Tankbag Audio Mixer question.

[Kupa]

I couldn't find a simple audio level/line mixer for sale anywhere that was small enough to carry on the bike. I guess autocom solves this problem, but the price tag is hefty.

My set-up needs? I have 3 audio devices I wanted to listen to in stereo, simultaneously through my Chatterbox GRMS x1. I wanted to have a volume control for the final mixed audio line- each device has it's own volume control, so I didn't need to build in additional line-in volume controls.

Cash is tight, so I built one.

Devices:

- 1. MP3/CD player

- 2. Valentine 1 warning audio

- 3. Police scanner to keep tabs on the CHP aircraft channels

Components needed:

6 10k 1/4 watt resistors

4 1/8 stereo audio jacks in housings

1 miniature audio Potentiometer, dual gang 1/2 watt

1 knob for Pot

1 small project box 1"x2"x3"

22 gauge wire

Solder

Shrinkwrap

The mixer works well, but has one small problem. Would really appreciate any advice on how I can get more volume out of the unit. It's about a third to a half as loud as any of the individual audio devices. I need a bit more volume to really make it work at speed.

Should I have used lower wattage resistors? IE: 1/8 watt

Would a 1/2 watt 200k Audio Potentiometer be limiting my overall volume?

Here are some project images:

The simple black box- easy to carry, with volume control out and three audio inputs to work with.

The inside circuitry. Shrink wrapped/soldered. About 15 bucks worth of parts, and about two hours of time.

Here's how it works. Only two inputs are shown in this image but there's room for a third, and the audio out actually goes into the headphones in my helmet. I run the Valentine 1 radar detector's audio out into the third input so I can ride fast, listen to ambient funk, hear the CHP aircraft channel chatter, and talk over the GMRS. If I could only get a cup of espresso with that.. :nerd

Here's the simple schematic I found online. I added a third input jack and a stereo potentiometer to control the volume out.

Cheers,

Coop

[Kupa]

I had used a boostaroo. It helped, but still wasn't loud enough.

I think the real problem is- it took posting the schematic to a whole forum before I realized that I fucked up in the circuit building. I soldered the resistors in the + Right and Left channels, rather than wiring it into the ground channel. DOH!

:twak:

I like meesing up in front of a crowd. Hell of a lot more entertainment value then.

:oops:

Cheers,

Cooper

[RichardCranium]

That is awesome. That is exactly what I tried to do a while back but I know dick about circuits. I tried finding some schematics online because I thought it would be simple enough to buy the stuff at radio shack and solder it all together. I finally just gave up. Any info you can provide on this project would be VERY much appreciated.

Brett

[Kupa]

That is awesome. That is exactly what I tried to do a while back but I know dick about circuits. I tried finding some schematics online because I thought it would be simple enough to buy the stuff at radio shack and solder it all together. I finally just gave up. Any info you can provide on this project would be VERY much appreciated.

Brett

I agree it will be awesome once I get back into the box and re-solder the resistors in the right locations. I found that schematic above online, and indeed got all my components at RadioShack. Next one I build needs to have the 1/8" inputs spaced evenly, so it looks a little less ghetto.

I'll post an update once I get the rewiring complete. This should work great as long as your audio cables are short from the headphone out of the devices and short going into the helmet headphones.

Check out the swank coiled headphone cable I made that's plugged into the MP3/CD player, that's actually my headphone cable for the chatterbox. Beefy so it gets whipped around less at 135.

RmeUp2-125... Make these? as in for sale? don't the folks at autocom need to put bread on the table? what am I? a robber baron?

:treadmill:

have any interesting stuff to trade? :cycle:

Cheers,

Cooper

[GrandPoobah]

Just came across this thread, but in case anyone's still interested:

Tesseract makes a product that does the mixing and amplifying that you're looking for, and it's significantly cheaper than the Autocom.

Changing the wattage of the resistors won't help. The attenuation that you've noticed is a characteristic of this type of circuit, and it increases for each input circuit that you include. The only solution that I know of is to add an amp after the mixer. I've been thinking of doing exactly that myself, using this design and building it all on one board. I'll post back if I ever get around to trying this.

One consideration for anyone thinking of doing this is that some electronics designed to run off of external 12 volt power use an amplifier configuration known as Bridge Tied Load (BTL). In these devices the negative speaker or headphone output terminal isn't at ground, instead it's given a signal that's the inverse of the positive terminal. With these devices the negative terminal shouldn't be tied to ground as in this mixer circuit. There's two ways that I know of to deal with this: one is to use a transformer to isolate the input source from the mixer, and the other is described in Figure 6 of this datasheet. The Valentine 1 does not use a BTL amp to drive it's headphone jack, but the Escort 8500 does, and your scanner might too.

[XXCited]

It would seem that the best way to handle this would be to have a priority on the inputs to mute the other sources. The detector would have the highest priority, cell phone 2nd, FRS radio 3rd and mps player none. That way whatever the source would have an uninterupted source. Is there anywhere someone could go to learn how to configure such a setup? New to electronics but this has peaked my interest. Also, how are the throat mikes for talking on an frs or cell while on a bike?

[Kupa]

Just came across this thread, but in case anyone's still interested:

Tesseract makes a product that does the mixing and amplifying that you're looking for, and it's significantly cheaper than the Autocom.

Changing the wattage of the resistors won't help.  The attenuation that you've noticed is a characteristic of this type of circuit, and it increases for each input circuit that you include.  The only solution that  I know of is to add an amp after the mixer.  I've been thinking of doing exactly that myself, using this design and building it all on one board.  I'll post back if I ever get around to trying this.

One consideration for anyone thinking of doing this is that some electronics designed to run off of external 12 volt power use an amplifier configuration known as Bridge Tied Load (BTL).  In these devices the negative speaker or headphone output terminal isn't at ground, instead it's given a signal that's the inverse of the positive terminal.  With these devices the negative terminal shouldn't be tied to ground as in this mixer circuit.  There's two ways that I know of to deal with this: one is to use a transformer to isolate the input source from the mixer, and the other is described in Figure 6 of this datasheet.  The Valentine 1 does not use a BTL amp to drive it's headphone jack, but the Escort 8500 does, and your scanner might too.

Kevin- great links. I think I may just go and buy one of the Tesseract v1. units. It's far better than I'm capable of building, and looks like it addresses all the needs I have for mixing audio on the bike. Price seemed reasonable as well.

The headphone amp pages are fantastic. It's great to see the humorous combinations of housing and circuitry.

Thanks for your input as well. The website I found the schematic on mentioned attenuation being an issue with additional inputs. I wish I understood all this better. Maybe a new research project for me is on the horizon...