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SOHA II Builders Thread - Page 39

post #571 of 1686
Good to know that you guys are making progress on your builds.
post #572 of 1686
Quote:
Originally Posted by wolf18t View Post
Glad to see that your build is going well. In what enclosure are you going to install your SOHA II?

SNIP

I'll also post a progress picture tonight.

Pretty well, my e12 isn't tripping, but I think the TL081 I have got blown up during the proto stage. I have a bunch on order for the Compact Hybrid

I am working two different case ideas right now, I'll post some pics soon... Looking forward to yours!

-Bill
post #573 of 1686
Quote:
Originally Posted by wiatrob View Post
Pretty well, my e12 isn't tripping, but I think the TL081 I have got blown up during the proto stage. I have a bunch on order for the Compact Hybrid
Well I hope you will have them pretty soon! If not let me know I think I have an extra TL081 in my parts bin.

As promised here are some pics I took yesterday while listening for my SOHA II for the first time. As you can see my SOHA will be installed in the recommended hammond case.




The PCB parts layout is way too tight for the upgraded MCAP Supreme coupling caps. That's the reason I had to install them offboard between the PCB and transfo. This is not a very recommended location but I heard no hum (knocking on wood) so I think that will be ok.




Now if only there was enough interest to the nice FPE panels group buy, my SOHA would have been almost completed.
post #574 of 1686
Quote:
Originally Posted by wolf18t View Post
Well I hope you will have them pretty soon! If not let me know I think I have an extra TL081 in my parts bin.
Thanks for the offer - Turns out it's not the TL081 - swapped it with my proto and it's good, but that's another post...


Quote:
Originally Posted by wolf18t View Post
As promised here are some pics I took yesterday while listening for my SOHA II for the first time. As you can see my SOHA will be installed in the recommended hammond case.
Looks nice! How's it sounding?
post #575 of 1686
Hmm. My voltages all look good - but my e12 won't trip (yup, me an that e12 again!) J1 and J2 and the opamps are in place.

I think I'm measuring the DC offset between the input side of R1/2E and ground, it spikes way up and then settles down below 2mV - stable on both sides.

Similar measurement on my working amp yield slightly higher mV.

The relay trips without the TL081 in place.

UPDATE - using 18ks for R1 and R2E
- but that should just chane the sensitivity, correct?

Any ideas?
post #576 of 1686
Thread Starter 
Yes, that's correct. The best way to test the offset is to measure between the lead of R8 (both channels) that sticks towards the center of the board and ground.

If the offset is that low then maybe the transistors in the e12 are cooked? Are you using BC units?

If the offset settles to only a few mV measure the voltage at the output of the tl081. It should also be near 0DC. This will tell us if it's the opamp or the transistors.
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 #577 of 1686
Thanks Runeight. Yes, BC550Cs -

There's something else going on, looks like a bad tube - I only get 5V difference between TB+ and TP, follows the tube...

After putting in the TL081 again, it works! Output is .07mV

Need to letthese old soviet tubes burn and see what happens...
post #578 of 1686
It lives - looks like a bad tube, no sound on the channel with the tube with 5V difference (6n1ps)

Not a bad tube, bad channel, time for some snooping...

EDIT: Hmm. seems to be a combination. One tube does produce a lower voltage difference across the anode (which follows the tube), but either still works in the left channel. Will bring home a meter capable of doing more precise Ac mV and see where the music stops.

The buffers on the dead channel are not getting as warm as the right. Currents are good across both R10s - 239mV.


Input stage or buffer?
post #579 of 1686
How about this for a cause: Test headphones have a fried driver!

I found a pair of earbuds in my ski coat from last season, so I thought they'd be a good test set.

Not so good.

Sounds great through my px-100s - burn in time!
post #580 of 1686
that can be so infuriating - glad you isolated the cause before stripping your amp apart ..dB


edit - listening to mine after some hiatus with the HP3's
post #581 of 1686
Quote:
Originally Posted by dBel84 View Post
edit - listening to mine after some hiatus with the HP3's
Been listening to new builds?
post #582 of 1686
Quote:
Originally Posted by pabbi1 View Post
Been listening to new builds?

There's a lot of winking going on! I'm enjoying the YH-100s, thanks Don!
post #583 of 1686
Quote:
Originally Posted by dBel84 View Post
that can be so infuriating - glad you isolated the cause before stripping your amp apart ..dB
I did find a cracked resistor and two cold-ish joints: and I learned more about how the amp works - this is the most edifying kind of troubleshooting!
post #584 of 1686
nudge nudge wink wink say no more .

well maybe one more Cavalli Audio rules ! ..dB
post #585 of 1686
Fully up and burning in. I very much like the high current build.

Excellent clarity/resolution- I don't know if it's the Toshibas - the bass seems tighter than with my proto build.
Especially nice through the graciously loaned orthos from dBel!

Kudos again Alex and all who participated in the process.
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