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Cavalli EHHA Embedded Hybrid Headphone Amp - Page 116

post #1726 of 1816

Is R21 completely counterclockwise? IC1 and IC2 are definitely not mixed up? All other initial checks are correct before you get to the output quiescent current?

post #1727 of 1816

did you plug the bjt into the mosfet spots?

post #1728 of 1816

@ Holland : No.

 

@ John : R21 is completely counterclockwise, IC1 & 2 are correct. I can't do the initial checks since the output resistors start lighting up.

The other board which is identical measures perfectly.

 

I am thinking of a faulty component upstream.

Could be the ICs or the diodes.

The toshiba transistors I had matched before using so they should be fine.

 

It seems that smeggy had a similar issue when he had his diodes inverted. Sachu seems to have fixed his amp but didn't outline the steps  involved.

Paging sachu..


Edited by gurubhai - 12/12/10 at 8:55pm
post #1729 of 1816

If the VBe is fine, then the problem most probably lies with the output transistors.

 

Also check Q7 (if this is on the old version board), making sure that the VBe transistor is good.

 

Use the diode check feature ont he multimeter for this.

post #1730 of 1816

Q7 was faulty indeed. I replaced it & all is fine again.

Thanks for the help sachu & everybody.

post #1731 of 1816

excellent...enjoy!! :)

 

edit: and what was the reason Q7 failed btw??

post #1732 of 1816

Redoing my case work... Ahhh man I should have just sourced the parts myself for the 2nd 2 channels (my dac is balanced so I figured what the hell... was moving the psus to a separate case anyhow) instead of GJA ;O  Not that I have a problem with GJA, dude is awesome... I am just overly impatient and I won a bunch of telefunken tubes off ebay recently.  I suppose a full set of 4 amperex tubes couldn't hurt.  My case work is much prettier this time around, but I think it's just gonna be kind of out of commission for weeks while I wait for the other 2 channels.  Actually not quite out of commission as I could still build it as a 2 channel with just the other 2 channels mia for now.  Kind of waiting on a single drill bit to finish my case work anyhow, but that should come this week.  Sadly, I've already drilled out the case for the EHHA because I have another amp I am building laid out for the same style case (using the same psu, won't be able to use both at the same time but oh well) that I will almost certainly be able to finish before I get my other stereo ehha kit.

 

So I am kind of torn between just using ac power for the filament heater still or making it dc...  With the trafo in another case is it really necessary?  I had a slight hum before but I think it was from the trafo being so damned close to the right channel input.  I could I suppose figure out how to fit possibly up to a sigma11 in there but is that gonna run real hot at a constant 1.32a?  Something else I should use?  Kind of leaning towards being lazy with just ac heater lines :P for heat as much as any other reason... or at least it certainly seemed like my attempted cheap dc regs so far were not really gonna be good for heating 4 tubes at once without some ridiculous heat sinking and I don't really have room to put 4 of them in there with the current psu case :O.  Any suggestions here would be appreciated.  I can use the case itself as a heatsink possibly if necessary but again the regulator itself can't be too huge.  (To use the case as a heatsink I would probably need something with the transistors near the edge of the pcb, s11 would be really tricky to heatsink that way.)  Would shielding over the input or heater ac lines be helpful here at all or completely unnecessary?

 

post #1733 of 1816

I would say go with te DC filament supply. Its worth it for this amp.

I had slight hum with my EHHA, so I made a simple LM317 based DC supply(similar to one in EHHA rev. A ) & the hum is completely gone.

 

@Sachi :No clue. The mosfets were socketed earlier & I have my suspicion on a faulty socket but I am not sure how that would lead to Q7 getting damaged.

Today has been a good day. The EHHA 1 is back online & I also was able to finally finish my rev. A build. The first impressions are really positive.o2smile.gif

post #1734 of 1816
Quote:
Originally Posted by gurubhai View Post

I would say go with te DC filament supply. Its worth it for this amp.

I had slight hum with my EHHA, so I made a simple LM317 based DC supply(similar to one in EHHA rev. A ) & the hum is completely gone.

 

@Sachi :No clue. The mosfets were socketed earlier & I have my suspicion on a faulty socket but I am not sure how that would lead to Q7 getting damaged.

Today has been a good day. The EHHA 1 is back online & I also was able to finally finish my rev. A build. The first impressions are really positive.o2smile.gif


I made a LM317 based DC supply myself... it got ridiculously hot powering just 2 boards.  Maybe I can try it again with different transformers... I tried with a 7v and a 18v (only used half?) and it was getting way too hot powering 2 6gm8 filaments.  Maybe this is something that would actually improve by increasing the load from 2 to 4 filaments... then again the weaker trafo was incapable of reaching 6.3v under load and it (the lm317) was still overheating.  Maybe a 12.6v with lower current?  The 18v trafo was supposed to be a 12v trafo but apparently the website I got it off of is retarded?  In any event I don't have room for ridiculous heatsinks in the PSU case really, I could mount it to the side (rear?) of the case possibly but I dunno... I guess I'll experiment with other transformers maybe...

post #1735 of 1816

Very nice stuff Ravi.

 

And yes, DC heaters an absolute must for this amp.

 

Weird about Q7..confused.gif..well atleast you got it working agian.tongue.gif

post #1736 of 1816

AC heaters are more susceptible to noise, but you may be able to pull it off with careful wiring choices.  I'm not quite sure how, but it'll be tricky due to the positioning of the inputs.  I haven't checked the PCB traces.

 

FWIW, I tend to favor regulation being next to the circuit, so DC travels less distances and the noise filtering occurs with short travel.  I tend to favor AC for running wire around outside the box.  If DC were generated in a separate box, I would presume a need for a filter on the power rails next to the amp boards, IMHO.

post #1737 of 1816

I mean I guess I will figure out a way to work the filament dc reg into the amp case and leave the trafo with the psu case (actually simpler than trying to stuff more potentially hot things into the psu case) if this thing still is way too hot when I try other transformers I am just going to stick to ac probably :(.

post #1738 of 1816

So should I get a 9v 2.75a toroidal for my dc reg trafo or should 9v 1.66a be sufficient?  (4 6gm8s should be 1.32a @ 6.3v?)  I guess I could order both heh.  Does a 15va 9v toroidal sound good enough? or should I go for the 25va?  I'm leaning towards the 15 ;O.   Sorry to be a bother.

post #1739 of 1816

There is current loss for rectification.  For a full-wave bridge rectifier you need to allow for 1.7-1.8x the DC current you need on the AC side.  2.3A should suffice.  For 9v, 15VA is not enough.  You need about 21VA for 9V, so a common transformer power rating would land you around 25VA.

post #1740 of 1816

Okay, thanks.  I got both anyhow will use the smaller one till I receive the other 2 ehha boards anyhow :O


Edited by BebopMcJiggy - 12/13/10 at 1:58pm
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