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?
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?
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 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?
Re: number of Fet's
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 80000µF 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.
kro5998 said:
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 80000µF 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.
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.
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.
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.
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.
Attachments
Re: How many Fets
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 65°C at the heatsink too...
m.
kro5998 said:
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 65°C at the heatsink too...
m.
Hi,
I´m in the last stages of finishing my Aleph X. The cases are almost ready and now I´m looking at the values of resistors/caps etc. to adjust for 20-21V of power supply voltage.
Most of it is quite straightforward but I´ve got a question concerning R14 and R15 (R31,R32).
If I look at the values for these used in the various Alephs there are two main groups using either 4k75 (Aleph 2, 4, 5) or 1k5 (Aleph 3, 30, 60) for R14.
This is not dependend on the supply voltage but more of the time the amps were produced.
This must have an influence on the behaviour of the active current source (voltage at the bootstrapping cap) but I´m not shure in what way. In the current Aleph-X schematic this value has dropped to 511 Ohms together with a lowering of R15.
Can anybody shed some light on this?
William
I´m in the last stages of finishing my Aleph X. The cases are almost ready and now I´m looking at the values of resistors/caps etc. to adjust for 20-21V of power supply voltage.
Most of it is quite straightforward but I´ve got a question concerning R14 and R15 (R31,R32).
If I look at the values for these used in the various Alephs there are two main groups using either 4k75 (Aleph 2, 4, 5) or 1k5 (Aleph 3, 30, 60) for R14.
This is not dependend on the supply voltage but more of the time the amps were produced.
This must have an influence on the behaviour of the active current source (voltage at the bootstrapping cap) but I´m not shure in what way. In the current Aleph-X schematic this value has dropped to 511 Ohms together with a lowering of R15.
Can anybody shed some light on this?
William
mmmm,
seems to be a difficult question so here´s the next one:
What is the generall opinion on the compensation caps/ are there already values known to be used with the boards?
I could start without them and ad when neccessary. How can I test this, what input signal and what load should I use?
william
seems to be a difficult question so here´s the next one:
What is the generall opinion on the compensation caps/ are there already values known to be used with the boards?
I could start without them and ad when neccessary. How can I test this, what input signal and what load should I use?
william
wuffwaff said:
I usually start without them, but you'll need a scope to watch
the circuit. As a rule, an ordinary resistive load is adequate
to provoke oscillation. If you are looking more extensively,
try hanging a .047 to 1 uF across the output terminals. If you
really want to see how bulletproof it is, drive an unterminated
length of Litz or Mogami or similar low inductance/high capacitance
cables.
any answers to my first question?? (the one about the active current source)
nobody answered my question
well, so for the first board I wil use 1k2 for R14/15 and R31/32. This is a bit less than what Aleph 60/30 and 3 were using (@min 25V) so should work for 20V
R11/27 are 27k for now and R12/34 will be a 5k pot to start with.
R source are all 0,33R (3x1Ohm 1% 1W metalfilm) using 12 Fets/channel at a total dissipation of 320-400 watts.
R1/4 are 4x 390 ohms 1W / 1% metallfilm
R2/42 are 12x 1ohm/1W/1% metalfilm
All the other values are as in the Aleph-X PCB revision 1.0- Bill of materials.
I will start with one board to see if this will work and what values to choose for ac-current-gain / bias setting.
William
Has anyone tried to do watercooling for their A-X? I'd like to be able to take the heat outside my room, which watercooling enables as I can place the radiator outdoors. How do I go about calculating heatsink size and flow rate?
Also, has anyone used fans? How do I calculate how much smaller I can make the heatsinks depending on air flow rate? Noise is not an issue since there are ways to quiet a fan, and I already have forced-air cooled transmitting tubes in my audio equipment.
Also, has anyone used fans? How do I calculate how much smaller I can make the heatsinks depending on air flow rate? Noise is not an issue since there are ways to quiet a fan, and I already have forced-air cooled transmitting tubes in my audio equipment.
