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EHHA Rev A - Interest Thread - Page 112

post #1666 of 1668

Hrmmmm.. I've reflowed things. Didn't find any bad soldering. Maybe this requires a 2nd look. I did notice you've had this problem as well as others. Seems the EHHA's design is prone to this because of it being DC coupled. Hence the reason for the servo.


I did find this...



Originally Posted by gurubhai View Post

Here's how I would have go about troubleshooting.


1) Look for any shorts


2) Double check all components.


3) Check the BJTs using the BJT sanity tutorial an amb forums :


If there is some confusion , compare the results with the other working board.


4) Check & compare the resistances of output mosfets


Replace the faulty devices and see if you can get it working.


I know this is basic stuff and I should know most of this by now. But I just want to be sure I'm doing it right. I'd hate to create more damage than what is done.


1. Checking for shorts. Best way to do this...


2. Double checking components... I'm assuming this means one has put the parts in the their proper place.


3. Check BJTs... I'll use the recommended site.


4. What resistance should I expect for output mosfets? And at what points should I check?


I think I'll have to uncase this puppy to get a better angle on what is happening. I suppose I can use the good board to help.

Edited by Mullet - 11/12/14 at 6:08pm
post #1667 of 1668

Gosh this thread is dead.


So I've finally gotten things sorted out and it's quite perplexing. I've re-flowed joints on the amp section of the bad board and used generous amounts of flux this time. I didn't change the wiring layout, so that didn't change. I did re-tighten the terminals due to removing the board for re-flowing. In any event, now things are working. I'm getting a maximum of 3mV offset on the bad board and around 1mV on the good board. There was a slight buzz, even with the pot totally turned down. I changed the power cable and have plugged it directly into my wall outlet and not the power strip I'm using. Now the buzz has gone away.


How does this amp sound?




It feels like all of my headphones are now totally driven with authority. There seems to be more width in sound stage compared to my other Cavalli DIY amp - the Compact Tube Hybrid. I guess you could say it's less congested. With more listening time and comparison to my other amps I'll be able to fully grasp what it does and doesn't do.


On to my next project... the journey begins...

post #1668 of 1668

Congratulations on your build!!!  Looking forward to seeing some pictures.  Good luck on your next build!



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