Back to the first post of this thread:
Did some mods, and the power supply now is +/-22V
The total bias is 7.78A
The AC current gain is 50%.
The number of fets is 16.
This is all for 1 channel, and according to berekening.xls I am supposed to have 100W into 8ohm and 121W into 4ohm.
The reality however, is different.
8ohm: 59W (19V*3.1A)
4ohm: 30W (10V*3A)
measured with a true RMS-DMM just before clipping.
I took pictures of the XY-axis scope result.
The amp is playing extremely well at low volume.
What could be wrong?
The first picture shows the result at 8ohm.
/Hugo
Did some mods, and the power supply now is +/-22V
The total bias is 7.78A
The AC current gain is 50%.
The number of fets is 16.
This is all for 1 channel, and according to berekening.xls I am supposed to have 100W into 8ohm and 121W into 4ohm.
The reality however, is different.
8ohm: 59W (19V*3.1A)
4ohm: 30W (10V*3A)
measured with a true RMS-DMM just before clipping.
I took pictures of the XY-axis scope result.
The amp is playing extremely well at low volume.
What could be wrong?
The first picture shows the result at 8ohm.
/Hugo
Attachments
Netlist,
seems like you don´t have enough ac current gain and 3A is the max you can get out of the amp.
What you can try is to measure clipping voltage with no or a very high load (the output to ground resistors for example). If you get around 28V (40 volts peak) then at least this part of the amp is ok.
Now you´ll have to see why you don´t get more than 3A . 3A would mean 4.2A peak current and a total of 4.2A bias (both sides) at 50% ac-current gain.
If as you say you´ve got 7.8 A you should have 7.8A peak and 5.5A rms. Since you only have 3A rms your ac-current-gain is only around 10%.
william
seems like you don´t have enough ac current gain and 3A is the max you can get out of the amp.
What you can try is to measure clipping voltage with no or a very high load (the output to ground resistors for example). If you get around 28V (40 volts peak) then at least this part of the amp is ok.
Now you´ll have to see why you don´t get more than 3A . 3A would mean 4.2A peak current and a total of 4.2A bias (both sides) at 50% ac-current gain.
If as you say you´ve got 7.8 A you should have 7.8A peak and 5.5A rms. Since you only have 3A rms your ac-current-gain is only around 10%.
william
Try this...
Something I've noticed (actually picked up from our learned friends on this forums) and might be something for you to look at is your PSU...
Your power supply construction has a LOT to do with the amp's ability to reproduce complex high frequencies (as found with female voices TA and Nora Jones). I noticed with my Aleph 5 that it's high frequency reproduction ability is severely hampered by not having smaller (faster) caps in parallel over the larger, electrolytic reservoirs. Nelson has a very good article about PSU construction that speaks of the finer details around this subject.
All boils down to the fact that the larger caps are not able to deliver the current (due to "internal impedance" and "induction") at the speed which the higher power, high frequencies require. Having a 10uF, a 1uF and a 0.1 uF over your cans makes one huge difference. If you have these check them for faults and play around with them.
Keep in mind that the X amp is basically a double-aleph construction - it is the secondary stage of an Aleph mirrored and shared from the same LTP input stage. This means that double the PSU speed could be required at some stages of music reproduction. You might be better off having these bridging caps applied to your positive side and negative side seperately.
I don't know what your PSU looks like but I bet this is part of your problem - if not the main culprit.
Let us know.
Vossie
Something I've noticed (actually picked up from our learned friends on this forums) and might be something for you to look at is your PSU...
Your power supply construction has a LOT to do with the amp's ability to reproduce complex high frequencies (as found with female voices TA and Nora Jones). I noticed with my Aleph 5 that it's high frequency reproduction ability is severely hampered by not having smaller (faster) caps in parallel over the larger, electrolytic reservoirs. Nelson has a very good article about PSU construction that speaks of the finer details around this subject.
All boils down to the fact that the larger caps are not able to deliver the current (due to "internal impedance" and "induction") at the speed which the higher power, high frequencies require. Having a 10uF, a 1uF and a 0.1 uF over your cans makes one huge difference. If you have these check them for faults and play around with them.
Keep in mind that the X amp is basically a double-aleph construction - it is the secondary stage of an Aleph mirrored and shared from the same LTP input stage. This means that double the PSU speed could be required at some stages of music reproduction. You might be better off having these bridging caps applied to your positive side and negative side seperately.
I don't know what your PSU looks like but I bet this is part of your problem - if not the main culprit.
Let us know.
Vossie
Thanks everyone, Highly appreciated.
I live with my AlephX for a few weeks now, and did some more listening test and tweaks. The former TA problems are gone now.
I will come back on the details later, and will try to post a more final version of the mods than is possible now.
I certainly have to change the big PSU caps to a higher voltage rating and I will try the bypass caps too. For the moment I only have four 330nF caps over the diode bridge.
The first five minutes, when the amp is still cold, I hear a small hum. In time I would like to add some nice chokes to the PSU, hoping the hum disappears completely.
You can find picture and more details of the amp here:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=14979
Thanks again for you input.
/Hugo
I live with my AlephX for a few weeks now, and did some more listening test and tweaks. The former TA problems are gone now.
I will come back on the details later, and will try to post a more final version of the mods than is possible now.
I certainly have to change the big PSU caps to a higher voltage rating and I will try the bypass caps too. For the moment I only have four 330nF caps over the diode bridge.
The first five minutes, when the amp is still cold, I hear a small hum. In time I would like to add some nice chokes to the PSU, hoping the hum disappears completely.
You can find picture and more details of the amp here:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=14979
Thanks again for you input.
/Hugo
Any caps could work
You don't have to go for the best caps (or most expensive ones) on the shelf. Give it a go with the normal 250v /??uF caps used for ripple smoothing over AC loads. Even they make a difference and I have not been able to pick up an audible difference between them and the melalised film caps for example.
The best to do is to give it a "calculated try" and see what happens...
Vossie
You don't have to go for the best caps (or most expensive ones) on the shelf. Give it a go with the normal 250v /??uF caps used for ripple smoothing over AC loads. Even they make a difference and I have not been able to pick up an audible difference between them and the melalised film caps for example.
The best to do is to give it a "calculated try" and see what happens...
Vossie
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