VU2ZAP experiments with TDA2822 Audio Chip

Raj VU2ZAP has done some experimenting with TDA2822 chip failures.

FCI chips were sourced locally and plugged in. No failure was observed when using the chip with normal volume.  However, when he raised the volume to a high level the chip failed immediately!

Solutions

1: Add a resistor in series with the 12V line maybe 10-15 ohms to drop the voltage.

2. Simple solution is to use only a 16 Ohm speaker or add a series 8-10 Ohm resistor with the 8 ohm speakers.

3. Cut the power track to the TDA and insert a 78L08 or 78L09 to reduce the voltage. There is a convenient track which can be cut.  Solder either an SMD or DIL regulator onto the board at this point. This track leads directly to the chip and filter cap (see photo below).

The center lead looks soldered, but is in fact floating.  However, the tab is soldered to the copper groundplane below. The white wire is part of Raj’s fix to prevent the filter relays from clicking during PTT.  Raj suggests the board as illustrated now needs a brush cleaning!

Raj observes that with this mod, audio is fine but distorts at high volume. The 9V voltage out does not drop at maximum volume.

Feedback on the solution from Jerry KE7ER

Jerry KE7ER says “This looks like a fine solution!   The fact that the 78L09 inherently limits current to something reasonable is a bonus.  And it fits in there perfectly!

Jerry suggest that it might be a little bit easier to just rip that trace out entirely. You could place the part up against the through-hole on one side and run a short wire to the other through-hole.

Gain should remain as it was at 12v.   Just that when you turn the volume up it distorts earlier.

If what you have on hand is the TO220 LM7809 (or any voltage from 5v to 9v), it will fit in there nicely as well.  Glue it face down to the board with pins hovering over  the trace that Raj has cut.   Or, if you don’t like glue, solder a short wire from tab to ground plane.

ST makes the 78L** parts in a SOT-89 package.   This is the same package as U2, the 78L05 for the IRF510 gate bias.

TI and Fairchild LM78L** parts only come in the SOIC-8 and TO-90 (also some dinky BGA that we don’t want to talk about).  Digikey and Mouser don’t sell ST’s SOT-89, so a bit harder to obtain. The SOIC-8 should do fine, solder the ground pins to the ground plane for heat transfer.   The TO92 could work, although it would likely heat up faster because the heat has nowhere to go.

The maximum available current draw from a 78L09 would limit the maximum audio level.    Apparently this provides enough audio for Raj, and limiting that current does protect the TDA2822.   If it gets to be too much current for the 78L09, it will shut down till it cools off.   Just what we want, if it’s enough audio power for your situation.

If you want more power and less protection, use the 1 Amp TO220 LM7809 (or 08 or 06 or 05) face down, flat on the board.   ST sells the 1 Amp L78** in the Dpak/TO252 package, about the same as the TO220.  TI sells the 500ma LM78M** in the Dpak/TO252 package, might be an ideal solution for moderate levels of current.

Any of the above could be made to work, and in fact any regulator providing between 5 and 9 volts.   This assumes you don’t have one of the clones made from factory floor sweepings that smokes at 7v.

Reference

Ashhar Farhan tells it as it is … the problem of the TDA2822

Ashhar Farhan VU2ESE, designer of the µBITx tells us the sorry saga of the TDA2822:

“Here is the story. This is going to cause a lot of heartaches. I chose TDA2822 after listening to a lot of bad press about the LM386. Upon looking at its harmonic distortions et al, it was found to be a reasonably good device. In, it went.

“Now, unfortunately, the TDA2822 production has entirely stopped. None of the standard suppliers, including mouser, newark, element14 have no stocks left. We tried to find other source of remaining stock from our reliable supplier who has been supplying to us in the past as well.

“He turned up with a batch. We tried the ICs in burn tests for. Ten of them on ten boards at full volume for a whole day. In retrospect, we should have tested every individual IC. That batch had these WX ICs as well. About 100 to 150 of these must have shipped, there is no way to know. The way it works is like this : Not all the ICs turned out by a factory are good. So work very well, some not so well, some don’t work at all. These wafers make it to the silicon industry underground where they are cut out from the wafers and packaged and sold as low grade versions of the same parts. We got a a hundred or so of these lemons.

“We finally located a source of brand new, high quality TDA2822s that are currently being shipped. They cost almost five times as much as we were paying while this was in production. Well, such is life.

“In the meantime, we have to look for alternatives to the TDA2822. I am highly inclined towards making a discrete device amplifier. We will never run out of discrete devices, the audio would be so much better. Does the gang have any ideas?”

Initial feedback suggests that there will not be a consensus reached on a replacement.  Some want to stick with the TDA2822 (assuming a reliable source of affordable devices can be found), some would prefer the ability to add in a module of the builder’s choice, and others would like to see the device replaced with discrete components.  David N8DAH suggests the drop in replacement –  NJM2073D-ND

Reference

KD8CEC minor firmware update v1.04

Ian Lee, KD8CEC, has released a further minor update of his firmware (v1.04).  You can download it here.

The changes since version 1.01 are as follows:
– Reduce cpu usage
– Change BFO Calibration step (50Hz to 5Hz steps)
– Change CW Frequency Display (frequency is more accurate when in CWL, CWU Mode)
– Optimized source code and reduced program size (97% -> 95%)

WA6ISP uBITx replacement Raduino

Mike Hagen, WA6ISP has previously supplied Raduino X and Raduino XP alternatives to the builder community for the BITx40 units.    He has been asked by many builders whether a µBitx Raduino replacement was planned.

He now has designed, built and tested a µBITx Raduino replacement.  This comes with the extra feature of having an i2c 16 port I/O expander on board. The Microchip Expander IC uses the Adafruit Library MCP23017 to create 16 more Digital Pins.

This replacement board is slightly bigger than the standard Raduino and has the Ardunio Nano facing towards the left rather than to the right.

Email Mike for further information or to order.   The cost of the bare board is US$12 and the built up board is $46.  Note that the bare board will require you to source all parts and  mount some fairly small surface mount devices.

µBITx constructors now have several alternatives to choose from in considering a replacement Raduino board: the WA6ISP uBITx Raduino, the W0EX Radi2cino and VK4PLN Raduino replacement.