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post #646 of 1688
Then it may be a solder bridge or even a bad trace on the board. It's rare but it could happend. Check carefully the trace between R9/R10/Q6 and a possible contact with the +15V rail trace.
post #647 of 1688
I found it! Looks like someone may have left a hair on the fab during etch.

I took a picture to show you guys what I found, perhaps it will help one of you out in the future. Check out the bridge between the traces at the solder pad for R10L (Q5L in lower right of frame). I cleaned a bit of solder off the pad so it would be easier to see and fix. I broke the bridge with an x-acto and all looks good now. Time to stuff the parts back on the board and double check everything.

Thanks again for all the input guys

http://www.smugmug.com/photos/477442952_AzUW7-L.jpg
post #648 of 1688
Output transistors Q6 and Q7 are too hot on both channels (90 Celsius degrees). The load is Denon D2000, 25 Ohm. How much may I lower the quiescent current without any sound quality loss?
post #649 of 1688
Quote:
Originally Posted by rnickl View Post
I found it! Looks like someone may have left a hair on the fab during etch.

http://www.smugmug.com/photos/477442952_AzUW7-L.jpg
I'm glad you finally found that bug!


Quote:
Originally Posted by kostalex View Post
Output transistors Q6 and Q7 are too hot on both channels (90 Celsius degrees). The load is Denon D2000, 25 Ohm. How much may I lower the quiescent current without any sound quality loss?
That's pretty hot. Runeight would be much, much, better than me to answer you. But I think there is no absolute answer on this one. It all depends at what level you listen to music and sensitivity of the phones. I feel that 100mA is a very safe biasing point, the CK2III is said to sound great and it is only biased at 35mA.

I'll keep and eye open for answers too as I plan to use my SOHA II with 32ohm Grados.
post #650 of 1688
Quote:
Originally Posted by wolf18t View Post
That's pretty hot. Runeight would be much, much, better than me to answer you. But I think there is no absolute answer on this one. It all depends at what level you listen to music and sensitivity of the phones.
I believe the BD139 Junction temp is rated for 150 degrees C - of course we wouldn't want to approach that, and Junction temp will be higher than what you measure outside - is your measurement from the transistor surface or the sink? Does the part have a good thermal bond to the sink?
post #651 of 1688
Quote:
Originally Posted by rnickl View Post
I found it! Looks like someone may have left a hair on the fab during etch.

I took a picture to show you guys what I found, perhaps it will help one of you out in the future. Check out the bridge between the traces at the solder pad for R10L (Q5L in lower right of frame). I cleaned a bit of solder off the pad so it would be easier to see and fix. I broke the bridge with an x-acto and all looks good now. Time to stuff the parts back on the board and double check everything.

Thanks again for all the input guys

http://www.smugmug.com/photos/477442952_AzUW7-L.jpg
Good job!

I recently read a discussion on the B22 mistakes thread where they talked about inspecting PCBs before a build. Everyone agreed it's very rare to find a mistake, but it happens. You just reinforced that. It's too bad you had to go through the headache though I didn't give my board that close an inspection, but you can be sure I will from now on If that had happened in other spots, it could have damaged something.
post #652 of 1688
Quote:
Originally Posted by wiatrob View Post
I believe the BD139 Junction temp is rated for 150 degrees C - of course we wouldn't want to approach that, and Junction temp will be higher than what you measure outside - is your measurement from the transistor surface or the sink? Does the part have a good thermal bond to the sink?
It was measured on heatsinks, case was open. Transistors are very well bonded using the thermal grease.
post #653 of 1688
I'm thinking of building a SOHA II for my dad as birthday present and saw that Jeff Rossel offers Kits for it.

Does anybody know how much they cost?
I wrote him an email this night but maybe someone here is quicker.

I'd like to build something with tubes and don't want to spend much more than 150$.
I've already got a SOHA I with Jisbos, would be boring to build that one again.
Maybe somebody has another suggestion for me?
post #654 of 1688
The glassjar kit is @ $200 shipped for everything needed for the build except wire and solder.
post #655 of 1688
Quote:
Originally Posted by Sathimas View Post
I'm thinking of building a SOHA II for my dad as birthday present and saw that Jeff Rossel offers Kits for it.

Does anybody know how much they cost?
I wrote him an email this night but maybe someone here is quicker.

I'd like to build something with tubes and don't want to spend much more than 150$.
I've already got a SOHA I with Jisbos, would be boring to build that one again.
Maybe somebody has another suggestion for me?
$210 shipped in the US with the case and transformer. Even without the case and transformer, it's still over $150.
post #656 of 1688
You could build runeight's Very Compact Hybrid Amp, although I'm not sure how hard it would be to get a PCB for it. I think there's a BOM for it; if not, I'm sure you could just ask runeight or cfcubed. Tube rolling is much easier and cheaper since there's only a single tube.
post #657 of 1688
Thread Starter 
Quote:
Originally Posted by kostalex View Post
It was measured on heatsinks, case was open. Transistors are very well bonded using the thermal grease.
Hi there. Sorry I'm late.

90C is too hot and shouldn't really happen with normal devices and heatsinks. Are you sure the current is 100mA through R10 and that you're reading a voltage drop of about 220mV on both channels?

If you are, then something else is wrong. First thing would be to check the TL+ and TL- test points for +/-15V.

If all four of these measurements are correct, then the temp measurement could be wrong. You've probably answered this already, but the heatsinks are the ones specified in the BoM? Did the parts come from Glass Jar?

Is there anything else not working correctly?
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 #658 of 1688
TPL is 41.2V and TPR is 38.3V, both are pretty low.

All parts are from GlassJar. I'll take a measurements tomorrow and let you know. Thanks for you help.
post #659 of 1688
Thread Starter 
Quote:
Originally Posted by kostalex View Post
TPL is 41.2V and TPR is 38.3V, both are pretty low.

All parts are from GlassJar. I'll take a measurements tomorrow and let you know. Thanks for you help.
If you have the latest rev of the board then you can adjust the B+. The TPL and TPR are actually pretty good. But if you increase the B+ above 60V you'll get more plate voltage.
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 #660 of 1688
Hey - Guess what I did! Installed the heater jumpers in the wrong orientation

I quickly realized something was amiss - but the right channel is now gone, TPR reads very low negative voltage. The short was across the common and 6.3V jumpers - doesn't seem like I could hurt anything else but that leg of the PS - no tubes were in at the time... unless this is a coincidental failure...
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