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SOHA II Builders Thread - Page 77

post #1141 of 1686
I have a similar hum, only with lower impedance higher sensitivity phones that does not change with respect to the volume knob and am looking for advice as well.

I'm sure you can implement that source switcher if you don't mind your input going through that switch.

I haven't measured my temperature, but more ventilation holes would never hurt!

I noticed that snap when powering down, I take it safe and remove the headphones when powering down or up.

Lastly, any comments on this mod?
http://www.head-fi.org/forums/6171572-post50.html
post #1142 of 1686
Thread Starter 
Hate to ask, but have those of you who have hum grounded the SG point to the chassis? And have you grounded the case of your volume pot?

The snap is the e12 tripping off as the output DC swings away from zero. This trip occurs at about 200mV and should protect the headphones from higher voltages even though they pop off. However, it is safe to remove the headphones before power up or down.
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 #1143 of 1686
I'm finally getting around to setting up my SOHA II. Everything is fine until the final measurements.

I'm getting the following.

TB+R: 59.9V
TB+L: 59.9V

TPR: 41.4
TPL: 52.4
post #1144 of 1686
Thread Starter 
Check the tail current in the left channel again and check the resistor values too. If all is well there then the tube is probably way out of balance. Have you swapped the tubes L/R yet?
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 #1145 of 1686
The tail current is 399.6 mV on both sides. I'll swap the tubes and check the resistor values tomorrow. I think I'm going to need a better magnifying glass to see the resistor values, or stronger reading glasses. They're easy enough to read off the board, but not on it.

Edit: Obviously not the tail current, but the voltage across R6R and R6L.

Edit: I swapped tubes and it didn't follow the tube so I'll check resistor values tomorrow.
post #1146 of 1686
Well I fried something. Rather than try to read the resistors, I measured them. All of them measured correctly. I had zeners socketed in R4. Thinking they may be bad, I replaced them with the resistors and remeasured everything. I got the similar results, but didn't write them down.

My wife called so I went to pick her up. After getting back home, I powered back up to take document the measurements. With one probe on TB+L, I touched the other probe to ground and got a spark and a puff of smoke. Now all of the test points in the power supply measure around 30mV.

Edit: It looks like it's my DMM. I tried to measure the household AC current and it comes up 140mV. I tried to measure a resistor and it flashes between 0 and 500 ohms. I'll have to buy a new one tomorrow.
post #1147 of 1686
Thread Starter 
Good luck. Did you possibly have the DMM on the DC amps setting when trying to measure the voltage? If so, maybe it's just the fuse? Grasping at straws.
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 #1148 of 1686
That could be, although I just bought a new DMM from Radio Shack on my way into work. It has a diode test mode so it's worth it anyway.
post #1149 of 1686
Hi All,

Noticed in the BOM that C1P, C2P and C5P need to be rated for 105C? Would a cap rated for 85C suffice?

Thanks!
post #1150 of 1686
Quote:
Originally Posted by pixeljedi View Post
Hi All,

Noticed in the BOM that C1P, C2P and C5P need to be rated for 105C? Would a cap rated for 85C suffice?

Thanks!
Depends on the ventalation of the case, Mine run around 60c.
post #1151 of 1686
Thanks Regal. Hmm... I'd better play it safe and go with the 105C rated ones then, as my case wont be as ventilated as yours.
post #1152 of 1686

Help : Jumpers for 5963 in SOHA II ???

Hi,

I'm finishing my SOHA II amp. I'm in the setup procedure. I will use 5963 tubes, and have to set the jumpers either to :
- 12,6V Series,
- 6,3V parallel.

If I check the 5963 datasheet, I see that 2 config are possible, the same as above :
- 12,6V Series,
- 6,3V parallel.

Help : what should I do ? Do the two config work for 5963 ?

Shall I set them to 12,6V ?

It is my first tube project... and I prefer not to blow them.

What should I look for experiments with other tubes ?

Regards.

JM.
post #1153 of 1686
set it for 12.6
post #1154 of 1686
Im not sure if it was in this thread but guys from polish forum Audiostereo.pl are now working on Soha MKIV clone. Here is link for forum thread: SOHA CLONE MK III - projekt PCB - Do It Yourself - Forum Audio - Audiostereo.pl
and links for MKIII schematics and pcb with some changes to original project:
http://tan.lcf.pl/klon_soha_II/klon_soha2_2.6.2_sch.pdf
http://tan.lcf.pl/klon_soha_II/klon_....2_mozaika.pdf
http://tan.lcf.pl/klon_soha_II/klon_soha2_2.6.2_top.pdf
http://tan.lcf.pl/klon_soha_II/klon_...2.6.2_elem.pdf
We all here in Poland want to thank Alex Cavalli for such a great design!
Peter.
post #1155 of 1686

ECC82 and 6922 ?

Thank's for the info for the 5963. I terminated the setup... and it works !!!!

First listenings with a USB Monica DAC and AKG701...

The amp is very clear, precise, quick. Strings are beautiful...

I do not know if amp and tubes require break in ...

I'd say that the first listening lacks a bit from flesh on voices and piano...

I also have RCA 6922 and RSD ECC82. What are the jumpers for those tubes ? Do I need to modify the different pot/currents on the board ?

Oh, And I have 59,8 V instead of 60V for TB+R and TB+L. Is it Ok or to low (and if too low, how to raise it above 60V) ?

Best regards and thank's for this project ;-)

JM
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