DESPERATION! No heater voltage on Stellar/Alctron tube mic power supply

[xeawr]

Here you can hear and see the differences between the two power supplies.
(ca. 40-50dB preamp gain + 40dB boost in DAW - don't mind my wall clock in the background)

TBONE PSU NOISE:

AUDIO (online player - link corrected)
https://voca.ro/jcyyuAPg8Id

ALCTRON PSU NOISE:

AUDIO (online player - link corrected)
https://voca.ro/jBvB2AHnlkb

 

[moamps]

I found two old original PCBs from power supply of stock Alctron HT-11A (https://groupdiy.com/index.php?topic=51377.0) during a cleaning some bins today.
R15 is 2 Ohms in original design, not 20 ohms which is obvious error in a schematics floating around. Just for reference.

 

[xeawr]

Awesome, good to know! Thanks so much!!!

 

[xeawr]

Pleeeeease, I still need your help!!!

I still have hum inspite of:

- removed the LM317 circuit, replaced  with a 7805+diode
- replaced most capacitors on the B+ side with real Nichicon ones (left only 2 original caps).
- tightly twisted the tranny secondaries
- made sure all DC components are as far as possible from the high voltage AC lines and the tranny
- reflowed the remaining solder joints, cleaned the pub

it all works but I still get hum!!!!

>> turning PS off: hum instantly disappears
>> switching just the 6.5v heater off: hum remains

It drives me nuts, I mean it's a power supply. How can these things give u so much of a headache????
Please please help me with this, I really want to find and fix the problem.

Thank you so much!!!

 

[Khron]

I don't suppose the power supply has a ground-lift switch for the XLR output, does it?

I'm thinking there's a possibility of a ground-loop occurring between the mic supply and your preamp / mixer / interface.

 

[xeawr]

Thanks Thron! Actually I had the same idea yesterday as I went to bed. I'm soldering a "ground-lift" cable now, see if that helps. Will keep you posted!

THANKS SO MUCH SO FAR!!!!

 

[xeawr]

Unfortunately it doesn't make any difference with the ground lift.  . Does it help knowing that the hum is not there when I power it off? (instantly cuts off)

Any hints where I could be looking for the culprit?

 

[Khron]

Where and how did you connect that?

 

[xeawr]

I took an XLR cable and removed ground from the male side of the XLR (neither pin1 nor the metal loop was connected)

 

[RuudNL]

Just build a new power supply. Much quicker!