that was joke about shop, there no drugs or pharmaceutical against sillines and impatience.
and only I am responsible for any my mooves.
and that resitors burned is not a joke.also 0,39 ohm one resitor down too. during that few minutes I measured across 0,39resitors(in good side that voltages was all 4 resistors diferent 0,49v and 0,36)
rtirion, really thanks for help , by one myself Iwould not find bugs. now I will try to see by myself where is problem. shouldnt be a big problem..
and only I am responsible for any my mooves.and that resitors burned is not a joke.also 0,39 ohm one resitor down too. during that few minutes I measured across 0,39resitors(in good side that voltages was all 4 resistors diferent 0,49v and 0,36)
rtirion, really thanks for help , by one myself Iwould not find bugs. now I will try to see by myself where is problem. shouldnt be a big problem..
Re: that was cool!
instead 100kohm I soldered in 100ohm .I bought 2 packets from store labeled 100kohm and 100ohm respectively. but inside of both bags sitting 100ohms resitors. didint understand how this could happen.
sorry my writing mistakeelviukai said:I checked all resistors and quess what- insted 100Kohm I soldered in 100ohm. how I did that? I carefuly mached resistors, BUT FORGET VALUES! i just put simply resistors back to pack paired. now I measured all left resitors in pack in both pack they are 100ohm. inspite on secon bag written100pieces 1% 100kohm!! is there any lawyers out there ? i think I will court my local shop fro things like theese. threy cut my life at least 5 years.
I turend on amp now for a few seconds and fets got hot , dc ofset reads 0,01v seems it should work.
instead 100kohm I soldered in 100ohm .I bought 2 packets from store labeled 100kohm and 100ohm respectively. but inside of both bags sitting 100ohms resitors. didint understand how this could happen.
This happens.
When I order resistors or any other part, I always check. Resistors with a DMM, the labels on the caps and transistors. If they match they go in the correct box. I never blindly stock them.
As for your source resistors, if they burn, most likely the mosfet is short circuit. As BobEllis said, make sure they are well mounted and perfectly isolated from the heat sink.
/Hugo
When I order resistors or any other part, I always check. Resistors with a DMM, the labels on the caps and transistors. If they match they go in the correct box. I never blindly stock them.
As for your source resistors, if they burn, most likely the mosfet is short circuit. As BobEllis said, make sure they are well mounted and perfectly isolated from the heat sink.
/Hugo
0,39 ohm problem
looks like I started one amps one channel two earlier tryings ended not so good one and 3 mosfets broken respectively. this time also started this dangeruos firing noise from resitors but luckily I turned of and then turned on again and for 5-10minutes it worked no burned resitors. trying to adjut fine bias L and R I noticed that on one side all 0,39ohm measures diferent from 0,38 to 0,52 and in the other side things is prety similar but one 0,30ohm shows 0,64V . when I starting increse resistanse with theese trims values goes up but how I should get 0,5v around all 0,39ohm resitors?. I do not want to get more than 0,64, but even woulkd be better to reduce.but how? maybe I should replace some resitors because I feel that even 50kOHM trimer seted up to 0 ohm is too much. BTW is this normal so diferent values? I tooked out and carefuly measured all resitors,prevent mistakes. fets are mached to 0,01V both 240 and irfp240. all others resitors are 1% tolerance. maybe problem is in 0,39ohm resitor? because they are 5% tolerance, should I replace this 0,39ohm resitor wihich shows 0,64v? my primaries are 20.7V and DC is 25V this make amp run hotter? my heatsinks is 2x 150x500 x 97mm height wings 27 pieces .pretty masive but it goted pretty hot during theese 7minutes.aleph5 was little bit colder. what preliminary power I am geting with 25Volts
thanks
looks like I started one amps one channel
two earlier tryings ended not so good one and 3 mosfets broken respectively. this time also started this dangeruos firing noise from resitors but luckily I turned of and then turned on again and for 5-10minutes it worked no burned resitors. trying to adjut fine bias L and R I noticed that on one side all 0,39ohm measures diferent from 0,38 to 0,52 and in the other side things is prety similar but one 0,30ohm shows 0,64V . when I starting increse resistanse with theese trims values goes up but how I should get 0,5v around all 0,39ohm resitors?. I do not want to get more than 0,64, but even woulkd be better to reduce.but how? maybe I should replace some resitors because I feel that even 50kOHM trimer seted up to 0 ohm is too much. BTW is this normal so diferent values? I tooked out and carefuly measured all resitors,prevent mistakes. fets are mached to 0,01V both 240 and irfp240. all others resitors are 1% tolerance. maybe problem is in 0,39ohm resitor? because they are 5% tolerance, should I replace this 0,39ohm resitor wihich shows 0,64v? my primaries are 20.7V and DC is 25V this make amp run hotter? my heatsinks is 2x 150x500 x 97mm height wings 27 pieces .pretty masive but it goted pretty hot during theese 7minutes.aleph5 was little bit colder. what preliminary power I am geting with 25Voltsthanks
Having that much variation in source resistor voltage (current) is NOT normal. Either the IFFP240s are not matched properly or they are mounted differently so they heat up differently.
Are all mounted with the same silpad/mica/grease and similar position on the heat sink? (not too close to an edge)
How did you match the FETs? At what current, what heat sink temperature, how long before you measure, etc.? All make a difference. FETs matched at 100 mA may be way off at 1A.
Instead of changing the trimmer pot, try increasing the value of your Source resistors to reduce the current. Source resistor choice is coarse adjustment, the trimmer pot is fine.
You could try matching the resistors, but your difference is far more than their 5% tolerance. To match resistors you'll need something more than a DMM, since the values are so low. Search for the "LMS Impedance Bridge" It is quick to build and I have found it quite reliable.
At your rail voltage, you're going to need some incredibly huge heat sinks to keep your Fet junctions reliably cool. Look for the AXE-1.2 spreadsheet.
A format comment: breaking your posts into paragraphs makes it easier to read. A new paragraph for each new idea helps a lot.
Are all mounted with the same silpad/mica/grease and similar position on the heat sink? (not too close to an edge)
How did you match the FETs? At what current, what heat sink temperature, how long before you measure, etc.? All make a difference. FETs matched at 100 mA may be way off at 1A.
Instead of changing the trimmer pot, try increasing the value of your Source resistors to reduce the current. Source resistor choice is coarse adjustment, the trimmer pot is fine.
You could try matching the resistors, but your difference is far more than their 5% tolerance. To match resistors you'll need something more than a DMM, since the values are so low. Search for the "LMS Impedance Bridge" It is quick to build and I have found it quite reliable.
At your rail voltage, you're going to need some incredibly huge heat sinks to keep your Fet junctions reliably cool. Look for the AXE-1.2 spreadsheet.
A format comment: breaking your posts into paragraphs makes it easier to read. A new paragraph for each new idea helps a lot.
ok thanks, this is only one board. I will check how others will act. I mathed about 10seconds before taking record at 14V and 1400mah to irf9610 I added 100-120ohm resitor before maching/ very interesting.. maybe 0,39ohm resitor is way to far for 5% tolerance. in other boards I am using precision Vishay dale rs 10w 1% resitors( do not conect theese bopards because 8eur piece for resitors is really matter ) how theese various val;ues 0,38 -0,48 and one 0,64 will influence sound? if I need resolder and remach 200pieces irf 240 it will be suicide as I understand at one side whern I regulate with 50k pots all voltage across source resitors should change at once all. so I can adjust only all 4 resitors voltage but not diferent.. very interesting why so much diferent voltages. I hope my heatsinks will handle this 25v rails 150x 500x 97mmwings . I will ad CLC or CRC circuit to drop voltage. regarding mosfets pacements no they are not very similar mountened(very long story) but also no worry about because I used this with aleph5 with no problems. but maybe ax is very critical to theese things.
) how theese various val;ues 0,38 -0,48 and one 0,64 will influence sound? if I need resolder and remach 200pieces irf 240 it will be suicide as I understand at one side whern I regulate with 50k pots all voltage across source resitors should change at once all. so I can adjust only all 4 resitors voltage but not diferent.. very interesting why so much diferent voltages. I hope my heatsinks will handle this 25v rails 150x 500x 97mmwings . I will ad CLC or CRC circuit to drop voltage. regarding mosfets pacements no they are not very similar mountened(very long story) but also no worry about because I used this with aleph5 with no problems. but maybe ax is very critical to theese things.
It is essential that you mount the mosfets properly on the heatsink. Good thermal contact is very important.
Do change the 75k's so you can at least fire up the amp and start increasing current from 0.
It's not that crucial to have 0.5V over the source resistors.
0.5V with 0.39ohm is 1.28A. I=U/R. That's quite a lot as a starter and easy to burn components if something's wrong.
/Hugo
Do change the 75k's so you can at least fire up the amp and start increasing current from 0.
It's not that crucial to have 0.5V over the source resistors.
0.5V with 0.39ohm is 1.28A. I=U/R. That's quite a lot as a starter and easy to burn components if something's wrong.
/Hugo
an closer to muonting side. theese which are ifernt do not have mountening problems,others could be but very unlikely, because I always put bigger heatsinks than amp need diddipate.after 40min. amp get pretty hot but I can easily touch hand and stay for a 10-15seconds so shuold I change 75kohm resitors to something lower 50kohm> but problem is only on one side. other side after adjustment 50kohm trimmer sits at about 50% dc ofset is 0,2-0,06V
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