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Old 8th July 2009, 04:43 PM   #1
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Default SOme great parts ready for a new project....ideas?

Hi everyone. This is my first post/thread. I am a law student interested in music and movies not to mention electronics (among other things). Since I recently upgraded to high def flat panel tv and can feel the need for some good sorround sound to couple with the image quality.

I have some experience in diy projects (I have built some high current power supplies, variable supplies, oscillator circuitry, cnc electronics) however I would like to start building my own amplifier set.

This is the material I have and here is the photo I took of some of it due to space on the table.

http://i365.photobucket.com/albums/o...8/Immag042.jpg

4x500 toroids (3x 36-18-0-18-36 and 1x 30-0-30-0)

6x 33,000uf 63v electrolytic capacitors

3x18,000 50v capacitors

2 aluminium containers

everything else I may need, I will be able to acquire.


I hope somone can suggest how to put to good use this equipment and provide me with some good advice on how to accomplish this project.
I have experience in using cad software and pcb routing however I woul prefer something based on proven schematics with possibily a ready to print pcbs.
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Old 8th July 2009, 10:27 PM   #2
Bigun is offline Bigun  Canada
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You've asked a big question. Designing and building a multi-channel amplifier is not a small project.

There are plenty of amplifier designs on the Forum that you can base your system on. Look at the DX, Symasym, Frugal, Patchwork to name a few.

But, it would be helpful if you were to tell us a bit more about your needs. Do you have speakers already ? Do you plan to have a powered sub-woofer or do you need to build an amplifier for a sub-woofer ? 5 or 7 channels ? Big and powerful or something more neighbour-friendly ? etc.
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Old 8th July 2009, 11:09 PM   #3
Fenris is online now Fenris  United States
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Simplest route with the best chance of success first time would be a GainClone type of project. The voltages are about right, they're compact, and don't need enormous heatsinks. You can also bridge/parallell them to make a bigger subwoofer amp. While many here are fans of Class A designs, you really need to have the rest of the system (speakers, source, room, cabling) up to pretty high standards to appreciate the difference, and you have to be willing to live with the inefficiency. Lousy speakers with the best amp in the world will still sound lousy. If you want to go the Class A route, there are plenty of designs, Neslon Pass has a few as well as a number of others in this forum.

I would recommend starting with a GainClone or a proven design as a first project. It also helps to know what speakers you have so that you can match the power requirements to your amp.
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Old 9th July 2009, 03:36 PM   #4
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thanks guys.

Well to be honest I am tackling this one from the bottom up. I would like to build an amplifier first and then (hopefully envolving family finances) go straight for some good quality speakers. I really don't think there is much point in tailoring my system now on low quality speakers since I might just change them in a couple of months.

I hope you see my line of reasoning behind this.

As far as the project is concerned I was looking into this one:

http://www.diyitalia.eu/index.php?op...d=55&catid=108

4 of these 1 per channel:

http://www.diyitalia.eu/index.php?op...=1&key=5&hit=1

My needs: I would like this system to be movie oriented. Sharp sounds, clear and undistorted signals (I like action and science fiction movies) but capable of being transformed into a music amplifier for the times I have friends over.

Basically If I have to spend now money omn this project I might as well build something worthwhile. Later on good speakers will obviously be on top of my list of things to buy.
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Old 9th July 2009, 10:22 PM   #5
taj is offline taj
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I noticed 3 things about this circuit that are atypical as compared to the amplifiers that we see here.

1) input impedance is higher
2) input capacitor is small, even considering the impedance
3) Bias adjust trimmer is wired dangerously

But then, I'm a noob, so I am probably wrong.

..Todd
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Old 10th July 2009, 02:15 AM   #6
jaycee is offline jaycee  United Kingdom
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That looks like a good circuit.
Also look at Quasi's NMOS based amps - these use VMOSFETS (like IRFP types) which are cheaper and easier to get.

The 36-18-0-18-36 toroid would be ideal if you wanted to add some preamp circuitry - the 18-0-18 supplies would quite nicely make regulated 15V supplies for opamps.

36V AC would get you about 50V rails so you'd get around 80W RMS into 8 ohms. This is plenty of power for domestic use, and tons better than most AV recievers you can buy.

Quasi's NMOS 200 amp would fit just nicely, I think!
http://users.adam.com.au/cgpap/QuasiWeb/index.htm
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Old 10th July 2009, 02:09 PM   #7
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THnaks for the suggestions.

I would like to add I managed to retrieve 100 (hundred)x 4700uf 63v capacitors. this gives me around 720000uf capcitor power.

Anyway I am looking for the most efficient design. Basically I would like something that gives me some good results (in terms of THD, and perceivable sound properties) yet makes the most out of the transformers and the cpacitors. 80w of rms power is a lot for domestic use but since I have so much transformer and capacitor power I was thinking of "squeezing" sometyhing more out of the system.
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Old 10th July 2009, 03:19 PM   #8
jaycee is offline jaycee  United Kingdom
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If you have 3 of those 500VA 36-18-0-18-36 toroids, why not use 2 of them ? You would need a fairly hefty softstart circuit for them both, but it's doable. You'd also need to make a big, solid case, but it seems you have the materials to hand to do that.

The biggest problem with standard AV receivers is a compromised power supply. They might advertise 100W per channel output, but that is usually 1 channel driven, and usually with 1% THD or worse - typically with only 300VA of transformer and 2x10000uF total PSU capacitance. Nowadays it is even worse as most of them are going Class D and allowing 5% THD or worse.

So, if you build something like 5x80W RMS with 0.01% THD and enough power supply capacity behind it to ensure that you can drive all channels to full load without degredation, you have already far surpassed anything you could buy reasonably. You will be very happy with the result and commercially you'd have to spend a hell of a lot to get the same standard.

At any rate, unless you can get a transformer with higher voltage taps, or rewind one for more than 50V rectified output, you're limited to around the 80W figure.

If you have built high current supplies and variable supplies then an amplifier should not pose much of a problem. The same principles in dealing with power wiring to the amps and from the speakers, grounding arrangements etc, all apply equally.

I'd definitely recommend Quasi's NMOS200 for this application. It is a good solid proven design that has been built by several forum members successfully. You could build 5 of the TO-247 version with the MOSFETs mounted on aluminium angle, and then bolt those to a big heatsink. You could even make use of some PC style fans coupled with a temperature monitor circuit to aid cooling when things warm up (you wouldn't hear the fans over the sound of the movie youre playing )
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Old 10th July 2009, 07:58 PM   #9
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very inspiring words. I will certainly look into the projects you suggested. Could you also suggest a good preamp to couple with the NMOS200? I am realy unsure of the strength of the signal from my dvd/blueray and satellite decoder appliances.

As you can see I am quite new at this. However I do have the material time and (hopefully) the necessary skill to accomplish well explained projects. My goal is to enjoy what I have built every time I use it; since I almost have a dedicated room for move watching I can see that happening quite oftebn in the future (that is of course if everything goes as planned).

Regarding the fans I already built several opamp lm50z based controllers. I get fairly good results in terms of cooling to sound ratio so that probably won't be a problem.

Do you suggest using all the capacitor power I have? I was thinking of dividing it like so:

front channels: 2x 33000uf + 40x 4700uf

rear channels: 2x 33000uf + 40x 4700uf

subwoofer (if used): 2x 33000uf + 20x 4700uf

The capacitors are computer grade low esr (33000uf) and chemi con snap in standard 4700uf. Can both types be used in this project? (I ask in terms of audio quality).

Thanks for your kind help. I will surely keep you apprised of my progress (if anything to ask for help )

Alex
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Old 11th July 2009, 10:06 AM   #10
AndrewT is offline AndrewT  Scotland
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Hi,
build a monoblock for each speaker. You need six for 5.1
If you can't afford this option, then build two channel amplifiers (you'll need three for 5.1).

The 36-0-36 500VA transformer will give about 110 to 120W into 8ohms (BJT output stage - a bit less with FET follower output stage). The 500VA can power two channels, i.e. 120W + 120W.

The 33000uF caps can power a single channel. If you want to run a two channel amp off a common supply then boost this to 33mF + 2or3 * 4700uF (for 8ohm speakers) for each polarity.
If you go to 4ohms speaker then double your capacitor requirements.
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