Aleph-X builder's thread.

If you are following Grey's original schematic you would not use
the SST505 part. It is an optional biasing method for D1a/D1b.

Use D1a (1N5239B)

Put a jumper from pin 1 to 3 on Q12a.

Put a jupmer on J1a.

Jumper on R48 and R49.

Use a 3 watt resistor for R21 if you have it. If not at least of some
value at 3 ohms.

I'd also use the McMillan resistors at R46 and R47.

No need to use jumpers at C7, C10... they can just be omitted.


Hope this is of some help... me not being the final word on anything!,
other than i did get the thing to work sticking close to Grey's schematic.
You did pick a little bit of a sticky project for your first
effort! Also read the Aleph-X WIKI too, lots of great info there.

maybe someone else will chip in if i've lead you astray.
 
Thanks moe29

i've removed the sst505
jumpered q12a
removed jumpers on c7 thru c10
added a 2.2ohm 3w resistor on r21

so now...
only R49, r48, j1a, and q12a are jumpered
btw i do have the mcmillan resistors in r46+r47

now when i turn the amp on, and speakers are connect, they "blip"... then no more sound
if i shut it off again and turn it back on, same gig...

i'm still feeding it 1kHz @ +18dBm w/ a 0mv offset
signal gets to the board fine (oscilloscoped)

thanks in advance everyone
 
hmmm... it seems like you are going to need more help than i can
provide. I really wouldn't hookup speakers until you get readings
that varify the amp is working and is stable. It's difficult to trouble
shoot a circuit from afar. Often it can be something trivial that you
are overlooking. Maybe take a fresh look at it tomorrow.

by no means am i an expert in amp building... It took me a day or
two to get the circuit working, after correcting obvious errors, and
learning a bit more about the circuit. I wouldn't reccomend this
amp as a first time project, but since your in there bailing, keep up
the work... maybe a picture or some better answers from the
more learned will get you up and running :)

All the big guns seem to be off discussing loftier questions in
another part of the Forum, rather than lending their expertise here...
 
question about output...

ok this telulex function generator feeds out a bnc, which i'm going to an F connector into rg6 coax...the pin inside the shielding is + and the shield is ground... i connected the ground to the - and the pin to + and i connected the SHD on the XLR connector to ground... this does and doesnt sound right

because the signal coming in isnt balanced... and i need a balanced signal
could this be why the fets arent turning on?

about ready to :smash: something! :mad:
 
before i omitted the c7-c10 jumpers, i got a steady signal out of the amp

Remove the jumpers, they are for frequency compensation. The 'C' designation is for capacitor. You have just coupled the signal from the differential pair to the outputs bypassing the output devices and disabled the output current sources.

There is no reason why you can't use current source Q12b. You would use it in place of jumper Q12a, but for now stick with what you have so we can get you going then you can switch back to the current source.

What is the voltage across D1a ( cathode is neg anode is pos) the stripe should be to the positive rail. What is the voltage across R17? What is the voltage across R24, VR2? What is your voltage across drain resistors R23 and R25?

The schematic I have is different than the board. I probably have an old version ( probably not the only one). J1a is drawn from R17 to ground and on the board R17 is connected to Q12 then to J1a or J1b. J1a goes to ground. J1b goes to the negative rail.

BDP
 
Preparing my Aleph X project

Originally I was planning the parts for my Aleph 2. Then, I found out the Aleph X PCB GP and purchased 4 PCBs. I grew interests in the Aleph X and is planning to use my prepared parts, may be, to make the mono-blocks of Aleph X into 100W version. While my parts is coming (mono block cases is still month away), I made my own project notes. I would like to share with you all. All comments, corrections are welcome! You can refer my preparation notes at:

http://www.penguinlovers.net/audio/alephx_proj.html

Thanks,

Thomas
 
BDP said:


Remove the jumpers, they are for frequency compensation. The 'C' designation is for capacitor. You have just coupled the signal from the differential pair to the outputs bypassing the output devices and disabled the output current sources.

>> I just removed the jumpers
>> Hehe, i know that "C" is for capacitor... i'm not that noobish :-D


There is no reason why you can't use current source Q12b. You would use it in place of jumper Q12a, but for now stick with what you have so we can get you going then you can switch back to the current source.

>> Okay, im' still on a jumpered q12a pin 1 to pin 3

What is the voltage across D1a ( cathode is neg anode is pos) the stripe should be to the positive rail. What is the voltage across R17? What is the voltage across R24, VR2? What is your voltage across drain resistors R23 and R25?
Across, voltage

>> d1a, .17v
>> r13, .13v
>> R24, .04v
>> vr2, 0v
>> r23, .01v
>>r25, .03v
>>obviously, this isn't correct... something is awry
>> w/ the c7-c10 j's, i still got 9.1 v on d1a, now i dont [something is wrong! :(]

The schematic I have is different than the board. I probably have an old version ( probably not the only one). J1a is drawn from R17 to ground and on the board R17 is connected to Q12 then to J1a or J1b. J1a goes to ground. J1b goes to the negative rail.

BDP


Thanks BDP :-D
 
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It Works, 100W AlephX Monolith

Finally got One of Two channels working last night. Will finish the second this week.

Absolute DC Offset +/- 20mV (floats)
+39mV offset + to - on terminals (haven't played with diff pair yet)

Standard 10mA diff pair bias but will increase at a later date.

Running 22.8Volt rails total bias of 11.6 amps.

After 3 hours of running the amp is hot. Much hotter than expected especially the rectifiers. FET Mount plate temp is around 60 - 65C. I used the Avid Thermal Tick recomended earlier in this thread. Once the stuff melts it works great. As of right now I can see that the outer plates hav'nt melted the grease yet. ( Can't use the oven since its too big and I don't even want to think about the WAF)

Sound is very good even with only one channel in operation. Definatly worth the effort.

Regards
Scott
 

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Those heat sinks look a bit scant. I can't tell from the picture how the heat is transferred from the inside fins to the outside ones; it takes a lot of meat to get the heat from point A to point B. Is there plenty of gap underneath so that air can enter from the bottom?
That said, it's clearly a massive hunk o' amp. Hope it serves you well.
And yes, the DC offset will tend to drift a bit. Won't hurt anything.

Grey
 
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Another Photo

Please forgive me for previously not giving credit where credit is do. Thanks to Nelson, Grey, HiFiZen, and everyone else for the dedication and willingness to share their ideas and knowledge for the benefit of the DIY community. Without you this stuff would be impossible.

The heat sinks were calculated to remove 500W of power per side at 30C temp rise. I de-rated them 50% for loss at metal to metal interface. This seems to be about right as the sinks are being asked to dissipate about 260Watts as it is operating now and the mounting plate is rising about 30-35C.

Grey as you said, the limiting factor for this design is the heat transfer from plate to plate. To improve this, I am seriously considering increasing the width of the spacers from .5x.5 inch to .75x.5 inch. This should significantly improve the effectivness.

The plate are cut at an angle on the bottom to promote better air flow.
 

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BDP said:
Do you have a good ground to the PCB? If you measure from PCB ground to cathode of D1a you should have positive rail voltage. What is the voltage from PCB ground to junction of D1a and R17.

>> I have no idea... i'm using a variable dc psu for testing psu, then i'll build one for this ax... so the varaible psu doesnt have ground output... how shoud i do that? do i need to?
>> i get 0 volts from the cathode of d1a... and 0 at the anode

Is J1a in. Resolder your connections.

>> j1a is in, continuity is checked, soldered is redone :(

BDP

thanks
 
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Thanks for the insight. I took some measurements today. With the room temperature of 20C the mounting plate runs 58C, outer plate runs 47C. This was after 4 hours of operation. I certanly will have to do something with it for the summer. I think Grey was right that there isn't enough mass between the plates to conduct the heat properly, or the aluminum that I used has a lower heat conductivity than my calculations.

Right now my biggest concern is the rectifier. It is running around 68C after 4 hours. In the previous photos you can see the rectifier assembly sitting on top of the transformer housing in the back center.

Temperature aside, this amp sounds sweet even on only one channel.

I should finish the second amp by this weekend

Thanks Again

Scott
 
Throw in a copper bar for the rectifiers to work as a heat spreader, a copper bar would also do the trick to get the heat to the heatsinks. You can make heat travel far and fast with the right copper bar.

Im working on a SOZ and the box for that is including more than 10 kilograms (20 pounds) of copper per monoblock.


Magura:)
 
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So far 58C hasn't been a problem. In the summer 58C will become 65C which may or may not be a problem. Output per device is 32Watts per the WIKI spreadsheet.

I am using the IRFP244 chips and don't have the spec sheet in front of me. I will measure the chip temps to see if I am still safely within operatin specs with derating.

I have a couple of extra sets of matched 244's as spares but it is a pain in the you know what to open the box up a replace them. The hardest part would be stuffing my woofer back in its frame.

Correct me if I am wrong but in a failure mode this circuit would drive one side to rail voltage. I would think it would take a while before the fuse blew given the size of the power supply.

I am currently using a 6amp sloblo which is marginal for long term operation. (I've allready blown one) In reality once I feel nice and secure (dangerous place to be) I'll raise it to 8 amps. Just the output devices will pull 5 amps on the line not including the losses in the power supply.

Scott