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12th November 2003, 02:36 PM  #1 
diyAudio Member

Aleph X power supply
I have searched through threads for posts, and posts for threads, and anything I found about the Aleph X I have put into a summary paper. The one part that is still up in the air though is the power supply.
I am hoping for help with designing a power supply capable of delivering 15 volt rails to the transistors into a 4.5 amp load. This will supply roughly 42 watts into an 8 ohm load using hifiZen's board. I am looking at using a 300VA with dual 120VAC primaries and dual 15VAC secondaries. Another issue here is actual values to use in PSUD2 (such as the resistance of the transformer, and the load to show at the end). I have tried both an 8 ohm load (as suggested if the speakers are 8 ohms), and a 4.5 amp current load. Both yield far different results. Also, changing the resistance of the transformer (as I can't find a value for plitron toroid) makes a large difference. Any help on these values would be appreciated The areas in yellow on my schematic are "options". The 2 0.03 ohm resistors on the mains are thermistors (ala CL60's). The two smaller caps in parallel on the right along with the RC networks would be placed as close to the transistors as possible. Thoughts / ideas / help? Thanks
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12th November 2003, 02:42 PM  #2 
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Join Date: Apr 2003
Location: Brantford, ON

C3 is redundant and should be a much smaller value

12th November 2003, 02:47 PM  #3 
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Join Date: Aug 2001
Location: Chicago area

Use the 4.5 amp. current needed for the amplifer as the load for the power supply.
BZ
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12th November 2003, 03:11 PM  #4 
diyAudio Member
Join Date: Nov 2002
Location: Place in the Netherlands

PSU
I used PSUD2 for simulating my powersupply. For the regulation number of the transformer I used the values found at www.plitron.com.
But I use a cheap 330VA 2x 15 V trannie so things worked out a little different . I am using the following setup CRC with for R 0.28 ohm. Both C's are 47.000uF. The voltage I get is ~17 volts. The bias is set to a total of 4,5 A per channel. As bridge I use 4 fast recovery diodes. 
12th November 2003, 03:21 PM  #5  
diyAudio Member

Re: PSU
Dirt,
Doh... first mistake noticed Cut and paste didn't give new numbers on the caps. However, the smaller values should be 100uF then 100nF... Quote:
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12th November 2003, 03:28 PM  #6 
diyAudio Member
Join Date: Nov 2002
Location: Place in the Netherlands

In the transformer dialog of PSUD was the posibility to fill in the VArating and the regulation and it calculated itself those other values.
I think the output is higher than 15 volts. So 1.06 * 15 = 15,9 V if no load is connected. But I have to little knowledge about this subject . 
12th November 2003, 04:56 PM  #7 
diyAudio Member
Join Date: Dec 2002
Location: Poland

Hi Mach_Y
1. I do not like snubbers on the primaries in the power supply. In my opinion they decrease dynamic. I would leave capacitor 100n – 330n only. 2. I think, that one CL60 on one supply line is enough. In your case differences in resistance between termistors could disturb work of the transformer. 3. Instead of capacitors C12 and C13 I would give a 1nF or so capacitor parallely to each diode in the bridges. 4. I would add one more R=0.1 ohm and C=20 000uF . Value of 40 000uF per line is too small for me. 5. I would omit R3, C14, R3, C15 This is only my opinion. Regards
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12th November 2003, 05:57 PM  #8 
diyAudio Member

Alright... great info, especially on the PSUD [...] button *slaps self*
Did a couple of simulations with changes, and came up with the following design. The simulation does not take into account R1 (thermistor) or the final caps (C7 and C8). The numbers in PSUD were for a 15 volt secondary rated at 10 amps (number for 300VA plitron). PSUD filled in values of 15.9 volts at no load with 90milliohms. Using bridge25 for the rectifiers, on a 4.54A load. Mean and RMS voltage across the current load is 15.014 volts with ripple at +/ 0.001 volts The numbers for the inductor are from JW Miller model 8113 (digikey part number M9848ND and are $14.33 each) which is a 5mH inductor rated at 8.9 amps with a DCR of 0.022 ohms. C1  C6 are all comprised of 10uF caps, C1 and C2 being 3 in parallel, C3 and C4 2 in parallel, and C5 and C6 by themselves. They are all Panasonic ECOS1EP103CA 10000uF caps, 25VDC rating (32VDC surge) with a max ESR of 0.058 ohms, and are $3.71 each at digikey. The resistor is two Mills noninductive wirewound resistors in parallel, values 1.0 ohms and 0.33 ohms to yield 0.66 ohms. They are MRA12 (12 watt rating) and are $3.50 each at www.percyaudio.com. They'll dissipate 9 watts combined. Any other suggestions?
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12th November 2003, 06:18 PM  #9 
diyAudio Member

I don't believe those iductors will work... you need a big coil with
fat wire (to paraphrase Mr. Pass). I use the MCM part number from the SOZ article. I've used them in a few amps and they work well. Some complain that they're cheap, but they've been fine for me, no problems. m. 
12th November 2003, 06:28 PM  #10  
diyAudio Member
Join Date: Dec 2002
Location: Poland

Quote:
How do you want put together 1 ohm and 0.33 ohm to obtain 0.66 ohm?
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