can any one help me?

[hti97088]

hi every one
i want to make an audio system for bus so can any one help me in a circuit for amplifier that can connect to 30 speakers that the bus have.

[sagarverma]

what is the voltage from bus battery?

[abid_rehan]

bus batteries may be of 24 volt or 24+24 volts but driving 30 speakers is a big ????
i d suggest hti to be more specific....in defining his needs.

[quasi]

You would do best with amplifiers driving into line transformers and then tapping each speaker off a common line. The line transformer will convert the amplifiers output to a higher voltage and this is used to connect to small speakers via small step-down transformers.

Do a search on public address systems and take a similar approach as public venues (not rock concerts).

Cheers

[sagarverma]

24v!

that is great!build tda7293 modular amps.they r stable at 16ohm or higher.16 ohm is advised.your bus speakers must be standard 4ohm.
so connect 4 in series to get 16 ohm net.modular app gives about 160w continous.so u get 40w per speaker assuming equal distribution of power.40w per speaker is great.so build 8 amps using 16 tda7293.and u have a great amp for your bus.
if 40w per speaker is too much,inc series resistance by connecting speakers.so u have more res. and less no of amps.

best scheme.build stereo modular amps.so each stereo amp has 4 tda7293 and each amp drives 8 speakers.

u have a single music source.connecting so many amps at the o/p of music source can load it dangerously.so use an audio buffer stage as mentioned in the datasheet of tl072 opamp as audio distribution circuit.

[quasi]

24 volts will give a theoretical 18 watts assuming no losses anywhere.

((24 / 2) x 0.707)^2 / 4 ohms = 18 watts RMS

Into 16 ohms it's only 4.5 watts or 1.2 watts per speaker.

To get more than that you will need to bridge them (36 watts) or use a step up voltage supply.

Cheers

[sagarverma]

hi quasi

i am currently building the amp that u have mentioned in this forum.its slowly progressing.will inform u when done.

now let me quote some text from tda7294 ic datsheet

"""""""""""""""""
BRIDGE APPLICATION
Another application suggestion is the BRIDGE
configuration, where two TDA7293 are used.
In this application, the value of the load must not
be lower than 8 Ohm for dissipation and current
capability reasons.
A suitable field of application includes HI-FI/TV
subwoofers realizations.
The main advantages offered by this solution are:
- High power performances with limited supply
voltage level.
- Considerably high output power even with high
load values (i.e. 16 Ohm).
With Rl= 8 Ohm, Vs = ±25V the maximum output
power obtainable is 150 W, while with Rl=16
Ohm, Vs = ±40V the maximum Pout is 200 W.
''''''''''''''''''''''''''''''''''''''''

now what u say??

[Silkworm]

Gentlemen, Do not forget the amplifier operated in the bus environment, reliability is important. also fully protection is necessary. I think if the operating voltage is 12V, the project can be done easier.

[quasi]

Originally posted by sagarverma
hi quasi

i am currently building the amp that u have mentioned in this forum.its slowly progressing.will inform u when done.

now let me quote some text from tda7294 ic datsheet

"""""""""""""""""
BRIDGE APPLICATION
Another application suggestion is the BRIDGE
configuration, where two TDA7293 are used.
In this application, the value of the load must not
be lower than 8 Ohm for dissipation and current
capability reasons.
A suitable field of application includes HI-FI/TV
subwoofers realizations.
The main advantages offered by this solution are:
- High power performances with limited supply
voltage level.
- Considerably high output power even with high
load values (i.e. 16 Ohm).
With Rl= 8 Ohm, Vs = ±25V the maximum output
power obtainable is 150 W, while with Rl=16
Ohm, Vs = ±40V the maximum Pout is 200 W.
''''''''''''''''''''''''''''''''''''''''

now what u say??

I have posted a link to the data sheet.

The amp will deliver 100 watts with rails of +/- 40v and this makes sense.

But with 24 volts and without a voltage raising power supply you can only get +/- 12 volts. The amp does not use any rail doubling techniques in it's switching. Whn you read datasheets you must also read the entire spec....i.e 180 watts of peak power (10% distortion @ 4 ohms) with rails of 100 volts.

Just because the amplifier can operate from +/- 12 volts it does not mean it will it will deliver 100 watts at that voltage. And let me assure you that without a rail switching supply the maximim voltage from 24 volts is +/- 12 volts.

Power = voltage^2 / load

http://pdf.alldatasheet.com/datashee...S/TDA7293.html

The rest is simply ohms law

[quasi]

I forgot the bridge mode bit. In bridge mode (push-pull) the amp can supply 24 volts peak voltage.

In this mode the available RMS power = (24 *0.707)^2 / 4 = 72 watts (if the amp can bridge into 4 ohms). Now in real life this will be somewhat less.

The amp will deliver more power but you need to use voltage raising techniques (DC-DC converter, rail switching etc.)