Sound systems - a working example

Status
Not open for further replies.

marshon

Member
OK guys,

I'm halfway through my suit build and I wanted to add a sound system. Not for music or general sounds, but for voice distortion.

What I wanted was a slightly metallic / robotic / radio voice. Something similar to a Star Wars Trooper helmet voice. Oh and being skint there was no way I was spending the $400 for the Darth Vader one! I also didn't want to pay for a kit. This thing has to be ultra cheap!
However, anyone who has seen my work will know that I don't want it to be crap either!

Seems that not many people on this site have tackled this in any great detail. So here are my thoughts, please feel free to jump in with yours too.

My thinking is to mount a car phone microphone in the front of the helm, speakers in the chest and bob's you aunties live in lover!

First thing then is to make a mic pre-amp, easy to find working circuits for this:

micamp.gif


This circuit will work with both dynamic and electret microphones

micamp2.jpg


The BC547 and the 2N3904 could be swapped for any amplifying / switching small signal NPN transistor. I have a bunch of 2N222A transistors so I'll try those.

Next we need a voice distortion circuit that actually works! - loads on the net that are crap, but this one is a little gem. I've seen it working and it's great. The voice is easily recognisable with words being clear whilst there is enough distortion to make a difference.

robo_voice.jpg


Then all we would need are an amp and speakers. This is causing me a few problems. When I saw the voice distorter working it was being run through amplified computer speakers. I think we need to be able to drive at least 4W into an 8ohm speaker to get decent volume, but all the amps I found (bar one) needed a 12 - 18V source to drive them.
I did find a 10W amp that runs off a 9V battery, but the circuit is very old (from a 1980's electronics mag) so I will need to redraw the schematic and see if all the components are still available and if alternates are available instead.

Once I've built the voice distorter I will post an update.
 
I like the idea but I was wondering if you checked out your local toy departments in your area? I know some of the toys have a voice distorter in their helmets. You may be able to tweak one or two to fit your needs without spending much and still get the quality you want. Good luck on your build.
 
Been a LONG while since I've read an electronics layout (like, year 9 science... so not THAT long, but I forgetz ); ) so I can't really comment on the workability of your design.

I'd just suggest picking up old amps and sound gear where you can and cannabilising them, as it's usually cheaper to do that then look for working parts individually. Good luck man, I can't wait to see how this turns out :D
 
I've spent about a week playing around with this idea.
I thought it would be cool if the system could play sounds, music and what not from an MP3 player, or a minidisk player etc.
I also wanted the sound distortion unit and possibly a bypass so that 'normal' voice could be used as well.

I have been playing with the distortion circuit above, as well as another using a 555 and 741 chip. I'm still fiddling with this set up.

So starting from the back and working forwards, the first thing we need is a speaker. This will also determine the power and volume requirements of the system. I went cannibalising old bits and pieces and ended up with four likely candidate speakers. A standard PC speaker about 2" across, a far better quality PC speaker 3" by 1.5", a car audio speaker 3.5" in diameter and a hi-fi small speaker from an active set that I found in a skip. All free.

I then breadboarded a basic amp and tested each speaker using the headphone output from my PC. It was very apparent that two of the speakers were way better than the others. The car audio speaker and the active set ones were much better sounding and louder than the others so they were discarded. I would have used the car audio speaker but i couldn't see a simple way to mount it in the amour. It was too deep at around 2 3/4" so I plumped for the active set one. This was mounted in a small cardboard housing that I made and then glued into the foam for the armour.

Now to the amp. there are three very common amp chips available that are pennies to buy. The 741 op-amp, the TDA2003 and the LM386. I was tempted to use the TDA2003 which can deliver 10W from a 9V supply, but I didn't have one in stock and it needs a heatsink. Furthermore our little speaker doesn't need anything like that amount of power to deliver good levels of volume.

The 741 is pretty old technology but there are millions of these chips still in circulation. I might use one on test as part of the distortion unit. So the little LM386 it is then. Good, almost all the power needed can be delivered by this chip giving an out put of just under 1W in the configuration below. plenty for our needs.

here's the circuit as designed and tested. It works just fine and sounds good through the little speaker. the design is almost straight from the LM386 datasheet and needs very few (and very cheap) components to work.

Full%20distortion%20unit.jpg


More updates as I work on it all.
 
Here's the back of the wiring loom for the speaker and some LEDs

new_project_wip_38_by_marshon-d3k4yeq.jpg


and here's the panel installed and on test

new_project_wip_40_by_marshon-d3k4ykh.jpg
 
OK guys n gals,

I now have a fully working system, I'll post up a video of it during the week.
However, a few things have come up during my experimentation. Firstly, people wearing a full helmet costume are basically unintelligible when they speak, so even without voice distortion it is so easy and cheap that it's worth fitting the basic system just so you can be heard!

Starting with the parts. You will need a microphone to get your voice into the system, condenser electret mics are EVERYWHERE these days. I managed to blag 4 out of the skip, two were from defunct cheapo Skype headsets, one was from an old in-car phone system and one came from an old telephone handset. These mics range from small to tiny and virtually every cell phone, laptop, dictaphone or other 'speak into' device now carries one.
Even if you have to buy one they are only about $2 each off ebay.

Here are the four I 'rescued':

DSCF3309.JPG


Top to bottom, they are:

Mic from a 3 dollar Skype set
Mic from an old Logitec Skype set
Mic from a telephone handset
Mic from an in-car hands free kit.

Al found in the scrap.
 
Well, since nobody else is replying: I think this is really interesting! You can be sure that I will shamelessly copy, steal and reproduce everything in this thread when the time comes :)
 
After working alongside several Stormtroopers, Biker Scouts, and Mandalorians...

Sound systems are a necessity.

How is your hearing?
 
We also need a way of getting sounds out of the system. Just about any speaker will do it, as long as It's small enough to fix into the suit somewhere. 8 ohm speakers from old PCs are ideal since they are generally about 2" in diameter which is big enough for reasonable sound and small enough to fit into the suit.

Again I found 3 in the scrap, one paper cone round one, one plastic cone round one and one paper cone 'rectangular' one. I love free stuff.
to buy one off ebay you are looking at about 3 bucks so they are still cheap.

Here's the round one as I found it and the rectangular one mounted in a resonating box made of cardboard (the plastic cone one is already in the suit).

DSCF3310.JPG


These will work perfectly well fr our needs.

Now we need a circuit to go in between them.
Before we go any further I am NOT an electronics engineer, I understand the basic fundamentals and I can read a circuit schematic and that's about it. What I have learnt is that for these kind of low voltage circuits the values and quoted part numbers can often be pretty non-critical and interchangeable.

So we need to amplify or 'boost' the signal generated by the microphone to a level that the speaker can output and that we can hear.
The amplifier is one of the most basic audio circuits and I have trawled the net for the simplest (and cheapest) ones I could find.
We can use the very common and very cheap LM386 chip for this, it's an amp on its own and requires very minimal addition parts to get it working, however it needs a higher level of signal to drive it than these little mics can deliver so we need to pre-amplify the mic output. We need a preamp.

We can make one with a single transistor, two small capacitors and three resistors. Total cost about 50 cents. Just about any general purpose NPN small signal switching transistor will do. I strip down any old electronic bits I can so i have a box of little transistors that will do the job. Very common ones are 2N2222a, 2N3904, BC108, BC109, it's an almost endless list.

If you have a transistor and don't know what it is there are normally markings somewhere on the body. Just Google the numbers and you should be able to find a datasheet.

You need two 0.1 uF capacitors (usually marked '104') which cost pennies, two 10k resistors and one 100k resistor. Again pennies and all available at Maplins or Radio Shack.

Next up date how to assemble the pre-amp - it can be made smaller than one inch square.
 
Here's the circuit I used for the preamp.

micamp2.jpg


It has so few parts that we could build it 'bug style'. This means that we simply solder all the correct leads together, with the end result looking like a dead bug. Dirty and not very attractive, but functional and tiny. Once assembled we can encase the entire thing in a glob of hotmelt glue, wait for it to set then glue it all into the helm.
Here's an example of bug style circuitry:

DSCN0950-filtered.png


The problem with this is the fact that you need to be pretty good at soldering and have a set of 'helping hands' to assemble the thing. Oh and don't forget to allow wires for the battery feed, the mic feed and the output feed!

We could also use the 'Manhattan Style' of construction. Using a piece of single sided copper clad board (from Maplins or Radio Shack) we cut a strip and then cut that into small squares or circles. These are then glued onto a small base board and the leads are then soldered to the raised bits. Like this:

MAKE_667.jpg


If you are really clever you can make a proper PCB by acid etch, but it's not really worth it, just use a small piece of Vero board, again available from Maplins or Radio Shack. You can fit the entire preamp onto a board about 1" square.
You only need to cut one track just a head of the Base of the transistor so that the capacitor (C1) is forced to bridge the gap. here's my test preamp:

preamp1.jpg


I could have cut the board even smaller than this. The bigger black cable is the incoming electret microphone, the shorter pair of red and black wires are the output and the longer pair the battery connection.

We now have a microphone and a preamp that is capable of delivering a signal large enough for almost any power amplifier.

Next the power amp design and construction.
 
OK, so we now have a microphone and a preamp. We are now able to deliver a 'line level' signal to the rest of the system.

Since we want to use a speaker to make the sound, we need more power at the output to drive the speaker. We need a power amplifier or power amp. We could use one of literally thousands of amplifier designs, but we are working with a very defined set of parameters here. First of all the amplifier has to be small enough to fit somewhere in our suit. Secondly it must be DC powered, and finally it must work off a low voltage - a 9V PP3 battery is small and light enough to fit into a suit so I used that as my limiting factor.

Now we have reduced our choices down considerably. We could use an amplifier design that uses many cheap parts (a standard transistor set up), but there are chips available which are an amplifier in themselves adn therefore require much less effort and space as far as we are concerned.

The two that immediately sprang to mind were the TDA2003 and the ubiquitous LM386.
The 2003 is an excellent little amp chip. It can deliver 10W into a 4 ohm speaker from 12V or around 3.5W into 8 ohms from a 9V source. That may not sound like a lot of power but for our needs it's overkill.
The only reason that I didn't use a 2003 chip is that it generates quite a bit of heat and therefore needs a heat-sink. This means more overall size and I didn't fancy putting any kind of heat-source into a foam rubber suit!

That leaves the LM386, these cost pennies to buy, need very few extra parts to work and can deliver about 1W into 8 ohms from a 9V battery. Perfect.
The chip is by no means 'hi-fi', but we're not really interested in fidelity (in my case the exact opposite in that I wanted it to sound slightly mechanical).

As to the actual circuit, I basically used one of the ones supplied on the PDF datasheet for the chip.
This about as simple and stripped back as I could find:

9V_amp.jpg


There is one thing missing from this circuit though. If we put another 0.1uF capacitor from pin 7 to earth and add another resistor and capacitor we can boost the bass output a bit.

This one is from 'free circuits', but there's no need to change the values from our earlier diagram. Stick with all 0.1 uF caps for the non-polarised caps and stick with a 220 uF electrolytic for the main cap.

amplifier_lm386_bass_boost.gif


Both these circuits work really well for our needs. the first, simpler version is perfectly good.

Again I built mine on vero board and you only need to cut the tracks between the pins of the 8 pin chip. the rest can be juggled into place on various other tracks.

Here's one I built as a test:

new_project_wip_41_by_marshon-d3k7mmc.jpg


You can see how small it is and I could have made the board a little bit smaller again.
I used an on board 'trim pot' for the volume control so that once set it remains at the same volume. You could use a control knob if you want to adjust it without having to open the control box once built.

Both the preamp and the power amp can be run from a single 9V battery, and with the mic in the helm and the speaker in the armour, this set up will work perfectly well for direct voice amplification.

In the next instalment we'll consider being able to hear yourself from inside the helm, and possibilities for voice distortion units to make it sound a bit different.
 
Status
Not open for further replies.
Back
Top