| cowanrg |
| 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? |
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| janneman |
Why take the risk? Figure out the right pinout, check it, and fix if necessary. If you don't do that and it still doesn't work after reversing, what have you learned? Nothing.
Jan Didden |
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| cowanrg |
hehe, true.
im just being overly worried because ive had so many problems getting this amp working. |
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| janneman |
Exactly. It's time to do it right for a change..;) ..don't take it too personal.
Jan Didden |
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| cowanrg |
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...
| quote: | Originally posted by janneman
Exactly. It's time to do it right for a change..;) ..don't take it too personal.
Jan Didden |
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| xcel |
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;) |
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| metalman |
| 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. |
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| Nelson Pass |
Actually, if you reverse Collector for Emitter, it should work,
but the breakdown voltage is low. |
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| Blues |
| as in my other post to you...to check q104 and 105, reversing it on your aleph 3 could be the problem and the B-E junction of 0.5V is fed into gates of q106-109. The 1.5V you are getting across r120-123 is the B-C junction voltage instead. |
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| cowanrg |
i think that did it...
it appears to be working fine. i need to measure current draw, it isnt getting horribly hot. BUT, maybe before it was just getting TOO hot.
this was one LONG troubleshooting period! |
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| dieringe |
| quote: | Originally posted by cowanrg
i need to measure current draw |
:eek:
I think you should ALWAYS measure the current if nothing else until you have listened to music for at least 5 hours!
At least that's what I do...
m. |
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| cowanrg |
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. |
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| highbias |
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 |
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| cowanrg |
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 :) |
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| wuffwaff |
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. |
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| highbias |
WOW! I am glad that you posted that. I don't recall reading about it on this site over the last two years but then I don't get here every day either and probably don't read most of the posts. I will do a search and report back here.
Mark |
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| Brian Donaldson |
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 |
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| cowanrg |
i think ill set it to thermal limits. they will dictate what i can do better than anything else.
wuffwaff,
i couldnt tell if you were trying to be a d*ck with that comment or not? |
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| wuffwaff |
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 |
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| Brian Donaldson |
Yes, I have the same understanding of limits. I didn't mean set the current gain to limit pos current at the same current as neg. I suggest setting bias as high as your heat sinks can take, then setting current gain so current limits for the pos with speakers load equals voltage limit for neg swing.
Ex.
36 v rails gives output max (neg) 32v
32v @ 8 ohm = 4 amp
your max bias 2.6A
set current gain to allow pos swing to give 3.9 amps
These are arbitrairy numbers I made up for easy math. |
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| wuffwaff |
Brian,
now I understand what you mean.
In this example you´ve set ac-current gain to below 50% (2.6A would give 5.2A at 50% ac-current gain) but what if (like in my case) you have to set the ac-current -gain to very high values to reach the current at a given voltage?
What do you think is the advantage of doing it this way and not going for 50%?
william |
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| JacekPlacek |
| quote: | Originally posted by Brian Donaldson
Yes, I have the same understanding of limits. I didn't mean set the current gain to limit pos current at the same current as neg. I suggest setting bias as high as your heat sinks can take, then setting current gain so current limits for the pos with speakers load equals voltage limit for neg swing.
Ex.
36 v rails gives output max (neg) 32v
32v @ 8 ohm = 4 amp
your max bias 2.6A
set current gain to allow pos swing to give 3.9 amps
These are arbitrairy numbers I made up for easy math. |
| quote: | Originally posted by wuffwaff
Brian,
now I understand what you mean.
In this example you´ve set ac-current gain to below 50% (2.6A would give 5.2A at 50% ac-current gain) but what if (like in my case) you have to set the ac-current -gain to very high values to reach the current at a given voltage?
What do you think is the advantage of doing it this way and not going for 50%?
william |
Maybe my question is not strictly concerned with considered problem but did anyone of You measure dumping factor with ac current gain about 50% and with higher gain ?
My expierences based on Aleph3 but with one output transistor not pair but with DC bias set to 2A gives me "poor" ( about 40 not 100 as it should) dumping factor and asymethric cliping for loads much lower than 8 Ohm ( 3.4 Ohm in my case which is lowest impedance of my speakers).
Seting ac current gain to
about 70% gives me dumping factor about 90 and more symethrical clipping. What do You think about that ?
Regards
Jacek |
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| cowanrg |
| its interesting that an a topic thats been discussed at least 50 times on the forum and can easily found be searching even needs to be discussed ;) |
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| Brian Donaldson |
Wuffwaff, you're right again, you could set the current gain higher and have more current if needed and a higher damping factor. My alephs were not used for bass, and I listened and tweeked to get what I liked. my choice was the lower AC gain number with higher bias. My point was that symetric clipping for your load is a good way to set the amp up. Also if you're under heatsinked, you can get the extra output with current gain and not melt.
It's DIY, play with it. Tour mom won't tell you it's nasty;) |
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| JacekPlacek |
| quote: | Originally posted by cowanrg
its interesting that an a topic thats been discussed at least 50 times on the forum and can easily found be searching even needs to be discussed ;) |
Searcher found only 5 threads where there are dumping factor
words and I did not find in them any what concerns in satisfied way my question. Do You imagine I will be reading manually all threads ? :-)
If You know tell me what threads say about my problem
BTH I have impression that many people build different Alephs without checking electrical parameter of their constructions. I'm almost sure that their clones do not work enough good as they could. Faith makes miracles.
Regards
Jacek |
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| wuffwaff |
Jacek,
maybe you should search for "damping factor";) ;) ;) :) :) :) :)
william |
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| JacekPlacek |
| quote: | Originally posted by wuffwaff
Jacek,
maybe you should search for "damping factor";) ;) ;) :) :) :) :)
william |
I feel confused :-) Such clerical mistake... I simply wrote it as I spell in Polish language.
Regards
Jacek |
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| uli |
| quote: | Originally posted by wuffwaff
Jacek,
maybe you should search for "damping factor";) ;) ;) :) :) :) :)
william |
MMMMMMMUUUUUUUUHAHAHAHAHAHA
:devilr: :devilr: :devilr: :devilr: :devilr: :devilr: :devilr: :devilr:
Uli
:nod: :nod: :nod: |
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