Building a 5.1 channel amplifier

[shashankrevankar]

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

[AndrewT]

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 !!!!!!!

[shashankrevankar]

Originally Posted by AndrewT

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.

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.

[Th3 uN1Qu3]

The better version is using a separate transformer for the subwoofer. Then again, one larger transformer can be cheaper than two smaller ones, and with a 350VA unit you'll do lots better than the original.

I'd use the TDA7294 on the sub. The 3886 sounds cleaner in the high end but i've always liked the 7294 for bass.

[sreten]

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.

[shashankrevankar]

Originally Posted by sreten

Hi,

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.

Thanks! But I have a doubt, will driving my speakers rated 12 watt by a 20 watt amplifier burn them out?
How to reduce the power of the circuit?

Also can u plz elaborate on bridging. I am newbie at amp design.

[AndrewT]

Originally Posted by AndrewT

..............The amplifier does not damage speakers, unless it goes faulty.
The operator damages speakers !!!!!!!

Originally Posted by shashankrevankar

Thanks! But I have a doubt, will driving my speakers rated 12 watt by a 20 watt amplifier burn them out?

you are in control of the volume knob.

[shashankrevankar]

Originally Posted by AndrewT

you are in control of the volume knob.

Got your point.. Thanks !!!!

Any suggestions about bridging?

[Th3 uN1Qu3]

Technically speaking 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 (so as to not burn out the satellites maybe?), you might want a bridged amp for the subwoofer.

Bridging is explained in layman's terms in Wikipedia.

[AndrewT]

Originally Posted by AndrewT

............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,

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

Yes, I agree. Bridging and it's complications is not needed.