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TDA1554 22W Amp


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Hi all,
I need to connect this amplifier to my car speakers, which are also connected to a car stereo. That would lead to 2 amplifiers connected in parallel, giving different output signals. Do I risk damaging this amp and/or the stereo's internal amp ?? I mean will something really get burned ?

If so, please suggest a *simple* way of connecting both at the same time. It doesnt matter with me if they can run together (mix) or if one of them gets priority over the other, just as long as all hardware is protected.

The amp I'm referring to

Thanks in advance :)

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You could just connect the audio output from the car amplifier into the 22W amplfier via an attenuator (nothing complex just a potential divider) into a mixer curcuit together with the input from whatever else you plan to connect to your 22W amplifier.

What's the point in this?

What you want to achieve?

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Hi Sherbo,
If you connect amplifier outputs together, severe damage might occur to both of them:
1) If both amplifiers are turned on, they will fight each other and produce unlimited current. One will go one way and the other will go the other way or try to hold the output at zero if it doesn't have an input signal.
2) If one amplifier is turned off, its output will be driven backwards by the amplifier that is working.

Since a switch isn't available having enough contacts, a relay having many contacts must be used.
A relay or extra mixer would be a nuisance in a car. Why use two amplifiers? Doesn't your car stereo have enough power and an extra input? 

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My car stereo doesn't have any inputs. It only has an amplified output.

I want to connect my mobile phone to the car speakers to emulate a (mobile car kit).

Here is what I'm thinking right now:

stereo (amplified) ----->Mixer ----> Speakers
Mobile -------> Amp --->|

Would this mixer work ??

I'm mainly worried about the sound quality deteriorating, with only one BJT the circuit seems too simple.
Btw, are the component values critical ? I'm not sure if I'll find 5 uF caps, and I'm thinking of powering it directly from the car battery (with a cap to reduce noise).

It's crucial to me that I take both AMPLIFIED signals then mix them. I want the circuit to act like a (black box) that I just plug into my speakers.

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You could build a simple FM transmitter and then connect it to your phone and then tune into it on your radio. ;D

But you've got it the wrong way round, you need to mix the signals before the amplfier. You would have to connect the output of the amplifier to one input of the mixer via an attenuator, the phone to the other, and the mixer's output to the 22W amplifier shown on this project.

There is no simple way to mix the outputs from two amplifiers with different signal sources without loosing a lot of the power.

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The output from the car amplifier will over drive the 22W amplifier and the pot on the mixer isn't enough to prevent this. You could try connecting the input of the mixer to the output of the amplifier via a 200K resistor.

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You are going to add a stereo mixer and a stereo amplifier only for a telephone?
All you need is a little 1W mono amp and a little speaker. Keep the radio separate.

You won't get 22W per channel with our project anyway. It is rated with a very high supply voltage of 14.4V. In your car the supply voltage is probably only 13.2V or 13.8V. The amplifier is also rated with 10% distortion that sounds horrible because it is very much over-driven and producing square waves. The amplifier will produce only 12W per channel into 4 ohm speakers with reasonable distortion. About the same as your car radio.  ;D


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You're right again audioguru.

What do you think about using the LM386?

Or this project?

I've designed one too but I've not got the design handy or I'd post it for you.


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