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Sanken S-40W bias problem/getting hot, any ideas?
Sanken S-40W bias problem/getting hot, any ideas?
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Old 10th May 2012, 05:31 PM   #1
flyingtele is offline flyingtele  New Zealand
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Default Sanken S-40W bias problem/getting hot, any ideas?

Hi folks, tonight I repaired an old JVC amp that I have been working on for a while, a JA-S11. It uses two Sanken S-40W output modules, I replaced one and the supplied part was faulty. I found another one and installed it, and the amp now runs fine, apart from one issue. The side that has been replaced gets much warmer much faster then the other side.
I thought it might have had parasitic oscillation but a quick check with the scope showed no signs of oscillations, which leads me to think that the modules bias is incorrect or needing adjustment.

I haven't done a load test on the amp, but will do soon. I have just ordered over 100 wire-wound resistors to make two 8 ohm 270W dummy loads, so once its built I'll crank it up and check its output.

Do these modules have any form of external bias control or is it fixed internally? I have included the schematic for the power amp section so you can see how it is implemented. I am hoping that someone with more skills than I can give me any ideas or tell me what could be causing the new unit to get overly warm compared to the other side, and if there is anything I can do to correct it. I understand they are an old module and the one I got supplied is second hand but it works, just with excess heat.

Any helpful comments or suggestions would be greatly appreciated, as I would like to get it running properly.
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Old 10th May 2012, 05:52 PM   #2
Tekko is offline Tekko
Join Date: Jan 2005
As you can see on the schematic, there is no way of doing a bias adjustment on these modules.

inside these modules, you will find something very similar to this one: STK407-050 without cover blasting it - YouTube
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Old 19th December 2012, 11:38 AM   #3
tiefbassuebertr is offline tiefbassuebertr  Germany
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Location: D-55629 Schwarzerden
check out an internal schematic of this Hybrid module from Sanken (post #1):
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