Super Leach diode problem

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supernet

supernet

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Joined 2001
I am buliding a stereo Super Leach amp this time and I do not understand where to put 4 diodes on heat sink. My amplifier has two heat sinks per one side. I put 4 PNP transistors at one and 4 NPN at the second, but where to put 4 diodes?

Thanks for help!!

Supernet
 
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BeanZ

Member
Joined 2002
Drill holes and put the diodes in the holes through the heatsink in between two middle transistors on the heatsink. I could be the heatsink with either the NPN or PNP. They should run at approximately the same temperature and will keep the amplifier thermally stable. Good luck

BeanZ
 
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hugobross

Member
Joined 2001
Another suggestion, I've used BYV29 diodes (see pic) for the bias circuit, they are easier to mount on the heatsinks (use also isolation!! and cooling paste).

I would use one heatsink per channel (so 2 NPN's, 2 PNP's and 2 diodes on one heatsink).

best regards,

HB.
 

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BeanZ

Member
Joined 2002
hugobross mentioned it but it can not be stressed enough. Make sure that you test the continuity between the tab on the TO-220 package to the heatsink. There should be no continuity! Catastrophic failure is emminent if there becomes continuity. I recommend the SIL-PADS by Berquist. They are good performers and you always know that there is not continuity.

BeanZ
 
peranders

peranders

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Joined 2002
sjostromaudio.com
Paid Member
Here is an another idea: You can use almost any PN-junction (diode) to create the -mV/degree thing. You can use isolated transistors. Connect the base to the collector, then you have a diode if you use base(collector) and emitter. You can also use (collector - base) and (emitter - base). These two types of diodes have different properties but in your application I think it's of no (or minor) importance.
 
BrianGT

BrianGT

Retired diyAudio Moderator
Joined 2002
chipamp.com
I would keep the original diode scheme and put them on one of the heatsinks and see how it works. If you have problems (such as one heatsink being hotter then the other), then put 2 PNP and 2 NPN on each heatsink instead. I talked to Dr. Leach about this a few months ago, when I was considering seperate heatsinks for my superamp, and I think he suggested 2 and 2 with the diodes on one, but I can't remember exactly, since i found a heatsink with 8 - to-3 holes to use instead.

Good luck,

--
Brian
 
sajti

sajti

Member
Joined 2003
hugobross said:
Another suggestion, I've used BYV29 diodes (see pic) for the bias circuit, they are easier to mount on the heatsinks (use also isolation!! and cooling paste).

I would use one heatsink per channel (so 2 NPN's, 2 PNP's and 2 diodes on one heatsink).

best regards,

HB.
Click to expand...


I think this is not a good idea. Mr. Leach used the diodes istead of the normal power transistor to reduce the capacity between the sensing device, and the heatsink. If You apply 4xTO220 diodes You will get 4 times capacity, and it will reduce the bandwidth (and even decrease the stability margin).
So I recommend to use the four diodes, and mount two of them to the NPN heatsink, and two of them to the PNP heatsink. With transistors, any small signal type is OK with 5mm hole in the heasink and use some glue to fix them.

sajti
 
jaycee

jaycee

Member
Joined 2004
If you have NPN transistors on one heatsink and PNP on another, you mount two diodes on each sink. At least, thats what Mr Leach says in his FAQ.

You are supposed to drill small holes for the diodes to go into and then glue them there, so that they have maximum coupling for sensing the heat.
 
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