interesting stuff...
(this is actually kinda neat that im learning all this, but i would rather have a working amp! and btw, thanks again to everyone. without you guys, it would be in the trash and i wouldnt go down to the shop for another 6 months.)
so... i measured across the C - E on Q104 and Q105. im getting 5.6v or something. i didnt write it down, but its around 5.5v. a little high, but i assume within tolerences.
now comes the interesting part...
i measured R120, R121, and some of the other power resistors... R120 and R121 measured the same as before, around 1.5v or so. way too much, and they were getting HOT. i could smell them and they were too hot to touch after just a few seconds of being on. However, R124 - R127 were cool to the touch, and only had a 0.007v drop across them. that seems way too low. i would assume its supposed to be a 0.5v drop across them. i tested these before they went into the circuit and am sure that they have the right values...
what is making them too cold, and others too hot? nelson, if you are out there, i would appreciate if you have any input as you are probably the most familiar with this circuit.
(this is actually kinda neat that im learning all this, but i would rather have a working amp! and btw, thanks again to everyone. without you guys, it would be in the trash and i wouldnt go down to the shop for another 6 months.)
so... i measured across the C - E on Q104 and Q105. im getting 5.6v or something. i didnt write it down, but its around 5.5v. a little high, but i assume within tolerences.
now comes the interesting part...
i measured R120, R121, and some of the other power resistors... R120 and R121 measured the same as before, around 1.5v or so. way too much, and they were getting HOT. i could smell them and they were too hot to touch after just a few seconds of being on. However, R124 - R127 were cool to the touch, and only had a 0.007v drop across them. that seems way too low. i would assume its supposed to be a 0.5v drop across them. i tested these before they went into the circuit and am sure that they have the right values...
what is making them too cold, and others too hot? nelson, if you are out there, i would appreciate if you have any input as you are probably the most familiar with this circuit.
R 124-127 should have no drop unless your driving a load. Are your gate stoppers (R116,117,118,119) mounted on the board and fets remotely located? If so, you amp may very likely be oscillating. I know this is a PITA, but you may need to move these resistor to the fets and jumper them on the board. You can easily check this with an o-scope. You can also omit Q109 and 107 for testing. the only difference will be 1/2 the bias.
The gate stopper resistor is to keep the fet from oscillating, and to do this it needs to be very close to the fet.
The gate stopper resistor is to keep the fet from oscillating, and to do this it needs to be very close to the fet.
hum, that very well could be the problem...
sigh. i wish i had a scope. i cant think of what else it could be.
when an amp oscillates, could that cause it horrible DC output? if thats the case, i think i might have it solved. the question remains, why was it NOT doing it before, and it is now? i think i could easily move those resistors over.
it seems to only have a problem when volume is applied. it can play very low without a problem. does this make sense?
sigh. i wish i had a scope. i cant think of what else it could be.
when an amp oscillates, could that cause it horrible DC output? if thats the case, i think i might have it solved. the question remains, why was it NOT doing it before, and it is now? i think i could easily move those resistors over.
it seems to only have a problem when volume is applied. it can play very low without a problem. does this make sense?
It's a funny thing. sometimes intermittent, sometimes yes sometimes no. Sometimes it can be osscilating and you not know until puff.
Yes, put the resistors inside the heatshrink at the fet. Before you go through the trouble of removing the one on the board, try it. The amp will work with both resistors. HF may be a little rolled off.
You should go to Ebay and buy a $50 B&K scope. No need for something expensive. you only need 20 mhz and 2 traces to do anything audio other than look ad 24 bit dac data. You seem to be far enough into this hobby to justify a used scope.
Yes, put the resistors inside the heatshrink at the fet. Before you go through the trouble of removing the one on the board, try it. The amp will work with both resistors. HF may be a little rolled off.
You should go to Ebay and buy a $50 B&K scope. No need for something expensive. you only need 20 mhz and 2 traces to do anything audio other than look ad 24 bit dac data. You seem to be far enough into this hobby to justify a used scope.
ive actually already removed the resistors from the board and have jumpered them. im going to add them in-line with the leads.
i was actually going to ask that eventually, maybe ill ask later what would be a good cheap scope to have.
but i digress...
oscillation seems to be probable. ive been doing some reading about oscillation and it seems that because i have longer leads, and ive now added terminal strips to make all this troubleshooting easier, it is most likely the cause... i think we've ruled out all the parts. ill let you know in a few minutes if its the problem.
can oscillation kill the amp though? should i worry about blowing something because its oscillating?
i was actually going to ask that eventually, maybe ill ask later what would be a good cheap scope to have.
but i digress...
oscillation seems to be probable. ive been doing some reading about oscillation and it seems that because i have longer leads, and ive now added terminal strips to make all this troubleshooting easier, it is most likely the cause... i think we've ruled out all the parts. ill let you know in a few minutes if its the problem.
can oscillation kill the amp though? should i worry about blowing something because its oscillating?
ok. its all rewired with the resistors right on the fets.
is there anything i should know about oscillation before connect a load? i read some threads of oscillating alephs that blew up when a load was connected. i dont want that
it appears to be doing the same thing... the power resistors are getting pretty damn hot without a load (well, just a couple of them, the ones that were said to stay cold are cold.)
i took a couple of quick spot measurements, and it appears im getting the same values as before . i can connect a load and see what happens, unless its a bad idea.
is there anything i should know about oscillation before connect a load? i read some threads of oscillating alephs that blew up when a load was connected. i dont want that
it appears to be doing the same thing... the power resistors are getting pretty damn hot without a load (well, just a couple of them, the ones that were said to stay cold are cold.)
i took a couple of quick spot measurements, and it appears im getting the same values as before
. i can connect a load and see what happens, unless its a bad idea.
im really pi**ed off right now.
it seems to run fine. i hooked up a dummy load, and it acts totally normal. i cant get dc out of it (except for a little turn on/off thump), but when its playing, its maybe 5mv or so, nothing bad at all.
the power even seems fine. my test speaker is blown from a last attempt, but it worked for a few seconds before the voice coil gave out (it measured 0.5 ohms before i turned it on, it was barely hanging on.) i had a meter on it the whole time and saw no DC (or too little to care about).
BUT{/B], the measurements are still off. R121 (i think, its hard to see from the schematic what is what on the board), is getting VERY VERY hot. it melted insulation on a wire that was touching it. it still have a 1.5v drop across it. its so hot, just doing a tap-test for temp is painful. there is no way you can touch it (even for a millisecond) and not get a painful little reminder that your amp is screwed up.
im at a loss. im not a quitter but im very very very close to just scrapping this thing. this is the third issue ive had with it. every time i solve an issue, a new one pops up. first it was the bad diode, then it was a hum, then it was no sound, now its running too hot.
can someone please help! (im not saying anyone hasnt up until this point, im just asking for new ideas or more help. you guys have been great)
im gonna go cry myself to sleep and hope some solutions come to me in my sleep.
it seems to run fine. i hooked up a dummy load, and it acts totally normal. i cant get dc out of it (except for a little turn on/off thump), but when its playing, its maybe 5mv or so, nothing bad at all.
the power even seems fine. my test speaker is blown from a last attempt, but it worked for a few seconds before the voice coil gave out (it measured 0.5 ohms before i turned it on, it was barely hanging on.) i had a meter on it the whole time and saw no DC (or too little to care about).
BUT{/B], the measurements are still off. R121 (i think, its hard to see from the schematic what is what on the board), is getting VERY VERY hot. it melted insulation on a wire that was touching it. it still have a 1.5v drop across it. its so hot, just doing a tap-test for temp is painful. there is no way you can touch it (even for a millisecond) and not get a painful little reminder that your amp is screwed up.
im at a loss. im not a quitter but im very very very close to just scrapping this thing. this is the third issue ive had with it. every time i solve an issue, a new one pops up. first it was the bad diode, then it was a hum, then it was no sound, now its running too hot.
can someone please help! (im not saying anyone hasnt up until this point, im just asking for new ideas or more help. you guys have been great)
im gonna go cry myself to sleep and hope some solutions come to me in my sleep.
kilowattski said:So when do we get to see pictures of the finished product?
i need to finish the second chassis still. you can see it put together and finished on my site though. i updated the aleph3 page on there last night, and you can see a finished picture on the front.
but, once i get the second chassis built and running, ill post some pictures. i suspect it will take 1 week to build the second one. (minus troubleshooting, i built the first one in 2 weeks from scratch, design and building). so, i think i could bang it out in a week.
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