Using two heatsinks

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I guess it would work decently enough if you put the driver + output for the upper side on one heatsink and those for the lower side on the other, with the bias transistor on whichever is most convenient... they should normally be heating up just about equally, assuming they're the same size. Maybe you can even bolt 'em together or something.
 
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Plenty of commercial amplifiers have used separate heatsinks in the past. Driver transistors are only mounted to the main heatsink because it is cheaper and/or more convenient to use only one heatsink. The dissipation of drivers doesn't necessarily track the output devices and AFAIK, there is no actual benefit to having either EF or Sziklai drivers thermally coupled their output devices.

Douglas Self discusses the heatsinking and bias control options for both topologies in more detail. You can find this in some editions of his handbooks and "Self on audio" books containing the original articles from Electronics World magazine.
 
I'm doing that on my AX6 board, as dynaco did on the predecessor ST120 PC14 board. Both output transistors are on a remote heatsink. The drivers have little individual heat sinks. Actually decoupling the drivers thermally from the output transistors is a positive good. If the output transistors get hot, the drivers don't also get hot from the thermal feedback and cause more drive current to come out. That thermal coupling may be a cause of why darlington output transistors have proven (reported by PA & guitar amp repairmen) to be such failure prone parts.
All 3 peavey PA amps I've disassembled have output transistors on their own heat sink in front of the fan, and the drivers on a remote board with their own little heat sinks. In the 3 level boost designs, the predrivers also have little heat sinks, also separate.
The only thing that has to be coupled thermally to the output transistors is the Vbe multiplier transistor that senses the output temperature and decreases the driver separation voltage accordingly to compensate. Or the diode stacks that preceeded the vbe multiplier for heat sensing in the older designs.
 
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music soothes the savage beast
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Hi, i am building a class-b amplifier and i am thinking in buying an individual heat sink for each driver. What are the problems that can come out of that?
Thank you


No problem with individual heat sinks...but why would you want classB? Are you looking for some special effect? Crossover distortion? Bad unpleasant sound?
 
using 2 heatsink in one channel.

Hi.It has been more than 1 year.
Because of i could only find heatsink with 165mm wide vertical fins in my country.I will put 2 together and make 330mm depth. (I not making horizontal because vertical fins make better heat dissipation) for class a amplifier projects i will build cases like this one.2 coolers in one channel.And connect them together with a stell connecting piece in the middle.(I want to use stell for higher strenght ,maybe aluminium connecting piece may be better for heat transfer eachother?)
KYYSLB WA20 Black Full Aluminum Home Amplifier Chassis Class A Amplifier All aluminum Amplifier Case Box DIY-in Amplifier from Consumer Electronics on AliExpress

My friend told that it is not a good idea because of there will not be a perfect heat conduction and there may be offset issues.He is also not building class a.Only class AB.Do you think it will be a problem?I remember using 2 coolers is better than one cooler for heat dissipation.
The cooler is here.
Happy new year to everyone!
Best regards
 

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Sure he means a-b

(OK, latish reply here!)


There are two ways to describe an optimally biased push-pull output stage.

Some call it class B because the transistors each conduct for 180 degrees at all signal levels, for a suitable definition of conduction.

These same people take class AB to mean class A for small signals, crossing over to class B at higher levels.

The second group think of the above two as both "class AB", taking class B to mean zero bias.

The first group call zero bias "class BC" since its class C for small signals (ie gross crossover distortion).
 
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Because of i could only find heatsink with 165mm wide vertical fins in my country.I will put 2 together and make 330mm depth. ... i will build cases like this one.2 coolers in one channel.And connect them together with a stell connecting piece in the middle.(I want to use stell for higher strenght ,maybe aluminium connecting piece may be better for heat transfer eachother?)

No problem in using 2 heatsinks and no need to thermally connect them.
You will always have an even number of transistors (2/4/6/8) so simply mount half on one, half on another.
Pick one for the thermal sensing transistor, in principle both heatsinks will heat up roughly the same.
 
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