Latest attachment.
http://www.diyaudio.com/forums/attachment.php?s=&postid=1578825&stamp=1218000976
It might work.
But personally I woul use a little bit more current to bias the GATES of IRFP140/9140
28Volt/100kohm ~ 0.3 mA
Make those 100 kohm resistors ~27 kohm .. or even 10 kohm
Would give: ~ 1 - 3 mA
Also I would connect those bias resistors ( 100kohm / 27 kohm )
BEFORE those gate stoppers ( 47 Ohm resistors ).
If you change from 100 kohm .. to 27 kohm,
then you should make those 47 kohm (in parallel with 4.7uF) smaller, too.
Maybe like 4k7.
And those two (now 47 kohm) should be connected to GROUND.
To try and keep, hold, the output MOSFETs at zero DC Offset.
The point between those two resistors, I mean, should be connected to GND.
http://www.diyaudio.com/forums/attachment.php?s=&postid=1578825&stamp=1218000976
It might work.
But personally I woul use a little bit more current to bias the GATES of IRFP140/9140
28Volt/100kohm ~ 0.3 mA
Make those 100 kohm resistors ~27 kohm .. or even 10 kohm
Would give: ~ 1 - 3 mA
Also I would connect those bias resistors ( 100kohm / 27 kohm )
BEFORE those gate stoppers ( 47 Ohm resistors ).
If you change from 100 kohm .. to 27 kohm,
then you should make those 47 kohm (in parallel with 4.7uF) smaller, too.
Maybe like 4k7.
And those two (now 47 kohm) should be connected to GROUND.
To try and keep, hold, the output MOSFETs at zero DC Offset.
The point between those two resistors, I mean, should be connected to GND.
Refering to this latest schematic, in Post #11
http://www.diyaudio.com/forums/attachment.php?s=&postid=1578855&stamp=1218005389
It looks better.
1. You use 12 kohm to bias GATES of MOSFET.
2. You have put this bias BEFORE gate stopper resistors (47ohm).
3. TL431 is an excellent VBE-multiplier, to set the IDLE Current of output stage.
For these MOSFET: IRFP140N / IRFP9140N, I would try something like 250 mA idle current.
Unless you are thinking of full CLASS A operation.
Nelson Pass used almost the same output stage in his F4 amplifier.
http://www.firstwatt.com/downloads.htm
The difference may be is he is Using Full Class A Current
You may have a look at details of his setup in this document:
http://www.firstwatt.com/downloads/f4_om.pdf
http://www.diyaudio.com/forums/attachment.php?s=&postid=1578855&stamp=1218005389
It looks better.
1. You use 12 kohm to bias GATES of MOSFET.
2. You have put this bias BEFORE gate stopper resistors (47ohm).
3. TL431 is an excellent VBE-multiplier, to set the IDLE Current of output stage.
For these MOSFET: IRFP140N / IRFP9140N, I would try something like 250 mA idle current.
Unless you are thinking of full CLASS A operation.
Nelson Pass used almost the same output stage in his F4 amplifier.
http://www.firstwatt.com/downloads.htm
The difference may be is he is Using Full Class A Current
You may have a look at details of his setup in this document:
http://www.firstwatt.com/downloads/f4_om.pdf
Good AndrewT.
There are some details I missed.
Most serious is of course having 12 kohm/ 100 kohm
from +30V and -30V.
Those should BOTH be the same value = 12 kohm.
About temperature sensing and VGS compensation.
Yes, this might be an issue.
But if setting the Ouput transistors fairly high biased like 250 mA or more, I think it can work well.
We are talking high current biased Class AB.
This would require also some well sized heatsinks, to reduce temperature changes to a lower level.
So, advce, when using TL431 and Class AB:
- do not use small heatsinks!
There are some details I missed.
Most serious is of course having 12 kohm/ 100 kohm
from +30V and -30V.
Those should BOTH be the same value = 12 kohm.
About temperature sensing and VGS compensation.
Yes, this might be an issue.
But if setting the Ouput transistors fairly high biased like 250 mA or more, I think it can work well.
We are talking high current biased Class AB.
This would require also some well sized heatsinks, to reduce temperature changes to a lower level.
So, advce, when using TL431 and Class AB:
- do not use small heatsinks!
xcicc said:
Two things.
1. As your resistors, capacitors and transistors have no names, it makes it difficult to speak and refer to your components in circuit.
Where is R1, R2, C1, C2, T1, T2 etc ??????
================================
2.In order to test if your circuit will work, you may simulate.
I would recommend you you download one SPICE simulator.
There are 2 freeware, which people here use:
Eagle CADSoft freeware version
http://www.cadsoft.de/freeware.htm
LTspice SwitcherCAD form Linear Technology
http://www.linear.com/designtools/software/switchercad.jsp
The 1 MOhm resistor at input, should be more like 1 kOhm.
The gain of this amplifier is
330 kohm / 220 ohm = 1500
This is too much for any power amplifier
For 2x30 Volt supply, a voltage gain of 20-30 would be more like it.
Explaination:
As the output of CD-player can be almost 1 Volt RMS
you only make amplifier work to hard, in making more then x20 or x30 for voltage gain.
( amplifier can max produce like 20 Volt RMS at output )
Regards
Lineup
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