Ok - to summarize my problem with Absolute DC Offset
I can acheive an Absolute DC offset of close to 0 volts only when the voltage drop across R23 and R25 is in excess of 4.95 volts and also results in the voltage across the source and output resistors to go all the way up to .63 volts.
When I reduce the current through the CCS by increasing VR2 the absolute DC jumps up to 7 to 8 volts.
If I am not mistaken an ideal situation would be to run the amp with voltage across R23 and R25 between 4 to 4.5 perhaps and the voltage across source and output resistors to be around .5 volts
Let me know if I am not being clear and if I need to express this with more details.
I can acheive an Absolute DC offset of close to 0 volts only when the voltage drop across R23 and R25 is in excess of 4.95 volts and also results in the voltage across the source and output resistors to go all the way up to .63 volts.
When I reduce the current through the CCS by increasing VR2 the absolute DC jumps up to 7 to 8 volts.
If I am not mistaken an ideal situation would be to run the amp with voltage across R23 and R25 between 4 to 4.5 perhaps and the voltage across source and output resistors to be around .5 volts
Let me know if I am not being clear and if I need to express this with more details.
voltage across R23 and R25 isn't reference in any way , except in case when amp is broken and need checking of every value .
1. decide what's Iq you wish to have through output mosfets
2. place voltmeter across R41 or R6 , and set desired Iq with Vr2 ; condition is to have min 10mA through each LTP side (3V92 across 390ohms) whatever Iq you choose
3. place voltmeters as needed and set offsets with VR1 and VR3 ; if you can't achieve that , write here what polarity of offset you have and I'll tell you what to alter
and please - write here what's absolute and what's relative offset .... I just can't remember which one is which
1. decide what's Iq you wish to have through output mosfets
2. place voltmeter across R41 or R6 , and set desired Iq with Vr2 ; condition is to have min 10mA through each LTP side (3V92 across 390ohms) whatever Iq you choose
3. place voltmeters as needed and set offsets with VR1 and VR3 ; if you can't achieve that , write here what polarity of offset you have and I'll tell you what to alter
and please - write here what's absolute and what's relative offset .... I just can't remember which one is which
Zen Mod
The absolute offset is measured across the Out+ to Ground and Out- to Ground and the relative DC offset is measure across Out+ and Out-
The IQ I would like to have is around 1.1 amp through each output Mosfet which over a .47 ohm resistor works out to .52 volts
If I adjust VR2 to give me .52 volts then the Absolute DC Offset jumps up to 8 volts.
On the other hand if I reduce VR2 such that I get 4.95 volts across R23 which is about 12.7 ma, I get .63 volts across the Output resistors (R6, R41) resulting in a Mosfet current of 1.34 amps and the Absolute DC Offset is down to under 100 mv
How do I reduce the mosfet current to 1.1 amps keeping the Absolute DC under 100mv? I could reduce R23 and R25 from 390 ohms to 330 ohms so the voltage across them drop from 4.95 down to 4.3 volts keeping the current at 12.7 ma through Q5/Q7. Not sure if this is the correct thing to do and if doing this will solve the problem.
The absolute offset is measured across the Out+ to Ground and Out- to Ground and the relative DC offset is measure across Out+ and Out-
The IQ I would like to have is around 1.1 amp through each output Mosfet which over a .47 ohm resistor works out to .52 volts
If I adjust VR2 to give me .52 volts then the Absolute DC Offset jumps up to 8 volts.
On the other hand if I reduce VR2 such that I get 4.95 volts across R23 which is about 12.7 ma, I get .63 volts across the Output resistors (R6, R41) resulting in a Mosfet current of 1.34 amps and the Absolute DC Offset is down to under 100 mv
How do I reduce the mosfet current to 1.1 amps keeping the Absolute DC under 100mv? I could reduce R23 and R25 from 390 ohms to 330 ohms so the voltage across them drop from 4.95 down to 4.3 volts keeping the current at 12.7 ma through Q5/Q7. Not sure if this is the correct thing to do and if doing this will solve the problem.
what is voltage across 390 ohms resistors when you have 1,1A Iq (0.52V across R41 or R6 )
if you are around 20mA through LTP (10 per leg ) everything is fine ;
so - first solving this part : while having 10mA through each leg of LTP , having 1.1A Iq
if needed - slightly decrease both 390 ohms resistors ( solder some in parallel , there is no need for jumping down to 330)
then - set offsets fiddling with VR1 and VR3 ; if offset is still on positive side , decrease both R11 and R33
after you manage all these ....... then is the time for setting AC gain .....
if you are around 20mA through LTP (10 per leg ) everything is fine ;
so - first solving this part : while having 10mA through each leg of LTP , having 1.1A Iq
if needed - slightly decrease both 390 ohms resistors ( solder some in parallel , there is no need for jumping down to 330)
then - set offsets fiddling with VR1 and VR3 ; if offset is still on positive side , decrease both R11 and R33
after you manage all these ....... then is the time for setting AC gain .....
Thanks for the quick reply.
I will double check the voltage across R23, don't have access to the amp right now.
I think the voltage was around 4.5v across R23 which works out to about 11.5 ma with voltage across R6 at .52
I will set things back to get the above readings and then decrease R11 and R33 (I think you meant R33 in your post not R13 right?). Lets hope that solves the problem with the Abs DC offset.
I will double check the voltage across R23, don't have access to the amp right now.
I think the voltage was around 4.5v across R23 which works out to about 11.5 ma with voltage across R6 at .52
I will set things back to get the above readings and then decrease R11 and R33 (I think you meant R33 in your post not R13 right?). Lets hope that solves the problem with the Abs DC offset.
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when you have "proper " bias through outputs , but offset is positive - that means that Aleph CCS-es are more "open" than needed ( programmed for more current than is going through lower mosfets) .
in that case you need to close down Aleph CCS-es , decreasing value of b-c resistance , of their programming bjt's ;
so - decreasing value of R11+VR1 chain ( on one side ) and R33+VR2 chain ( on other side) ;
if happens that you knock VR's to zero , that means that you need to decrease value of their adjacent resistors
simple , isn't it ?
in that case you need to close down Aleph CCS-es , decreasing value of b-c resistance , of their programming bjt's ;
so - decreasing value of R11+VR1 chain ( on one side ) and R33+VR2 chain ( on other side) ;
if happens that you knock VR's to zero , that means that you need to decrease value of their adjacent resistors
simple , isn't it ?
I did as you recommended, reduced R11 and R33 to 10K and managed to bring the bias current on the mosfets down to 1.2 amps with the Absolute DC offset under 25 mv stable for 5 to 6 hours! The voltage across R23 and R25 continued to be 4.9 volts. The amp sounds very good and I am wondering if I should live with the 4.9 volts across R25/R25, given that everything else is in perfect order.
In any case, I tried to achieve the same result by increasing VR2 and brought the voltage across R23/R25 down to 4.3 volts - but this resulted in the absolute voltage jumping up to 8 volts. I couldn't go down to 4.0 volts across R23/R25 as the VR2 was at the upper limit. Then I tried to remove a resistor I had in parallel with R26 and forgot to put the amp off while soldering.
Next thing I know, the mosfets turned off, and I was seeing only .7 volts on R25 and 4.3 volts on R23. I suspect somethings gone horribly wrong, will need to figure out what device went Kaput. I already replaced Q5 and Q7 and it didn't help. So it's some other device - will investigate further and report back.
Thanks for all the help. I think I should soon have a working amp 🙂
In any case, I tried to achieve the same result by increasing VR2 and brought the voltage across R23/R25 down to 4.3 volts - but this resulted in the absolute voltage jumping up to 8 volts. I couldn't go down to 4.0 volts across R23/R25 as the VR2 was at the upper limit. Then I tried to remove a resistor I had in parallel with R26 and forgot to put the amp off while soldering.
Next thing I know, the mosfets turned off, and I was seeing only .7 volts on R25 and 4.3 volts on R23. I suspect somethings gone horribly wrong, will need to figure out what device went Kaput. I already replaced Q5 and Q7 and it didn't help. So it's some other device - will investigate further and report back.
Thanks for all the help. I think I should soon have a working amp 🙂
Hi
I have a Aleph-x Rev 1 PCB that is semi complete.
Where can I purchase matched components for the board?
Lastly is there a better or more improved PCB available?
Thanks
Jozua
I have a Aleph-x Rev 1 PCB that is semi complete.
Where can I purchase matched components for the board?
Lastly is there a better or more improved PCB available?
Thanks
Jozua
What do you need?
I can help you with the matched IRFP240; if you prefer buying from the US, Jack (TechDIY) might be an option too.
Hannes
I HAD AN ALEPH-X
AND TRY TO HAVE THE PERFECT WAVE DAC FROM PS-AUDIO
AND IT TOLD THAT IT HAS 5.6 VOLT MAXIMUM OUTPUT VOLTAGE RMS
SO WILL IT BE GOOD TO DRIVE ALEPH-X WITHOUT PREAMP?
AND TRY TO HAVE THE PERFECT WAVE DAC FROM PS-AUDIO
AND IT TOLD THAT IT HAS 5.6 VOLT MAXIMUM OUTPUT VOLTAGE RMS
SO WILL IT BE GOOD TO DRIVE ALEPH-X WITHOUT PREAMP?
Voltage schematic Aleph-x Grey
Hi guys,
Has anybody got a similar schematic with some reference volages for the Grey's version (about 34-40W output).
Cheers!
Hi guys,
Has anybody got a similar schematic with some reference volages for the Grey's version (about 34-40W output).
Cheers!
hi Zen Mod
thank you i have done my homework measuring and routing all my aleph X..
it is supposed to use Kristijan schematic, they are so much a like with a little differences..
im a little confused about measuring voltage wheter its AC or DC..
V AC accross Current source resistor are the same with paralleled Output resistor which is 0.019V AC
(i keep getting random reading with my el cheapo DMM arround 0.011VAC - 0.019VAC, but they are the same V both side when i measure it at the same time)
Voltage Accross Current Source Resistor are about 480mv DC - 500mv DC.. you can see on schematic below for each irfp240
input are like greys sch i see 4 diode's for each channel. but at pin 2 (GND) there no resistor to ground and from ground to diode's. i think they straight go to ground. see my attachment below..
notice big difference in resistor after trimpot original sch say its 75k and in my amp its only 15K..
are there any problem in my amp? becoz i think its output are very low
Bias can't be increase further even the pot is not turn to max
From the circuit above. I change the rail voltage from 22 to 15V, remove output device to only one pair per side(Grey's version)
However, bias per device can only turn to 1A instead of 1.5A, I think the two resistors 1.5K bias the Bc550 need to change, any sugguestion on the value?
From the circuit above. I change the rail voltage from 22 to 15V, remove output device to only one pair per side(Grey's version)
However, bias per device can only turn to 1A instead of 1.5A, I think the two resistors 1.5K bias the Bc550 need to change, any sugguestion on the value?