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SOHA II Builders Thread - Page 41

post #601 of 1686
I'm glad that what just the Zeners. And how your SOHAII sound?
post #602 of 1686
Quote:
Originally Posted by runeight View Post
Good idea. I'll try to get to that later.

Busy ! Busy! Busy?
post #603 of 1686
Quote:
Originally Posted by wolf18t View Post
I'm glad that what just the Zeners. And how your SOHAII sound?
It sounds very nice! Compared to my MHSS, I think it has a larger soundstage and more clarity. The differences are a little subtle, but they are there. I haven't listened a lot though, so it's hard to point out the differences. I did a quick comparison last night, and immediately could hear a difference, but it will take more time to really understand the differences.

I think I'll go back and work through the setup steps again to verify the pots are set correctly though.
post #604 of 1686
Please, help. My friend has some questions regarding the SOHA II he is building now. He do not know English so I would ask

Current trough tubes (I think you name it "bias") is set to 2 mA. Both TB+L and TB+R are 60 V. There is big spread between TPL (44V) and TPR (30V). And the difference between TPR and TB+R is 30V, what is much higher than 19V recommended. Section "Setting the Ttail current for the input stage" recommends to see Troubleshooting, which does not help.

Amp works fine anyway, both measurements and listening tests are OK.

What should he do, if any?
post #605 of 1686
Quote:
Originally Posted by kostalex View Post
Please, help. My friend has some questions regarding the SOHA II he is building now. He do not know English so I would ask

Current trough tubes (I think you name it "bias") is set to 2 mA. Both TB+L and TB+R are 60 V. There is big spread between TPL (44V) and TPR (30V). And the difference between TPR and TB+R is 30V, what is much higher than 19V recommended. Section "Setting the Ttail current for the input stage" recommends to see Troubleshooting, which does not help.

Amp works fine anyway, both measurements and listening tests are OK.

What should he do, if any?
Both L/R channels have a higher voltage drop than the expected 19V. That's probably not a big problem but if it is...:

- I would double check first the R4L and R4R resistor value to be sure these are 18Kohm.
- What tubes type are installed, and are these new/used?
- Also did he have to replace some suggested part in the BOM, like the BC560C and BC550C to other NPN transistors? If so, maybe a huge change in the Beta value could to this.
post #606 of 1686
I also add that if he have another tube set I would also redo the tail current BIAS procedure with them to see if that change anything.
post #607 of 1686
Tubes are new, they are from the kit I bought at glassjaraudio.com in December. According to the order form tubes are NOS 5692, transistors are Mouser 863-BC560CG and 863-BC550CG. Tomorrow I may ask him for exact part numbers.
post #608 of 1686
Quote:
Originally Posted by wolf18t View Post
I also add that if he have another tube set I would also redo the tail current BIAS procedure with them to see if that change anything.
Unfortunately, he has not.
post #609 of 1686
Thread Starter 
Kostalex, as you know TPR is too low. This could actually be a bad tube. That would be the first thing to change if you can.

Then you might try the tail current adjustment on the right channel again to be sure that it is right. If it is correct and if R4 is really 18k then it has to be a bad tube.

Try measuring the voltages on both leads of R4R to ground and tell us what they are.
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 #610 of 1686
Swap the tubes, then measure again. See if the differences switch channels. If they do, then it's a tube problem. If it doesn't, probably not the tube.


I have a problem related to my SOHA II

It sounds so good with my 650s, I don't like my work rig anymore (580s and MHSS)

Looks like I am gonna build another SOHA II for work
post #611 of 1686
Thread Starter 
Quote:
Originally Posted by Hayduke View Post
Swap the tubes, then measure again. See if the differences switch channels. If they do, then it's a tube problem. If it doesn't, probably not the tube.


I have a problem related to my SOHA II

It sounds so good with my 650s, I don't like my work rig anymore (580s and MHSS)

Looks like I am gonna build another SOHA II for work
I like to hear things like this.
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 #612 of 1686
sorry if this has been asked already (i also performed a fruitless search), but could the SOHAII also serve dual duty as a pre-amp?
post #613 of 1686
Thread Starter 
Yes, it should do very well as a preamp. In fact, it might make a really good preamp because it can drive cables.
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 #614 of 1686
I'm looking at ordering a kit and I had a couple of questions before I do. When I built my SS, I fried the mosfets when I was a little careless with the DMM probes. Can someone suggest what parts to order extras of if I'm similarly stupid while building this? I'd hate to have to wait on a Mouser order for one transistor.

I noticed towards the end of the other thread there was discussion of prepunched panels for the case. Are these available?
post #615 of 1686
Thread Starter 
Hi Scompton. It's a great amp.

The parts that seem to be killed most frequently are the MPSA42s followed by the opamps. There was one instance of blown up rectifier diodes. I don't recall anyone damaging anything else, but I'm sure I don't remember all of the posts.

So you can order extras of those. Then to be really safe you might order one extra for each of the regulators and a few extra of the BC550/BC560. I would think this is enough.

Others may have better ideas based on personal experience.
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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