TDA2050 Hi-Fi Chip Amplifier Resistor Pick Help

[ecks]

Hello,

I have a bit of experience in electronics, but it mostly through coursework and I would like to build something practical. I had some TA2050s lying around so a friend of mine suggested I build the amplifier shown in http://diyaudioprojects.com/Chip/DIY-TDA2050-Hi-Fi-Chip-Amplifier/. I was looking at resistors R1, R2 and R3 and they don't look like the regular resistors we have lying around in the lab, ie we have stuff that looks like R4. I know that resistors are rated for different watts, but unfortunately from the description it doesnt say what rating I should look for. Would it be okay to make due with regular resistors that look like R4, or would I need to look for the bulky ones?

[TimFox]

I would use a 2.2 ohm, 2 or 3 Watt "flame-proof" cermet resistor (metal oxide) for R4.
For the other resistors, use 1/4 or 1/2 watt metal film resistors (1% would be a good idea, but not absolutely necessary).
As an old person, I like military-style RN60 resistors for the metal film units.

[flynwill]

You can use ordinary 1/4 watt carbon film resistors for all 4 parts.  Metal film and higher precision are nice (and will work if you have them laying around) but are hardly necessary in this application.  I note that the schematic calls for R4 to be a 2W part, but I can't see any reason why, with that 0.47 uF cap in series it isn't going to see very much current unless you feed the amp full power 20kHz.  Possible, but not very likely in normal usage (although I suppose if you want to design for the worst case...).  I note that in the picture R4 appears to be a normal 1/4 watt part.

[Zero999]

Carbon film can be used but it's more noisy than metal film and resistors are cheap so you may as well pay a tiny bit more and use metal film.

Two bridge rectifiers seems unnecessary. Centre tap the transformer and use one.

The 2k2 bleeder resistor seems a bit low. It's not even required for safety as the voltage is too low to be a hazard, especially when the power is disconnected. The TDA2050V has a quiescent current drain of 55mA at +/-22V, dropping to 30mA at +/-4.5V which is greater than the current through the bleeder.

The TDA2050V is obsolete so beware you may have difficulty sourcing spares and you certainly shouldn't market this.

The absolute maximum voltage rating is 50V so running it off a 18-0-18V transformer is cutting it a bit close, given the voltage will be higher when unloaded and if the mains voltage is on the high end.

Read the datasheet before building this:
http://www.st.com/web/en/resource/technical/document/datasheet/CD00000131.pdf