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SOHA II Builders Thread - Page 94

post #1396 of 1686

Regal,

Thank you for the information.

post #1397 of 1686

Just wondering about the reference to d1h-d5h in the parts list for the power supply on Cavalli Audio.  I'm guessing this no longer applies to SOHA II, which only seems to use UF4004 diodes in the PS.  Is that right?  Thanks :)

post #1398 of 1686

I believe so...

post #1399 of 1686
Thread Starter 

Egads, the parts list is wrong. Please use the excel BoM. It looks correct to me.

 

The parts list was right at one time so I must have overwritten it with the wrong page. Sorry about that.

Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
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post #1400 of 1686

 

So, I finished my SOHA II recently with no notable hiccups throughout the build. Initial setup goes well. TL+, TL-, TH, and TB+ all measure what they should be and all is good in the world. Then, of course, things get a little weird. 

 

While testing the buffers, I can not get any voltage readings across either of the R10 resistors. That said, 8-10 seconds after I power it up I hear the relay click on. I proceeded reluctantly, strapping J3 to test the regulator just to see what happens, but ran into trouble there too. For both TB+L and TB+R I get around 110V (the same reading I get for TB+ in the first step) and adjusting P1P does nothing to change this voltage. 

 

Any ideas? 

 

Thanks in advance for any help.

 
post #1401 of 1686
Thread Starter 

Several questions:

 

1. What are the rails when the buffers are connected through the jumpers?

2. Are the O/P transistors in the right orientation?

 

You should get something if the devices are all correct and you have + and - rails.

Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
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post #1402 of 1686

I put all the BD139s on backwards and feel really, really dumb right now. Right side of the board is working fine now (R10R voltage is 200mV), but the left side is all out of whack. Upon power-up, the voltage across R10L spikes up to 1.4V and the transistors on that side get VERY hot very fast. My gut tells me that I damaged the transistors while trying to desolder them from the board. That said, are there any other reasons this could be happening?

 

Thanks for pointing me in the right direction runeight. 
 

Quote:
Originally Posted by runeight View Post

Several questions:

 

1. What are the rails when the buffers are connected through the jumpers?

2. Are the O/P transistors in the right orientation?

 

You should get something if the devices are all correct and you have + and - rails.

post #1403 of 1686
Thread Starter 

You should replace both BD139s on the bad channel and have some BC550Cs handy in case you need to replace those too.

Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
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post #1404 of 1686

 

Well, I just replaced all the both the BD139s and the BC550Cs on the left side of the board.

 

Good news: I'm now able to properly set the voltage across R10 on both sides and currently have it at 230mV.

Bad news: Relay doesn't click at all now. (Which weirds me out because it was clicking even when I had the BD139 backwards)

I swapped out the opamp because I had an extra TL081 around, but the change yielded no effect. The diodes also check out.

 

Should I raise the voltage on both to produce a higher idle current? Could the e12 transistors be the culprits? 

(replaced the e12 transistors and still no click)

 

Again, thanks for the help.

 

I should also note that I was was only able to get the correct voltage across R10L after changing out the BC550Cs, which I did after changing out the BD139s did not work. 

 

Edited by ShogunWarPig - 8/2/10 at 7:18pm
post #1405 of 1686

Just completed my build, thought I would share the finished photo.

 

IMG_7212_3164.jpg

 

I have an interesting problem.  I get a buzz in the left ear that comes on in the phones when the e12 circuit allows the audio through and goes away about 5 minutes later.  I have tried swapping the tubes from side to side as well as using a different pair of tubes and the buzz stays in the left ear in all cases.  I have also tried grounding the volume pot as well as all other components to the star ground with no effect.  When the buzz goes away it is sudden and all at once.  One second it is there and fairly loud in the left ear and the next it is completely gone and quiet.  Also, this noise doesn't change by turning the volume pot up or down.  Any ideas what this could be?

 

Thanks! 

post #1406 of 1686

Just finished my build and want to share a photo of the finished result.

 

IMG_7212_3164.jpg

 

First off, this thing sounds incredible!  I'm currently running some 8416 tubes in it and love the way this little amp sounds!  Thanks Runeight for the help and for sharing the design.

 

I do have one issue left unresolved.  On the left side I get a buzz that starts up as soon as the e12 opens up letting audio through to the phones but goes away after about 5 minutes.  I have tried swapping the tubes left to right and tried some different tubes as well with no effect.  The buzz stays in the left ear and is fairly loud.  The buzz goes away very suddenly, sometimes with a slight pop, and then its gone leaving very quiet (noise free) listening.  Also the buzz is not affected by the volume pot.  I do have some 60hz hum in the system but only at very high volume levels so i can live with that.

 

I've tried grounding all of the various components to the star ground with no effect.  Anyone have any ideas what this could be?

post #1407 of 1686
Quote:
Originally Posted by capernicus View Post

Just finished my build and want to share a photo of the finished result.

...

 

Wow! Very cool capernicus, great job. It's very similar to a design I made for my SOHA II (I'm assuming it's a SOHA II, please correct me if I'm wrong), but finally I ended using a galaxy case (which is in progress right now...) instead of building my own wooden case (just got lazy ).

 

Are you having any issues with the heat? I see no ventilation holes in the top, and I'm a bit worried about heat dissipation in my own build, but if you have no problems with your case I should be safe.

post #1408 of 1686

Thanks for the kind words, and yes its a SOHA II.  They Jury is still out with regards to heat.  The bottom has a lot of holes in it (maybe 20 .5" diameter holes) and I did make the holes for the tubes up top extra large so there is some good convection cooling going on through the box.  The top and bottom plates are very thick Al, about .2" thick, and get warm to the touch after it has been on for a while but but not so hot that you can't leave your hand there.

 

I'm contemplating some additional vents on the top of the box but want to do it in a way that looks good.  I can't seem to drill nice clean holes in the Al plate - probably my cheap drill bits and drill press have something to do with it. 

post #1409 of 1686
Quote:
Originally Posted by capernicus View Post

I'm contemplating some additional vents on the top of the box but want to do it in a way that looks good.  I can't seem to drill nice clean holes in the Al plate - probably my cheap drill bits and drill press have something to do with it. 


Maybe you could just drill the holes through the aluminum and not worry too much, and then cover the series of holes with another wooden trim piece parallel to the one over the tube holes. 

 

It's a sharp looking case. 

post #1410 of 1686

That was one of the ideas I was considering, I'm going to think about it a little and see what I come up with.  Do i make it square or maybe an oval, or something curvy with the band saw to contrast all of straight and square edges... its fun to think about.  

 

I am more concerned about the buzz i hear on startup at the moment, not sure what is going on there.

 

I LOVE the sound of this thing though.  Good luck with your build!

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