Has anybody built an Aleph-x to this spec??? - diyAudio
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Old 24th April 2004, 06:51 PM   #1
D3 is offline D3  England
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Default Has anybody built an Aleph-x to this spec???

Hi I would like to know if anybody is building or has built an Aleph-X to around this sort configuration..............

1000va 18-0-18 simple POWER SUPPLY 'C'
16 IRFP044N 8A BIAS.................................

I would like to discuss build issues etc ...............
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Old 24th April 2004, 07:25 PM   #2
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Default Power Supply voltages

I know from the group buy that the transformer is 18v RMS - what is your required DC voltage? Also 18v?
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Old 24th April 2004, 09:35 PM   #3
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Well, if you are using only capacitors in the power supply (no resistors or inductors) then the rails will be just over +/-24V, to give a power output of about 120W into eight or four ohm loads, with its peak output somewhere around 5-6 ohms. This will also mean about 1A of bias per fet so you should be able to get away with rather large source resistors (of up to about one ohm without getting into power dissipation probelms, but around half that would probably be best) which will mean your FET's will not have to matched quite so accurately (which is nice).
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Old 25th April 2004, 02:29 AM   #4
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We are shipping XA100's this month. I believe they correspond
roughly to that description.

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Old 25th April 2004, 09:24 AM   #5
D3 is offline D3  England
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Default Thanks for replying...

I am unsure what the rail voltage.........will be under load........
unloaded it sould be approx 18x1.4=25.2v.....................
I was thinking that loaded........after interpolating other threads...
I would be looking at 21 or 22volts..............given that I have quite a heavy bias................

This being the case I noticed thain the original Wiki page that the
IRFP044 was one mosfet suggestion - ideally not running over 20v.......however I belive this has been largley superceded with IRFP044N. From what I can gather.........the 'n' variation has a slightly lower voltage tolerance and lower capacitance.

Am I pushing the envelope too much voltage wise?????

At the end of the day this amp is for 'pleasurable' listening......
I don't wan't something unreliable......and likely to smoke!!!!!

....can the power supply be tweaked to bring me into the 'comfort' zone.....without losing performance................
or am I paranoid................and just go for it!!!!

Arghhh......

Kind Regards
Richard

(Thank you for your reply Mr Pass......nice to know highly regarded XA100 ..... is a similar spec)
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Old 25th April 2004, 09:51 AM   #6
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Hi, I think you may have under estimated your rail voltage a bit there, as I have generaly found that trasformer manufacturers specify the load voltage for the secondaries, so that if you are drawing less than the rated power (which you will be at draw of around 300-400W from a 1000VA transformer). Therefore I would if anything say that your supply will be slightly higher than rated (with a typical regulation of the transformer being about 4% for that sort of size), around 26.5V (or 25.5V after the rectifier diodes).

This also means that if you do run the simple, capacitor only, filter on your PSU you will be dissipating around 400W, which even with the big heatsinks you have may be pussing the limits on safe opperating temperatures for the MOSFETS a little (but will probaby be ok, as the die temperature should stay below 100 degres C so long as your room temp isn't too high).

However, this does mean that you could include either resistors or inductors into your power supply filter to drop a couple of volts from the supply, giving a slightly lower rail voltage to your FET's (I think the 044's should be fine still on 25V though if you don't want to do this) and a slightly better smoothing on your power supply.

But, basicaly, I would say that as is the rails will be somwhere between 24 and 26 volts at your amp, and either way you should be fine running as is, as there will only be very marginal differences in power dissipation and the voltage shouldn't be too high for the IRFP044's either.

One question that I do have though, is if there is any reason that you only want to run capacitors to smooth your power supply? Is it just too keep things simple, or do you want to try nad get as much power as you can out from the design?
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Old 25th April 2004, 10:52 AM   #7
D3 is offline D3  England
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Default simplicity!

I am a firm believer in simplicity...............I sort of come from the school of american engine design..............why bother with 4 valves percylinder and complex cam shafts.............when a simple large capacity engine..........will do the job..................
nascar engines verses formula 1.................

My idea was to use a large transformer and 6 of the large 68,000 caps+ your bridge per monoblock................for a strong basic relatively low ripple supply................however I didn't want to fry my mosfets......



Kind Regards
Richard
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Old 26th April 2004, 08:30 PM   #8
jojo is offline jojo  Netherlands
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Default something like this

Quote:
My idea was to use a large transformer and 6 of the large 68,000 caps+ your bridge per monoblock................for a strong basic relatively low ripple supply................however I didn't want to fry my mosfets......
You mean something like this? the suply delivers about 25 volts
to feed 16x IRFP240 per channel.Im aiming at 6.7A of bias per channel.

grtz Jojo
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Old 26th April 2004, 11:24 PM   #9
Kram is offline Kram  United Kingdom
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Hey jojo, I was messing around with layout ideas for my amp on sunday and I came up with exactly the same arrangement as you have in your pic. I can imagine a few other people doing it this way as well now.

sorry D3 to clutter up your post with something not exactly relevant.

Thanks
Mark
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Old 27th April 2004, 07:04 AM   #10
D3 is offline D3  England
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Default My amp

Thanks everybody for posting..................

I have been drawing up my Aleph monoblocks on CAD....when the drawings are a little more polished I will post on here.............

However........I notice that jojo's amp is a very similar layout!

kram.....I might be able to get a reasonable deal on metal work......if you use a similar design to myself.....................
I will try and post it later today.................

Cheers everbody .......keep posting!!!!!
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