to depend on output, which may differ dramatically from 1


3 your'e looking more at a mixing board, which probably won't include a mic pre, but might.


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 Post subject: Re: Amp Circuits
PostPosted: Mon Mar 09, 2009 5:17 pm 
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Check out the venerable LM386 chip.
There are a couple bazillion circuits found on google using this chip for basic audio amps.
In its simplest form you can build an amp using about 4 components.


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 Post subject: Re: Amp Circuits
PostPosted: Mon Mar 09, 2009 9:17 pm 
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darus67 wrote:
Check out the venerable LM386 chip.
There are a couple bazillion circuits found on google using this chip for basic audio amps.
In its simplest form you can build an amp using about 4 components.


Cool, thanks. I'll start with that.

Image

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 Post subject: Re: Amp Circuits
PostPosted: Tue Mar 10, 2009 6:35 am 
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You might also look at Digi-key and just page through some of their selections. There are a whole new generation of audio amplifiers with similar simplicity, but added features such as de-pop circuitry and built-in mute functionality.

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 Post subject: Re: Amp Circuits
PostPosted: Thu Mar 12, 2009 10:15 pm 
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Radio Shack had the parts for that Amp circuit, so I breadboarded it tonight. I think I made a better radio than Amp.

My understanding is that 0.05uF caps are deprecated for 0.047uF, but I also substituted the 250uF electrolytic for a 220uF (that's all RS had), not sure of the impact of that.

Also, I used my Atari Punk Console as input and I'm not sure I have them connected correctly, just a single wire is going from the output of the APC to the input of the Amp. Should the grounds of the two circuits be connected somehow?

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 Post subject: Re: Amp Circuits
PostPosted: Fri Mar 13, 2009 8:29 am 
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noise wrote:
Also, I used my Atari Punk Console as input and I'm not sure I have them connected correctly, just a single wire is going from the output of the APC to the input of the Amp. Should the grounds of the two circuits be connected somehow?


Yes.

Yes yes yes yes YES.

Remember, all electrons want to travel a circular path- they leave some source, go out into the "world" (their local circuit), do some work (the amount of which is dictated by their voltage), then come home to the source at the end of their "day" (a couple of nanoseconds, really). Electrons are smart, though- if they can't see a way out of a circuit, they won't enter.

How do you have the two systems powered? Are both running on batteries? Wall warts? One of each? If you're using batteries for either half of the system, you definitely need to connect the grounds. Things get a little more complicated for wall warts, and there can be dangers inherent in connecting the grounds of two wall warts together depending on how they are manufactured.

I'm glad you asked these questions- it brings up another whole list of things I need to cover in my class.

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 Post subject: Re: Amp Circuits
PostPosted: Fri Mar 13, 2009 9:32 am 
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uptownmaker wrote:
How do you have the two systems powered? Are both running on batteries? Wall warts? One of each? If you're using batteries for either half of the system, you definitely need to connect the grounds. Things get a little more complicated for wall warts, and there can be dangers inherent in connecting the grounds of two wall warts together depending on how they are manufactured.

I'm glad you asked these questions- it brings up another whole list of things I need to cover in my class.


Each is powered by a 9V battery, so how would I connect the grounds, bridge the negative posts of the batteries?

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