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Old 9th December 2004, 05:03 AM   #541
Prune is offline Prune  Canada
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That is designed as a passive crossover, although the author shows how an active version can be made. I intend to use a passive versin, but I'm not sure if the gain of the Aleph-X is enough. The DAC with volume control set to maximum outputs buffered 7 V peak-to-peak (balanced). What fraction of rail voltage does the Aleph-X clip at?
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Old 9th December 2004, 02:02 PM   #542
fish4u is offline fish4u  Philippines
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Prune and byteboy,
thanks for the replys, appreciate it!
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Old 9th December 2004, 06:32 PM   #543
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Quote:
Originally posted by Prune
What fraction of rail voltage does the Aleph-X clip at?
Figure on losing 3 volts off the rail - 2 volts to the saturation
of the Mosfet and 1 volt Source resistance.
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Old 13th December 2004, 01:49 AM   #544
kro5998 is offline kro5998  Netherlands
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Default number of Fet's

I am planning to build a pair of low power Aleph-x's (20-30 Watts)
How many Fet's should i use 4 or 8.

For the psu i plan to use a 350VA tranny for both rails and a MB3510 bridge and a CLC filter with 47000uF/3mH per rail.

Heatsink (per channel) is 260 * 200 * 40 (0.38C/W) and a separate heatsink for the bridges.

Any suggestions?
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Old 13th December 2004, 03:43 AM   #545
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I am using HiFizen's boards for my Aleph-X and I am using 12 IRFP240 fets per channel. I would like to use terminal blocks on the PCB to connect to the external IRFP 240 fets. A 5mm pitch pcb terminal block fits perfectly in the holes where the single IRFP044's were to be connected. On my external CSS and Gain boards I have mounted the gate resistors and source resistors. I can put some jumpers on the board so the terminal blocks will work. My question is if I have to run the sense lines from source on the CSS and Gain board or can I use the sense line on the PCB which is connected thru the sense resistor to the source at the terminal block?
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Old 13th December 2004, 04:06 AM   #546
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Cancel my last question because after I thought about it I realized I can't do what I wanted with the sense resistor. How have others handled the sense resistors using HiFizens Aleph-X boards with external transistors?
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Old 13th December 2004, 05:03 AM   #547
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Default Re: number of Fet's

Quote:
Originally posted by kro5998
I am planning to build a pair of low power Aleph-x's (20-30 Watts)
How many Fet's should i use 4 or 8.
For the psu i plan to use a 350VA tranny for both rails and a MB3510 bridge and a CLC filter with 47000uF/3mH per rail.
Heatsink (per channel) is 260 * 200 * 40 (0.38C/W) and a separate heatsink for the bridges.
Any suggestions?
I have 100W dissipation per channel (about 30W at 8ohms), I use 4 transistors, my heatsinks are 300x250x25 and not black. gets quite hot, so yours should be enough if they are black.
240VA transformer per channel, schottky rectifiers and 80000F per channel, no coil. works well for half a year now
you get better distribution of heat and probably a bit less distortion with 8 transistors
m.
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Old 13th December 2004, 12:08 PM   #548
kro5998 is offline kro5998  Netherlands
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Smile How many Fet's

Thanks Dieringe.

I was just wondering if i had enough bias current per Fet to achieve good lineairy when using 8 devices.
According to the axe spreadsheat the heatsink will get to around 67 C. The junctiontemp will be 91.8 with 4 and 79.8 with 8 Fets.

What kind of bias and current gain settings do you use and what is the value of youre source resistors?

btw.the heatsinks are black.
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Old 13th December 2004, 12:33 PM   #549
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Default Off Board Sense Resistor

Kilowatski,

I mounted the sense and ground resistors to the heatskink using a copper bussbar. This worked quite well and allowwed me to use many resistors in parallel. These resistor really don't get that hot so where you mount them isn't critical as long as it get some air.
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Old 13th December 2004, 01:19 PM   #550
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Default Re: How many Fets

Quote:
Originally posted by kro5998
Thanks Dieringe.

I was just wondering if i had enough bias current per Fet to achieve good lineairy when using 8 devices.
According to the axe spreadsheat the heatsink will get to around 67 C. The junctiontemp will be 91.8 with 4 and 79.8 with 8 Fets.

What kind of bias and current gain settings do you use and what is the value of youre source resistors?

btw.the heatsinks are black.

I use 2x12V transformers to get maximum output at 8ohms, should be about 1.5A per transistor(?). low voltage -> higher current...
dont know if that would be enough for 8 tr.(0.75A)
My source resistors are 0.33 ohms
I have something like 65C at the heatsink too...

m.
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