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PostPosted: 24 Sep 2008, 06:35 
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I recently got into circuitry when i decided to rewire my rickenbacker 330 copy. Now it's this frankenstein monster with phase and parallel and series and mid scoop and bass contour. I wanted to keep going tho so I figured I'd build a little amp and stick in the hollow body. I built the little gem from runoffgroove.com with volume open and just stuck the battery, the speaker and the board in with some velcro. The speaker is at the entrance of the top horn, so I get great sustain and feedback. This crazy wailing if I want it too. Pretty controllable. It's awesome! I then put a red LED in to make it sexy voodoo magic.

I've built a buncha smokey amps for my friends since, and now I want to build an amp with a tin lunchbox I found. It's got the last supper on both sides. It's gunna be great! On one side of jesus, a guitar amp! On the other side, an amp for my drum machine. And the brightest whitest LED I can find, right above jesus head. I want it to be so bright you can't look at the amp when it's on.

For the guitar amp, I think i've settled on the noisy cricket design from beavisaudio.com. But i'd like to try to do a bridged version of it for more power. Not sure how this would work, I think I'd just copy the other bridged versions I see, with some changes. I've really only used the lm386 for my projects. I'm also still trying to find the right speakers. I have a rectangular 16 ohm spekaer and a square 16 ohm speaker. I could do them in parrallel, right? How much do lm386 amps put out???? I have a 5 ohm speaker than sounds pretty good, but I need to understand the speaker impedance and the amp output.

I'm really not sure it will work for the drum machine. I think I'd just need a headphone amp thing goin on. But I really have no idea what to do. I don't think the lm386 will work for a drum machine will it? I have some tda 2002s and tda 2003s but the designs I find online don't work that good.

Any suggestions for either side of the amp?? It will have two power sources. 9v adapter for both sides. I have a buncha lm386s. Here are pics of the box and stuff.


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PostPosted: 24 Sep 2008, 09:55 
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I probably cant answer all your questions but I think I have a few for you.
The LM386 is super low power. Between .2W and .4W. You get about 1% distortion at .2W and 10% at .4W. Thats into an 8Ohm speaker.
16Ohm and it seems that about .45W is about max.
4Ohm and it looks like about .35W
You would think that the power output would increase with the lower speaker impedance, but thats not what the datasheet shows.

The two 16Ohm speakers in parallel will look to the amp like one 8Ohm speaker.
To understand speaker impedances and how amps see them look at this page http://www.termpro.com/articles/spkrz.html

You said some designs are not working that well for you with the TDA series. If you need help with that I think we would need to know what designs you used and what the problems were, specifically.
There is really no reason I can think of that the TDA would not work for your drum machine.
TDA2003 will give you 2W at 9V. Maybe you double up the batteries and get 18V. Then you can get approx 9W into a 4Ohm speaker, so presumably you would get 4.5W into 8Ohms, and you would really need to stock up on the batteries as they would get eaten up pretty fast. A wallwart might be a better idea to supply power to a TDA chip. For some reason the TDA chip likes low Ohm loads. It does well with 1.6 to 2Ohm loads. The TDA 2002 looks pretty similar to the TDA2003 but is just a bit lower power. For instance with 16V the 2002 gives 6.5W into 4Ohms while the 2003 gives 8W into 4Ohms at same voltage.
MAX OPERATING VOLTAGE for the 2003 is 18V so probably to 9V batteries is not a great idea. A 16V wallwart might be your best bet. The datasheet does include a circuit and a pcb board layout if you are inclined to make your own boards. Here is the datasheet link http://www.st.com/stonline/products/lit ... da2003.pdf
Dont forget that without batteries you need to make a power supply or make sure your wallwart outputs DC. Even then you may want some small power supply caps in your circuit before the + and - power inputs to your chip.
Ri

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PostPosted: 24 Sep 2008, 10:09 
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thanks I know I still got a lot to learn. I have limited access to parts so I just pick a design and go for that. I didn't use any from the datasheets. I guess I should stay away from wiring multiple speakers to the same amp for now. I'm just trying to get the most power and performance from the little tin lunchbox I'm building it in.

If I use the TDA 2002 or 2003, I will have to up the power to get more volume?


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PostPosted: 24 Sep 2008, 10:23 
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hey according to the link you gave me, two 16 ohm speakers wired in parallel would be 8 ohms. 16 X 16 / 32 = 8 ohms??


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PostPosted: 24 Sep 2008, 10:37 
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2003 will give slightly more power. Wiring your two 16ohm speakers will actually allow your amp to output a bit more power since it will see less resistance.
Yep two 16Ohm in parallel is 8 ohms.
The datasheet has a decent little circuit on it and if you have the parts its worth a try and will probably sound great. If you are only going with what you have on hand you might be getting a junky sound depending on what parts are of what quality.
Try using some paper in oil caps or polypropylene for low values and Panasonic FC series of electrolytics for high values. Use Dale RN55 series resistors (metal film) rather than carbon comp. Dont use ceramic caps at all.
Page 6 and 8 of the 2003 datasheet are going to be the most important to you. They include the circuit and the bill of materials.
To purchase the bill of materials with the type of parts I suggested you could spend as little as 10 dollars for stereo, but I think you are doing mono so cut that in half. Its hard to buy Paper in Oil piece by piece so if you were to use those (the sound nice and smooth) your price would go up by probably $20 for 10 of them on ebay shipped from Russia or somewhere near there.

You always have to up the power to get more volume. Just figure that your circuit will probably be 60% efficient or to make it real easy figure 50%. Take the voltage of your battery and multiply it by the maH (milliamp hours) and divide by one thousand. That gives you the watts you can push into the amp from that battery in one hour before the battery dies. Now divide that number by 2 and you get approximately the wattage your amp will push.
You could pack a 50 watts into that lunchbox if you wanted. I dont know how many watts you want but I am sure you could get whatever you need to fit in it. But then you need to build a power supply and we get to around $2 per watt and maybe $3.
If those 16Ohm speakers are identical I would run them in parallel. It will be louder. If they are not identical its to easy to try both anyway. Why not? Your are not risking hurting the speakers and all it takes is two pieces of wire.
Dont worry about being a newb, this is the place for newbs like you and like me :)
Ri

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PostPosted: 24 Sep 2008, 11:19 
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never heard of paper and oil caps. hmmm. Sound hard to get. Russia???

I guess I will to a tda2003 for the drum machine part. I have a 2.1 mm jack for an adapter. I was going to use two on the lunchbox so I could power both of them with 9v adapters. I could get a 11v or 12v adapter with the same size right?

Still unsure about the guitar side. The noisy cricket is quiet. All the single lm386s are kinda quiet. I'm thinkin a bridged little gem, or trying to do something else with the lm386s bridged. I want a tone and volume and gain control tho.

My biggest wonder is which speakers to use tho.


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PostPosted: 24 Sep 2008, 12:36 
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Not hard to get, just take a few weeks. The same size poly's will cost a lot less and sound similar but you might like the PIOs better. Lots on ebay. If you decide you want to try them they are easy to get and I will help you find them. Polys are available everywhere. Mouser, DigiKey, www.apexjr.com, and ebay are where I get all my parts. On ebay try to buy from someone you can get lots of your parts from to minimize shipping fees. Dont pay right away, make them send you a combined invoice with one fee for shipping rather than one fee for each item.
You can use whatever adapter you want as long as it fits. With this low voltage and wattage you are not going to burn out an adapter or any wires.
If you buy your wallwart from www.cui.com you can call them up and ask which female adapter you need to buy from them to fit your wallwart. Or you could take your wallwart to RadioShack and try plugging it into every adapter they have til you get a match. Or, you could just solder wires right onto the wallwart's adapter and keep the wallwart in your lunchbox, then open the lunchbox and out pops the wallwart and you plug it into the wall. Then, of course it will be permanently attached to the amp.
It looked like that noisy cricket had tone controls and the guy posted the schematic so that should be easy. Hmm.. bridging them with dueling tone controls might be weird, but it would probably work fine.
The speakers are the least of your worries. You have three you want to try. Just plug them in once you are done with the amp and see which one or two you like best. It will push all of your 3 speakers individually or in parallel. No problems there.
Ri

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PostPosted: 24 Sep 2008, 18:08 
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Hi nopainkiller

What an interesting case. Yeah the LM386 is only good for about 1/2W. The noisy cricket design looks good and it is well documented.

Anything with two 9V is not going to be over 1W since they can only deliver much current. Is this meant to be a practice amp?

Cheers

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PostPosted: 24 Sep 2008, 19:47 
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Yes, it's just meant for fun. I was planning on a 9 volt battery for each amp. And then a jack for each of them for a 9v adapter. I want to play the drum machine and play guitar out of the same amp, just a few feet away from me. Really for convenience, so I can just flip two things on, and start playing. I can't find anything about a drum machine chip amp anywhere. If I biuld the 386 or any other amp exactly like the datasheet, it should play clear right? I tried it with the lm386 and the tda 2002 and it was scratchy and distorted and trebly, and gainy. I did not use the correct components tho, since all I had on hand were 220 caps instead of 250, and .047 caps instead of .05 and so on. Can't find all parts on the net without minimum order requirments. Like 500 bucks or something!!! like 250 caps!I Can't find anything but 220!!

I really don't fully understand how these circuits work. I've only slopped together stuff I've seen on runoffgroove.com and beavisaudio.com. I


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PostPosted: 24 Sep 2008, 20:49 
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Those numbers for the caps were fine. That should not have caused problems for you. I dont know what was wrong but it was not your selection of components.
Try www.mouser.com and www.digikey.com and ebay for your components. And of course I always have to plug www.apexjr.com.
You wont have those kind of minimums. Really you can buy one of just about anything.
I have had bad solder joints make things screech and scratch before, but maybe Gio or another contributor would have comment about your problems. I doubt it at this time though since really there is not yet enough to go on to get an idea what might have happened.
Ri

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