SOme great parts ready for a new project....ideas?

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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/oo98/Alexontherocks_2008/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.
 
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.
 
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.
 
Disabled Account
Joined 2009
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?option=com_zoom&Itemid=55&catid=108

4 of these 1 per channel:

http://www.diyitalia.eu/index.php?option=com_zoom&Itemid=55&page=view&catid=108&PageNo=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.
 

taj

diyAudio Member
Joined 2005
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. :rolleyes:

..Todd
 
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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Joined 2009
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.
 
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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Joined 2009
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
 
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.
 
Well For now I can just start with 2 and see where that goes. I really can just add "modules" along the way. However a 5.1 system would clearly be ideal (given I actually happen to have 5 speakers and a subwoofer).

Regarding the power requirements I am a bit confused.

You said that the 6 (33,000) capacitors can be used for a single channel. This would mean 198000uf. I am confues because you then wrote: 33mF + 2or3 * 4700uF for each polarity (in case of a 8 ohm speaker).

Now: if I use 6 caps I get 198000uf per channel

If I use 2x 33,000uF caps + 6x 4700uf I get 94200uf per channel.

I do however have 100X 4700uf, can I use them all? and aside from this matter, supposing an 8ohm speaker for each channel what capacitor requirements should I ultimately have? around 100000uF?

Question DO I have to couple the quasi 200 with some kind of preamp? How can I add some kind of volume control for the amplifier without degrading sound quality?
 
33000uF = 33mF and is sufficient for one channel. Some would say it's more than enough for two channels.

So a single channel amplifier gets one pair of 33mF giving +-33mF per monoblock.
One two channel amplifier gets +-33mF shared between two channels but, in my view that leaves you a bit light. So adding some of your spare 4700uF to give >+-40mF shared between two channels will allow you to drive a pair of 8ohm speakers.
How can I add some kind of volume control for the amplifier without degrading sound quality?
you have no choice. We all need some form of volume control irrespective of whether it degrades quality or not.

Do not put your volume control in any of your Power Amplifiers. Ensure all your Power amp channels have the same gain.
For a 5.1system you will need a 6channel volume control. That is a project of it's own, particularly since all six outputs should be buffered to offer a low output impedance to each of the Power amp channels.
 
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Joined 2009
Wait a minute. When I use mF I mean microfarad thus I have thirtythreethousand microfarads of capacitor power per cap (the big ones). With mF do you mean microfarad or millifarad?


So I actually have over sevenhundredthousand microfarads of capacitor power at my disposal.

Also can you direct me to some project for a multichannel gain control?

Thanks
 
Disabled Account
Joined 2009
thanks for clearing that (In italy I sometimes see microfarad written with "mf" or "uf"). I am honestly surprised at just how much capacitance is required according to you guys! :)

I have built supplies with excellent ripple correction and instant load response (0 to 55A on 2v dc) with nothing more than 18,000uf (plus more caps to avoid instant spikes and improve ripple).

Oh well I guess this is challenge in more ways than one.

For now the project is comprised of:

1) 2 toroidal transformers ewven though I have 4

2) 720,000uf I can distribute on various channels

3) 4.1 channels obtained with 5 Quasi 200 boards

4) Preamps? Do you any suggestions for this one?

5) gain control? Do you have any suggestions for this one too?

6) Vumeter (I have a project ready to be built)

7) very important: I am looking for a good softstart circuit. Every toroidal will also be fitted with a 230v filter board to avoid 50hz hums and "cr**" from the mainlines.

any help will be appreciated.

Also if you feel I need more of anything just say so. I have connections .... :)
 
Alexontherocks said:
I am honestly surprised at just how much capacitance is required according to you guys! :)

I have built supplies with excellent ripple correction and instant load response (0 to 55A on 2v dc) with nothing more than 18,000uf
18mF for a power amplifier driving an 8ohm speaker is good.

BTW,

f = femto = 10^-15

F = Farad = capacitance
 
AndrewT, I actually meant power supply. I built a very inefficient linear power supply to drive a 40w coherent solid state laser. As all diode based laser the voltage is low but the current absorption is quite high.

IT was designed to aid in some cnc work but strangely enough it proved more useful as training ground for more complex builds.

Regarding The "F" I know that F stands for Farad but I assumed that uf could only be interpreted as microfarad.


Hoewver if I happen to make mistakes regarding the theory behind the construction please correct me. I am a law student but know of combustion engines and electronics from selfteaching and learning. As often happens this makes me passionate about the subject but not very "technical" regarding the theory as long as it is unnecessary to accomplish my objectives. (However I do know the basic theory regarding capacitors and the issues envolved with high capacitance)

Sorry for the off topic:

Regarding the project I also have another question.

Can the amplifier benefit from a regulated voltage supply? I ask because I would get 48,44v rectified as output. As a result of load and changes in load this value may change. Can it negatively affect the amplifier in terms of output and sound quality?
 
That depends on who you ask. Most amps are built with an unregulated power supply. Most power amps have more than sufficient PSRR that the ripple doesn't matter. As long as you have enough juice (transformer VA and capacitance) to ensure that the voltage doesnt sag by more than a couple of volts under load, it's fine.

A regulated supply for a class AB amp is difficult. Effectively you've got another amp providing the power to the main amp, and an equivalent amount of heat dissipation.

A preamp is probably not required, at least not gain. The one sticky point is attenuation (a volume control) - there aren't many 6-channel potentiometers! You will either have to come up with a method to link 3 regular dual pots together, or look at digitally controlled attenuation such as the PGA2311. The digital route requires knowing how to program a microcontroller, though.
 
Disabled Account
Joined 2009
thanks for your answer.

I could have designed something with a series of 2n3771 but it would have been probably very inefficient now that I think about it.

I have 3 toroids I can use for a total power of 1500va. I think it is enough.

Regarding the pots I coul start by building 4 channels plus a subwoofer so I would probably need a front channels pot for right and left, a pot for the rear channels and a separate for the subwoofer. The only problem is that I really don't know where I can fit it in (in a schematic) for the best possibile results.


P.s. I actually have 4 toroids (500va) but I think 2000va is really wasted on a project designed for home entertainment.
 
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