New Builder learned so much from his mistakes he now wants to rebuild

[Paul Birkeland]

If the 12AU7 doesn't light up at all, that is a feed from B7/B8 to A4/A5/A9.

If both halves of the 12AU7 don't glow, that would have to be a bad connection at either B7, B8, or A9.  I can't see A9.

 

[Agweeks]

Both sides of the tube light up. Could it be anything else?

 

[Paul Birkeland]

Are your MJE350s in backwards?

 

[Agweeks]

No. I went back and checked. The text faces the narrow line.

 

[Paul Birkeland]

Ah, yeah, I see that now.

Typically when I see high voltage on the OA/OB terminals on the small board, that's a solder joint on the middle leg of the MJE-350.

...but you have both sides high, hence my curiosity that potentially the 12AU7 isn't glowing and nothing is conducting.

 

[Deluk]

From post#18 the Crack was working fine with Mac and Tidal. Changes made were non Crack so logic would say that the fault is external. The RCA's were probably left in place during the change to the Schitt DAC. No, that doesn't explain the apparent led fault. If they were fitted the wrong way round the Mac system wouldn't have worked I guess.

 

[Agweeks]

This feels odd.  The amp worked.  All the LEDs were on, the volts and resistance was good.  I listened to it through my Mac streaming tidal masters with my HD6xx headphones.  Life was good.  Then I took it down stairs and plugged it into the bifrost and it didn't work.  I tried lots of scenarios down there, changing out the cords, plugging into different outlets, using a PC, plugging up my iphone with--and without--the phone plugged up via the camera adapter.  Eventually I brought the amp back up here and discovered the LED's don't light up.  I went back to the instructions and followed them, reflowing joints and testing voltages.  I went to the forum and read threads on what could be wrong.  I even replaced the LED's.  Finally I come to you because I'm stuck.

I've reflowed the center leg of both MJE-350's.  I've reflowed the joints for B7/B8 and A4/A5/A9.  The Bifrost works with the iphone.  I'm listening to it now through my Stereomour. 

On the outer side of the LED attached to A3, the voltage reads 179.  On the leg soldered to the center tap, it reads 172. The other LED reads the same.

Attached are photos of the LED's not working and both sides of the 12AU7 lit up.

Thanks,

AGW

 

[Paul Birkeland]

On the outer side of the LED attached to A3, the voltage reads 179.  On the leg soldered to the center tap, it reads 172. The other LED reads the same.

Well, those should be 1.5V above ground.  There's likely a broken ground wire or one that is soldered poorly and causing this issue.

 

[Agweeks]

I reflowed all of what I understand to be a ground wire.  I am assuming black wire is used to designate ground.  I found where lug 18 is reading 89 volts.  I reflowed it.  It still reads 89 volts.  I checked the direction of the rectifiers and found them to be correct.  Could this be it?

AGW

 

[Paul Birkeland]

What DC voltage do you get between terminals 12 and 3?

Rectifier orientation is not the cause of this issue.

 

[Agweeks]

What DC voltage do you get between terminals 12 and 3?

175

 

[Paul Birkeland]

OK, 12 and 3 are supposed to be wired together in the amp.  Your 12 and 3 are not wired together. 

The common problem I find when I see this condition is that there's a loose black wire on the headphone jack.

There is 100% a broken, missing, or unsoldered black wire in your amp. 

 

[Agweeks]

Ok.  I found that if I measure between 12 and the ground lug on the volume pot that the LED's on the 12AU7 illuminate.  Thoughts?

 

[Paul Birkeland]

You have a loose, broken, or disconnected ground wire in your amplifier. 

 

[Agweeks]

Does the fact that I can illuminate the LED’s by grounding the volume pot isolate the problem to the volume pod or does it also make it possible the grounding issue is somewhere else?

 

[Paul Birkeland]

You have a loose, broken, or disconnected ground wire in your amplifier.  There are ground wires on the volume pot as well (the black ones).

You have 170V DC between terminal 12 and terminal 3.  These are supposed to be connected by wires.  Yours are not.  This is the problem with your amplifier.  You need to fix this problem with your amplifier before bringing in other information. 

There is a wire from 12 to the headphone jack.
There is a wire from the headphone jack to 3.

One of these is not doing its job.  Please focus on fixing this and leave everything else for later.

 

[Agweeks]

It was the wire from the volume pot to terminal 3.  I wired that and the amp works.  The voltage for A3 is now 1.5.  Do I need to check anything else?

 

[Paul Birkeland]

If the DC voltage from 3 to 12 was 175V, then you have another one that's loose.  A loose wire from terminal 3 to the volume pot would not create that symptom.