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Old 16th December 2012, 07:31 PM   #51
sonnya is offline sonnya  Denmark
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Quote:
Originally Posted by Lazy Cat View Post
VSSA - Very Simple Symmetrical Amplifier, something in between SSA and TSSA. Similar schematics posted a lot of times but not exactly the same.

With only six transistors you can get genuine current feedback, high bandwidth amplifier, capable of driving 4 ohm speakers. PCB can be very simple and small too.
I do not know how to say this. But such a circuit i have rejected as the VAS transistor current accelerates very fast to dangerous level without very good cooling.

As they get warmer they get higher hFE and lower VBE drop -> more current -> hotter -> higher hFE, lower VBE -> more current -> hotter ... Get the picture??
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Old 16th December 2012, 07:33 PM   #52
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Hi LC i playing at this time with eagle...
First for TO3 as ia had layout for TO3 Lateral SSA. Will show you as it been ended. After it's easy to swap to plastic case.

Marc
Super Cool Marc
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Old 16th December 2012, 07:46 PM   #53
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I do not know how to say this. But such a circuit i have rejected as the VAS transistor current accelerates very fast to dangerous level without very good cooling.
Yes but there's certain limit level of input collector current reached when it is thermally stabilized. 15k resistor defines max input collector current, also VAS collector current rising itself will stop when heatsink power dissipation reaches certain temperature. It is perfectly normal process as long as input is stable and not forcing VAS current over the limits in a cummulative process.
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Old 16th December 2012, 07:54 PM   #54
sonnya is offline sonnya  Denmark
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I just wanted to say that cooling is necessary on the VAS like 20K/W heatsinks
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Old 16th December 2012, 08:02 PM   #55
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I just wanted to say that cooling is necessary on the VAS like 20K/W heatsinks
Of course as I already mentioned in post #39, VAS BJT's needs them, could be one common or two separates.

This project is fixed in complexity and will stay as it is. PCB will be our Christmas gift to DIY-ers for these long winter evenings hehe
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Old 16th December 2012, 08:06 PM   #56
sonnya is offline sonnya  Denmark
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Of course as I already mentioned in post #39, VAS BJT's needs them, could be one common or two separates.

This project is fixed in complexity and will stay as it is. PCB will be our Christmas gift to DIY-ers for these long winter evenings hehe
Matchbox kits???
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Old 16th December 2012, 08:11 PM   #57
caglarm is offline caglarm  Turkey
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PCB will be our Christmas gift to DIY-ers for these long winter evenings hehe
İts Christmas gift
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Old 16th December 2012, 08:12 PM   #58
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Yes in SMT and all.
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Old 16th December 2012, 08:19 PM   #59
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Super Cool Marc
Here first attemp...107*93mm; Size could be smaller but 10 polycaps and 2200 40v too. I have some improvement in mind to deduce pcb dimensions

Marc
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File Type: png VSSA_TO3_brd.png (36.3 KB, 1400 views)
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Old 16th December 2012, 08:30 PM   #60
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TO-3 mosfets are so tempting to have them in one of the amps, could it be VSSA? Let's see ... well done Marc.
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