Troubles with E3 Headphone Amp kit

[yvlasenko]

Hi there!

I'm building my first DIY amp, the E3 Headphone Amp from ebay: E3 headphone amplifier kit+UPC1237 Protection WLX-4 | eBay

For some reason, the R25 and R26 resistors are overheating, both left and right... Don't know how to deal with that, any clue appreciated.

The schematics I've got from seller is attached bellow.

Any general thoughts on this are welcome.

 

[yvlasenko]

My bad. I've forgot to soldier leds...
After installing leds, it powers up, but there is 50Hz noise. Will work on it.

 

[2000impreza]

Interesting looking amp. Don't forget to check for DC offset before plugging headphones into the amp.

 

[yvlasenko]

Thanks, I've checked that.

The only odd things are humming noise and 0.1VDC fluctuation anywhere on the board, including headphones out. Don't know how to deal with it yet.

Interesting looking amp. Don't forget to check for DC offset before plugging headphones into the amp.

 

[sgrossklass]

Have you double-checked all the rectifier diodes and verified proper operation of the regulators?

Do Q5/6 test good (diode test)? What about Q1/2? It's not impossible that some of them were damaged.

 

[yvlasenko]

Hi, sgrossklass!
I've double-checked diodes and transistors, everything looks good. The regulators give the proper voltage.
I've tried to short the input while powered on, the noise gets lower, touching the radiators make it lower too. Touching the volume pot makes it higher.

 

[yvlasenko]

I've added 100uF in parallel to C5/C6, and the noise is almost gone!

...but then I accidentally shorted side radiators, and it looks like I've fried negative regulator...

Will continue after changing the regulator...

 

[yvlasenko]

I've swapped the regulators for new ST's and added isolated thermal pads between transistors and the radiators. Now I can only hear some noise when the volume pot is on it's max in the night when it's quiet. Looks like everything is ok now

 

[yvlasenko]

I just found I made a stupid mistake

The transformer's secondaries were connected the wrong way:

--||---- +
) || (
) || ( Secondary A
) || (
) ||---- -
) ||---- -
) || (
) || ( Secondary B
) || (
--||---- +

instead of:

--||---- +
) || (
) || ( Secondary A
) || (
) ||---- -
) ||---- +
) || (
) || ( Secondary B
) || (
--||---- -

That was the reason of noise...