Banned
Joined 2002
Magnus,
2.94A really is quite a lot for a 30 but if your heatsinks are big enough and the power supply hasn´t got any problems I would leave it this way.
If not you can reduce the bias by lowering the value of the bias resistor. I also had 2.8A from when first firing up my Aleph 5 and lowerde R19 to about 38k. The cause for this higher bias is probably the lower hfe value of the BC550 I used instead of the ztx450.
william
2.94A really is quite a lot for a 30 but if your heatsinks are big enough and the power supply hasn´t got any problems I would leave it this way.
If not you can reduce the bias by lowering the value of the bias resistor. I also had 2.8A from when first firing up my Aleph 5 and lowerde R19 to about 38k. The cause for this higher bias is probably the lower hfe value of the BC550 I used instead of the ztx450.
william
Swede: I have A3 (modif. 30) too. It runs on 2.5A per rail. As have no possibility to match IRFs best as possible, I adjusted the current by different values of resistors ( from 0.33 to 0.68), bias current is about 0.87A ( +- 0.05) per T0247. I have much better heatsinks and it works (cools) good.I am afraid you heatsinks are too small for you current. I advise to go down.
Did you perform any measurements ( distorsion, etc.)? I noticed strage thing - high distorsion and different ration of harmonics - one channel with prevailing 2nd and second with 3rd. harmonics.
http://www.diyaudio.com/forums/showthread.php?threadid=4499
Your experience?
Did you perform any measurements ( distorsion, etc.)? I noticed strage thing - high distorsion and different ration of harmonics - one channel with prevailing 2nd and second with 3rd. harmonics.
http://www.diyaudio.com/forums/showthread.php?threadid=4499
Your experience?
Banned
Joined 2002
Aleph30 measurements again
Hi,
It was quite some time ago I did my initial measurements. Now when I have some real speakers to play on (finished my ProAc 2.5 clone project the other day) I had to assemble the second channel. No pictures yet, but I found out that one of the channels were a lot hotter than the other one. Both gets really hot, but I got the answer from Mr. Pass a couple of months ago, pointing towards the "BC550 transistor instead of ZTX450"-direction.
Here are the measurements:
Well I believe I dissipate 127W on the left channel and 93W if my calculations are right. I'd like to keep myself in the 100W playfield. I know I have quite a bad matching of the Q's on the left channel. (I wonder how bad it can be?)
So, my question (for which the answer I've been searching for on the forum for a while today) is:
Is it correct to lower the value of R19 to decrease the bias? Should I tamper with any other resistors?
Best regards,
//magnus
Hi,
It was quite some time ago I did my initial measurements. Now when I have some real speakers to play on (finished my ProAc 2.5 clone project the other day) I had to assemble the second channel. No pictures yet, but I found out that one of the channels were a lot hotter than the other one. Both gets really hot, but I got the answer from Mr. Pass a couple of months ago, pointing towards the "BC550 transistor instead of ZTX450"-direction.
Here are the measurements:
An externally hosted image should be here but it was not working when we last tested it.
Well I believe I dissipate 127W on the left channel and 93W if my calculations are right. I'd like to keep myself in the 100W playfield. I know I have quite a bad matching of the Q's on the left channel. (I wonder how bad it can be?)
So, my question (for which the answer I've been searching for on the forum for a while today) is:
Is it correct to lower the value of R19 to decrease the bias? Should I tamper with any other resistors?
Best regards,
//magnus
New measurements
Well...
We'll se how it turns out with R21. I did that aligatorclip thingie...
It turned out pretty good... Cool, I never thought of using a large value resistor in parallell with R19. R19//470k = 43.1k
It looks a lot better now.
UrSv, bring something nice for dinner when you get to my place tonight! I'm starving. ;=)
Best,
//magnus
Well...
We'll se how it turns out with R21. I did that aligatorclip thingie...
It turned out pretty good... Cool, I never thought of using a large value resistor in parallell with R19. R19//470k = 43.1k
It looks a lot better now.
An externally hosted image should be here but it was not working when we last tested it.
UrSv, bring something nice for dinner when you get to my place tonight! I'm starving. ;=)
Best,
//magnus
Hello Swede,
I've just replaced the trimmers for R19 and R21 on my Aleph 5 and they were quite different for left and right channel.
On the left R19 is 47k and on the right it`s 100k. Both values lead to 2.4A bias. The main influence is the difference in the source fets where the "sence resistor" is connected so when matching it would be intelligent to use values in the same range for left and right channel current source fets (I will do this for my upcoming monos).
R21 turned out to be 390R for both channels as an optimum value for sound quality with my speakers (about 2.5 ohms all the way). This means a ac current gain of a bit over 60% for 6.8A peak current (still 1A shy of the original Aleph5 spec wich was 8A). This value gives 52watts/8ohms and 90watts/4 Ohms
It is true what URSV said that the current gain is also affected by R19. When upping the bias from 2 to 2.4A, ac-current gain went from 50% to 43%. I think this is caused by the changed "input impedance" of the BC550/ZTX450 in combination with 19.
william
I've just replaced the trimmers for R19 and R21 on my Aleph 5 and they were quite different for left and right channel.
On the left R19 is 47k and on the right it`s 100k. Both values lead to 2.4A bias. The main influence is the difference in the source fets where the "sence resistor" is connected so when matching it would be intelligent to use values in the same range for left and right channel current source fets (I will do this for my upcoming monos).
R21 turned out to be 390R for both channels as an optimum value for sound quality with my speakers (about 2.5 ohms all the way). This means a ac current gain of a bit over 60% for 6.8A peak current (still 1A shy of the original Aleph5 spec wich was 8A). This value gives 52watts/8ohms and 90watts/4 Ohms
It is true what URSV said that the current gain is also affected by R19. When upping the bias from 2 to 2.4A, ac-current gain went from 50% to 43%. I think this is caused by the changed "input impedance" of the BC550/ZTX450 in combination with 19.
william
R21, how does it work?
Hmm...
I'm still not with you (yet). Can we take this slooow so even I can understand it.
Start with "what is it for, the R21?".
And what do you mean with the gain? I'm really interested, but have not yet got the grip of R21. I hope you don't think I'm stupid and uneducateable. ;=)
How do you calculate those 60% and the 6.8 amp.
I believe I know how you calculate the current though, but not the 60% (since I don't understand the figure/number).
Best,
//magnus
Hmm...
I'm still not with you (yet). Can we take this slooow so even I can understand it.
Start with "what is it for, the R21?".
And what do you mean with the gain? I'm really interested, but have not yet got the grip of R21. I hope you don't think I'm stupid and uneducateable. ;=)
How do you calculate those 60% and the 6.8 amp.
I believe I know how you calculate the current though, but not the 60% (since I don't understand the figure/number).
Best,
//magnus
Hi Swede,
Actual calculations are somewhat complicated it seems but implementation is easier. I think that essentially R21 measures the AC current in the negative part of the output stage and feeds that back to the current source which is then driven to share the work for the output current. Nelson replied in a previous thread:
"When you parallel devices in an Aleph but want to
vary the bias per device, you look to the value
of the Source resistances on the current source
(the bank on the positive half), and also (referring
to the Aleph 60 schematic) resistor R19.
After you get the DC figure you are looking for, you
want to adjust the AC gain of the current source so
that the current source provides about 50% of the
output AC current.
The easiest way to do this is to build the circuit
without R21 and operate it at 10 watts or so into a
load while measuring the AC voltage across R46-51
which are the Source resistors on the negative half
of the amp. Put in a value for R21 which halves
the AC voltage across R46-51, and you'll know that
the current source is doing half the work."
Hope this helps
/UrSv
Try:
http://www.diyaudio.com/forums/sear...id=68434&sortby=lastpost&sortorder=descending
Actual calculations are somewhat complicated it seems but implementation is easier. I think that essentially R21 measures the AC current in the negative part of the output stage and feeds that back to the current source which is then driven to share the work for the output current. Nelson replied in a previous thread:
"When you parallel devices in an Aleph but want to
vary the bias per device, you look to the value
of the Source resistances on the current source
(the bank on the positive half), and also (referring
to the Aleph 60 schematic) resistor R19.
After you get the DC figure you are looking for, you
want to adjust the AC gain of the current source so
that the current source provides about 50% of the
output AC current.
The easiest way to do this is to build the circuit
without R21 and operate it at 10 watts or so into a
load while measuring the AC voltage across R46-51
which are the Source resistors on the negative half
of the amp. Put in a value for R21 which halves
the AC voltage across R46-51, and you'll know that
the current source is doing half the work."
Hope this helps
/UrSv
Try:
http://www.diyaudio.com/forums/sear...id=68434&sortby=lastpost&sortorder=descending
Tony D., Swede,
current gain can be calculated by measuring the maximum output current.
For a current gain of 50% half of the output current is delivered by the current source so max. peak output current is twice the bias current.
So if the max. peak current is 6.7A and the bias is 2.4 A then the ac current gain is (6.7-2.4)/6.7x100%=64%
I came to this value by raising the current gain (lowering R21) until the sound coming out of the speakers didn´t sound "compressed" anymore. I´m still not shure what the actual effect is cause normally I don´t listen at these power levels. So at "normal" listening levels the current source won´t turn of but it will take a larger part of the current, leaving the bias current through the other fets more constant.
As soon as I´m able to set the bias to 4A I will know if it´s only the power that counts or if there are other effects too.
For a very good explanation of the circuit it would be good to read the patent a few times (or even more often).
william
current gain can be calculated by measuring the maximum output current.
For a current gain of 50% half of the output current is delivered by the current source so max. peak output current is twice the bias current.
So if the max. peak current is 6.7A and the bias is 2.4 A then the ac current gain is (6.7-2.4)/6.7x100%=64%
I came to this value by raising the current gain (lowering R21) until the sound coming out of the speakers didn´t sound "compressed" anymore. I´m still not shure what the actual effect is cause normally I don´t listen at these power levels. So at "normal" listening levels the current source won´t turn of but it will take a larger part of the current, leaving the bias current through the other fets more constant.
As soon as I´m able to set the bias to 4A I will know if it´s only the power that counts or if there are other effects too.
For a very good explanation of the circuit it would be good to read the patent a few times (or even more often).
william
Enlightenment!
Hi,
As usual, knowledge just makes you realize how little you know... ;=) Just when I thought I knew how an amp is working, this little master piece with just a handful of parts, it got back to me and demands some more investigation.
I've been reading old posts in the forum for an hour now, even though I should have gone to bed. The conclusion is that I now know that there is some really good use to change the R21 value. I also know that I will have a couple of more hours of reading the patents as well.
Thanks William and Urban. (by the way, thanks Urban for the food.)
I need (would like to have) more measuring equipment as well! Knowledge is really expensive nowdays...
Best,
//magnus
Hi,
As usual, knowledge just makes you realize how little you know... ;=) Just when I thought I knew how an amp is working, this little master piece with just a handful of parts, it got back to me and demands some more investigation.
I've been reading old posts in the forum for an hour now, even though I should have gone to bed. The conclusion is that I now know that there is some really good use to change the R21 value. I also know that I will have a couple of more hours of reading the patents as well.
Thanks William and Urban. (by the way, thanks Urban for the food.)
I need (would like to have) more measuring equipment as well! Knowledge is really expensive nowdays...
Best,
//magnus
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