[stixx]

 Thanks, but I haven't found the size on Alex's site.

 
The board in question is from Amb Labs... the Epsilon 12 muting thing.
 

 

[Chs177]

  Is C3 properly installed? It looks weird.
 
Can you confirm R17 value.

C3 is properly installed.
R17 is 1,5K.

 

[FallenAngel]

C3 is properly installed.
R17 is 1,5K.

 
1) Look at every transistor and make sure they're in the correct position (2705/1145) and of course, confirm the 540/9540 are in their correct position.
2) Flip the board over and take a clear photo.

 

[Chs177]

   
1) Look at every transistor and make sure they're in the correct position (2705/1145) and of course, confirm the 540/9540 are in their correct position.
2) Flip the board over and take a clear photo.

Thank you! One board is up and running. I'm working on second board.

 

[Chs177]

Both boards are up and running. EHHA have an amazing sound. I'm find out a lot of useful information from this thread. Thanks all!

 

[FallenAngel]

Finished my build, fixed some grounding issue but still getting hum when the volume is above 50%. Any ideas on how to deal with it?

 

[greyhorse]

FallenAngel,
 
Congrats on building up the EHHA.
Overall your build looks ok, but please let me know the following:
 
1. Input impedance of your pot.  I think I had a 100K Black Beauty in mine, but I seem to remember swapping it out with a 10K TDK conductive plastic unit after being plagued by hum.
2. Is your star ground connected to the chassis properly?  It's hard to see from above.
 
It's minor, but your safety earth connection to the star ground runs parallel with the 30VAC, so maybe if your star ground is floating it's picking up the AC.
I prefer to drop the safety earth to chassis right at the 120V socket.  This also gives you the option of raising the star ground from earth by a few ohms (like with a NTC).
 
Otherwise I'm not seeing too much wrong.
 
-Jeff

 

[bluemonkeyflyer]

  FallenAngel,
 
Congrats on building up the EHHA.
Overall your build looks ok, but please let me know the following:
 
1. Input impedance of your pot.  I think I had a 100K Black Beauty in mine, but I seem to remember swapping it out with a 10K TDK conductive plastic unit after being plagued by hum.
2. Is your star ground connected to the chassis properly?  It's hard to see from above.
 
It's minor, but your safety earth connection to the star ground runs parallel with the 30VAC, so maybe if your star ground is floating it's picking up the AC.
I prefer to drop the safety earth to chassis right at the 120V socket.  This also gives you the option of raising the star ground from earth by a few ohms (like with a NTC).
 
Otherwise I'm not seeing too much wrong.
 
-Jeff

 
Guys,
 
I've read the entire thread. I have my EHHA Rev A up and running on a rectangle of plywood.
 
I FUBAR'd one channel by boogering the power supply trying to remove/replace a faulty LED. Ordered another 1/2 kit from Jeff and built it in lightning speed compared to the snail's pace the first go round. I had horrible snap, crackle, and pops from the new build. I finally narrowed it down to the V+ side of the amp MOSFET. Whenever I applied any kind of force on the amp heat sink, the noise got worse or went away depending on the side to side pressure. So, I reflowed the solder joints  of the MOSFET and the largest resistor on that side. That took care of the rice crispies.  
 
I still have some hum at greater than 75% volume pot but that's negated by going to 50% volume pot and adjusting the source volume. I suspect the residual noise may attenuate once I have the amp installed in a proper metal enclosure. 
 
Being a kindergarten electronics-soldering Newbie, I would not be this far along without this thread and mostly the ongoing advice and guidance by an amp building guru widely known on this, and other, forums....To You, Sir, hats off and much gratitude.
 
The sound quality is wonderful!  Thank you, Dr. Alex, for making this project possible.  OK, onward to Bijou and CKK3 builds.
 
~BMF

 

[FallenAngel]

It's a 50k black beauty. When I disconnected earth ground, the noise is MUCH lower.
 
The star ground is connected to the chassis via ground loop breaker (lowered noise).
 
I'll try to move the star ground to the IEC.

 

[FallenAngel]

Moved the grounding to chassis-ground based with a ground loop breaker to IEC. Still seems that the only way I get very low noise is to remove the IEC from the equation, but that's obviously not idea.

 

[Chs177]

  Still seems that the only way I get very low noise is to remove the IEC from the equation, but that's obviously not idea.

Why not? I saw many advices to don't connect power ground at all to avoid problem with hum and noise.
Now I'm not connected power ground and have no noise at all on very sensitive headphones.
You may also consider to use socket with EMI filter. May be it will help.

 

[FallenAngel]

Don't have one right now, but may need to check that.

 

[funch]

Here are some pix of my first Rev.A. Scroll to post #1282. As you can see, I took the term star ground literally. All of the ground wires, including from the IEC
and headphone jack, connect to a brass 6/32 machine screw.  I never had a problem with hum.
 
http://www.head-fi.org/t/506984/ehha-rev-a-interest-thread/1275

 

[FallenAngel]

  Here are some pix of my first Rev.A. Scroll to post #1282. As you can see, I took the term star ground literally. All of the ground wires, including from the IEC
and headphone jack, connect to a brass 6/32 machine screw.  I never had a problem with hum.
 
http://www.head-fi.org/t/506984/ehha-rev-a-interest-thread/1275

 
Very nice build.
 
I don't think I connected my 6.3V supply to ground, so I'll do that next.

 

[stixx]

  Why not? I saw many advices to don't connect power ground at all to avoid problem with hum and noise.
Now I'm not connected power ground and have no noise at all on very sensitive headphones.

Not a good idea. You can omit connecting power ground in digital gear or other low power devices, but you should never do that in anything that contains the word "amplifier". 
When you only can get your gear humfree with leaving ground unconnected your wiring or else is bad.
There's also information posted on the Cavalli site about alternate wiring to try in case of hum.
 
Member Sathimas posted a while a go that he needed new (better) transformers to get rid of hum (probably because of the proximity of the trannies to the amplifier boards). When you have a good central ground point where all the individual ground wires are connected you should not have hum. Of course also tie the heater supply to that point! (--> Fallen Angel). Also try to have the rectifiers facing away from the amplifier boards.
 
I am at No 12 in my row of headphone amplifiers, and none of them had/has hum issues... I didn't even need Ground Loop Breaker.