Doug Self Preamp from Linear Audio #5

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Hicoco

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Joined 2018
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redjr said:
I fitted some MUR820G diodes to DS series regulated PS (blue board) and all is well. Instead of temps of 140F, I'm getting more respectable temps of between 75-85F. Both regulators at around ~78F. And these temps are under load. I've adjusted the trim pots to get +-14volts ouput. Everything is cool to the touch. I'm happy and the sound of my DAC output stage is great!

Thanks Hicoco for suggesting the 820Gs.
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Great !!!! i did not work on it yet..Did you change the 47nf??
 
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Hicoco

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Carl_Huff said:
The bubbles at the top are the rail voltage adjustment pots and the large bubble at the bottom is where you select input AC voltage. Once assembled you will have a premium grade series regulated adjustable power supply
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711388d1540484422t-doug-self-preamp-linear-audio-5-a-pwr_supply-jpg

Hi Carl, i just plug all the part together for the first time today (PSU, Preamp, I/O, selector) no music yet, just oscilloscope with 1000Kz/150mV at the input.
I noticed after 10 minutes that the PSU is warm at the BD139 (61℃) and BD140 (50℃). I have 200mA (17V+) and 180mA (17V-) with the selector at 1er input (XLR).
With no load @ the PSU, i don't have this issue.
 
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Carl_Huff

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kadproducts.com
Hicoco said:
Hi Carl, i just plug all the part together for the first time today (PSU, Preamp, I/O, selector) no music yet, just oscilloscope with 1000Kz/150mV at the input.
I noticed after 10 minutes that the PSU is warm at the BD139 (61℃) and BD140 (50℃). I have 200mA (17V+) and 180mA (17V-) with the selector at 1er input (XLR).
With no load @ the PSU, i don't have this issue.
Click to expand...

Hmm, did you put a dab of thermal grease under the BD139/BD140 devices and their heatsinks?

It sounds to me that you are not getting a good thermal couple between those transistors and their respective heatsinks.

Please note that some BD139/BD140s have an exposed metal mounting surface that must be electrically isolated from it's respective heatsink using a mica or silicon insulator.
 
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Hicoco

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Mark Tillotson

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Thermal pads like silpad are a composite of silicone and a good heat conductor as filler. The silicone rubber can conform to the surfaces of device and substrate, the filler particles increase the thermal conductivity. Mica cannot conform to the surface as well, but has a reasonable bulk thermal conductivity. Diamond film would be really good for this, if it was affordable, as it has extreme thermal conductivity (better than metals).

diyralf we are not talking about silicon.
 
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Hicoco

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Carl_Huff said:
Hmm, did you put a dab of thermal grease under the BD139/BD140 devices and their heatsinks?

It sounds to me that you are not getting a good thermal couple between those transistors and their respective heatsinks.

Please note that some BD139/BD140s have an exposed metal mounting surface that must be electrically isolated from it's respective heatsink using a mica or silicon insulator.
Click to expand...
I changed the SK 104-2 ( External Length - Metric 25.4mm) with SK104-6 ( External Length - Metric 63.5mm) heatsinks and the temperature drops of 10℃ on each side. But now i am too hight for my 1U chassis....i am curious to now if they are any other option than to change the heatsinks.. Carl, did you check for any oscillation on your boards ?? Thanks




 
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Hicoco

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Carl, may be this is the answer....
The NE5534AN (PDIP-8) is obsolete. They sent me the NE5534AP (PDIP-8).
Looking at the datasheet of both, the Operating Supply Voltage range are different:
NE5534AN : From +/- 3 V to +/- 20 V
NE5534AP : From +/- 5 V to +/- 15 V
what is your thought?
i didn't check with an oscilloscope.
 
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