Ot - Tda2616

[Malc C]

Sorry for the off topic thread, but I need some help reading the datasheet for a TDA2616 hi-fi amp. (http://www.nxp.com/acrobat_download/datasheets/TDA2616_Q_CNV_2.pdf)

it states +/- VP of 21 v max. Is this max +21v on pin 7 and -21v max on pin 5 (ie 42 volts across the supply) - or is it 21v max across these pins (ie 10v +/- to each pin)

The reason I ask is I've built one of the 2 x 15w amp kits (http://www.velleman.be/nl/en/product/view/?id=9184) from Velleman (purchsed from maplin) and the thing smoked shortly after switch on (halfway through a tack so it started to work !).

I've used a DVM and the transformer is outputting 2 x 13vac (or 26vac with the centre tap gnd) - the kit uses 4 x 1N5004 and a couple of 2200uf caps to provide the DC needed. I removed the damaged amp and measured the voltages betwen gnd and pins 5 and 7 which was -17.34 and +17.34. Now if the the max voltage is +/- 21vdc on each rail the supply voltages should be well within this.

Its the note that confuses me (yeah I know easily done !)

Note to the limiting values
1. For asymmetrical power supplies (with the load short-circuited), the maximum unloaded supply voltage is limited to
VP = 28 V and with an internal supply resistance of RS ³ 4 W, the maximum unloaded supply voltage is limited to 32 V
(with the load short-circuited). For symmetrical power supplies the circuit is short-circuit-proof up to VP = ±21 V.

Any pointers as to what the actual datasheet says would be apreciated

[Chippie]

Having read the data sheet and looked at the application drawings, I conclude that the max 'symmetrical' voltage that the chip can stand is 21 volts on pins 7 and 5...pos and neg respectively...so that equates to a max of 42v...

Using an asymmetrical supply the limitation is 28 volts...The values are limited by the short circuit current limiting circuitry on chip....

So, why did the amp self destruct?...Instability?

[Malc C]

Thanks for the comments. I thought that it should be fine as they suggest a 2 x 12 vac transformer capable of two amps.

We originally used a transformer from his old train controller, which worked fine for a couple of days, but we did notice it was buzzing a lot (the thing is 20 years old and really needs re-dipping in varnish to stop the laminates moving) - so I replaced it with a 50va 0-12vac times 2 transformer from maplin when they were having a clear out (saved £6 :) ) - this was brand new and like I said, lasted enough time to get halfway through a track on the CD before we noticed the sound quicky becoming distorted and smoke coming from the IC.

I've ordered two replacement TDA2616 from RS, but in the mean time have purchased a nother kit and will give that a go (costing me a fortune - would of been cheaper buying my son a set of powered speakers for his PC !)

[Malc C]

Now I'm really getting Fuc**d off with this. Just built the new kit from scratch, took my time checked the board and re-made all the connections just in case the inputs were shorting and causing the issue. The one modification I made was to the PCB was to fit a row of female headers so I could plug the chip in (just in case soldering it in was causing the problem) It also ment that I could test the supply voltages without risking the chip. I was getting -18.6 volts and +18.6 volts on pins 5 and 7. - all good so far.

I then connected the input to a source, pluged in the speakers and turned on - all seemed OK so I removed the plug and left it for a while before inserting the chip. Plugged it in and turned on the mains and she smoked again !!!! with hum from the speakers !

The only think I can think of is that the supplied mica insulator isn't doing its job and the bolts are some how shorting the thing out ??? It says in the data sheet that the internal block is at the same potential as pin 5 (-ve) and that's where most of the smoke comes from - Other than that I'm at a lost (and £45 out of pocket :( ) - just have to wait for RS to drop of the order and I'll try it without fitting a heatsink to see if that works !

[Chippie]

Mal,

I dont know how much RS charge for the chip, but I've used EastLondonComponents in the past(when I used to repair tv/video stuff)...They list the inline and qil devices at £3-50 and £3-00 respectively plus vat...delivery is usually quick..

A quick check with an ohmmeter between pins 5, 7 to the heatsink might be a good check b4 powering up..(granny and eggs?)

[Malc C]

LOL - I've always wondered where that saying came from, especially as you should blow an egg rather than suck !!

Thanks for the info. The part from RS is £2.84 plus VAT and I don't pay carriage :) and hopefully will be here on Tuesday. I did run the meter between the heatsink and all pins and didn't get any reading, so I gather its just a bad batch of chips. I've been reading / posting on the velleman forum and it seems quite a common thing with most of their audio kits as they either blame poor workmanship of the builder or simply suggest replacement of the offending chip or transistors.

I'll do more testing when the new parts arrive, and if it checks out will power one up without heatsink first just to rule taht out. I mean as circuits go its one of the simplest ones to build, and if the power rails are right, no shorts on the output then what else could it be apart from crap components - and to have it happen with two kits can't be coinciedence :(