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Old 11th July 2009, 11:28 AM   #11
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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?
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Old 11th July 2009, 01:35 PM   #12
AndrewT is offline AndrewT  Scotland
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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.
Quote:
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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Old 11th July 2009, 03:52 PM   #13
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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

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Old 12th July 2009, 05:22 AM   #14
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Sorry, another question.

Those the powersupply have to be voltage regulated?

IF yes then I can build something out of an lm317 and several 2n33771 transistors but I'd rather receive confirmation from you guys before I start planning.
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Old 12th July 2009, 06:36 AM   #15
N Brock is offline N Brock  United States
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uF=microfarad
mF=milifarad

1mF=1000uF

I am interested in what you come up with. Good luck.
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Old 12th July 2009, 07:42 AM   #16
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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 ....
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Old 12th July 2009, 09:16 AM   #17
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by Alexontherocks
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
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Old 12th July 2009, 09:50 AM   #18
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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?
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Old 12th July 2009, 01:30 PM   #19
jaycee is offline jaycee  United Kingdom
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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.
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Old 12th July 2009, 02:48 PM   #20
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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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