I am wondering if any one has built this amp. Output power is 360 Wrms under 8 ohms or 550 Wrms under 4 ohms Any Comments and suggestions?
http://users.swing.be/edwinpaij/ampli_mosfet_360_w.htm
Bushulo
http://users.swing.be/edwinpaij/ampli_mosfet_360_w.htm
Bushulo
see this thread: http://www.diyaudio.com/forums/showthread.php?s=&threadid=81477&pagenumber=1
I built a few of these, they work fine, but I had to do some minor changes in design.
I built a few of these, they work fine, but I had to do some minor changes in design.
Hello Bushulo
I viewed the schematic.
Some considerations on this.
1) the zener diodes are not a good idea to use for voltage drop or biasing like this circuit.A simple resistor is much better for noise and distortion.
2)in this configuration,the supply voltage on first and second stage must to be higher respect to the mosfet stage(4-5 volts) and stabilized
3)the circuit have no protection.For this high power a DC and SOA foldback protection are needed
4)the amount of NFB is high.Take care on oscillations and stability problems.
5)you do not use the IRF mosfet type but only the 2SK-2SJ.This devices are thermal stable when the quiescent current are across 200 mA each.200mA x 12 mosfets is a very high heat to be dissipate at no signal input
6)more important:the circuit have no value for the components.For this you should to be pay.
I think that a more correct schematic can also built.
I don't like this
Regards
I viewed the schematic.
Some considerations on this.
1) the zener diodes are not a good idea to use for voltage drop or biasing like this circuit.A simple resistor is much better for noise and distortion.
2)in this configuration,the supply voltage on first and second stage must to be higher respect to the mosfet stage(4-5 volts) and stabilized
3)the circuit have no protection.For this high power a DC and SOA foldback protection are needed
4)the amount of NFB is high.Take care on oscillations and stability problems.
5)you do not use the IRF mosfet type but only the 2SK-2SJ.This devices are thermal stable when the quiescent current are across 200 mA each.200mA x 12 mosfets is a very high heat to be dissipate at no signal input
6)more important:the circuit have no value for the components.For this you should to be pay.
I think that a more correct schematic can also built.
I don't like this
Regards
Hi Chris
Sorry for my mistake.
You are right:the D1-D6 in this circuit are necessary because the Vcb max of the BC550-BC560 are lower than your respective supply voltage rail.The zener cause a DC voltage drop.
Why not use the low noise 2SC2240-2SA970?
They are 120V max and the zener are not necessarily.
Vittorio
Sorry for my mistake.
You are right:the D1-D6 in this circuit are necessary because the Vcb max of the BC550-BC560 are lower than your respective supply voltage rail.The zener cause a DC voltage drop.
Why not use the low noise 2SC2240-2SA970?
They are 120V max and the zener are not necessarily.
Vittorio
Hi Vittorio,
It is possible that the power rating may be exceeded as well depending on the tail current.
-Chris
It is possible that the power rating may be exceeded as well depending on the tail current.
Maybe the same reason they didn't provide a regulated supply for the front end with a 5 volt level over the main supplies. I don't think the driver stage can properly handle the gate charge anyway.
-Chris
I agree Chris
This is for the T9 and T10 moreover.
Many years ago I have built a similar (Dynaco) amp.
Symmetrical dual differential input stage and second cascode stage with power mosfets on output stage.
In my first power on the amp it did not work because I forgotten to mount the two passive load resistors across the collector of the two transistors(named in this circuit T9 and T10) and the output of the amp .
An oscillation it was produced.
I had to add some compensations before that you noticed me of this error......
This is for the T9 and T10 moreover.
Many years ago I have built a similar (Dynaco) amp.
Symmetrical dual differential input stage and second cascode stage with power mosfets on output stage.
In my first power on the amp it did not work because I forgotten to mount the two passive load resistors across the collector of the two transistors(named in this circuit T9 and T10) and the output of the amp .
An oscillation it was produced.
I had to add some compensations before that you noticed me of this error......
Chris
I'm completely of agreement with you.
Also I have abandoned this design some years ago for the J-fets.
I have seen some other projects on the linked site:it seems that
the power mosfets are the IRF type.
If this is true,the amp are not suitable to built because not thermal compensation are present.
A better design can be made....
I'm completely of agreement with you.
Also I have abandoned this design some years ago for the J-fets.
I have seen some other projects on the linked site:it seems that
the power mosfets are the IRF type.
If this is true,the amp are not suitable to built because not thermal compensation are present.
A better design can be made....
nn, I used a sligthly different schematic from the beggining (see the thread I reffered to), it has diff the current sources connected to +-15V, DC feedback and thermal sensing transistor to correct the IRFP´s gates.
I just added 150pf parallel to first feedback resistor because of oscillations, zeners on gates, and have added +-10V for the VAS stage. Also changed the DC servo connection by crossing the 1Meg-100n-1Meg by 100K because it oscillated at say 0.3Hz.
I just added 150pf parallel to first feedback resistor because of oscillations, zeners on gates, and have added +-10V for the VAS stage. Also changed the DC servo connection by crossing the 1Meg-100n-1Meg by 100K because it oscillated at say 0.3Hz.
Hi darkfenriz
Yes,on some condition,with large alternate input signal,the Vcb limits of the BC550-560 can be exceeded with power supply of 85V for the input differential,and a risk of destroy is for the current regulators.I don't know the current on this stage,but this is very low due to the power characteristics of the BC.
Moreover, as Chris has said, the second cascode stage has some problems to drive the gate capacitance of the output mosfets,it seems that they are the IRF devices.
If this is true,a thermal runaway it happens.
This is not a good design...
Cheers
Yes,on some condition,with large alternate input signal,the Vcb limits of the BC550-560 can be exceeded with power supply of 85V for the input differential,and a risk of destroy is for the current regulators.I don't know the current on this stage,but this is very low due to the power characteristics of the BC.
Moreover, as Chris has said, the second cascode stage has some problems to drive the gate capacitance of the output mosfets,it seems that they are the IRF devices.
If this is true,a thermal runaway it happens.
This is not a good design...
Cheers
Hi darkfenriz
Yes,on some condition,with large alternate input signal,the Vcb limits of the BC550-560 can be exceeded with power supply of 85V for the input differential,and a risk of destroy is also for the current regulators.I don't know the current on this stage,but this is very low due to the power characteristics of the BC.
Moreover, as Chris has said, the second cascode stage has some problems to drive the gate capacitance of the output mosfets,it seems that they are the IRF devices.
If this is true,a thermal runaway it happens.
This is not a good design...
Cheers
Yes,on some condition,with large alternate input signal,the Vcb limits of the BC550-560 can be exceeded with power supply of 85V for the input differential,and a risk of destroy is also for the current regulators.I don't know the current on this stage,but this is very low due to the power characteristics of the BC.
Moreover, as Chris has said, the second cascode stage has some problems to drive the gate capacitance of the output mosfets,it seems that they are the IRF devices.
If this is true,a thermal runaway it happens.
This is not a good design...
Cheers
Hi darkfenriz
Yes,on some condition,with large alternate input signal,the Vcb limits of the BC550-560 can be exceeded with power supply of 85V for the input differential,and a risk of destroy is also for the current regulators.I don't know the current on this stage,but this is very low due to the power characteristics of the BC.
Moreover, as Chris has said, the second cascode stage has some problems to drive the gate capacitance of the output mosfets,it seems that they are the IRF devices.
If this is true,a thermal runaway it happens.
This is not a good design...
Cheers
Yes,on some condition,with large alternate input signal,the Vcb limits of the BC550-560 can be exceeded with power supply of 85V for the input differential,and a risk of destroy is also for the current regulators.I don't know the current on this stage,but this is very low due to the power characteristics of the BC.
Moreover, as Chris has said, the second cascode stage has some problems to drive the gate capacitance of the output mosfets,it seems that they are the IRF devices.
If this is true,a thermal runaway it happens.
This is not a good design...
Cheers
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