EHHA Rev A - Interest Thread

[stixx]

Hi,
 
Strange indeed. It should not matter how you connected the two wires...you should have more than 10V
at the input. Could it be that one of your toroids is a 6V unit?   

 
OK.. stupid reply since you have a toroid with two secondaries. Have you rechecked your readings and
have you tried with reversed connection?

 

[Sathimas]

First - a small preview what it's gonna look like
 

 
Now - the two secondary windings are both 10.3V without load,
 
 
I did reflow all the solder joints and it works correctly now ...

 

[Sathimas]

No easy win here...
 
Attached the rest of the wires and found that the DC-offset on the right channel
does not drop - I'm reading 24V across G and OUT.
 

 
The other channel is working fine.
 
 
Since I'll be going on holidays tomorrow I won't be able to do any more testing,
but nonetheless I'd be very happy about some hints where to start looking for the error.
 

 

[funch]

I purchased a semi-completed Rev A that had offset issues. It turned out that there was a cold solder joint on one of the resistors.
I believe it was R12 iirc.

 

[jdkJake]

No easy win here...

Attached the rest of the wires and found that the DC-offset on the right channel
does not drop - I'm reading 24V across G and OUT.

:mad:

The other channel is working fine.


Since I'll be going on holidays tomorrow I won't be able to do any more testing,
but nonetheless I'd be very happy about some hints where to start looking for the error.

How about some pics? Top and bottom, as much light and focus as you can muster.

 

[Sathimas]

I won't be able to post some pics before the 23.09.2013, since I'm on holiday right now
(And getting married this saturday  )
 
But I can't wait to get this amp to work, since I'm working on it for about 2 (!!!!) years.

 

[stixx]

 First - a small preview what it's gonna look like

very nice wrap job... looks like a can of worms.. or human internals.
You must be a surgeon then

.
 
 
 
And CONGRATULATIONS to your wedding!

 

[Sathimas]

 

 

 
Here are the requested pictures, hope the are sufficiant.
 
I did also reflow all the solder joint, but still the offset is at 25V !

 

[stixx]

No expert in troubleshooting solid state stuff... your soldering quality looks really good, and as far
I could see parts orientation and such is all good also.
Did you check your DMM...? They can be faulty, and 25V offset is very high. Maybe also check that all
your semiconductors are in the good place on the pcb.

Good luck!

 

[Sathimas]

DMM is definitely o.k. - I did the initial check of all other boards with that one.
 
I'll try to check the transistors too - always possible to have them in the wrong place...
 
It's a pity runeight himself isn't present here anymore...
 
But i don't know where to ask anywhere else...
 

 

[gurubhai]

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.

 

[holland]

http://www.elexp.com/t_test.htm
 
 
Diode test your transistors, something is probably blown.  I would start with the VAS stage and servo booster, Q6, Q7, Q8, Q9, Q12, Q13, Q14 and Q15.  Another thing you can try, just to get bearings, is to pull the servo on both channels and measure voltages at different points, especially on the current mirrors.  Make sure the trimpot is set at the half way mark first.  Do note that some of the transistors in the current mirrors are set up to be a diode drop.  They will look like the attached.  When you diode test, that part will appear as a short, and should test exactly like a diode (such as 1N4001).
 

 
 
I haven't checked your pictures since stixx said it looks good.

 

[Sathimas]

I'll be back with results as soon as I can, but do not have the time today or tomorrow,
so don't check for results before friday here.
 
Thanks for the advice so far.

 

[holland]

No worries.  Just make sure you are looking at the schematic as you are doing this.  Results can vary depending on how transistors are wired.  That said, you can brute force it and change a bunch of transistors for the heck of it, but that can be a big PITA unless you have a desoldering station.

 

[Mullet]

I'm about to embark on my EHHA Rev A journey. Been waiting for a while -- built "The Wire" and a really nice ES9023 based DAC first. I'm planning on using the E12 and have used it in the past with the CTH. With the CTH I had to lessen the threshold for when it triggers. I still even find with certain headphones, the AKG K240 Sextetts for example, that it's pretty easy to get the E12 to trip. I'm thinking this might have more to do with the implementation in the CTH vs. other amps. Some tubes are worse than others. Other headphones don't have the issue as much. For example, orthos don't cause the CTH E12 to trip that easily or at all. What are everyone's experiences with the E12 in the EHHA Rev A? Did you guys find that upping the tripping threshold was required? Also, has anyone tried the EHHA Rev A with the Sextetts? If so, are they a good match? I figure I'll wait til January or February before I buy my kit from Glassjar. Just want to have my research all in order first. I'm thinking at this point socketing all the OL and CL gain resistors and going with an initial gain of 5 or so.