ok, so after my long struggle, i think ive ACTUALLY found out what's wrong. i noticed that i have both MPSA18's and BC546's in my parts bin. the BC546's leads are backwards compared to the MPSA18's. I THINK i have the MPSA18's in backwards! i was looking the other's data sheet for some reason when i installed them. can the amp still work with this in backwards? i dont want to reverse it and blow the amp. ive had oversights before, so it might be right afterall... so, can i hurt anything by reversing it?
haha, i hear ya. since ive started this, everything ive "fixed" has created a worse problem. im just paranoid.
it seemed to have worked. my test speakers are fried, gonna go see if i can get some new ones! it measures ok i guess...
it seemed to have worked. my test speakers are fried, gonna go see if i can get some new ones! it measures ok i guess...
janneman said:Exactly. It's time to do it right for a change....don't take it too personal.
Jan Didden
I've had the same problem (reversed transistors, in my case BC550C).
The effect; the current sources didn't function thereby prohibiting the entire amp to function properly.
My advice (just like Janneman's) would be not to fool around, but fix it rightaway. I've been there and I've done that. Works like a charm ......
Xcel
The effect; the current sources didn't function thereby prohibiting the entire amp to function properly.
My advice (just like Janneman's) would be not to fool around, but fix it rightaway. I've been there and I've done that. Works like a charm ......
Xcel
It is amazing how small things can cause big problems. Don't get too frustrated, as you're not the only one to have struggled with troublesome problems. If you want some commiseration, read my troubles getting my headphone amp up and running here where noise in the temporary test PS was causing wierd behaviour. I didn't figure it out until I gave up trying to solve it and built my final PS, at which point the problems dissappeared.
hmmmm,
i measured current draw off the + rail, and it measured 1.836A. its supposed to be about 2.2A right? that was at idle, and under full load it was around 1.76A or so. is that anything to worry about, or is it close enough? it is running much cooler now, so i was thinking of increasing the bias until it gets a bit hotter.
i measured current draw off the + rail, and it measured 1.836A. its supposed to be about 2.2A right? that was at idle, and under full load it was around 1.76A or so. is that anything to worry about, or is it close enough? it is running much cooler now, so i was thinking of increasing the bias until it gets a bit hotter.
Great you've fixed it!! The higher the bias the better it will sound. Just watch the sink temperature very close. Replace R-113 with a 100K trimmer set to 50K to start out. Raise the resistance to increase the bias current and temperature. I removed this resistor completely from my 2's! Also check the AC current gain and adjust R-114 as necessary so that it clips symetrically.
Mark
Mark
haha, cool!
that was my next question. i just bought a 100k linear pot that will mount nicely on the backside of the case for on-the-fly adjustments. (sometimes when i just want to watch tv, i can turn it down i guess).
"Also check the AC current gain and adjust R-114 as necessary so that it clips symetrically."
i dont get what you are saying there... i get "measure ac current", but how do i adjust R114 "so that it clips symetrically."
once again, you guys give me too much credit
that was my next question. i just bought a 100k linear pot that will mount nicely on the backside of the case for on-the-fly adjustments. (sometimes when i just want to watch tv, i can turn it down i guess).
"Also check the AC current gain and adjust R-114 as necessary so that it clips symetrically."
i dont get what you are saying there... i get "measure ac current", but how do i adjust R114 "so that it clips symetrically."
once again, you guys give me too much credit
Highbias,
setting ac-current-gain so that it clips symmetrically is not the way to do it!
This means that you will have a very high ac-current-gain and your max current matches the one set by the current limiter on the negative side.
An Aleph should always clip on the positive side (when current limited).
The current limiter on the negative side is only there to protect the amp in case of a shortcut and should never come into action when listening to music.
Cowanrg,
just set ac-current-gain as explained for at least 50 times on this forum.
setting ac-current-gain so that it clips symmetrically is not the way to do it!
This means that you will have a very high ac-current-gain and your max current matches the one set by the current limiter on the negative side.
An Aleph should always clip on the positive side (when current limited).
The current limiter on the negative side is only there to protect the amp in case of a shortcut and should never come into action when listening to music.
Cowanrg,
just set ac-current-gain as explained for at least 50 times on this forum.
I would respectfully disagree with Wuffwaff's remarks on current gain setting.
I would set standing bias as high as you dare (within thermal limits) then set current gain so the positive swing doesn't current starve (too much) before the negative swing voltage limits into a load equal to you speakers.
in other words, set to the threshold of current limiting pos swing
I would set standing bias as high as you dare (within thermal limits) then set current gain so the positive swing doesn't current starve (too much) before the negative swing voltage limits into a load equal to you speakers.
in other words, set to the threshold of current limiting pos swing
Cowangr,
no, just didn´t feel like writing something you could find by a simple search.
Brain,
the clipping on the positive side is influenced by two things:
rail voltage
peak current (set by bias and ac-current-gain)
the clipping on the negative side is influenced by:
rail voltage
setting of the current limiter
As long as there´s no current limited (pos or neg) the clipping should be symmetrical. When current is limited it should be on the positive side, otherwise you will throw away available power. If it clips first on the negative side you should adjust the neg current limiter!
By setting the clipping symmetrical (you can only do this for one load) you adjust your ac-current-gain to fit the negative current limiter (wich is only used to protect the amp). This will only by accident give 50%. You will end up with 70 or 80% ac-current-gain as the neg current limiter is normally set with quite a margin!
William
no, just didn´t feel like writing something you could find by a simple search.
Brain,
the clipping on the positive side is influenced by two things:
rail voltage
peak current (set by bias and ac-current-gain)
the clipping on the negative side is influenced by:
rail voltage
setting of the current limiter
As long as there´s no current limited (pos or neg) the clipping should be symmetrical. When current is limited it should be on the positive side, otherwise you will throw away available power. If it clips first on the negative side you should adjust the neg current limiter!
By setting the clipping symmetrical (you can only do this for one load) you adjust your ac-current-gain to fit the negative current limiter (wich is only used to protect the amp). This will only by accident give 50%. You will end up with 70 or 80% ac-current-gain as the neg current limiter is normally set with quite a margin!
William
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