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Carrie USB-Powered Headphone Amplifier - Page 61

post #901 of 913
Quote:
Originally Posted by Avro_Arrow View Post
 


Other than having to charge up that big a55 cap bank, it's just a three channel CMoy.

I think the 100mA should at least get it running. Just add up the quiescent current

for the three channels and add in how much current you think you may draw under load.

 

Ok noob questions: How do I calculate the quiescent currents and the current of the load?

 

I'm guessing if I can find the output RMS voltage at normal volume, and the impedance of the headphone, I can calculate the load current. But how do I find the RMS output voltage?

 

I'm clueless how to find the quiescent current of the Carrie.

post #902 of 913

You can use the sensitivity rating on your headphones to guess-timate the voltage required to drive them to a reasonable

level and use their impedance to figure out the rough current.

You can get the quiescent current for the op amps from the data sheets.

post #903 of 913
Quote:
Originally Posted by Avro_Arrow View Post
 

You can use the sensitivity rating on your headphones to guess-timate the voltage required to drive them to a reasonable

level and use their impedance to figure out the rough current.

You can get the quiescent current for the op amps from the data sheets.

 

OK I'll go digging trough some data sheets tomorrow.

 

If there's no way to have more than a guess-timate on how much current my headphones draw, I'll just take my amp meter out and test them. That should work, right?

post #904 of 913

Comparing this---->

Quote:

 

 

To this--------->

 

 

 

 

 

 

 

And the datasheet for the Tantalum Capacitors installed in the C1 positions

 

(http://www.mouser.com/ds/2/212/F3100_TaDipRad-507115.pdf)

 

Screen cap---------->

 

 

 

I'm wondering if they are still installed backwards.

 

The idle current for a Mini3 should be 24mA. :wink:

post #905 of 913
Holy smokes! I never realized those capacitors had a polarity! Nice find! I'll switch them the right side tomorrow. Thanks a lot! biggrin.gif

Hopefully my ldo is not fried and will still work after that...
post #906 of 913

I'd be more worried about the capacitors then the regulators but they're over-spec'd enough that they should be OK.

(it's not uncommon for damaged tantalum capacitors to explode when they fail)

post #907 of 913

Alright so I reversed the caps, but I still only get 1.9 V out of the LDO. What's more, I only get 1.9 V at the input of the LDO. I'm guessing it's shorted and pulls the DCP into over current protection. Pulling the LDO out and the DCP outputs 24 V.

 

Interesting to note is the polarity of those capacitor is not marked on my PCB. The print is simply not there.

post #908 of 913

A vacant U2.... sounds like a good time for a sanity check.

Measure the resistance between the output pad (the pad closest to the front of the PCB) of U2 and ground.

What's the reading?

(should be in the high K ohm range and will wiggle around as the caps do their thing)

post #909 of 913
Quote:
Originally Posted by MisterX View Post
 

A vacant U2.... sounds like a good time for a sanity check.

Measure the resistance between the output pad (the pad closest to the front of the PCB) of U2 and ground.

What's the reading?

(should be in the high K ohm range and will wiggle around as the caps do their thing)

 

Moves around 2 K ohms. 

 

I measured just about everything I could think of but didn't find any short.

post #910 of 913
Thread Starter 

Any chance for high res shots of the bottom side of the board? All that resoldering can't be good for those traces. From your previous posts, sounds like the TL750 and DCP are both working fine independently of each other.

 

When I put in a tantalum caps backwards, it went up in flames; it went up because I was surprised and threw it in the air. I wonder if yours are shot and need replacing.

post #911 of 913
Quote:
Originally Posted by joneeboi View Post
 

Any chance for high res shots of the bottom side of the board? All that resoldering can't be good for those traces. From your previous posts, sounds like the TL750 and DCP are both working fine independently of each other.

 

When I put in a tantalum caps backwards, it went up in flames; it went up because I was surprised and threw it in the air. I wonder if yours are shot and need replacing.

 

Nothing happened to my caps when I first powered the amplifier up. I doubt 1.9 V is enough to kill them... but anyways. You think I should try to power the board without the caps in, see what happens?

 

I'll take my scanner out and scan the bottom of the board. Pictures later today.

post #912 of 913
Thread Starter 

I was thinking more of the reverse polarity damaging the caps, but taking them out wouldn't be a bad idea to experiment.

post #913 of 913

So my scanner proved to be unable to take pictures of PCBs, so I went on and bought a DSLR. Here's what I could do with it. You can download the originals and zoom in all you want.

 

 

 

 


Edited by KimLaroux - 1/28/15 at 11:56am
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