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EHHA Rev A - Interest Thread - Page 112

post #1666 of 1671

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...

 

Quote:

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 :

http://www.amb.org/forum/howto-bjt-sanity-check-t59.html

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 1671

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?

 

Fantastic!

 

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 1671

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

 

Me

post #1669 of 1671
Quote:
Originally Posted by Mullet View Post
 

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?

 

Fantastic!

 

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...

sorry for the late answer.

May be you get a faulty pcb.

I'm working on a pcb without this annoying noise, i will post somme pictures when i receive it.

post #1670 of 1671

Yeah, the noise thing is weird. It had gone away and now it's back with a vengeance. I don't think it's my input wiring (RCAs). I'm using belden cable for the wire, which includes three wires - black, red, and gnd. I usually cut either black or red and keep the gnd. Then I wire both the gnd and either black or red depending on left or right channel. Both go to my pot inputs. I'm using the AMB RK27 board with an RK27. I've tried isolating the RCA jacks using those fancy Rean RCAs. I'm pretty certain they are isolated from the chassis. Or at least I think so. Anyway to tell for sure?

 

I'm thinking my star ground wiring is correct. I'm using the alternate wiring instead of the primary wiring on Alex's site. The only things that I can think of that relate to noise would be my transformers being too close. Can I just use copper foil to shield them?

 

I'll probably take everything apart and start with different star ground wiring to see if that helps. I actually have a ground loop breaker in the mix, but it doesn't seem to have an effect to removing hum.

 

I have some pix that I'll upload in a few hours.

post #1671 of 1671
Quote:
Originally Posted by Mullet View Post
 

Yeah, the noise thing is weird. It had gone away and now it's back with a vengeance. I don't think it's my input wiring (RCAs). I'm using belden cable for the wire, which includes three wires - black, red, and gnd. I usually cut either black or red and keep the gnd. Then I wire both the gnd and either black or red depending on left or right channel. Both go to my pot inputs. I'm using the AMB RK27 board with an RK27. I've tried isolating the RCA jacks using those fancy Rean RCAs. I'm pretty certain they are isolated from the chassis. Or at least I think so. Anyway to tell for sure?

 

I'm thinking my star ground wiring is correct. I'm using the alternate wiring instead of the primary wiring on Alex's site. The only things that I can think of that relate to noise would be my transformers being too close. Can I just use copper foil to shield them?

 

I'll probably take everything apart and start with different star ground wiring to see if that helps. I actually have a ground loop breaker in the mix, but it doesn't seem to have an effect to removing hum.

 

I have some pix that I'll upload in a few hours.

Yes you can cover the transformer with a copper foil. Don't forget to put the foil to the ground.

The problem with the ehha is the number of cables that float around.

This the reason why i did my own pcb.

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