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Help on the TDA2005 amplifier!

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LAN_403

HVLOVER!!

Sat Dec 26 2009, 02:27AM

Registered Member #2567 Joined: Wed Dec 23 2009, 11:56PM
Location:
Posts: 11

Ok so this is my problem. I got the TDA2005M amplifier (atleast i think it is....it just says TDA2005 8840M or somethin like that) so from what i can gather, it is the mono amplifier as shown in this schematic:

every single part that i used in there is what it says with a few minor differences....like the 120k resistor is 112k on mine, the 36ohm is 40ohms on mine, on resistor 7 and 8 R7 is 1ohm and R8 is 2ohms since i couldn't find another 1ohm resistor. other wise, everything is what the schematic calls for. all capacitors are atleast 25v and the max input voltage is 18.5volts. i was meticulous in making sure that everything was connected in the right way...took me a stupid hour and a half. it was more of a free hand soldered connections. i didn't bread board it but i plan on it tomorrow just to be safe.

now, just to be sure, the black bars mean ground and on the capacitors mean the negative side right?
my powersupply is more than capable of handling the power requirements so i know that's not a problem, i didn't reverse the negative and positive connections accidentally and the ic never heated up when i had it on "full" power. (18vdc)

one thing i did think could be a problem tho was the input...this is a mono amplifier so it's only one channel. now, to connect my mp3 player to the circuit i am using a stereo jack to plug into the headphone jack of my player and i have stripped the other end off so that it exposes three leads. one lead going to each headphone and the third lead being what i believe is a common ground type of thing for each speaker. now when i am connecting the leads to my input on the amp, do i connect just one lead to the input pin and leave the common lead out? or do i connect the common lead to the negative voltage source and the second lead to the input pin? i hope i am making sense here.

one last question...it's kinda a stupid one but the 6th pin IS connected to the little metal flange at the top of the ic right??? i've been having that flange directly connected to the heatsink and all of my grounds going connecting to the heatsink with no direct connection to the 6th grounding pin....i am also assuming that the 6th pin/heatsink also acts as the negative voltage connection?

Conundrum

Sat Dec 26 2009, 10:35AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

could be the problem, ALWAYS assume that the tab connection is high impedance but may read negligible resistance to pin 6.

connect pin 6 to ground. Also, with headphone connectors the sleeve is typically Gnd and the ring and tip are R and L channels.

it might be worth putting a 1K resistor across the input as some cheap mp3 players etc *need* a load or the output will be flaky at best. (learned this the hard way)

What are you using for cooling? these chips can and will get HOT (I don't recommend soldering a piece of copper to the tab but at a pinch it will work) best to use a proper IC heatsink.

Hope this helps, -A

HVLOVER!!

Sat Dec 26 2009, 04:52PM

Registered Member #2567 Joined: Wed Dec 23 2009, 11:56PM
Location:
Posts: 11

i have the ic mounted on a large heatsink and i have a fan i can use just in case it gets too hot. i'll try what you said! hopefully it works! thanks!

HVLOVER!!

Sat Dec 26 2009, 06:45PM

Registered Member #2567 Joined: Wed Dec 23 2009, 11:56PM
Location:
Posts: 11

alright so i have just connected all of the grounds to the actual grounding pin and now when i connect the voltage source in, the negative going to the 6th pin and the positive where the schematic says the positive should go, the speaker makes noise!! like as soon as you tap the connection to the battery (when one polarity is already connected) the speaker gives a little....buzz type of noise?? that's the best i can describe it. it stops as soon as i either remove the connection to the battery or if i leave the battery connected. when i run the circuit off of my homemade bench top variable voltage regulated power supply, the chip picks up some of the ripple on the output (from the transformer) that wasn't filtered and it is amplified on the speaker. i made sure it was coming from the speaker and not my cooling fan by touching the speaker cone and the noise stopped. when i released the cone, it started up again. so, it seems like the chip itself isn't broken. now here my problem, when i connect my mp3 player (which is a creative zen) it doesn't make any noise...i checked the actual cable i was using with my ohm/volt meter and i made sure that i had one channel that was going to be used. the L channel with the ground cable going with it. i connected one cable to the negative of the battery and the other cable to where the schematic says is the input. and of course...it didn't work....so i tried putting a 2k resistor on one of the cables (in series) and once again...it didn't work....

it seems that i have a connection problem. am i right by putting the other cable to the negative on the battery? if i'm wrong where should i put it?? i'm so close, i just need to know where to put the inputs into.....anyone know for sure?

HVLOVER!!

Sat Dec 26 2009, 07:51PM

Registered Member #2567 Joined: Wed Dec 23 2009, 11:56PM
Location:
Posts: 11

ok now i just realized how stupid i was.....i was putting both of the wires from the cable on the output of the mp3 player to the negative side.......so dumb...anyways should i put the other wire to the positive supply? or would that blow my mp3 player....i have a mp3 player that i can test with, just in case it might blow everything up. i'm worrried it would make a "short circuit".

the reason why i have this idea is because, as i said in my last post, that the chip was amplifiying the ripple voltage from my homemade powersupply and makin a small 60hz noise. the point is, the chip is AMPLIFYING! and the signal is coming in on the positive and negative supply pins....does that mean i should connect the audio input to the positive and negative supply pins too? i just don't want to blow my player.

Proud Mary

Mon Dec 28 2009, 10:51AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

If you place your finger on Pin 1, or a short piece of wire soldered onto it, you should hear a loud 60Hz hum as your body acts as an antenna for the mains frequency from which there is little escape.

If this doesn't happen then, you have made a mistake somewhere down stream of pin one. If you do get a loud hum, it means that
the error is upstream - - the way in which you have coupled pin one to your signal source.

The hum you do describe is more likely to be due to poor layout than ripple.

Stella.

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