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SOHA II Builders Thread - Page 95

post #1411 of 1686
Thread Starter 
Quote:
Originally Posted by ShogunWarPig View Post

 

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. 

 



Please measure the voltages on all the pins of both channel opamps. Let's see what the amp thinks it's doing.

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 #1412 of 1686
Thread Starter 

Capernicus, are you still having the buzz?

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 #1413 of 1686

 

Well....... I feel like there's something wrong with my build, but I really don't know what is it .

 

It seems like it can't drive my HD650 correctly (not to mention my K1000). When I turn up the volume to not very high levels (a bit more than half the excursion of the potentiometer), the e12 trips off and on. Besides, even at low listening levels that don't cause the e12 to trip, sometimes the amp sounds somehow distorted.

 

Everything seems to be ok, except for the voltage drop across R10. With P2L and P2R fully opened, all I can get is 200mv on both sides. I've already changed both potentiometers and changed Q6 and Q7 (replaced BD139 with 2sc2238 with same results). I have also tried with different tubes.

 

I'm about to start a new one from zero, because I have the feeling that I've messed something and I don't know what .

 

Any ideas will be very helpful.

post #1414 of 1686
Quote:
Originally Posted by runeight View Post

Capernicus, are you still having the buzz?

 


Runeight, yes I am, not sure what it is.

 

As I mentioned, the buzz is only in the left channel and doesn't follow the tubes if I switch them and it only lasts for the first 5 minutes or so immediately after power-up, then it goes away instantaneously.  Turning the volume knob doesn't do anything.

 

Other than that it works great!

 

Thanks for the help!

post #1415 of 1686

I have had a similar buzz in mine for a while. It started after I did the mod to up the tube current, as I reported in this post:  http://www.head-fi.org/forum/thread/374941/soha-ii-builders-thread/1230#post_6500229

I have just lived with it until now, it goes away after 2-3 minutes and is low level.

post #1416 of 1686

beautiful work here

 

post #1417 of 1686
Quote:
Originally Posted by Alcaudon View Post

 

Well....... I feel like there's something wrong with my build, but I really don't know what is it .

 

It seems like it can't drive my HD650 correctly (not to mention my K1000). When I turn up the volume to not very high levels (a bit more than half the excursion of the potentiometer), the e12 trips off and on. Besides, even at low listening levels that don't cause the e12 to trip, sometimes the amp sounds somehow distorted.

 

Everything seems to be ok, except for the voltage drop across R10. With P2L and P2R fully opened, all I can get is 200mv on both sides. I've already changed both potentiometers and changed Q6 and Q7 (replaced BD139 with 2sc2238 with same results). I have also tried with different tubes.

 

I'm about to start a new one from zero, because I have the feeling that I've messed something and I don't know what .

 

Any ideas will be very helpful.


hi all, i have similar problem with my SOHA II. It was working fine for half of the year till yesterday when i turned it on, it wont play any music. When i adjust the volume, e12 will trip but no music was played.

 

swapped tubes but it didnt help anything. Checked my source DC offset, its 0mV. any idea where should i check next? 

post #1418 of 1686
Thread Starter 

If you would please measure both ends of R10 on both channels with respect to ground. Let's see what the buffers are doing.

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 #1419 of 1686

did some quick measurements

 

at TB+ test point, the voltage is 19.5v with respect to ground

 

pin1 of HV+ measures 19.6v with respect to ground

pin2 of HV+ measures 16v with respect to groun

 

The left side of R10L measures 220mv right side measures 2mv

 

measurements for R10R is the same as R10L

 

from this, can i say that HV+ need to be replaced?

post #1420 of 1686
Thread Starter 

No, not yet. Break jumper J3 and measure TB+ again. If it measures over 100V then it is probably the regulator. If it still measures low then the voltage doubler in the PS is failing.

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 #1421 of 1686

after breaking J3, the voltage measures 22.4v at TB+

post #1422 of 1686
Thread Starter 

Hmmm. Then something in the voltage doubler section is failing. First question is, have you changed your transformer wiring at all? Do you have the CT correct on the two windings? I know this is a ridiculous question now, but I have to ask. Can you please describe how the secondaries are wired to the power terminal block.

 

This will be hard to diagnose if the transformer is wired correctly.

 

Check all the caps and diodes in the doubler. This would be C8P through C12P and D7P through D12P. Make sure these are all in the right orientation for polarity. Diodes are cathode strip away from the board.

 

Did TB+ at one time actually measure correctly?

 

We'll figure this out eventually.

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 #1423 of 1686

the amp was working wonderfully for half a year till few days ago. 

 

i noticed that the transformer was humming when the amp was turned on. i dont remember that happening till recently

 

the secondary winding pairs, red black, yellow orange are wired as follows

 

red to 15

orange to 15

black and yellow are connected together to 0

 

the transformer output is giving 17v when its rated 15v, 1A. should i be concern with this?

post #1424 of 1686
Quote:
Originally Posted by Cloud View Post

 

 

 

the transformer output is giving 17v when its rated 15v, 1A. should i be concern with this?


That should be normal.  

 

I would would check all the doubler caps for continuity across their poles,  electrolytics tend to fail if the amp is too hot inside they should test as an open circuit if not, it(they) will need replaced.  Did you follow the 50% open "rule" ?

Also if you have a diode test on your dmm you can check the rectifiers.

post #1425 of 1686

would you mind to elaborate more on the 50% open rule?

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