Hi!
I just need a final confirmation - during to some different reasons (mainly short of $$
) I've reached a decision to scale down a bit the first of my two A5 projects ...
So - I have soma "spare" transformers with 18V secondaries - that just calls the conversion into A3 😀
I have heatsinks that are capable of dissipate 200W/stereo (but 300W would be probably allready too much for them - and as said no $$$ to buy new at the moment) - again - A3.
And I have allready soldered PCB for A5 - but it's a "flexy PCB" - so the number of input fets can be variated 😀
I have enough PSU capacitors 😀 (at least something I'm not short off 😀)
So now I have two choices:
- direct scaled down A5 with 12 output transistors and just adjust necessary resistors because of lower PSU voltage
- make a sort of balanced input Aleph3 with 8 transistors, etc ...
I find second option better - I guess there is no need for those 2 additional pairs of transistors considering lower PSU rails ...
And if I'm correct - it's just important to match appropriate values for bias setting and voila - my "crosser" will be born 😀
I just need a final confirmation - during to some different reasons (mainly short of $$
) I've reached a decision to scale down a bit the first of my two A5 projects ... So - I have soma "spare" transformers with 18V secondaries - that just calls the conversion into A3 😀
I have heatsinks that are capable of dissipate 200W/stereo (but 300W would be probably allready too much for them - and as said no $$$ to buy new at the moment) - again - A3.
And I have allready soldered PCB for A5 - but it's a "flexy PCB" - so the number of input fets can be variated 😀
I have enough PSU capacitors 😀 (at least something I'm not short off 😀)
So now I have two choices:
- direct scaled down A5 with 12 output transistors and just adjust necessary resistors because of lower PSU voltage
- make a sort of balanced input Aleph3 with 8 transistors, etc ...
I find second option better - I guess there is no need for those 2 additional pairs of transistors considering lower PSU rails ...
And if I'm correct - it's just important to match appropriate values for bias setting and voila - my "crosser" will be born 😀
A-30
Build an A-30. Use all your transistors and crank up the bias.😎
I built one with 8 outputs per side and a 21-0-21 800va transformer with a C-R-C-R to drop the voltage to 26. I can't get it away from my son.
Build an A-30. Use all your transistors and crank up the bias.😎
I built one with 8 outputs per side and a 21-0-21 800va transformer with a C-R-C-R to drop the voltage to 26. I can't get it away from my son.
Hmm - is there big difference (I know - I will check it out in schematic) between A5 and A30 - because as said - A5 PCB is allready assembled together ...
Hmm - what I like most at A3 is 60W/4R - because my speakers have 5R ... I see A30 has "only" 40W ...
Well - what needs to be done is a little more deep look into things (now you've give me another option 😀) so ...
Well - what needs to be done is a little more deep look into things (now you've give me another option 😀) so ...
Thanks mr. Nelson - I've made a short comparison of A3, A30 and A5 schematic - in the topology itself there are really just few differences - and Ok, I would have (Ok that I would do anyway) to change few resistor values ...
Now I have these Q:
- how come A3 had such high capacitance bank in PSU??
- What limits A30 power in 4R comparing to A3?
Now I have these Q:
- how come A3 had such high capacitance bank in PSU??
- What limits A30 power in 4R comparing to A3?
Just to check it out - biases for original A3, A30 and A5 were??
I have in mind somethin like - A3 around 2,5A, A5 2,1A and A30 ??
I have in mind somethin like - A3 around 2,5A, A5 2,1A and A30 ??
2.5 or higher
Bias at 2.5 amps with 24 volts at the MOSFETs will give you 45 watts @5 ohms and 50 watts@ 4ohms.😀
Bias at 2.5 amps with 24 volts at the MOSFETs will give you 45 watts @5 ohms and 50 watts@ 4ohms.😀
Yep 😀
And 2,7A will give me magic 60W 😀 But also (according to that sheet) around 135W dissiptaion/channel 🙁 Which could allready be a little overdosed for my two heatsinks ...
BTW - another Q - if I use 4 heatsinks (like original Aleph) - BUT I mount transistors only on two (and so avoid long wirings) - but I DO connect all four heatsinks with massive Al "corner blocks" - will it spread the heat pretty proportional or will I get two HOT heatsinks and two medium warm ??
And 2,7A will give me magic 60W 😀 But also (according to that sheet) around 135W dissiptaion/channel 🙁 Which could allready be a little overdosed for my two heatsinks ...
BTW - another Q - if I use 4 heatsinks (like original Aleph) - BUT I mount transistors only on two (and so avoid long wirings) - but I DO connect all four heatsinks with massive Al "corner blocks" - will it spread the heat pretty proportional or will I get two HOT heatsinks and two medium warm ??
Now I don't understand it anymore at all ... 🙁
I've done some simulations with wuffwaff's excell sheet:
- if I take rail 34V, bias 2,5A and AC current gain 50% - i get 60W/8R BUT only 50W/4R (and the climax at 6R with 75W) ... Hmm - does that mean that in "real life" AC current is somewhere around 62-63% or what's wrong with my calculation??
And also - A3 - 25V rails, 2,5A bias and 50% - 30W/8R, again 50W/4R and climax at 4,5R with 58W.
So from this point of view - it's almost same for my speakers wheter i would made A3 or A5 ... ?!?!? Hmmm ...
I've done some simulations with wuffwaff's excell sheet:
- if I take rail 34V, bias 2,5A and AC current gain 50% - i get 60W/8R BUT only 50W/4R (and the climax at 6R with 75W) ... Hmm - does that mean that in "real life" AC current is somewhere around 62-63% or what's wrong with my calculation??
And also - A3 - 25V rails, 2,5A bias and 50% - 30W/8R, again 50W/4R and climax at 4,5R with 58W.
So from this point of view - it's almost same for my speakers wheter i would made A3 or A5 ... ?!?!? Hmmm ...
Just replace R19 and R21 (on A2 scem) with pots and adjust ac current gain and bias until you find the right balance of heat, and current gain to suit your needs, then measure and replace with fixed resistors.
Hi Primoz,
you´re right, to reach the specs at the specified bias it is neccessary to dial in a bit more ac-current-gain or a bit more bias.
William
you´re right, to reach the specs at the specified bias it is neccessary to dial in a bit more ac-current-gain or a bit more bias.
William
Hi Primoz,
either that or maybe the power into 4 ohms was lower. Just look at some old tests where power was measured.
William
either that or maybe the power into 4 ohms was lower. Just look at some old tests where power was measured.
William
Primoz,
the formula to calculate the ac current gain should be:
gain = (R1/R2)x(R3/R4)
where:
R1 = output sense resistor (A30: 0R47 / 6)
R2 = sorce resistor of aleph current source (A30: 0R47 / 3)
R3 = senseresistor of source of aleph current source (A30: 1k)
R4 = feedbackresistor of outpt sense resistors (A30: 820R)
=> (0,07833/0,15666)x(1000/820) = 0,5 x 1,2195 = 0,6097
=> ac current gain is ~ 61% with Aleph 30.
Uli
the formula to calculate the ac current gain should be:
gain = (R1/R2)x(R3/R4)
where:
R1 = output sense resistor (A30: 0R47 / 6)
R2 = sorce resistor of aleph current source (A30: 0R47 / 3)
R3 = senseresistor of source of aleph current source (A30: 1k)
R4 = feedbackresistor of outpt sense resistors (A30: 820R)
=> (0,07833/0,15666)x(1000/820) = 0,5 x 1,2195 = 0,6097
=> ac current gain is ~ 61% with Aleph 30.
Uli
COOL!
Now I'm learning something 😀
THANKS GUYS!!!
That will help me a lot in "constructing" my AlephCrosser 😀
Now I'm learning something 😀
THANKS GUYS!!!
That will help me a lot in "constructing" my AlephCrosser 😀
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