Aleph-X builder's thread

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#402
Voltage over R2, R3, R42,R43 drops only when current is flowing throu the speaker and that means this is only AC, so in normal quiet state there is no DC drop at those resistors. Tell me the voltages over: R5, R6, R40 , R41; they schoul be equal arround 400..600 mV depending on biasing. But they schould be as close together as possible, assuming the Q1,Q2,Q10&Q11 were matched properly and VR1 & VR3 were setup properly.

Do you get heat on transistors Q1,Q2,Q10,Q11?

Piotr
 
#403
The voltages are around R5=( 0,410 & 0,405 ) R6= ( 0,415 & 0,420 ) R40= ( 0,430 & 0,432 ) R41= ( 0,440 & 0,441 )

mosfets a gething hot...whell the heatsinks a hething hot...I cant tach mosfets bacause they have some AL bar over it, so i dont kow how hot they are...

I have only put 16V but I was calculating with 20V at the end ( source resistors are 0.5 Ohm... )
 
#405
And still NO SOUND. . . :scratch: 😱
Are the X crossing not miss-matched? I mean, are R23&R25 corectly driving the adequate output branches? Neglecting to this will cancel AC gain and probably could lead to instabillity. . .
Duble check all the wiring! Remove D2...D5, they serv only to protect Q5, Q7 from blowing out just in case you accidently forward static voltage or mains to the input. Prehaps they short the input in case you used wrong diodes.

Piotr.
 
#408
Hi Yoke,
I am very interested in your thread.....I have a similar amp planned running 20v @ 8amp bias........mine are is just a pile of components at the moment......


Good luck hope you get.....good sound soon............

How many fets are you driving???
 
#410
Ok how can I calculate bias and AC current gain...
My goal is 4A and 50% current gain...( 8 mosfets per chanel )

I have 0.5 Ohm source resistors , voltage on them is 0.440 V and R2,R3 are 0.22 Ohm ... ( I have one source resistor per mosfet ( total 8 ) and R2,R3,R42,R43 are like in AXR1 shematic ( total 4 per chanel )

Do I nead more paralel R2,R3 ??? or is everithing fine ???
 
#411
Hi Yoke......
Thanks for the reply sounds good..........I am building 2 mono blocks (20v 8a) and one stereo (20v 4a).

The Stereo one is exactly as yours........so your thread is fantastic....

I am interested in how much heat your monster is pushing out..
what sinks are you using?..........it would be great when she's cooking ..... to post the temps you are getting....


It would also be really good if you could take a load of digital pic's
and email them to me...........

I am interested in a real close up of the board.....showing components clearly.....+ a pic showing you fet wiring.....

Good luck hope your start up goes well!!!! Keep us posted

Kind regards
D3
 
#412
yoke said:
Hi D3...
I have 8 mosfets per chanel ( 20V , bias 4A ) ... I hope it will give me around 50W on my 6.5Ohm speakers...
I am thinking of buying digital camera just to show my litle monster...
Click to expand...

Good idee 😉 Show us your stuff.
I am also at same stage with my 100W AX , 22V /rail , 6.3A bias, 12 Fets / channel. At present they run quit hot - 70°C on Fet's. :hot: Hope they last. DC offset between + and - worries me abit. Just about 0.00mV - can it be :scratch: 😉 Offset to ground is still 3.8V. But music sounds beautifull. Will also post a pic or 2 on completion.
 
#413
yoke said:
Ok how can I calculate bias and AC current gain...
My goal is 4A and 50% current gain...( 8 mosfets per chanel )

I have 0.5 Ohm source resistors , voltage on them is 0.440 V and R2,R3 are 0.22 Ohm ... ( I have one source resistor per mosfet ( total 8 ) and R2,R3,R42,R43 are like in AXR1 shematic ( total 4 per chanel )

Do I nead more paralel R2,R3 ??? or is everithing fine ???
Click to expand...


anyone, any coment on this :bawling: :bawling: :bawling:

I have read this and this make me wonder did I did everithing fine ;

FROM WIKI Aleph-X

Measure the AC voltage across the paralleled R2/R3 output resistors, and across R5 (a big advantage is two voltmeters).
Trim R12 until the voltage over R5 is equal to the voltage over R2/R3.
Now your Current source is set to 50%.
Repeat the same procedure for the R34-side.
Measure the value of the 1.5K trimpots and replace them with fixed resistors.


And now the maths:
The adjustment above is correct only if R2/R3/R5 are the same value. The theory behind this is quite simple. The AC current across the source resistor R5 should be half the AC current going through R2/R3. Suppose you measure 0.05V across R5 and 0.05V volt across R2/R3:
0.05V / ( 0.22 / 2 ) = 0.45A
0.05V / 0.22 = 0.227A
(1 - (0.227 / 0.45)) * 100 = 50%


Another example with different resistors and four current source transistors:
Suppose you have 4x 0.22 ohm as paralleled output resistors, and 4x 0.47 ohm as current source resistors.
0.05V / ( 0.22 / 4 ) = 0.91A
0.05V / ( 0.47 / 4 ) = 0.425A
(1 – ( 0.425 / 0.91)) * 100 = 53.3%
You can now adjust R12 for optimal 50%.
You could also have taken 8 parallel 0.22 ohm resistors
Then only the voltage across the resistors has to be equal.
(Credits for the nice math goes to Edwin Dorre)


So should I add more 0.22 resistors in paralel with output resistors to have total of 8 ( now I have 4 ) per chanel 😕
 
#414
This is how my case will look like...This is picture I took some time ago...


ax-case.jpg


It's seams that heatsinks are not big enough to dissipate 100W...People who soo them told me that they can dissipate 250W each...but after 30minutes they get really hot , I can place my hand on them for just 1-2sec...( this is with 25V , voltage on R5 are 0,420V , so its 21W per mosfet )

I still did not figure out how you calculate or set current source to 50% ??? any tips 😕
 
#415
O.K.
I have another problem...
I manage to set current gain to 50% but problem is when I set everything and after I disconnect amplifier and turn it on after some time my current gain is not the sime as it was...some times is 60% and some time is 40%...

:bawling: :bawling: :bawling:

What could be wrong???
I'am getting tired of trimming it all day...

Any help???
 
#417
Don't trim , just listen to your favorate tunes 😉
When you set it up the whole thing has some temperature. After you swich off and back on the unit cooled down so before chceking allow it some 30 mins (or more depending how long it was off) to stabilize thermal condition of the circuit.

Piotr
 
#418
Thanks Piotr for replay...
I am frustrating because some times heatsinks don't even get chance to cool down and I still get a difference...

I will give it a try one more time ...Yesterday I set everything right so I will see in one our will it stay the sime...

untill then it will play music...
 
#420
Hello Yoke,
At this point I have no idea . . . next week I will build a next X version, so having it on my workbanch I will tweek and try to understand the biasing and seting up the Ac gain then I will tell about my discoveries 😀
Until then enjoy the music.

Piotr

BTW : Is someone knows where in London I can buy Rubycon black Gates NX caps?
 
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