Opinions on the eBay amp modules - EBB250 - diyAudio
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Old 29th September 2012, 09:17 PM   #1
JPM14 is offline JPM14  United Kingdom
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Default Opinions on the eBay amp modules - EBB250

Has anyone tried these? It is a mosfet module similar looking to a Maplin amp with an L bracket. The main difference is that it uses IRFP240 / 9240 vertical fets. There is a temp compensation thermistor built in. I have two which I bought recently. They seem to work quite good. 30 it costs for the bigger of the two boards which has 4 fets.
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Old 29th September 2012, 09:27 PM   #2
Bone is offline Bone  United Kingdom
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Can you post the circuit, you can't quite see it on eBay?
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Old 29th September 2012, 09:45 PM   #3
JPM14 is offline JPM14  United Kingdom
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will have to dig out the sheets that came with it and put it on. It is almost the same as the Maplin circuit but has an extra transistor where the usual 47k dropper resistor is from the +ve rail to Tr1 and Tr2
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Old 30th September 2012, 08:17 AM   #4
Bone is offline Bone  United Kingdom
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The trouble with the Maplin circuit is that it is only suitable for Lateral Mosfets which have a negative thermal coefficient. Using vertical FETS like the IRFP240 etc will need the 1k variable bias adjust pot replacing with a bias transistor mounted on the heatsink, otherwise if used hard, thermal runaway could occur destroying the output transistors.
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Old 30th September 2012, 10:42 AM   #5
JPM14 is offline JPM14  United Kingdom
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Yes but the EBB250 is slightly different and has a thermistor (on the L bracket) in parallel with the bias pot. I have tried it from cold to 90C and the quiescent current remains constant enough to ensure thermal runaway won't happen
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