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Help requested - CMoy with TLE2426 getting extremely hot - Page 2

post #16 of 26
Thread Starter 

Quote:

Originally Posted by tangent View Post

Sounds like time for board pics.  Macro photos, both sides.  Use a tripod and lights, if you can.


It's not soldered to a board yet. I specifically built it on a breadboard because I knew I'd make beginner mistakes. Ideally, I'd like to iron out this odd behaviour or at least persue it to the point where I know I have no control over it.

Should I just go ahead and solder everything anyway? It seems like a waste if I have to start desoldering so I can swap components.

post #17 of 26

Your problems could be due entirely to that white slab of trouble you're using.  It adds huge amounts of parasitic capacitance, which analog components do not like at all.  It also adds fair amounts of parasitic inductance and parasitic resistance that can vary depending on how well the leaf contacts are grabbing the various components.

 

I only use solderless breadboards for very simple low-speed digital and DC circuits.  For analog, good quality sockets are as far down the road toward solderless breadboards as you should go.

post #18 of 26
Thread Starter 
Originally Posted by tangent View Post

...that white slab of trouble...


 

Ok, before I solder things up incorrectly, I have made a layout of the protoboard and the components. Would somebody be able to quickly look it over and steer me away from horrible mistakes? I've checked it several times and I think it's ok, but I'm a bit curious about the placement of C1. Is it ok where it is or must it be physically before the TLE2426 on the board?

th_42473_Protoboardlayout_122_591lo.jpg

My attempted layout of the components on the protoboard. Follows my schematic posted above.

 

If everything is ok, I'm going to put this together and then try it out again.

 

Thanks for all the help so far.

post #19 of 26

Your layout is wrong

You have reversed the Output and - in

on your op amp.

 

Maybe my schematic will be easier to follow...

 

CMoy DIP8.bmp


Edited by Avro_Arrow - 5/24/10 at 6:06pm
post #20 of 26

I think....

 

On your drawing, +(wall) never makes it to pin 8 of the opamp so your TLE2426 never gets a positive feed from pin 8

 

cheers

FRED

post #21 of 26


It goes through the 24 volt regulator.

That through me off at first too...

Quote:
Originally Posted by Fred_fred2004 View Post

I think....

 

On your drawing, +(wall) never makes it to pin 8 of the opamp so your TLE2426 never gets a positive feed from pin 8

 

cheers

FRED

post #22 of 26
Thread Starter 
Originally Posted by Avro_Arrow View Post

Your layout is wrong

You have reversed the Output and - in

on your op amp.


I'm not sure what you mean by reversed output and - in. I followed the pin assignments on the datasheet for the op-amp. Pin 1 is definitely an output. I do notice that you have four capacitors after your TLE2426 and some which are much larger than mine. Can you explain the reason for that?

 

What your schematic did make me do is check my schematic and layout yet again. And you know what, I found something missing. I had forgotten an entire resistor in my schematic and it wasn't on my breadboard. I've gone and updated my schematic and layout. I added the resistor to the breadboard, but there's still the problem of the voltage becoming unbalanced when I plug into my laptop as a source. I was rather hopeful, but, oh well.

 

I'd still like somebody to take a quick look at the layout and give it an 'OK'. I'll then solder it up.

th_56550_ModifiedSchematicv2_122_252lo.jpg

Corrected schematic with the added resistor.

 

th_56542_Protoboardlayout_122_588lo.jpg

Corrected layout following the schematic above.

 

Thanks


Edited by Jamdat - 5/24/10 at 8:26pm
post #23 of 26

Because there are no values on your breadboard drawing, it looked

like your output resistor was your feedback resistor.

Your schematic looks fine.

If you remove R8 and R9 (optional resistors) from your

breadboard drawing it will be less confusing.

Otherwise, it looks fine now.

 

My schematic was something I did a year ago.

I would not do it the same way now.

 

Good luck!

post #24 of 26
Thread Starter 

Alright, I've put this down on some protoboard. Lesson learned here: stripboard is sometimes easier - solder bridges are much harder to make intentionally. And solid core wire breaks if you bend it too much. Good things to learn. I managed to blow up my LM7824 regulator and so I had to head out to the electronics store to get a new one. It seems to be better.

I have images of my board for people to look over and catch errors and also as an example (perhaps of what not to do) for the benefit of fellow beginners who might see this in the future.

 

th_30669_1_1_122_69lo.JPGth_30716_1_2_122_201lo.JPGth_30760_1_3_122_39lo.JPGth_30801_1_4_122_983lo.JPG

Top of the board. The wires sticking out are where I clip the power, source, and headphones.

 

th_30847_2_1_122_987lo.JPGth_30889_2_2_122_111lo.JPGth_30937_2_3_122_377lo.JPGth_30979_2_4_122_229lo.JPG

Bottom of board. I've cleaned the rosin with alcohol. The leads to some components aren't clipped since I was swapping components in and out. I also used 'S'-jumpers for those interested.


So, on to my testing. Tangent, I don't know if this is because it's now on protoboard or because I put in a new regulator but that funky voltage imbalance thing that happened when I plugged into my computer disappeared! Genius you are. I was very excited, but noticed a hiss in the headphones when I had them plugged in. So I went off reading some more troubleshooting stuff.

First thing I did was lower the gain down to 3 (4.7k resistor). The hiss was still there, along with an awful crackle. There was also clipping at a very low volume. So out those resistors came and in went 2k resistors to put the gain up to 6. This eliminated the crackle and clipping, but not the hiss. So next up was the resistor on the output (R8 and R9 in my schematic). I had a 100 ohm resistor from another project, so I put that in (lowest value I had). Still a hiss. I reread Tangent's troubleshooting page and decided to put 100 ohm outside the feedback loop. Hiss gone!

What are the disadvantages of the resistance outside the loop? "[B]ad side effects" are mentioned, but never elaborated on. Everything seems to be a bit quieter. Also, should I remove the 100 ohm resistor inside the feedback loop now that I see that the resistance outside the loop works?

Another thing: while measuring the amp's current draw, I looked carefully at the datasheet (http://www.ti.com/lit/gpn/opa2132). I noticed operating voltage is 2.5V - 18V. I'm putting 24V through it. That's probably bad. Should I change to an 18V regulator? I ask because when I unplug the source I get really bad buzzing (the stereotypical buzz you hear in movies when somebody plugs a guitar into an amp). I thought this might be an oscillating amp and the high voltage might be the cause.

Thanks for the help so far!

post #25 of 26

Well, a bit OT, but since this design uses a TLE chip to improve on the virtual ground I thought I would give it a try.

I have a Sennheiser HD-470 with 60 ohm impedance. Will the TLE be enough to drive it. I read on Tangents site it cannot handle to much load on itself.

 

Will a TLE be OK, or do I need to add an LMH632 buffer to make it drive these headphones.

post #26 of 26

Jamdat:

The op amp can handle +-18 volts...36 volts total, your 24 volts is fine.

 

Barsk:

The TLE has to handle the return current from the op amp.

Most of these small op amps only put out as much as the TLE

can return so the whole thing will overload at the same time.

If you are listening so loud that the amp starts to sound bad

then it is time for a bigger amp. If the amp sounds good

then you are fine with what you have.

 

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