2.1 Sound System Based on Amplifier Circuit

[narno]

Hello~

I am planning to make a 2.1 sound system with the following circuit which is based on IRFP240 and IRFP9240 MOSFETs is shown here.

According the description of IRFP9240 datasheet( http://www.kynix.com/uploadfiles/pdf9675/IRFP240.pdf ) and the diagram picture,the amplifier operates from a +45/-45V dc dual supply and can deliver 100 watt rms into an 8 ohm speaker and 160 watt rms into a 4 ohm speaker.This Hi-Fi amplifier circuit is suitable for a lot applications like general purpose amplifier, guitar amplifier, keyboard amplifier. Well,a basic dual power supply is used for the amplifier circuit.

 

 

My spec is given below.I have some doubts regarding the project.It will be great if I get someone’s valuable suggestions from here.

Spec

======

drivers :

1. 12 inch 100 watts 4 ohms subwoofer – 1

2. 10 inch 50 watts 8 ohms woofer – 2

3. 8 inch 50 watts midrange – 2

4. tweeter – 2

 

amplifiers:

1. 150 watt RMS at 4 ohms drivers – 3

( 1 for subwoofer and 2 for left and right channel)

 

20 – 200 hz lowpass filter – 1

low mid high control board – 2 ( for left and right channels)

low mid high passive cross over – 2

 

my doubts :

1. do I need to use a preamp in this circuit ? because I am splitting the input into two different amplifiers (sub and left right). I think preamp will just only increase the voltage level of the input signal, but when we split a signal into two actually the current is divided into two. Will the preamp be helpful in current gain?

2. I will use 20-200 hz lowpass filter before the subwoofer amplifier, do it act as a preamp ?

3. In common I have seen bass and treable control knobs in amplifiers but I want to use low, mid and high controls, is it okay? if yes please suggest me some links to get low, mid and high control board circuits.

4. I am planning to fix all these circuits in a single casing so can i use a single transformer to the entire system, if yes please specify the voltage and amps.

5. i have heared that the amplifier should be 50% more powerfull than the drivers to get good performance at max volume levels , so I decided to upgrade your circuit from 100 watt to 150 watt, so what kind of changes should I do with the given circuit ?

6. I want to add a short circuit or overload protection fuse in this system, suggest some links to get some idea about this.

7. One woofer, midrange and tweeter will be connected parallely to the one channel of stero amplifier, so I think two 8 ohms drivers can make 4 ohms load. I didn’t considered the tweeters impedence. Do the tweeter have impedence ? or is it significant ?

8. Im also planing to do a LED spectrum analyser and digital volume controls with remote. These features will be added later. If u have ideas about these please share.

Thanks.

[WRGKMC]

Please clarify some things.

 

You posted this on a bass guitar forum. Are you planning on using this for bass guitar or some other Hi Fi application. The answers you need are based on what you're targeting your end results to be. I suspect its some Hi Fi application given all the speakers you chose but there are so many things thrown in here that simply don't add up to show me that you know where you're going. (which is why you likely posted here in the first place)

 

Your preamp circuit is a super basic op amp. I wouldn't expect it to exactly knock your socks off. If this was a simple Hi Fi driver you have no EQ and this circuit wont get you there. You'd have to rely on perfect speaker fidelity to get you optimal sound and what you have listed there doesn't even get you close. If this is supposed to be for an instrument as the diagram says, this is super basic stuff. You could do much better using a guitar pedal that drives your gain up to line level and drive a power amp, or a bass pedal designed to drive a mass guitar up to line level and do the same thing.

 

Next

i have heard that the amplifier should be 50% more powerful than the drivers to get good performance at max

You have that backwards. The drivers should match in RMS or be higher. 50% higher is typical, More then 100% is overkill.

 

Next, you have no power amp schematic listed here. Its like you posted a wish list and have no experience in building. People cant make suggestions unless you have a clear idea of you central design. Its like you've choses wheels, hubcaps, stereo system for a car, but you have no car to put them in, simply an option list of a few items, relatively unimportant in the much larger scope of things.

 

You're working from the outside in instead of the inside out when it comes to a design from an end users aspect. You have to design circuits from a totalitarian view. This is what engineers do for a living. They have a complete understand of all components used and how they interact with each other. They combine them into circuits mathematically and every change made has a repercussions on every other component in the circuit. You cant simply string together fragments from a wish list, especially if you don't have a basic schematic to begin with.

 

What I suggest you get is an electronics cad program where you can design your own circuits. Then get some books on basic electronics. Better yet go take some classes at the local college or trade school. I took 3 years in electronics, (6 months short of an engineering degree) and I see no plan here, just a bunch of fragments from an end user. Even if I copied an existing design to get you there, the money you'd spend would be wasted because you can simply buy something that will do everything you listed and cost hundreds if not thousands of times less. The wheel has been around for a long time. So have many devices. Why are you wanting to reinvent the wheel?

 

I can say, Bass amp circuits needed to drive sub s require high power transistors, and good cooling systems and heavy duty power supplies to provide the kind of current needed to push bass drivers. A typical bass amp usually needs to produce 300~500W just to keep up with an guitarist using a simply 35W amp that pushes mostly midrange.

 

Its also important to know wattage is simply a power consumption rating. It has nothing to do with actual distortion free loudness at different frequencies. The speaker efficiency dictates how loud an amp can be for a given wattage. Every 3 db in speaker efficiency is double the volume. A speaker rated for 100dB SPL can be nearly 8 times louder then an 80dB.

 

The ears do not hear frequencies linearly. Bass dB's need to be 100dB higher then mid frequencies to sound linear to our ears. If you designed 3 identical amps and drove the highs lows and mids separately, the HF would be over powered and the LF underpowered compared to the mid frequencies. Hi Fi systems have big bass and treble boosts to make the sound appear linear to our ears. From your wish list you show no indication your understand anything about this.

 

Even the drivers being 4 and 8 ohms indicates you haven't learned your first grade ohms law yet. 4 and 8 is series gives you 12 ohms. In parallel you get 3 ohms. Both are oddball impedances which are hard to work with. Electronic components are built to meet common fixed standards. The costs and difficulty calculating increase when you use oddball impedances like that.

 

You can biamp 4 and 8 ohm speaker through separate amps, but your cost and power supply requirements double. You'd be better much better off running a pair of 8 ohm speakers for a total of 4 ohms and use a simple inexpensive passive crossover. Better yet run a wider ranged woofer that can handle sub lows and upper lows. Its much easier to design a single speaker cab with a linear response then it is to chop up all your frequencies and try and get multiple cabs or multiple drivers within a cab to balance, Running separate amps for each driver becomes even more difficult because you need to acoustically tune them and more expensive to drive them.

 

Some of your best Hi Fi systems ever made use a single power amp and simple 2 way speakers using a passive crossover. If you've successfully built a simple system before you'd know this. A bi or tri amp system is a much more complex challenge. You seem to be skipping too many rungs on a ladder by jumping too far above basics before you even understand them. If you find you need a sub, simply buy one with the amp and crossover built in.

 

Unless you're doing all this for educational purposes, I don't see much point in it. You'll never build anything as good as what you'll get from a factory, even if you spend hundreds of times more. I see nothing here that's unique or new that cant be gotten from a good used surround amp used for TV. Manufacturers have entire engineering teams who take older designs and redo them. They don't reinvent the wheel with every new product either. Something like a JVC has thousands of predecessors that engineers draw off of when designing a new product, changing a know here or adding a switch there is simple. Its all done on a computer now within a cad program.

 

Electronics is pure physics. Unless you understand what the atoms are doing and know how to manipulate them using various materials of different specs, and can mathematically predict what they will do, you don't have the tools to tackle design. Not many people actually do. You have loads of copycats and chop shops ripping circuits apart but pure design is rare indeed.

 

Takes allot of experience. Heck I been working in electronics for nearly 50 years and most of my designs were simply rediscoveries of things other people already though of and are using in circuits already. You're dealing with physics, algebra and trigonometry getting components to work together. There's no way around that. You want to get into design, you not only need to be expert at those things, but you have to go beyond the basics and be creative with those basics. Math comes before the build if you expect things to work. if you're impatient and only want the end results, you'll never get there trying to design and build you own stuff.

 

Heres some examples. The site has the recommended power supplies as well.

 

A Monoblock Class D 600W power amp for $57. Just needs a power supply. https://www.parts-express.com/sure-electronics-aa-ab31241-1x600w-tas5630-class-d-amplifier-board--320-311

 

A 4 channel Class D amp - 100W a channel. $47 https://www.parts-express.com/sure-electronics-aa-ab33182-4x100w-at-4-ohm-class-d-digital-audio-amplifier-board-sta508-(t--320-335

 

Sub Woofer Crossover $7 https://www.parts-express.com/variable-low-pass-filter-electronic-subwoofer-crossover-preamp-board-with-gain-control--320-670

 

Stereo Preamp with Treble mid and bass $18. https://www.parts-express.com/yuan-jing-ne5532-stereo-preamplifier-volume-control-board-with-treble-midrange-and-bass-to--320-6542

 

The shipping costs alone needed to buy these parts would cost me 4X as much, no less finding them all and adding in the labor time to build them. The first unit could easily cost me 1000X to build with parts and labor.

 

Again, if its for educational purposes, go for it. I just see it as allot of work for what you get back. Some things are worth investing time to learn. Others are fruitless. Most circuits are disposable theses days. Even if you have the knowledge they don't pay to build or repair.

 

 

[ThudMaker]

I'd post this in Craig V's forum. There are some really bright people over there who may be better than the basissts.

[Hooligan]

Over my head on most of this, but I say go for it just for the experience!

 

I remember always counting tweeter impedance in my speaker building days, and the car audio junkie in me still likes matching rms power on the speakers and the amp rather than over or under powering drivers. Good luck on the project and pics required if you make it happen!