BOSOZ balanced pre - for novice - questions

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Toroidal blow

Hello, I have a problem. I need your help.
I have done the power supply circuit and I have tested it as Nelson described in his article using 15 kohm load for each channel. The problem is that toroidal get a damage. When turn on the power I heard a little hum from power transformer for a few second and after silence. So I have smelt the bad smell of plastic. I turn off the power, I waited some minutes. I heard some crakling from the toroidal thath were hot...Some ideas???
 
I think I have found the mistake. I have done a mistake with the connection of the secondary. There are 4 wire; in the trafo there is a write: sec 60V - Red/60V - Brown/60V. For each channel I have connected one wire red and one brown. I think thath the correct way is 2 wire red for one channel and 2 wire brown for other channel. I tested now the trafo and it seems work: without load I have mesured 65 V between 2 wire of the same color... Now I dont'know how to do. How can I check components of power supply? Are they broken/burned? May I try to test power supply as is using a fuse?
 
Hello, I have a problem. I need your help.
I have done the power supply circuit and I have tested it as Nelson described in his article using 15 kohm load for each channel. The problem is that toroidal get a damage. When turn on the power I heard a little hum from power transformer for a few second and after silence. So I have smelt the bad smell of plastic. I turn off the power, I waited some minutes. I heard some crakling from the toroidal thath were hot...Some ideas???
Looks like you did not use your Mains Bulb Tester (MBT) to power ON your transformer.

You need to use the MBT every time you power ON a new, or modified project.
 
I do more or less the same thing...long power chord and turn on the light!!! I put circuit in the near room and pray!!!
Today I decided ti desolder all the components: there are few parts, I do the power supply another time. Rectifier bridges were fried, continuity between legs. I have bought double of components in case of mistake! Capacitors seems ok, mosfets i throw away. I let on board only resistors that are not damaged and irrush suppressor
 
Second attempt

Hallo, after few months I have remade my power supply pcb.
I have changed all parts, except the resistors and thermistor.
Now I check the circuit using bulb light test.
I have some questions that i would clarify before to turn on the light.

- Shall I test the power supply without load? If I dont'use a load (15 kohm Pass says) does bulb light test work well?

- Nelson Pass in his explanation text says "Earth ground from the AC cord is attached to the chassis for safety, and is connected to the circuit ground through a power thermistor (bright idea from Frank DeLuca). This gives some resistive isolation for prevention of ground loops but goes to small values of resistance in case of catastrophic connection to the live AC line.". Shall I connect circuit ground to AC ground during the test?


Thank you!!!
 
Are you using the power supply PCB from the article?

If yes, when you mount the PCB board in your Power Supply enclosure the circuit ground
is connected to AC ground (as long as you have a connection from the AC inlet
Earth to a grounding screw and washer on the chassis.)

i just plugged my PSU in without a load and got good measurements...

I question you adding the complexity of the Light Bulb tester if you aren't
100% up on building a PSU. I'm not sure how it would effect your measurements.

post some pics and let's see what ya got
 
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