Specialty headphone amp: Is it doable?
Mar 30, 2002 at 7:54 AM Thread Starter Post #1 of 12
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The headphone jack on my Panasonic 570 is getting sort of crappy, and I want to commision a kind DIYer to build an amp for me. However, I do not want a seperate box, since I use the player as a true portable for exercise, etc.

I got the idea that someone could build a barebones amp inside the case of the outboard battery pack that comes with the 570. It would run off of 2AAA batteries (I use low impedance headphones) and have a simple 1/8" input and 1/8" output with a small, inexpensive pot, maybe even one of the thumbwheel pots like on the headphone out section.

Given the size constraints, is it doable?
 
Mar 30, 2002 at 3:32 PM Post #2 of 12

CaptBubba

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How big is the case? The biggest problem would the the power, because very few opamps canrun off of 3V, a 9V battery would be much better.

Some people have made cmoy amps in the space of a 9V battery.
 
Mar 31, 2002 at 2:23 AM Post #4 of 12
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The case is a bit bigger than 2 AA batteries laid end to end. rickcr42 seems confident it can be done. I specified 2 AAA because I assumed that's as much as anyone could shoehorn in the case and still have enough room for the circuit. If it can be done with 3 (and I assume their are opamps that can use 4.5 volts) that would be fine.

I suppose another configuration would be to punch a hole in the side of the case, trail battery leads out of it and connect a 9v that way, and glue straps to the cd player to hold the battery in place.

The most important question...is anyone willing to build this amp for me? We can talk terms if you're interested at jdtippitisit@hotmail.com.
 
Apr 1, 2002 at 5:48 AM Post #6 of 12

eric343

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Well, maybe with a custom PCB (or dead-bug construction) and SMD, yup it's doable. Especially since the AD825 opamp is SMD and puts out enough current that it dosen't need a buffer. Of course, it's only availible in single configuration, so that's where the double-sided PCB comes in. One side would be one channel. Using some layout tricks and all-SMD components we could probably fit one in an AA battery. If we went with an SMD OPA2134, we could probably go smaller.

Of course, I'm not sure about the 825's power requirements. But the 2134 should go ages off a 9V.
 
Apr 1, 2002 at 1:11 PM Post #7 of 12

skippy

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i believe the minimum for the ad825 is something like +/-5v, though i t works fine on +/-4.5v. gotta remember that most opamps like dual supplies so with 3 AAA batteries, you can get only a bit more than +/-2v.
 
Apr 2, 2002 at 6:47 AM Post #9 of 12
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So a 9v power supply would be the only real choice if I wanted an increase in sound quality? I could live with that.

I think it would be best to hardwire the input and trail out a few inches of cable terminated in a right angle stereo mini plug, and have the headphone out as the only jack on the unit.

Now the question is, who want to build it for me?
smily_headphones1.gif
 
Apr 2, 2002 at 4:14 PM Post #10 of 12

tangent

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The size of the SL-CT570 battery pack plus a 9V battery isn't much smaller than a mint tin. That would be the easy way to solve this problem.

I guess I could try doing a second version of my micro-cmoy amp, which was built in a mint tin not much bigger than a 9V battery itself. That amp was a usability mess, though. You couldn't tug on the cords without ripping the thing apart, for one thing, because there wasn't even enough room inside the case to add strain reliefs.
frown.gif
The tin really is too small -- even if you fix the problem with the cords, getting the battery in and out and turning the power on and off is difficult. I could probably do a better job the second time 'round, if I could find a mint tin halfway between that mini one and a regular Altoids/Penguin size one.

You might PM sijosae to see if he'd be willing to do one for you -- he's better at the miniaturization stuff than I am. If you haven't seen his work, examples are in that thread I linked to.
 
Apr 3, 2002 at 7:15 AM Post #11 of 12
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Well, I wanted it built in the battery pack because the battery pack was physically designed to attatch conventiently to the player, without having an extra box bouncing around in my pocket (I will be using this combo as a true portable for music on the go). Glueing a couple of velcro straps to the underside of the player to hold a 9v in place would not add much more bulk, and I would have a player/amp combo in a single, VERY portable unit that would provide superior sound reproduction.

An additional box is not part of the design parameters I'm looking for, and I don't think it really would be necessary since I'm not looking to drastically improve sound quality, just tighten things up a bit.

In reference to the cords, I wonder if putting a bit of hot glue on the cables on the inside and outside of the hole in the case would help with strain relief? The hot glue wouldn't be hot enough to melt the cable, and is somewhat flexible, but solid enough to where a gentle pull would probably hold.
 

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