marus said:... and this is my bias
Hi Marus,
It will be very difficult to match the bias evenly across the output devices. In real terms it does not really matter and the fact that you have a degree of current sharing already is a good result.
The trouble with setting bias with mosfets is that it's done right at the turn-on threshold and because of the large transconductance even well matched FETs can show differences.
At regular listening levels the FETs will tend to share the load more evenly.
I have never worried about it and I suggest you don't sweat it either.
Cheers
Q
vuthanh6 said:
As already advised you can use the IRFP240 without any problems. In terms of substituting the 2SC1845, you will need to find a transistor with similar specifications. You can use a transistor with a different Vce depending on what rails you are going to use. The transistor must have a Vce at least 1.2 times greater than the maximum possible rail voltage (one rail).
So I guess a little research is in order.
Cheers & good luck.
Quasi
Hi,
the LED drops a near constant voltage. The Vdrop varies with type and is usually in the range 1.6V to 3.5V.
If you connect a LED across 24V, the relay coil, then you will blow it up.
You must set a current limit and this is easily achieved with a resistor sized to drop the excess voltage at the current you want to flow through the LED.
the LED drops a near constant voltage. The Vdrop varies with type and is usually in the range 1.6V to 3.5V.
If you connect a LED across 24V, the relay coil, then you will blow it up.
You must set a current limit and this is easily achieved with a resistor sized to drop the excess voltage at the current you want to flow through the LED.
AndrewT said:
I'm talking about an LED assembly with a built in resistor and rated for 24V. Check out this link.
http://www.rsindia.com/cgi-bin/bv/r...feceeldgkidhgh.0&cacheID=innetscape&Nr=avl:in
Today i found a power supply of +/- 76 V DC (only 5.000uF/rail), i changed resitros to 18k and 33k, adjust bias again to 30mA/pair and turn it on. And then ..... distorsion from the first watt ....
I think i go crazy ....
Quasi , can you tell me where i can verify some voltages to know that everything it's ok ?
(sorry my damn english)
from the first watt ....I think i go crazy ....
Quasi , can you tell me where i can verify some voltages to know that everything it's ok ?
(sorry my damn english)
Connectig LED to output amp
....vuthanh6 to connect a LED to SPK u can test this circuit
....vuthanh6 to connect a LED to SPK u can test this circuit
An externally hosted image should be here but it was not working when we last tested it.
resistor value is 680 ohm / 1w 
... and the bias is :
[ 33mA ] [ 27mA ] [ 30mA ]
[ 32mA ] [ 29mA ] [ 29mA ]
verry good ! but what is with this distorsion ?
i check everything 100 times ... it's ok
R6= 18K , R17= 33K at +/- 76V DC
First time i use at 40V with this resistors and ... the same distorsion it have. I put 2,7K and 22K and .... no distorsion (at 40 DC).
[ 33mA ] [ 27mA ] [ 30mA ]
[ 32mA ] [ 29mA ] [ 29mA ]
verry good ! but what is with this distorsion ?
i check everything 100 times ... it's ok
R6= 18K , R17= 33K at +/- 76V DC
First time i use at 40V with this resistors and ... the same distorsion it have. I put 2,7K and 22K and .... no distorsion (at 40 DC).
marus said:... and the bias is :
[ 33mA ] [ 27mA ] [ 30mA ]
[ 32mA ] [ 29mA ] [ 29mA ]
verry good ! but what is with this distorsion ?
i check everything 100 times ... it's ok
R6= 18K , R17= 33K at +/- 76V DC
First time i use at 40V with this resistors and ... the same distorsion it have. I put 2,7K and 22K and .... no distorsion (at 40 DC).
Hi Marus,
I have replaced the Nmos350 / 500 schematic on my web site with the one that shows key current flows. Using ohms law you should be able to work out what the voltages should be across components.
Have you checked the DC offset?
Cheers
Q
jethari said:
Hari,
What I have done is take the PSU voltage intended and scale to the 75VDC rail design. This allows me to scale the parts list far easier than trying to figure out what the transistors part of the current flow. The main reason I have taken this approach is because I cannot find a SPICE like program that is useful to me in Linux.
There are lots of them in Windows, but I am not creating a Windows system to use a Windows based SPICE program. I would think using a SPICE type program would enable you to see how to acheive the same currents with different PSU voltages.
Regards,
John L. Males
Willowdle, Ontario
Canada
07 September 2007 22:59
Official Quasi Thread Researcher.