## Tuesday, 16 December 2014

### TDA2005 Stereo Amplifier

One of the readers has asked me to help them design a stereo amplifier using the TDA2005 audio IC from ST Microelectronics.  Its an all in one integrated stereo amplifier chip.  All a design engineer needs to do is read and understand the datasheet, apply the information and build the circuit!

Here is the datasheet:

The device itself is quite popular and has been used in several automotive audio applications and computer speaker systems.  I've seen it and it's variants over the years.

Here is the schematic diagram.  It's taken directly from the datasheet example, I added a volume control dual gang potentiometer and a 1k resistor to the input stage but apart from that it's exactly the same as the example.

The circuit is easy to understand. Most of the work is performed by the circuitry contained within the TDA2005 amplifier. C1 & C2 are input coupling capacitors and block any DC voltage present in the input audio signal.  C10 & C11 are also DC blocking capacitors and C7 & C9 block DC voltage from the feed back loop to the differential inputs of the amplifiers. Resistors R3 and R5 (and R4 and R6) set the level of negative feed back. C10 and R7 (and C11 and R8) provide a high frequency load for stability where the loudspeaker's inductive reactance may become excessive. C4 and C5 provide power supply decoupling or filtering.

The gain is set by the formula 1 + (R3/R5).  So in the case of the above circuit it is:

Av = 1 + (1200 / 33)

Av = 37.36

The gain may be increased by reducing the feedback resistors R5 and R6. A value of 22 ohms would provide a gain of approximately 55. If you need much more than 60 gain, it would be better to use a preamplifier such as the LM386 Ruby amplifier circuit and then and then amplify it.

The maximum supply voltage for this Kit is 18V and the minimum current is 2A. Check the power supply voltage and current and check the polarity before turning the amplifier on.

Unfortunately there is no spice model available for the TDA2005 circuit so I cannot provide a simulation.  I have not actually built the circuit yet so I also cannot provide a video of it in operation. I have ordered the components however and as soon as I make a PCB I will populate it and post a video of it working.  Here is the PCB layout top and bottom layers:

 PCB Top Layer with components

 PCB Bottom Layer
Here is the bill of materials:
 Part Value Description C1 2.2uF 16V Electrolytic Capacitor C2 2.2uF 16V Electrolytic Capacitor C3 10uF 16V Electrolytic Capacitor C4 100uF 16V Electrolytic Capacitor C5 100uF 16V Electrolytic Capacitor C6 220uF 16V Electrolytic Capacitor C7 220uF 16V Electrolytic Capacitor C8 2200uF 16V Electrolytic Capacitor C9 2200uF 16V Electrolytic Capacitor C10 100nF 50V Ceramic Capacitor C11 100nF 50V Ceramic Capacitor C12 100nF 50V Ceramic Capacitor IC1 TDA2005T Stereo 10W Power OP AMP J1 POWER_JACKPTH DC Power Jack JP1 Audio Input 3.5mm Audio Jack JP2 Dual Gang Potentiometer 10k Dual Gang Pot JP3 Dual Gang Potentiometer 10k Dual Gang Pot JP4 Speaker Terminals 5mm Screw Terminal JP5 Speaker Terminals 5mm Screw Terminal JP6 Alternative DC power input 5mm Screw Terminal R1 120k 1/4W 5% Carbon Film Resistor R2 1.2k 1/4W 5% Carbon Film Resistor R3 33R 1/4W 5% Carbon Film Resistor R4 1.2k 1/4W 5% Carbon Film Resistor R5 33R 1/4W 5% Carbon Film Resistor R6 1R 1/4W 5% Carbon Film Resistor R7 1R 1/4W 5% Carbon Film Resistor R8 1k 1/4W 5% Carbon Film Resistor R9 1k 1/4W 5% Carbon Film Resistor PCB PCB to mount components on Heatsink Heatsink for TDA2005

Here are some renders of the PCB and what it might look like when populated.  I haven't got a model for the TDA2005 so it doesn't show that part:

Here is the PCB etched and drilled ready for component population:

The picture below shows the completed circuit.  I am actually very impressed with how well it sounds.  I think the bass response could be better but it's still very good and clean.  I would like to change the layout slightly as some of the capacitors are a little close together.  I would also like to make some more room around the amplifier device so I can fit a decent size heatsink as the one I currently have fitted is not reducing the heat enough.

Here is the proof of function!

The maximum amount of output from the amplifier depends upon the supply voltage, current and speaker impedance.  In order to get 10 Watts on each channel the designer must ensure a supply capable of 15 Volts and 2 Amps and a speaker impedance of 1.6 Ohms.  A higher speaker impedance will cause the amplifier to draw more power and not output 10 Watts.  I reckon I'm getting 6 Watts per channel which is more than acceptable for my purposes....

Here are the Eagle design files if people wish to make their own:

That's all for now...Enjoy people and take care - Langster!