Uli: Thanks...I'm not a big technical book reader 
William:
I usually don't believe very much in burn in of components but in the case of my Aleph-X the offset voltage settled after a few days, say a week or so.
Don't know why or exactly what stabilized but the end result was better. I mean, in the first hours/days I had to adjust a lot and couldn't get the thing really stable. After a period these problems disappeared.
/Hugo
William:
I usually don't believe very much in burn in of components but in the case of my Aleph-X the offset voltage settled after a few days, say a week or so.
Don't know why or exactly what stabilized but the end result was better. I mean, in the first hours/days I had to adjust a lot and couldn't get the thing really stable. After a period these problems disappeared.
/Hugo
Hi,
I´m finally back home again and had quite some time to think about some changes I would like to make to change hum, and absolute DC behaviour.
One change I made just now was to make the feedback paths (wires) th same length and twist them lightly until they reach the circuit board. This helped a bit so now hum is only there with my ear against the woofer. From 10cm you can´t hear it anymore. If this is still too much for my other speakers I´m afraid I´ll have to shield my torobars and toriod.
On the subject of absolute dc offset it seems to me that it must be possible to make it a bit more temperature independant. Now it starts at 8V and goes to almost 0V within an hour. Leaving the top off or blowing some air onto the circuit board sees the offset go up again.
What I would like to try is to bias the zener a bit higher (from 3mA to 6mA) or maybe use a different kind of voltage reference.
Next up would be a lowering of the resistance from output to ground (now 4x390Ohms parallel to 5x or 6x) but I don´t really like it cause it will cost some output power.
If somebody has another method I would be pleased to hear it!
William
I´m finally back home again and had quite some time to think about some changes I would like to make to change hum, and absolute DC behaviour.
One change I made just now was to make the feedback paths (wires) th same length and twist them lightly until they reach the circuit board. This helped a bit so now hum is only there with my ear against the woofer. From 10cm you can´t hear it anymore. If this is still too much for my other speakers I´m afraid I´ll have to shield my torobars and toriod.
On the subject of absolute dc offset it seems to me that it must be possible to make it a bit more temperature independant. Now it starts at 8V and goes to almost 0V within an hour. Leaving the top off or blowing some air onto the circuit board sees the offset go up again.
What I would like to try is to bias the zener a bit higher (from 3mA to 6mA) or maybe use a different kind of voltage reference.
Next up would be a lowering of the resistance from output to ground (now 4x390Ohms parallel to 5x or 6x) but I don´t really like it cause it will cost some output power.
If somebody has another method I would be pleased to hear it!
William
Hi,
I tried two things since yesterday:
Upping the current through the zener from 3 to 6mA changed abs DC offset but not the way this changes over time so this is not the way.
Changing the output resistors to 5x390Ohms (78 ohm) had more effect. The offset now changes less from cold to warm and is below 1V after 20 minutes. Lowering the output resistors further will probably see an even better behaviour but I will leave it at this value for now.
The third possibility would be to change the 4k7 resistors to 3k9 or 3k3 but if I remember well this will also reduce the gain.
William
I tried two things since yesterday:
Upping the current through the zener from 3 to 6mA changed abs DC offset but not the way this changes over time so this is not the way.
Changing the output resistors to 5x390Ohms (78 ohm) had more effect. The offset now changes less from cold to warm and is below 1V after 20 minutes. Lowering the output resistors further will probably see an even better behaviour but I will leave it at this value for now.
The third possibility would be to change the 4k7 resistors to 3k9 or 3k3 but if I remember well this will also reduce the gain.
William
Try lowering the output R's a bit more.
I just went trough Nelson's comments on this matter and 30 ohm would be a minimum. Lower will start burning too much power.
If that doesn't help try lowering the 4.7k's. I could have a look but IIRC I used 3.9k. Worked very well, I never used the output R's.
Also, but I'm not sure anymore about this one: there is some kind of optimal bias point that stabilizes the Abs. offset. Go higher or lower and it starts drifting again. Bear with me for this last tip, it's just something from vague memory and could be wrong.
Edit: I had a quick look at the 4.7k's and it looks like I used 2k.
Indeed a bit low but it works.
/Hugo
I just went trough Nelson's comments on this matter and 30 ohm would be a minimum. Lower will start burning too much power.
If that doesn't help try lowering the 4.7k's. I could have a look but IIRC I used 3.9k. Worked very well, I never used the output R's.
Also, but I'm not sure anymore about this one: there is some kind of optimal bias point that stabilizes the Abs. offset. Go higher or lower and it starts drifting again. Bear with me for this last tip, it's just something from vague memory and could be wrong.
Edit: I had a quick look at the 4.7k's and it looks like I used 2k.
Indeed a bit low but it works.
/Hugo
Hi Hugo,
Thanks. I´ll try 3k9 and see what happens. Like I said, once warm the value stays more or less the same. It´s only the big difference between cold and warm that I don´t realy like. It starts at -6V now, is at -2V after 5 minutes and stays below 1V even after a few hours of idling.
William
Thanks. I´ll try 3k9 and see what happens. Like I said, once warm the value stays more or less the same. It´s only the big difference between cold and warm that I don´t realy like. It starts at -6V now, is at -2V after 5 minutes and stays below 1V even after a few hours of idling.
William
HI,
tried 3k9 and 3k3 for R46/47 without a lot of difference. Absolut Offset is below 1V after 40 minutes and then very slowly reaches 0V after heating up. I think I´ll leave it there for now. Diff offset stays at 12-16mV independent of these changes.
Changed C9 and C10 to 3n3 (from 4n7). Now I´ve got an almost perfect square wave on 6 Ohms, a bit of overshoot on 8ohms and a bit rounded on 4 Ohms.
Measured the gain for different loads and frequencies:
1kHz unbalanced in, 8Ohms: 19,81dB 2Ohms:19,29dB
10kHz unbalanced in, 8Ohms: 19,70dB 2Ohms:18,81dB
20kHz unbalanced in, 8Ohms: 19,64dB 2Ohms:18,43dB
100kHz unbalanced in, 8Ohms: 18,74dB 2Ohms:15,96dB
The gain for + and minus out wasn´t the same and always around 1.3dB lower for the minus out. I´m not shure what causes this..........maybe the unbalanced input?
Changing R46/47 from 4k7 to 3k9 didn´t change the gain.
Damping faktor is around 50 with these values.
William
P.S. still haven´t tried putting in C7 and C8
tried 3k9 and 3k3 for R46/47 without a lot of difference. Absolut Offset is below 1V after 40 minutes and then very slowly reaches 0V after heating up. I think I´ll leave it there for now. Diff offset stays at 12-16mV independent of these changes.
Changed C9 and C10 to 3n3 (from 4n7). Now I´ve got an almost perfect square wave on 6 Ohms, a bit of overshoot on 8ohms and a bit rounded on 4 Ohms.
Measured the gain for different loads and frequencies:
1kHz unbalanced in, 8Ohms: 19,81dB 2Ohms:19,29dB
10kHz unbalanced in, 8Ohms: 19,70dB 2Ohms:18,81dB
20kHz unbalanced in, 8Ohms: 19,64dB 2Ohms:18,43dB
100kHz unbalanced in, 8Ohms: 18,74dB 2Ohms:15,96dB
The gain for + and minus out wasn´t the same and always around 1.3dB lower for the minus out. I´m not shure what causes this..........maybe the unbalanced input?
Changing R46/47 from 4k7 to 3k9 didn´t change the gain.
Damping faktor is around 50 with these values.
William
P.S. still haven´t tried putting in C7 and C8
Banned
Joined 2002
Wuffwaff,
Have you tried adjusting one of the Drain resistors in the diff pair. By controlling the current to make it equal in each branch...that is 1/2 of the total bias current on the CCS. You could do it by replacing one Drain resistor with a trim pot and monitoring DC offset at the outputs. Or monitoring DC voltage across one Drain resistor while adjusting the other then just do ohm's law with the resistor/trim pot value. You might have done this before.
Allan
Have you tried adjusting one of the Drain resistors in the diff pair. By controlling the current to make it equal in each branch...that is 1/2 of the total bias current on the CCS. You could do it by replacing one Drain resistor with a trim pot and monitoring DC offset at the outputs. Or monitoring DC voltage across one Drain resistor while adjusting the other then just do ohm's law with the resistor/trim pot value. You might have done this before.
Allan
Jleaman,
ah well,
at the moment there´s only one and the sound (mono) through a Dynaudio Audience 42 is very promising.
I choose to do all my testing and trying on one example and after that I´ll start to finish the second one. Circuit boards don´t really like if you solder and desolder them frequently.
But sometime this week I hope to have the second one up and running.
Blues,
dc offset is only 12-16mV so no need to adjust the drain resistors. It´s the absolute dc-offset I was talking about.
This is also almost 0V but starts at a relatively high -6V.
William
ah well,
at the moment there´s only one and the sound (mono) through a Dynaudio Audience 42 is very promising.
I choose to do all my testing and trying on one example and after that I´ll start to finish the second one. Circuit boards don´t really like if you solder and desolder them frequently.
But sometime this week I hope to have the second one up and running.
Blues,
dc offset is only 12-16mV so no need to adjust the drain resistors. It´s the absolute dc-offset I was talking about.
This is also almost 0V but starts at a relatively high -6V.
William
finished the second board last night.
Killed two IRF9610 while matching
must be the very dry air (it´s very cold at the moment) causing more static activity.
I managed to get them to 0,002V (out of 25) at 20mA after 5 minutes. I hope this will give the same decent dc offset the other channel has.
I modified the AX bom file a bit so it now contains the resistor and capacitor values I used for my 12Fet 22V version. Will zip it later and put it here for download.
So now I only have to drill and tap the holes for the fets, hardwire the output stage and connect everything. I hope this will happen before Saturday.......
William
Killed two IRF9610 while matching
must be the very dry air (it´s very cold at the moment) causing more static activity.I managed to get them to 0,002V (out of 25) at 20mA after 5 minutes. I hope this will give the same decent dc offset the other channel has.
I modified the AX bom file a bit so it now contains the resistor and capacitor values I used for my 12Fet 22V version. Will zip it later and put it here for download.
So now I only have to drill and tap the holes for the fets, hardwire the output stage and connect everything. I hope this will happen before Saturday.......
William
the second one is running. Worked almost immediately (after I saw I had two BC550 put in the wrong way round......)
Rel offset <5mV
Absolute offset as in the other channel starting somewhere at 6V then going down.
7,2A bias, 105 watts/8Ohm, 149watts/ 4Ohms, 75watts/ 2Ohms
This one also displays some hum so I´m afraid I´ll have to do something about it (shielding?).
At the moment they are playing on my pair of dynaudios and sounding just fine. Will take them down sometime today.
William
first impressions
well,
it does sound different..........
Bass is just as deep as with my A5 but more controlled and punchy in the 80-100Hz range (a bit like my Crescendo in this region).
The midrange doesn´t have the bloom the A5 has, it sounds a bit cleaner and faster.
Highs are also show a bit more detail but are not harsh.
Depth is a big bigger.
The right channel is OK, the left one has a bit of hum with my ear against the speaker. Maybe fiddling around with input and feedback wires will help.
My AC-balanced power transformer surely is getting quite hot and humming along (mechanically). I will probably have to replace this or get another one to share the load.
At the moment the differences in sound are clear but, depending on the music, not always for the better. I will have to listen a bit more and let everything "burn in", play a bit with the ac-current-gain etc. etc. before I buy new transformers and change them into a pair of Aleph 2´s
William
well,
it does sound different..........
Bass is just as deep as with my A5 but more controlled and punchy in the 80-100Hz range (a bit like my Crescendo in this region).
The midrange doesn´t have the bloom the A5 has, it sounds a bit cleaner and faster.
Highs are also show a bit more detail but are not harsh.
Depth is a big bigger.
The right channel is OK, the left one has a bit of hum with my ear against the speaker. Maybe fiddling around with input and feedback wires will help.
My AC-balanced power transformer surely is getting quite hot and humming along (mechanically). I will probably have to replace this or get another one to share the load.
At the moment the differences in sound are clear but, depending on the music, not always for the better. I will have to listen a bit more and let everything "burn in", play a bit with the ac-current-gain etc. etc. before I buy new transformers and change them into a pair of Aleph 2´s
William
William,
Does your circuit include the common-mode feedback resistors as endorsed by NP and others? I think these along with the 30 ohms of resistors to ground at each output help tame some of the DC offset.
I've read from the AX thread they use resistors in the range of 1k to 5k from each output to the diff amp tied Sources.
Allan
Does your circuit include the common-mode feedback resistors as endorsed by NP and others? I think these along with the 30 ohms of resistors to ground at each output help tame some of the DC offset.
I've read from the AX thread they use resistors in the range of 1k to 5k from each output to the diff amp tied Sources.
Allan
William,
do i understand this right, the output is at 6V DC in the moment of turning on the amp and then dicrease to something like some mV immediately (like a turn on thump) or does it stay at 6V for some time and then dicrease by stabilising of the circuit ?
This would be a big concern to me because some speakers doesn´t like this behaviour.
Regards
Frank
do i understand this right, the output is at 6V DC in the moment of turning on the amp and then dicrease to something like some mV immediately (like a turn on thump) or does it stay at 6V for some time and then dicrease by stabilising of the circuit ?
This would be a big concern to me because some speakers doesn´t like this behaviour.
Regards
Frank
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