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post #1546 of 1688


I'm building SOHA II as well. I bought the fuse listed in the BOM but now I'm wondering if it works in europe? My mains voltage is 230v so should I get a smaller fuse?

Another thing that crossed my mind: I have a couple of meters of expensive coaxial cable, would that work for the input connection?

I hope someone is still reading this thread.

post #1547 of 1688

Yes, and yes.


Any metal that conducts well would work for input wiring for another amp, however whether it is suitable is another matter. FWIW I use Belden 1505A as my input wiring as it is double shielded, but it is a bit stiff to bend around. I probably will do the same for this amp, that is if I ever get started (again) on doing this.

Edited by Navyblue - 2/7/12 at 4:31am
post #1548 of 1688

Thanks, relieving to see people still get help with the SOHA.

My limited knowledge in electronics tells me the fuse should be 250mA so I'm going with that. With any luck I'll have it working tomorrow. Pics coming later!

I'll just use the coax cable since it's shielded and the impedance level probably won't have any effect.

post #1549 of 1688

I am not sure if you can call that help. tongue.gif I know little about electronics too. I have built another amp so I kinda know some general stuffs. However if I were to meet a real electronic problem I am very much clueless. On my own SOHA II board I only have stuffed a handful of resistors, it's been that way for many months already and it's not moving any time soon. biggrin.gif

post #1550 of 1688

Well, you helped with the fuse at least :D The closest one I have is 315mA so it'll have to do.

I'm 40% electronics engineer now so I should have some idea of what I'm doing. I'm seriously lacking some confidence in electronics though. Probably a positive thing. It's good to make sure when you want something to work right away.

No idea how you can possibly wait that long to get your SOHA II running :D

I expected to have it done this week but ran into problems with the case so it got delayed. Today I powered it for the first time and got the following numbers:


TL+: +15.02v

TL-: -15.01v

TH: -12.9v

TB+: 115v


TH seems a little off, what's the tolerance?

post #1551 of 1688

Is TH heater supply? If so I personally think it is not something very critical to achieve very close tolerance. I really have no idea, but if I were you I'd be comfortable to go ahead. However if I were you I probably won't be taking electronic advice from me. tongue.gif


My first amp (a 3 channels Beta 22), it took me 2 years and 7 months to get it running and boxed up. It was dormant for a long time, I basically resigned to fate that I spent quite a bit of money for a bunch of junk in my living room. I rushed it again towards the end because my pre amp in my speaker setup was dead and the cheapest way for me to get a decent replacement is to complete this amp. And more than half a year later I did some further minor addition that I was too lazy to perform initially. biggrin.gif


I got into this SOHA II right after I finished the Beta 22, back then my preoccupation was with headphone amp. I don't think the need factor is going to kick in in the foreseeable future, so if I were to count on that I will probably never be able to complete it at all. I move from one hobby to another and I would come back. But even my current hobby came back to audio lately, I am more into headphones and less into amp at the moment. I really have no idea when I will get moving again. I'll see if this one would exceed the previous record. confused_face.gif

post #1552 of 1688

Yeah, TH is heater supply. I assumed it was ok and moved on.

Now, however, I have no voltage drop at all across R10L (and R10R). Both ends are reading -14,98V. The only thing I got with the search function was someone who had Q6 and Q7 installed wrong way. Mine are text-side to front which is correct I guess. However, when I test those BD139s, I get 0,62v B-E AND E-B. Are my transistors fried or what could be the problem?

Argh, I'm going to have to unscrew the board again.

Only took half an hour to do it last time since my standoff isn't exactly the right height and my solution isn't very easy to implement :D


Wow, I guess I'd give up now too if I had a descent amp, but I broke my last amps pcb while modding it.  I think I'm going to replace the BD139s unless someone has a better idea. I really hope my SOHA II won't take as long to complete as yours :D

post #1553 of 1688
Originally Posted by Veiko View Post

Yeah, TH is heater supply. I assumed it was ok and moved on.

Now, however, I have no voltage drop at all across R10L (and R10R). Both ends are reading -14,98V.

As in, you place both probe at either side of R10 and you get 0 mV?

post #1554 of 1688
Originally Posted by Navyblue View Post

As in, you place both probe at either side of R10 and you get 0 mV?

Either side reads -14.98 to ground, and I get 0mV across the resistor, side to side.

post #1555 of 1688

Yep, the BD139s are most likely all bad. Now, before I change them, what could have caused this?

post #1556 of 1688

I don't think I have enough understanding to provide any insightful answers.


However, heat, static, bad components elsewhere or wrong orientation all could kill transistors.

post #1557 of 1688

Ok, well, I'll have to be more careful with my iron, ESD, etc.

Now that I think about it, there's a good chance I could have shorted something with my wrench while trying to get the board out. As said, it's a little harder than removing a screw.

And it didn't cross my mind that I could probably somehow bleed the caps from the top of the board.

Q5 and Q8 seem to be damaged as well so looks like I'm going to have to replace more transistors. Are there other parts I should check for damage?

The test point voltages are still what they should be. Does that mean that the regulators are still good?

Edited by Veiko - 2/11/12 at 5:55pm
post #1558 of 1688


I'm building SOHA II as well.

At this moment only 2 parts cannot be found in mouser and Digi-key

They are

Metalized Polyester/Polypropylene Film Capacitor 1μ 63V

C1E, C2L, C2R, C6L, C6R

Mouser 581-BF074D0105J   Digikey 478-3367-ND


C4E,C5E Metalized Polyester/Polypropylene Film Capacitor 10n 63V

Mouser 581-BF014D0103JDC   Digikey 478-3373-ND



just wondering if

505-MKS02.01/63/5 http://www.mouser.com/Search/ProductDetail.aspx?R=MKS0C021000B00JSSDvirtualkey50520000virtualkey505-MKS02.01%2f63%2f5


505-MKS21/63/5T http://www.mouser.com/Search/ProductDetail.aspx?R=MKS2-1%2f63%2f5Tvirtualkey50520000virtualkey505-MKS21%2f63%2f5T


are good alternate?

post #1559 of 1688

Don't count on my opinion, but I see no reason why those caps wouldn't work. Just make sure the lead spacing is correct.

post #1560 of 1688

Well, I got those BD139s off the board and they aren't broken after all.

It's going to be over a week before I can continue this project, so, any ideas are welcome meanwhile.

I couldn't get the BC550s off for now, I'll give those another try when I get back from my holidays.

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