[CaptBubba]

Get your mind out of the gutter!

How often have you only had one jack, but instead needed multiple ones? For example... if you have one laptop, four 5 hour flights, and three people who want to be able to listen to the dvd that is currently playing.

Behold: the 3-Some!

Separate volume controls for each jack, will use 2x 9V batteries. Of course, it has to look good at the same time, both not to be an eyesore, and not to look like an explosive device.

Nude 3-Some:

Here's the actual chips doing the outputting:

Tons of fun, a pair of ad843s drive the volume controls to keep input impedence constant, while a buf634 in low b/w mode provides the virtual ground. Output is handled by two pairs of opa134s and a pair of opa227s.

I made the mistake of not checking things as I built it. I realised this when I went to fire it up. AND IT WORKED!! It is very very cold in a place that is normally very very hot.

 

[eric343]

Cool!

I made a similar device; my solution was an LM386 (mini-power-amp-chip) driving 10 jacks each with a 10ohm resistor in series with it... no separate volume controls, but hey it worked.

 

[Vdubjunkie]

That is totally cool. and I do have to admit the title drew me in very quickly. I guess my mind was in the gutter. I may attempt to copy you on this design for my home pc arrangement. I will soon have 3 computers attempting to share one set of speakers. I don't really think I'll need amplification though, so that will surely simplify things.. of course it also may not be fun enough that way, so maybe I will use opamps anyway

btw, on a side note, I will be taking flight soon and wonder how much trouble if any you have received boarding with such a device. I was hoping to take my mint amp. In my mind just looking at it makes it clear it isn't complicated enough to tear a hole in the side of the plane, but.. what is your experience with this?

 

[CaptBubba]

Sweeet, I can fit 8AA's in this thing. I hate 9V batteries.

 

[tangent]

Quote:

It is very very cold in a place that is normally very very hot.

And you soldered the chips down, too! You must have been feeling lucky.

Quote:

I don't really think I'll need amplification though, so that will surely simplify things.. of course it also may not be fun enough that way, so maybe I will use opamps anyway

You need amplification:

1. If there's nothing in between the headphones, their impedances are in parallel. For three headphones, that triples output current requirements. Heaven help you if you used Grados in a setup like that. Eric is getting away with this because the LM386 is a small power amp: it can supply enough current to drive a low impedance speaker array.

2. If all of the headphones are the same type and everyone listening can agree on a volume level, then you're fine. If one of those isn't true, you need separate amplification for each headphone. If the headphones aren't all the same, the volume from each will be different. If the listeners want separate volume levels, the sanest way to give it to them is with independent amplifiers for each output jack.

3. Your setup might have enough voltage to drive the headphones directly, and it may even have its own volume control, so technically you don't need "amplification". However, you do at least need buffering. If you just put a volume control in between the source and the headphones, the source sees the headphones in parallel with the volume control, giving a very low impedance, and thus a very high load. Also, this means the source has much less control over the headphone drivers -- try putting a 47K resistor on the output of a CMoy amp and see what happens. Then change it to 22K (as if you were turning the volume knob) and see how it changes. This is the effect of a pot in between a source and headphones.

Quote:

how much trouble if any you have received boarding with such a device. I was hoping to take my mint amp.

I have no experience, but it seems to me that the more "manufactured" something looks, the better off you'll be. And if you're using a mint tin for your amp, it's clearly a DIY enclosure, but it's easy to open it and show people that it's got manufactured guts in it. Keep the interior neat and you'll have done your best to keep your amp.

I wonder, though, if a security person flags an item as "illegal", is the only option confiscation? Can you go back into the airport and find a post office and mail the amp to your house or your destination so they don't take it away? A DIY'd amp represents a pretty big time investment, and sometimes a big parts cost, too. I'd hate to lose one to an overly paranoid airport security screener.

Quote:

Sweeet, I can fit 8AA's in this thing. I hate 9V batteries.

I was wondering what you were going to do with all that extra space. I agree -- AA's are far superior, when you can get away with using them.

 

[eric343]

Regarding the airport thing:

RECASE IT. That box looks HIGHLY suspicious.
Look into a Hammond 1455 or a case from Extrutech (www.xtech.com). At the bare minimum, a Hammond plastic case will also do. JUST DON'T USE ONE FROM RADIOSHACK LIKE THAT! That thing looks like a bomb to ME, and I know what's inside.

If you can afford it, use FrontPanelExpress to get silkscreened panels, and include "Sony" somewhere in that font that Sony uses... You want it to look as professional as possible!

If you can, pull a Sony or Panasonic logo off another piece of gear and put it on the amp. That works wonders...

 

[Vdubjunkie]

Quote:

Originally posted by tangent I wonder, though, if a security person flags an item as "illegal", is the only option confiscation? Can you go back into the airport and find a post office and mail the amp to your house or your destination so they don't take it away? A DIY'd amp represents a pretty big time investment, and sometimes a big parts cost, too. I'd hate to lose one to an overly paranoid airport security screener.

This was pretty much my concern as well. Thought my scavenged parts mint tin amp wouldn't be a crippling expense to lose, I am more concerned with the effort put into it than the $
I'm leaning toward playing it safe, but may call the airport and see what they say.
Quote:

Originally posted by tangent You need amplification:

I guess I wasn't thinking too clearly because to begin with what I really need is something to take 3 input sources and possibly even have a selector switch to put them out to the same set of speakers as opposed to headphones. In that scenario amplification wouldn't be necessary if I am thinking correctly, but I wonder if I would need anything much more than a bunch of 3.5 female jacks a selector switch and some wire..

 

[tangent]

What you have then is a "passive preamp". Do a search to find out what's been said about them. They're not without their problems, too.

 

[Voodoochile]

Cool stuff, Captain! Now it can be your turn to ask the people in the seats next to you if they would like to rent some headphones for the 'in flight' movie.

At least they would be nice cans, instead of the telephone operator headset they try to give you normally

.

I would recase also, and do label the controls volune, audio in, headphones, etc. It sounds ridiculous, but should help.

 

[CaptBubba]

Things I still need to do:

Add knobs to the volume controls (works wonders for the look)
Paint it
Add labels to the controls
Leave headphones plugged in at all times

I may buy and apply a US flag sticker to the top, or would that be too much? I'm thinking when the security guy opens it and just sees a few AA batteries and chips and a familty of three waiting patiently he should let it through. I mean, I can always turn it on to show them it is what I say it is.

 

[eric343]

Well, it's held closed with screws, so that will mean a fair delay at security...

Don't bother with the American flag, bother with a Sony logo. Seriously.

 

[akar]

There is no need to do anything to it.
Just put it in your bag and let it go through the x-ray with the rest of your stuff.
They can see what's in it, labels aren't fooling anyone.
If all it took was some labels and stickers to get bombs on planes, terrorists would have stock-piled Sony stickers.

 

[rickcr42]

Quote:

I may buy and apply a US flag sticker to the top, or would that be too much? I'm thinking when the security guy opens it and just sees a few AA batteries and chips and a familty of three waiting patiently he should let it through. I mean, I can always turn it on to show them it is what I say it is.

Quote:

There is no need to do anything to it.

tough call on the security thing . even if X-rayed what security guy/gal would have a clue as to the function ?

best way is to actually demo the amp (and then direct him/her to head-Fi hehe ) leaving no doubt as to the purpose of such and maybe it is time for on of the box manufacturers to come up with transparent covers at least mint tin amp can be easily opened and being so small leave little room for explosive devices

maybe even use a multi mint tin solution with the main input section/power supply and then individual amp boxes velcroed together , each easily opened for inspection

dunno

 

[akar]

The TSA screeners are mostly on the look-out for sharp objects, or items that can be used as hand held weapons.
But the person operating the x-ray is on the look-out for explosives.
Things get color coded as they pass through, if he/she can see it clearly in the x-ray, you'll be fine.
You will have more trouble with a laptop or portable DVD player, due to the battery, than you will with your DIY amp.

 

[akar]

Here are a couple pics of a "2-some"