"Millett Hybrid" redux: NuHybrid headphone amp, using the Korg Nutube

[Astro13]

Edit: (posted this twice on accident, my bad)

 

[Astro13]

Assuming you have set the bias to the recommended approx. 11VDC for TP1 and TP2 to GND (TP3) the fact that the bias fluctuates is a bit troublesome. It's usually pretty steady.
Some possibilities that might make the 3.3V regulator run hot:
1) Power supply is above 24VDC causing the regulator to dump excess voltage beyond the original design spec
2) Filament current limiting resistors R11 and/or R16 are significantly less than 150 ohms
I've had troubles in the past with the thru hole plating on some of Pete's boards so you might check and see if any of the top side pads need touch up soldering if the solder did not flow through the hole from the bottom to the top at any hole locations that have topside trace connections.

Re-soldered both of those, My PSU is a 24 volt, I dont know what else to do about that.
(Edit: One of the legs on Q2 was not soldered on correctly, That fixed some of the distortion, but the regulator still burns to the touch)

 

[ShaolinGrump]

CigarBox NuHybrid came to me with a few broken solder points. All found. All fixed. 40% on the ALPS pot is plenty for sticker-modded HD8xx.

 

[Astro13]

CigarBox NuHybrid came to me with a few broken solder points. All found. All fixed. 40% on the ALPS pot is plenty for sticker-modded HD8xx.

Very nice! Quick question, how hot does your voltage regulator get? The coin is a very interesting heatsink

 

[ShaolinGrump]

Very nice! Quick question, how hot does your voltage regulator get? The coin is a very interesting heatsink

I don’t even know which thing is a voltage regulator. Just got it fixed and playing stereo today.

 

[Astro13]

I don’t even know which thing is a voltage regulator. Just got it fixed and playing stereo today.

Its beside the solder points for the headphone jack. A little black square with three leads and a metal "tab" with a hole in the top. From the pictures, it looks like it has a small coin or something bolted to it as a heatsink. Its the only thing in the amp that seems to generate heat, and in my case, it gets to around 80 degrees C.

 

[ShaolinGrump]

I’ll check it on Monday. I left the amp at work where I can get more listening hours.

Is the penny safe to touch during operation? I am not sure if I have a compatible touchless thermometer.

 

[Astro13]

I’ll check it on Monday. I left the amp at work where I can get more listening hours.

Is the penny safe to touch during operation? I am not sure if I have a compatible touchless thermometer.

Electrically, you should be fine, But I burned the tip of my finger on the regulator. Using a contact thermometer should be find, just be careful and don"t short it out. Only touch the penny.

 

[ShaolinGrump]

@Astro13 testing heat finally this afternoon

Amp has been running 15min. Touch the edge of the penny, start counting. At count 5, minor pain but no skin burn. At count 8, slightly more pain and I ain't holding the penny anymore, but still no burned skin.

 

[Astro13]

@Astro13 testing heat finally this afternoon

Amp has been running 15min. Touch the edge of the penny, start counting. At count 5, minor pain but no skin burn. At count 8, slightly more pain and I ain't holding the penny anymore, but still no burned skin.

Okay, Thank you, that is somewhat consistent with my readings. Yours is probably less hot because it has the penny as a psudo heatsink