help needed on 10 channel amp

[prozach7]

This is my first post, so hello to everyone.

I am starting an new business so I am trying to get cheap help wherever I can.

Here is my situation. I need to amplify 10 different sound effects that are stored on ten ISD1416 recording chips. Each one needs to be amplifed seperately with their own speakers. I need about 30 watts rms for each sound. From what I have read so far on the boards, it looks like the lm3886 may be the best for price and what you get.

I would like to put all of the amps on one circuit board with one power supply...if possible.

What do you think is the best place to start?

Thanks in advance.

Zach

[Luke]

try making some chip amps, easy to get going, are relatively cheap and sound good.

http://chipamp.com/lm3875.shtml


seeya ab

[Nigel Goodwin]

Perhaps you could explain further what you're trying to do?, currently it's rather confusing? - wanting seperate amps and spekers, but then on the same board?.

[jimbo1968]

Is your product one big box with 10 speaker outputs on the back?
Or do you want a standalone 10ch power amp ?
What are the size/ aesthetic constraints?

A classic power amp layout with a heatsink and 5channels on each side of the box, and all the outputs on the back seems like a good starting point.

I can't think of a neat way of putting all 10 on one pcb/heatsink

[prozach7]

Thanks for the help so far.

Let me give you some more details.

This is going to be a sound track for dark ride. When people pass by an object, a sound will come from it. I would like to make the audio and amplification all in one box and if possible one board.

So, when triggered by a person, the ISD sound chip plays the recorded message which is then amplifed and sent to a speaker somewhere in the ride.

The layout of the board does not matter since it is an "industrial" piece. I think 5 ouputs on one side and 5 on the other is perfect.
The sound quality does not need to be great, just good.

My first question is it possible with one large power supply to supply all the amps? Then can I use 10 chip amps to run each channel. What chip amp would you recommend. (approx. 30w rms).

Thanks,

zach

[AndrewT]

Hi,
easily possible to run all the chipamps off one PSU.

How many messages might play at once?

Then the PSU should be about 1.5times the power of one channel times the maximum number playing co-incidently.

[otherside]

What is you speaker impedance?

I would reccomend 5 x LM4765. I think this would be the most cost efficient solution. (BTW you can get them for free from National as samples).

I think 5 ICs are much more easier to place and heatsink them than 10. You could run them of a 25V rail (for 8ohms) and depending on the your answer on AndrewTs question you can determine the VA for the transformer.

Layout can be quite easy to build as repeated blocks horizontal or vertical on the board. Easiest approach is having a front panel of inputs and a backpanel of outputs. To reduce the cost and make much easier the assembly of the whole thing you can use PCB-To-Case connectors, so basically what you'll have to do after building the PCB just place it on the case, no wires no mess.

There is only one drawback to this, you'll have to use a heatsink on top (bottom on construction) of the PCB and bend the ICs pins at 90 Deg. (You can mount the h/s with some nice tricks like holes on the PCB to pass the screwdriver)

Another way is to use the heatsink on the sides but then you get long lengths on the signal paths which is not very good.

How many of these do you need? If you need only one then PCB cost will be ok with this setup. However because of the board size which is large if you go for a lot of then then it's cost inefficient.

Another way to do it is design one pcb for 2 channels, again based on the front-back idea and have the heatsink on the side of the board. Considering that for one of these ICs your heatsink would have to be around 2C/W (based on 25V over 8Ohm) which is not too long, your board can be small (120x50mm). Because of the small board size you can order multiple PCBs and will come cheaper.

[jimbo1968]

As with the power supply, if the channels are only playing intermmitently then you can use a smaller heatsink, so putting 10amps on one heatsink is feasible.

How many boxes you intend to build will determine whether it's worth designing a 10ch pcb or just buying eg 5x lm4780 boards, there are a few to choose from.

Now I'm thinking of a modular approach. 1 or 2 channels per pcb, mounted with input and output sockets to a piece of aluminum. These are then screwed to a common heatsink. This would give expandability for the next project and simple line replacement of a faulty channel.

[prozach7]

Ok, so I think the way to go is with five 2 channel amp boards for cost and ease of replacement.

I will be using 8ohm speakers and the messages usually play for less than 5 seconds and then are off for about 15 seconds. However, there may be a time when they are all played at once, but only for the 5 sec. and then off again for 15 seconds. This situation should be rare.

So what size power supply do you think I should use for this situation.

Thanks,
zach

[AndrewT]

Hi
If you were going for maximum fidelity I would say go with 10times1.5times 30W. But these are voice messages that will not drive to amps at peak output for very long.

So instead I suggest you try only 4 or 5times giving a transformer of 200VA to 250VA. Not too big nor expensive.
I would run each dual amp off it's own rectifier/smoothing cap supply. But again the loss in intelligibility will probably be acceptable to run all the amps on a common dual polarity PSU.
Each pair of 30W amps needs +-10mF of smoothing or +-50mF for a shared PSU.
I have suggested you skimp on the transformer but recommend you give serious consideration to maintaining a full +-2mF/Apk of total output when all ten amps could be running in parallel.

The suggestion made earlier of plug fit to allow easy maintenance sounds very necessary if down time is important to you.