Aleph 30

[swede]

Did some measurements

Hi again,

Couldn't resist... The amp was there, waiting for me.

I read the thread on biasing an Aleph 2:

http://www.diyaudio.com/forums/showthread.php?&threadid=4752&highlight=aleph+bias+resistor

Marijan had measured his amp in a number of places.

On one channel I got the following readings:

Rails: +/- 22.5 V
Current on positive rail: 2.6 amps
Hmmm... that gives 117 W idle(?).

R11 (221 ohm) 5.60 V
R14 (392 ohm) 4.11 V
Vce Q5 4.06 V

Source resistors:
+chan (R34 - R36) 0.39 0.45 0.54 [V]

-chan (R37 - R39) 0.51 0.42 0.47 [V]

Well, that seems to be pretty high on the source resistors... And the FET's are not that very well matched. (I could almost tell that by touching the FET's earlier today. Two of them seemed to be cooler than the others).

Let's see here:

I = U / R

R34 0.39 / 0.47 = 0.83
R35 0.45 / 0.47 = 0.96
R36 0.54 / 0.47 = 1.15
-----------------------------
2.94 Amps

R37 0.51 / 0.47 = 1.08
R38 0.42 / 0.47 = 0.89
R39 0.47 / 0.47 = 1.00
-----------------------------
2.97 Amps

My output FET's are IRFP240 which I got from Fairchild. They are TO247 packages and I use silicone pads to mount them on the heatsink.

I find it strange that my humongus heatsink get so warm. I have to take a couple of pictures and post them here, so you'll see what I mean.

Freddie wrote earlier in this thread that his bias current was about 2.1 amps. Mine is close to 3 Amps... Weird...

Can I do anything about this? How hot can the heatsink/transistors get before they get ruined? If I'm fine with almost 3 amps bias current, I won't to anything.

Best regards,
//magnus

 

[swede]

Weird measurements

Hi again...

I believe Mr Kirchoff is not on my side today (
I1 + I2 + ... + In= 0) ...

If I have 2.6 amps on the positive rail, it can't be possible for me to have almost 3 amps bias current...

Must be my multimeter that isn't correct enough. It's a CalTek Instrument CM4200. It cost me $100 so I hope it is not that bad after all... ;=)

Well, what I believe is that it is out of calibration between current measurement and voltage measurement.

 

[dieringe]

What is Aleph 30?

Could anyone tell me what an Aleph 30 is?
It's not an Aleph 3 as described in a3srvr0.pdf, or is it? I only count 4 output FETs in that schematic.

martin

 

[swede]

Hi,

http://www.volksamp.com/products.htm
http://www.volksamp.com/downloads/a30manr0.pdf

//magnus

 

[jleaman]

look like a simple enough amp to build any one fab the boards around here .. i might try this project..

 

[Nelson Pass]

It's an updated Aleph 3 with 6 outputs and a cheaper
heat sink / chassis and a few front end improvements.

 

[swede]

easy enough

Hi,

The Aleph 30 is really simple to build. Make a search on "Aleph30 PCB" and you'll find a couple of PCB layouts. I did mine based on panos29's design.

Though I already (after a couple of hours of listening) believe 30 Watts is not really enough for me. I think I'll build an Aleph 60 shortly. That will probably do fine. But for Jazz and Classical music, 30 Watts is more than enough.

Best regards,
//magnus

 

[jleaman]

hey swead you should post a pic of your new heat sinks that yuor using i would like to see i might have some forsale that will do yo well they hold them to-3 ill take apic and post and yuo tell me what yuo think i think it will be perfect for you ..

J

 

[jleaman]

( hehe ) i twill also hold the other types too.. the pic will say a 1000 words..

J'

 

[dieringe]

thanks, just reading the article...

yes this sounds interesting. As the Zen seems to be too weak either for me or for my 4ohm speakers, I probably should try it...



swede, did you match the transistors? how many did you have to buy? the IRF240s are 10 euros each here...

martin

 

[jleaman]

here is one

 

[jleaman]

here is two

 

[transducer]

JasonL,

Can you tell me the dimensions of your heatsinks, including the depth of the fins? How much do you want for them, in Canadian $. I'm in Toronto. I'm leaving for vacation tomorrow back on the 6th.

Thanks,
RonS

 

[jleaman]

3/4 from back of base to tip of fins and the initial heatsink ie flat back is 7" x 12" and the l's on the base are 2 " aand the base thickness is 1/4 " and the l's are the same if yuo need any more info let me know and i dont know what to charge i know i cant use them and i want to get 2 heat sinks for my aleph 5's im making mono blocks and need 2 heat sinks one per block ..

J'

 

[wuffwaff]

Dieringe,

you can get IRFP240 for about 2,5 euro each from http//www.schuro.de. This will save you quite a bit and you don´t have to mount TO3´s

william

 

[dieringe]

voltage regulator?

thanks wuffwaff it's a pain ordering from schuro but if they are that cheap...

But: what are the values of R1 and the two (!?) R8s?


Could a voltage regulator like in the zen revision 3 be possible and helpful?

m.

 

[swede]

Help(?)

Hi again...

Nobody seemed to notice my last question... I have to be persistent then. ;=)

I = U / R

R34 0.39 / 0.47 = 0.83
R35 0.45 / 0.47 = 0.96
R36 0.54 / 0.47 = 1.15
-----------------------------
2.94 Amps

Isn't almost 3 amps bias current a little bit high for an Aleph 30, or should I just leave it like that?

Best regards,
//magnus

 

[jleaman]

crank er up to 50 amps then buy a stinger and a clip and start wledin ..

 

[fcel]

Magnus,
Just for comparison and to give you some reference figures, I'm pretty sure it's 2.5A for the Aleph 2. So, 3A for Aleph 30 is definitely too high. But it could till work, I guess, if you have adequate heatsinks, add some additional components etc.

 

[fcel]

Magnus,
I just looked at the service manuals .... it says 2A rms for Aleph 3 and for Aleph 2, it's 2.5A rms. I hope we're talking about the same thing.
I understand that Aleph 3 is a little different from Aleph 30 but I don't remember what's the difference .... may be higher current for Aleph 30?