Building a 5.1 channel amplifier

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shashankrevankar

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Joined 2011
#1
Hi everyone!

I had an Altec Lansing FX5051 system and its amp has gone bad. I m not able to get it repaired from anyone, so I have decided to design my own amp for the speakers which are btw awesome.

Front/Rear Left/Right - all four are 12W @4ohms, 10%THD
Center - 13W @4ohms, 10% THD
Subwoofer - 28W @8ohms, 10%THD

Can you please direct me to some links or give me some ideas on starting with this project?
I would preferably want to design a solid state or chip amp.
Also, how much more power can I pump into these speakers?
What are the ICs that I can use & where will I get the circuit diagram for this design?

Plz help me out. My PC is without speakers for around 4 months 🙁
 
#2
Your speakers are a mix of 8ohm and 4ohm. That creates a problem in determining the PSU voltage to use.

I suggest you design for 50W into 4r0, using lm3886 chips, to match your 4ohm speaker loads. Then you can use the same PSU to power a 30W into 8r0 chipamp for the bass only channel.

This allows you to build one box , fit one PSU and 5 channels of amplification inside it. That's the cheapest route, but also the most compromised. The transformer should be around 200VA to 500VA.

Read ESP, Decibel Dungeon and Chipamp Threads.

Personally, I would do it quite differently, but that would cost more.

The amplifier does not damage speakers, unless it goes faulty.
The operator damages speakers !!!!!!!
 
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#3
AndrewT said:
Then you can use the same PSU to power a 30W into 8r0 chipamp for the bass only channel.

This allows you to build one box , fit one PSU and 5 channels of amplification inside it. That's the cheapest route, but also the most compromised.
Personally, I would do it quite differently, but that would cost more.
Click to expand...

Thanks for suggestion Andrew. Which chip do you suggest for the center & subwoofer channels? lm3886?

Also please tell me the method you would adopt. I would not like to settle for the compromised version.
 
#5
Hi,

No. The best budget option is to use a total supply for all chip amps
and use the same chip amp (two of them) in a bridged arrangement
off that same supply for the 8 ohm subwoofer section.

(Almost certainly likely why the sub is 8 ohm, the speakers 4 ohm.)

So you want 4 ohm chipamps that can be bridged for 8 ohms.

7 chipamps in total, one pair bridged, to give a 5.1 amplifier,
6 channels, all off the same common supply, if on a budget.

The LM1875 will output 20 watts into 4 ohms on a +/-25V supply.
With the same supply, it gives around 40 watts bridged into 8 ohms.

For this you will need an 18-0-18V AC 100VA to 150VA transformer.

rgds, sreten.

With 7 amplifiers and for a computer, go chipamps, its a lot easier.
For each amplifier have some juicy decoupling caps near them.
 
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#10
AndrewT said:
............I suggest you design for 50W into 4r0, using lm3886 chips, to match your 4ohm speaker loads. Then you can use the same PSU to power a 30W into 8r0 chipamp for the bass only channel.

This allows you to build one box , fit one PSU and 5 channels of amplification inside it. That's the cheapest route,
Click to expand...
you don't need to bridge any of the amps. A single LM3886 is enough for that subwoofer. But depending on the transformer voltage that you choose
Click to expand...
Yes, I agree. Bridging and it's complications is not needed.
 
#12
AndrewT said:
Yes, I agree. Bridging and it's complications is not needed.
Click to expand...

Hi,

Simply not true. Bridging is not complicated, as a search on it for the
LM1875 will reveal. If you can't manage that then you shouldn't be
building amplifiers. We have had run ins regarding required amplifier
powers in the past, your attitude is IMO totally unpragmatic, and
more to the point pedantically unrealistic and technically wrong.

Your simply wrong, bridging for the sub allows a single simple supply.

20W for each 12W satellite and 40W for the 28W sub should be fine.

It is needed for the best solution, which is one big single supply.
You can't argue with that, as its done all over the place. Like
I said, the reason the sub is 8 ohm and the rest 4 ohm is that
allows the arrangement I'm describing, that is how it is done.

rgds, sreten.
 
#13
Is that the simplest way to achieve success?
That's where my pragmatism comes in.
Both your way and my way will work.
Bridging is more complicated and relies on more skill of both the builder and the designer.
Single chipamps working off a common PSU are easier to get right.
 
#15
shashankrevankar said:
AndrewT has got a point. Every design should be made as simple as possible.

So i was searching for some new ICs and I found a 6 channel amplifier by TI
TAS5186A

Here is the link to datasheet

http://www.ti.com/lit/gpn/tas5186a

How about using this IC to provide a one box solution for home theater?
Click to expand...


Hi,

You should note from the data sheet the sub channel is twice the
power of the other channels, but requires the sub to be half the
impedance of the satellites, that is one way of doing it.

In this case though it is double, so its not a suitable solution,
and FWIW its implementation seems nothing like being simple.

With a single supply and the sub double the sats impedance,
the way to do it is 7 chip-amps, with two bridged for the sub,
that is, if you want double the sat power into the sub, you do.

rgds, sreten.

Single channel :

An externally hosted image should be here but it was not working when we last tested it.


Bridged channel :

collection-of-little-bridged-power-amplifiers2_med.gif


Rail voltages should be +/- 25V AFAICT.
 
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#17
shashankrevankar said:
Yeah Sreten I get the point.

Do you have any idea about a single 6 channel chip that could suit my needs?
Click to expand...

Hi,

Hey, its not my fault you have 4 ohm sats and an 8 ohm sub.

No I don't, any six channel amplifier 4ohm amp will put out less into the sub.

FWIW if using 7 chip amps, two bridged seems too complicated, and you
think that single digital amplifer chip would be easier, perhaps you should
not be building anything, as the issues do not seem apparent to you.

(connecting up that 44 pin chip is an amateurs nightmare .....)

FWIW depending on how the original was made, it may be a lot easier
to fix that than "design" a six channel amplifier. Alternatively buy a
used 5.1 amplifier / speaker set*, I've seen those cheap, that does
indicate 4 ohms for the sats and 8 ohms for the sub, I can near
guarantee it will contain 7 chip amps, two bridged, and will also
have the active filtering etc you will need presumably.

It is also possible the original amplification contains some active
or line level EQ, in that case a straight 5.1 amplifier will be worse.

The best option required informed information, though looking
at the FX501 spec I'd say fixing it is the safest sensible option.

What is wrong with it ?

rgds, sreten.

* replace the speakers with yours, is the basic idea.
 
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