Roender's FC-100 prototype and builder's thread - Page 57 - diyAudio
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Old 28th November 2012, 02:20 PM   #561
lucylu is offline lucylu  England
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Default Head hurts

Now i have the shunt transformer i decided to test both shunts that i made months ago ,negative works 37.8 but positive nothing zero volts then smell smoke switch off ,looks like r33 resistor burnt and led looks dead ,this happened to both shunts i have check and checked .can someone please advise



Rudi received resistors thank you
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Old 28th November 2012, 03:48 PM   #562
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Can you post a pic of your shunt boards?
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Old 28th November 2012, 04:13 PM   #563
lucylu is offline lucylu  England
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I took my time,,,,the led and r33 removed thanks john
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Old 28th November 2012, 05:06 PM   #564
AndrewT is online now AndrewT  Scotland
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The Rudi shunt regulator boards are OK.
It must be an assembly error.

Well almost OK,
either omit the film caps across the diodes or substitute a cap + resistor in series for each cap location.

Don't invite oscillation of the supply due to stupidly inserting a cap with an unknown inductance !
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Old 5th December 2012, 06:49 PM   #565
jprco is offline jprco  Canada
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Lucylu re. post #558.
Your photo's of the FC100 PCB's shows that the correction to the 1uf capacitor and 2 resistors connection suggested by Rudi has not been made.
Rudi: another question for you. What are the NFB points used for on the FC100? Are they used to measure something? I can't find a reference to their use.
Jean
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Old 5th December 2012, 08:15 PM   #566
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Jean, the abbreviation "NFB" stands for "Negative Feedback". A proportion of the output (speaker) signal is fed back to the input,
after being inverted.
The NFB is "just another track" (though a long one) and has nothing to do with measurement.

Best regards - Rudi
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Old 6th December 2012, 12:22 AM   #567
jprco is offline jprco  Canada
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Thanks, Rudi. So what do we do with these points? Leave them alone, jump them together permanently to enable negative feedback or join them to on/off switch so we can choose the dynamics??? Nothing in the guide or builder's manual that I can find on the subject. Are these there simply for more seasoned DIYer's to play with??
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Old 6th December 2012, 03:35 AM   #568
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Burnt psu...
Transistors in wrong locations is a possibility.

Gajanan Phadte
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Old 6th December 2012, 06:50 AM   #569
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Jean, on page 36 of the "FC-100 Builder's Guide" I have written:

After you have finished the Backend PSU, connect the NFB Takeoff point to the NFB -point in the frontend on the solder side of the board
(right red line on page 27) and the frontend GND (STARGND) with a "thick" solid wire (to achive a very low-impedance connection) with the
BACKEND-GND (the other red line on page 27).

Please read the manual carefully and follow the instructions on how to do the adjustment of the quiescent current / BIAS.

Best regards - Rudi_Ratlos
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Old 6th December 2012, 10:09 AM   #570
AndrewT is online now AndrewT  Scotland
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Another that adopts a project and refuses to give it the time (to read the manual) the project deserves.
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