TDA2030A audio amp module for 99p

[Neil Purling]

I get to answer my own question as there was a plastic bag with Chinese writing waiting for me at home. 11 days door to door from Hong Kong.

[Neil Purling]

I am putting the 25VA 12+12V transformer inside the casing of a scrapped power supply out of a PC for screening & safety. The box has a IEC socket and switch already, (single-pole), which is not ideal, but with the lid on nasty voltages are locked away inside.
I want a couple of 1/4" jacks and a fuse holder.

The printed circuit board looks to have some useful capacitors & I have removed one of the heat-sinks as well as the horse's tail of useful wire.

[orbanp1]

Hello Everyone,

I got these modules:
http://www.ebay.ca/itm/6V-12V-Single...kAAOSwT6pVgpdt
I believe these are the ones that are selling for 99p.

I got five of these yesterday and tried one.
It does not work right, it has parasitic oscillation on the output, and the IC is quite warm with no input (no surprise there)!

Looks like they did not follow the suggested application example given in the datasheet:
http://www.alldatasheet.com/datashee.../TDA2030A.html

There are only two electrolytic caps in the module, one for the output, the other for filtering the supply voltage.
The application example uses five electrolytic caps altogether.
The other caps are monolithic SM caps, the value is not indicated on them.
One thing can be verified though, the Zoebel-network uses 5.1 Ohm resistor instead of the suggested 1 Ohm!

The modules, as received, without repair, are only good for scavenging components from them!
I did contact the seller, will see how does he replies.

Peter

[G6Tanuki]

That looks a bit different to the ones that have been described further up the thread (which are clearly rather more electrolytic-capacitor-enriched) - https://www.vintage-radio.net/forum/...1&d=1440590473

[paulsherwin]

The bare chips are available from similar sellers at 3 for 99p including postage.

[orbanp1]

Originally Posted by orbanp1

...
It does not work right, it has parasitic oscillation on the output, and the IC is quite warm with no input (no surprise there)!
...

Well, did some more tests. Now the output does not oscillate all the time.
The difference is the coax cable (or lack of it) that I used to attach the mV-meter and the scope to the amp output.

The RG-58 coax cable has about 82pF/meter capacitance, plus the meter's input capacitance, while the scope's own probe with cable has only about 15pF or 70pF capacitance, depending on the probe setting.

Capacitive load on a opamp style audio amp could cause instability.
That audio amp module, as it is, is only marginally stable!
Looks like it was not a bright idea for the manufacturer to deviate form the suggested Zoebel-network!

As for not using electrolytic caps in the other places, simulation shows that the low-end -3dB frequency is about 200Hz, assuming 200nF values for those monolithic caps.

Hope this helps,

Peter

[ben]

I just ordered a couple of modules similar if not identical to the one at the start of the thread. Link here. Not 99p, but two units for less than a fiver delivered from HK, hardly breaking the bank! Will update when they come.

[Neil Purling]

I bought one of the amplifiers in the link. There are some pictures of the thing I bought in post #21.
The 99p module will need a power supply and the input has a preset level & not a potentiometer.
Mine has a very good heat-sink, which is well-worth the extra.