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NAP250 amp boards & regulator boards

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JeffYoung

JeffYoung

Member
Joined 2017
Here's my lovely HPA-1 clone:

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And here's its dirty little secret (note the crossed legs on the A992):

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drmaftoon

Member
Joined 2018
I used another 150 ohm and before it burnt, I measured +ive voltage.
I can confirm that regulator works, I can adjust the voltage, I reached 38 volts before it burnt and I have run out of supplies :)
However the resistor on -ive rail works absolutely fine, problem is on positive rail only, one option would be to use a higher wattage resistor but please guide me if I should or not?
Thanks
Sajjad
 
JeffYoung

JeffYoung

Member
Joined 2017
drmaftoon said:
I used another 150 ohm and before it burnt, I measured +ive voltage.
I can confirm that regulator works, I can adjust the voltage, I reached 38 volts before it burnt and I have run out of supplies :)
However the resistor on -ive rail works absolutely fine, problem is on positive rail only, one option would be to use a higher wattage resistor but please guide me if I should or not?
Thanks
Sajjad
Click to expand...

Something else must be wrong. The resistor should only be dissipating 3.2mW.

Check the polarity of D5 and D6, and the resistance of R7. (Also check D5 and D6 for being shorted.)
 
JeffYoung

JeffYoung

Member
Joined 2017
I can see the polarity in your last picture -- it's correct.

Just for debugging, replace the burned resistor with something on the order of 10K or 20K. Then see what voltage you're getting on the base of TR5. (It should be two diode drops below your rail -- or about 54.5V.)
 
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drmaftoon

Member
Joined 2018
My power supply consists of 2x40v 500VA toroid, 2 33000uf Kemet with 2 bridge rectifiers as suggested by Jeff.
I am going to use this, one for each channel, like Nap 135, in two separate boxes. I love my ears so I will not be driving it hard.
1-Do I still need to install a fan with heat sink, like in 135?
2- is there any wiring precaution I need to undertake when wiring one regulator and one amplifier board to above mentioned power supply?
Thanks
Sajjad
 
JeffYoung

JeffYoung

Member
Joined 2017
No, that's the impedance (although that number will also factor into the amount of heat generated).

But I was mostly looking for the sensitivity number. It's quoted in the link you posted as 92dB, which is reasonably high. I very much doubt you'd need a fan.

What size is the room?
 
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