tl;dr Modified a CMoy with TLE2426 which gets super hot. Normal or horrible beginner mistake? Question at bottom and tests/explanation in between.
Hello Head-Fi forums. I've been lurking around here for a while, but now I need to actually ask for help.
I had a need to listen to TV with headphones and this led me to the CMoy amp. I settled on Tangent's helpful tutorial and diagrams since I am coming into this with little electrical knowledge. After buying all the components, I proceeded to royally screw things up by reading the diagrams backwards, getting frustrated with my iron, putting things in backwards and upside down, and completely frying things. It turned out to be such a mess so I threw it all out and started again.
I've done extensive reading of pretty much every page on Tangent's website. I spent lots of time looking at the discussion on virtual grounds. For my second attempt, I decided no slightly modify the CMoy design to incorporate a better ground. So, my design now has a 24V DC power source running through a 7824 regulator (the DC adapter puts out 30.2V with no load, so I am above the dropout voltage of the regulator). I then have a TLE2426 (TO-226 3 pin package) splitting the voltage equally. Then I have the op-amp hooked in. The schematic that I have created is below. Yes, that's right, it's just the TLE2426 circuit from Tangent's page mashed into the CMoy circuit like the total beginner I am. Is it the best, I have no idea. Does it need more/less components? No clue.
My modified CMoy schematic incorporating a TLE2426 and LM7824.
I've laid everything out on a breadboard to test it. I used my computer for a sound source. I plugged the adapter in, clipped alligator clips onto my headphones and sweet, sweet music came pouring out. My mashing in of the TLE2426 worked. I was very happy, listened to an entire song and then... burned myself on the TLE2426!! Holy crap is that thing running super hot!
My breadboard with everything laid out.
I got worried, so I did some playing around. I first checked every connection and verified that it was laid out correctly. What I found was that, with no headphones hooked in, nothing got hot at all. Input DC voltage was 30.1V. The voltage coming out of the 7824 (measured from the 'out' pin to the '-' pin of the DC jack) was 23.7V (exactly what it should be). The 7824 was not hot (maybe a bit warm, but barely). The TLE2426 split the voltage exactly down the middle (like it should). Between the 'IN' pin and '-' on the jack was 23.7V. Between the 'OUT' pin and '-' was 11.85V. Perfect. So with no sound hooked up, everything is working out alright.
I then did some experiments with sound on and a multimeter. What I found was that as soon as the sound started, the voltage between the 'OUT' pin and the '-' pin of the DC jack (which was previously 11.85V) was now 19.1V. This got me thinking that there was too much voltage and the TLE2426 was getting hot because of it. So I did some more experiments where I put the ground connections in different places.
Some terminology: I have a 3.5mm cable plugged into my computer. There are three clips attached to it, L, R, and Ground. L and R go into the inputs of the amp. I have called the cable connected to this ground 'Gcp'. The L and R output of the amp is clipped to my headphones. There is another cable clipped to the ground part of my headphone plug. I have called this 'Ghp'. Gcp = ground from computer jack Ghp = ground clipped to headphone plug
How I got sound from my computer. White=Left(tip), Yellow=Right(ring), Black=Ground(sleeve).
How I got hooked up my headphones. White=Left(tip), Yellow=Right(ring), Black=Ground(sleeve).
Now the results of my test:
Gcp disconnected, Ghp connected to Vground: Loud buzz.
Gcp disconnected, Ghp disconnected: very very faint sound. Op-amp is working because it starts crackling when I raise the volume. Op-amp gets hot. TLE voltage is 11.85V.
Gcp disconnected, Ghp connected to '-' DC jack: No sound. op-amp got super hot really fast.
Gcp connected to Vground, Ghp connected to Vground: TLE2426 gets very hot. TLE voltage is 19.3V.
Gcp connected to Vground, Ghp disconnected: Faint sound. Op-amp warm. TLE voltage is 11.85V.
Gcp connected to Vground, Ghp connected to '-' DC jack: No sound. Op-amp got very hot.
Gcp connected to '-' DC jack, Ghp connected to Vground: TLE very hot. Voltage 2.9V.
Gcp connected to '-' DC jack, Ghp disconnected: TLE and op-amp ever so slightly warm. Voltage 11.85V.
Gcp connected to '-' DC jack, Ghp connected to '-' DC jack: Op-am gets hot. Also sound only comes out one channel.
Judging by my testing, it seems the best is that there should be no ground connection going to the output. But this makes no sense.
I then hooked up a 9V power adapter (7824 falls out of regulation and has an output of about 7.7V) With this voltage source, nothing gets hot, but the voltage between the TLE 'OUT' and the '-' DC jack is 4.44V instead of the 3.85V like it is with no headphones connected. Everything else is fine (it even sounds ok). It seems that with both power sources, the TLE voltage for common ground (which should be half of the input) jumps up by a big chunk as soon as I plug things into Vground.
My breadboard. Lower blue stripe is '-' from DC, Lower red stripe is "+" from DC, Upper blue stripe is +24V from the regulator, Upper red stripe is Virtual Ground from the 'OUT' pin of the TLE2426.
Another view. The brown jumper feeds the regulated voltage. Orange and green jumpers are connected to Vground. The left hand alligators are outputs and the right hand ones are inputs.
Another view in case anybody can see an error in my wiring.
Question: Rounding out my rambling post into a question for more experienced members: Is the TLE2426 getting extremely hot a normal occurance, am I hooking things up incorrectly, or am I doing things really wrong in the schematic?
As I read more, I'm beginning to think that the TLE2426 is actually going into protection mode and putting more voltage on the virtual ground rail. Thats why it works fine with no load. Why would it be doing this? I don't think there should be any excessive current anywhere in this circuit. Is it my laptop causing this?
Sorry about the long post, but I wanted to give lots of information.
Thanks in advance for your help.
