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Old 27th August 2010, 02:16 AM   #11
Enzo is offline Enzo  United States
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mdm, generally open means infinite resistance, the circuit path has an open spot, as though the wire was cut in two.

Zero ohms or very low resistance - free flow of current unimpeded - is generally referred to as a "short circuit" or just short.
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Old 27th August 2010, 12:45 PM   #12
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how about replacing all fets and then make the same testings with transitors mounted on a heatsink ?

also reading the instructions once or twice more might help a bit
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Old 27th August 2010, 12:51 PM   #13
AndrewT is offline AndrewT  Scotland
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reading and understanding the instructions will be a big help.

If there is an instruction that one cannot understand on reading it, then that is the time to ask the question, not after one has powered up the project and worse, after one has blown up the project.
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Old 27th August 2010, 06:39 PM   #14
mdm102 is offline mdm102  Russian Federation
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Unfortunately I don't have spare mosfets, I've ordered some matched pairs today at tech-diy.com.

I've burned mosfet, as I said, during biasing. I don't know why, but turning VR made no sense. I adjusted VR to 476ohm (450-500ohm Anthony recommended) before begining of biasing, then I started to turn VR counter-clockwise to 0ohm. VR has 0-500ohm nominal. My DMM was set to VDC and measured across 10ohm 1W resistor. During turning VR I always had 156-158mV. This was very strange for me, because I carefully read instructions and many times. Maybe I did wrong connections? I don't know. You can see my installation here: ImageShack Album - 3 images

here you can see a part of Anthony's instructions regarding pre-flight test and biasing: http://img202.imageshack.us/img202/9833/300se.gif

I've checked every resistor that Anthony mentioned in instruction in Pre-Flight test chapter to check to be sure that module work fine, and all check-measurements for both modules were absolutely correct.

I can't bias the second module too. Same problem with biasing, but I didn't burned it, now I very carefully turn VR, I tried to go down 250ohm, also zero effect, I afraid to burn the second module if I'll go lower 250ohm.

I will be very very glad if you help me to get it work. Thank you all!
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Old 28th August 2010, 07:42 AM   #15
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for example : is it this type of led used in the original circuit ...??? cause if the circuit used a standard green led for a courent source changing this with blue that draws 10 times the curent will mess up the circuit but look nice ...

others that made that amp can tell us that since we dont have schematics here for that
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Old 28th August 2010, 08:51 AM   #16
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Quote:
Originally Posted by mdm102 View Post
I tried to bias amplifier module, but overturned VR at some moment, it is single turn VR

Multi-turn cermet pots are your friend, cheap, and should be bought before you fry another set of mosfets
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Old 28th August 2010, 09:57 AM   #17
mdm102 is offline mdm102  Russian Federation
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Sakis, this is commercial amplifier module, so no circuit scheme with it. Module goes with installed SMD components, I just installed thru-hole components on it and tested it after this, and it works ok, but I cann't bias it. I don't know why. Seems I did all things right to the instructions, but no effect. I'll try today to test biasing transistor, maybe it does not do its job.

Globulator, I agree with you, but too late
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Old 28th August 2010, 09:30 PM   #18
mdm102 is offline mdm102  Russian Federation
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Got it to work!Yahoo!!)) I just have to go down 200ohm with VR and voltage began to rise up! Amp works fine! I have to wait for mosfets for the broken amp and get it to work to. Thanks you all for help!
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