All three mosfets must be electrically insulated from each other. thermal coupleing makes no difference in bias. Thermally coupleing the diff pair will make the dc offset more stable, but most people don't bother. Most people don't even use sinks.
I bought 2 bars of copper 3/16" x 2" x 36" on Ebay for something like $18.00. Made nice busses
I bought 2 bars of copper 3/16" x 2" x 36" on Ebay for something like $18.00. Made nice busses
This is why people recommend L instead of R...it doesn't change (much) the voltage coming through. With resistance, it's a balancing act. The more resistance you use, the better your filtering will be. The flip side of the equation is that the more R you use the more voltage drop and heat you'll have to deal with.
Inductors are superior but cost more, and are bulkier & heavier. Bulk and weight aren't a problem to DIY folks, but cost is a nuisance to those whose wallet has been on a diet. (Hint: Wind your own.) If you go with resistors, you can calculate the heat (I squared R), and voltage drop (E over I) easily enough, just plan ahead and you'll be okay. Unless you want to get really nutso, stay under 5 ohms; don't be ashamed to go under 1 ohm.
Don't get confused when you read the specs on an inductor and see that it has, say, one-tenth of an ohm resistance. It's apples and oranges. It's the inductance, not the resistance, that makes an inductor worthwhile. Inductors have the added benefit of increasing filtering as the frequency increases. Resistors have a flat response. This translates as inductors being better at taming incoming RF and such.
Grey
Inductors are superior but cost more, and are bulkier & heavier. Bulk and weight aren't a problem to DIY folks, but cost is a nuisance to those whose wallet has been on a diet. (Hint: Wind your own.) If you go with resistors, you can calculate the heat (I squared R), and voltage drop (E over I) easily enough, just plan ahead and you'll be okay. Unless you want to get really nutso, stay under 5 ohms; don't be ashamed to go under 1 ohm.
Don't get confused when you read the specs on an inductor and see that it has, say, one-tenth of an ohm resistance. It's apples and oranges. It's the inductance, not the resistance, that makes an inductor worthwhile. Inductors have the added benefit of increasing filtering as the frequency increases. Resistors have a flat response. This translates as inductors being better at taming incoming RF and such.
Grey
We have a Metal Supermarket here in SLC. I love those guys over there...not the cheapest to buy from but they also do any shearing or cutting for free while many metal vendors charge anywhere from 2.00 to 30.00 per cut. They also will order in anything you might need that they don't normally stock and you only have to buy what you want of it.
Mark
Mark
Also beware with the CLC. The inductor is not able to dissapate more than about 8 watts or so without getting hot enough to melt the insulation in the center of the coil. My first try was around 2 ohm, 2.5 mh. the extra resistance made the PSU sim look great, but at 6A the inductor dissapates 18 watts and gets too hot for comfort. I'm resorting to mounting a big *** pair of 3 ohm 100 watt wire wound vitreous ceramic type resistor on the outside of the amp in back because I need to dump a few volts.
I think I'm going to try both CLC and CRC filters.
Mr, Rollins
What would the inductor value be if I'm trying to shed couple of volts. The Tranformer I'm looking at has a 35v+35v secondary and If I 'm looking to get +- 45v at the rails, according to Mr.pass my Transformer secondary should be 33v+33v.
Mr, Donaldson,
I was wondering if the total bias current is my "I" and voltage I want to drop is my "E" when I'm calculating for the resistor.
All the help is greatly appreciated.
Regards.
SAAD//
Mr, Rollins
What would the inductor value be if I'm trying to shed couple of volts. The Tranformer I'm looking at has a 35v+35v secondary and If I 'm looking to get +- 45v at the rails, according to Mr.pass my Transformer secondary should be 33v+33v.
Mr, Donaldson,
I was wondering if the total bias current is my "I" and voltage I want to drop is my "E" when I'm calculating for the resistor.
All the help is greatly appreciated.
Regards.
SAAD//
SI,
If you're wanting to drop voltage, it's generally better to use resistors. One of the reasons to use an inductor is that it keeps voltage losses to a minimum.
As for a resistor, one or two ohms should do the trick. Make sure the resistor has sufficient wattage capability.
Of course, you could also use both inductors and resistors.
On the other hand, the Aleph 2 would be perfectly happy with that extra couple of volts.
Grey
If you're wanting to drop voltage, it's generally better to use resistors. One of the reasons to use an inductor is that it keeps voltage losses to a minimum.
As for a resistor, one or two ohms should do the trick. Make sure the resistor has sufficient wattage capability.
Of course, you could also use both inductors and resistors.
On the other hand, the Aleph 2 would be perfectly happy with that extra couple of volts.
Grey
actually, you may come up a little short of 45V rails with 35V secondaries.
I used a VM 1000VA with 37V secondaries and i'm right at, or a
1/2 volt under 45 Volt rails.
It all just depends on how you build your power supply. I used a
Thermistor for inrush current suppression on the AC mains, and
a CLC arrangement (2 mH inductors). You loose a volt here and
there... but being off a couple shouldn't matter that much.
Go for the 35/35, i'm sure it'll be fine for you!
I used a VM 1000VA with 37V secondaries and i'm right at, or a
1/2 volt under 45 Volt rails.
It all just depends on how you build your power supply. I used a
Thermistor for inrush current suppression on the AC mains, and
a CLC arrangement (2 mH inductors). You loose a volt here and
there... but being off a couple shouldn't matter that much.
Go for the 35/35, i'm sure it'll be fine for you!
One more question : If I deceide to add more output devices(4 IRFP240) per channel what are the changes do I have to make to the circuit to acomodate those extra devices ?
The problem is that I build the 2nd set of cabinets a little too big and was wondering if I could use up the space, and I got very inefficiant speakers and a very dead room sonicly.
Regards.
SAAD//
The problem is that I build the 2nd set of cabinets a little too big and was wondering if I could use up the space, and I got very inefficiant speakers and a very dead room sonicly.
Regards.
SAAD//
Everything else being equal, adding more output devices will increase bias and dissapation. At some point, the capacitance of the extra outputs will lower the high frequency roll off. Your power output is limited by rail voltage and current. If your speakers are 4 ohm or less, the extra current will increase power out. I think current starving becomes an issue below 6 ohms with the stock Aleph 2.
If you dig up my old thread, I ran 8 devices per side and decreased the source resistance to almost double the bias.
If you dig up my old thread, I ran 8 devices per side and decreased the source resistance to almost double the bias.
Hello,
i´m new to this forum and first of all i want to thank everybody for the great information i got here.
Since this thread is about Aleph 2 i think you can help me on my problem with an Aleph 4.
I built up a prototype and it worked fine, 20mV DC out right from the start. After putting together the final version the output voltage raised to -21 VDC !
I´ve checked everything several times, replaced to zenerdiodes that where damaged, but still no success.
The measurements are:
Z9-> 9,2 V
Q3-> 3,4 V
R3-> 5,6 V
R24-> 86 mV
Sourceresistors 1,5 Ohm-> 66 V on currentsource
Sourceresistors 1,5 Ohm-> 24,3 V on outputstage
PSU+- 45,5 V
I´ve no idea what the problem could be, maybe you have an answer to this.
Thanks in advance
Frank
i´m new to this forum and first of all i want to thank everybody for the great information i got here.
Since this thread is about Aleph 2 i think you can help me on my problem with an Aleph 4.
I built up a prototype and it worked fine, 20mV DC out right from the start. After putting together the final version the output voltage raised to -21 VDC !
I´ve checked everything several times, replaced to zenerdiodes that where damaged, but still no success.
The measurements are:
Z9-> 9,2 V
Q3-> 3,4 V
R3-> 5,6 V
R24-> 86 mV
Sourceresistors 1,5 Ohm-> 66 V on currentsource
Sourceresistors 1,5 Ohm-> 24,3 V on outputstage
PSU+- 45,5 V
I´ve no idea what the problem could be, maybe you have an answer to this.
Thanks in advance
Frank
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