Has anyone tried adjusting the current limiter (Q4, R15, R16) to a higher current limit say 12A? Right now the setting is about 10A at 70% ACI gain. Adjusting the ACIG higher to 75% will allow for 12A on a 3A bias. By replacing R16 with 110 ohms on the current limiter and R21 to 619 ohms will set the current limit to 12A and ACIG to 75% respectively. I think this will help the A2 on dynamic load impedance dips to about 2 ohms. Source and sense resistors' should also be increased to 5W. A more muscular PSU and heatsinks will be needed too.
NP might have tried this...
NP might have tried this...
wuffwaff said:
I bit confused now - mr. Nelson says that with increasing ac-c-gain above 50% you'll get distortions, you say that by doing that you get less distortions ...
Bbbb ... ???
OK, it will be much easier for me when I'll have Aleph infront of me and I'll be able to do "real time" tests ....
Stabist said:
That's not what I said. If you are measuring distortion, the
higher gain on the current source always gives less measured
distortion. Below 50%, the current output will clip earlier, above
50% the AB point occurs earlier. All this depends on bias - if
you have more bias, both the clipping point and AB point
occur at higher levelss or not at all.
wuffwaff said:
William, that's what I meant in post#43. Adjustment of the current limiter to a higher value like 12A will mean less distortion when a speaker dips in impedance to say 2 ohms. At 69% ACI gain (stock A2 setting), this is the right setting to maximize the 10Apk on the current limiter and about 40V of the rails. 10A is enough for impedance dips of 4ohms but once it hits about 2ohms distortion sets in badly. 12Apk with 75% ACIG just about maximizes both +/- V and +/- I peaks before distortion sets in.
Other Alephs can be adjusted similarly. I am thinking of the Aleph 3 with an Aleph 5 power capability...maybe I should start a new thread.
- I did mixed up few terms ... Allright Hi,
If i understand it correctly the aleph-2 is at its best with an 8 Ohm load.
I like to build the Thor in the future, and its impendance is 4 Ohm with dips at 3 Ohms.
Is it possible to modify the aleph-2 for better performance at 4 Ohm without destroying its character, and which methode is the best.
1. Current gain settings.
2. Changing bias by removing R19.
3. Changing bias by lowering values of the source resistors.
4. Other possibilitys i would never think of.
Edwin.
If i understand it correctly the aleph-2 is at its best with an 8 Ohm load.
I like to build the Thor in the future, and its impendance is 4 Ohm with dips at 3 Ohms.
Is it possible to modify the aleph-2 for better performance at 4 Ohm without destroying its character, and which methode is the best.
1. Current gain settings.
2. Changing bias by removing R19.
3. Changing bias by lowering values of the source resistors.
4. Other possibilitys i would never think of.
Edwin.
Hi Edwin,
I think the A2 will work fine with 4 Ohm loads.
Changing ac-current-gain will alter the character so upping the bias is one good possibility. If you do this by changing the source resistors you will have a bit higher efficieny (less voltage loss over the source resistors).
Another possibilty would be to lower the power supply voltage to around 35 Volts and up the bias accordingly. This will give you the same dissipation and a lot more power into 4 Ohms.
William
I think the A2 will work fine with 4 Ohm loads.
Changing ac-current-gain will alter the character so upping the bias is one good possibility. If you do this by changing the source resistors you will have a bit higher efficieny (less voltage loss over the source resistors).
Another possibilty would be to lower the power supply voltage to around 35 Volts and up the bias accordingly. This will give you the same dissipation and a lot more power into 4 Ohms.
William
hi people!
For my understanding:
Which function has the pre-loading resistor at basis by aleph / ax ccs? Normally is it sufficiently without them, the current will be limited by basis-emitter voltage (~0.65V) across the source resistor. Or not?
I think about a trim-pot between basis and emitter and higher value of source resistor so i can set the bias better.
Has anyone tried this? Actually I tried an CCS for ax with 23V rail and 0,33 Ohm source resistor for 2A bias, 44W/FET (IRFP254) by 52°C heatsink temperature. My ax should have 8amps bias-> 4x 2devices parallel ~350W dissipation/ch
greetings
adam
For my understanding:
Which function has the pre-loading resistor at basis by aleph / ax ccs? Normally is it sufficiently without them, the current will be limited by basis-emitter voltage (~0.65V) across the source resistor. Or not?
I think about a trim-pot between basis and emitter and higher value of source resistor so i can set the bias better.
Has anyone tried this? Actually I tried an CCS for ax with 23V rail and 0,33 Ohm source resistor for 2A bias, 44W/FET (IRFP254) by 52°C heatsink temperature. My ax should have 8amps bias-> 4x 2devices parallel ~350W dissipation/ch
greetings
adam
wuffwaff said:
Hi William,
no i mean the resistor from the cap+ at collector (R-C-R) to base.
For example by AX (Grey´s schematic) is this 100k pot + 47,5k resistor.
NP used for source resistors by aleph´s values from 0,47 (Aleph 3) to 2.2 Ohm (Aleph 1). I think a higher value for source resistor helps by sharing the current between Fet´s.wuffwaff said:
greetings
Adam
Hi,
so you meant R19. This is used to reduce the bias with a given source resistor. You can leave it out for maximum bias.
My remark about the source resistors has nothing to do with the fact that they were used in previous designs. You´re right about the current sharing but they will cause larger voltage losses and lower efficiency.
William
so you meant R19. This is used to reduce the bias with a given source resistor. You can leave it out for maximum bias.
My remark about the source resistors has nothing to do with the fact that they were used in previous designs. You´re right about the current sharing but they will cause larger voltage losses and lower efficiency.
William
Being motivated by this thread, I have created a very compact PCB layout for Aleph30. I plan to build it, and more info can be found here:
http://www.diyaudio.com/forums/showthread.php?postid=595498#post595498
http://www.diyaudio.com/forums/showthread.php?postid=595498#post595498
Attachments
No, I'm still not getting bored, but I was thinking about a version of an Aleph that would look almost like a chip amp (at least sizewise)
It also seems like nobody really pushed the envelope of those amps yet, and that's what I'm hoping for with this minimalistic layout, very short signal path and possibly, more exotic components implemented.
This would also give me a better perspective, how chip amp compares to a single ended, class A design, implemented in a similar fashion. I was considering not more than lets say 4,700u capacitance with Aleph. This wouldn't be too low, wouldn't it?
It also seems like nobody really pushed the envelope of those amps yet, and that's what I'm hoping for with this minimalistic layout, very short signal path and possibly, more exotic components implemented.
This would also give me a better perspective, how chip amp compares to a single ended, class A design, implemented in a similar fashion. I was considering not more than lets say 4,700u capacitance with Aleph. This wouldn't be too low, wouldn't it?
I never mentioned chip amps are class A.
And never assume that something may seem too low. I'm presently using 100u only with my chip amp. For some people 1000 seemed too low, but even now, 100 is not too low, and has certain advantages over higher capacitance values.
But as a matter of fact, I was rather joking about 4,700u only, although I don't mind trying them like that. I have nice Sikorel caps ( 22,000/40 ) which seem perfect for that amp.
And never assume that something may seem too low. I'm presently using 100u only with my chip amp. For some people 1000 seemed too low, but even now, 100 is not too low, and has certain advantages over higher capacitance values.
But as a matter of fact, I was rather joking about 4,700u only, although I don't mind trying them like that. I have nice Sikorel caps ( 22,000/40 ) which seem perfect for that amp.
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