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Old 9th December 2012, 02:02 PM   #3691
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Thank you. I'll try it.
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Old 9th December 2012, 02:41 PM   #3692
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I've tried it with a MOSFET pair. The amplifier oscillates now from 53 volts. The oscillation has weakened. I am making a PCB with drivers. Thank you for supporting
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Old 9th December 2012, 03:33 PM   #3693
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Lazy cat, may-i suggest-you to post measurements of your amps ?
HD, IM and bandwidth ?
There is surely a visible benefit with the use of your CSS.
About the CSS, it would be interesting to show what's happens at their outputs at Hf (1Mhz) while full signal in the amplifier ?

Coolwater, while you fight with stability problems, may-i suggest-you few tips ?
First to try to increase the open loop bandwidth as much as possible, means reduce as much as possible the miller caps.
You can work on the output zobel and a cap // to the serial resistances of the feedback path to tune the phases.
An inductance in output can help too, if the problem is too much capacitance in the load.
If you use a simulator, in order to track the problems, do not forget to remove the input filter cap, when you track the phases.
Hoping it will help.
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Last edited by Esperado; 9th December 2012 at 03:46 PM.
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Old 9th December 2012, 03:53 PM   #3694
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Hello Esperado, a good idea, thank you. A trimming capacitor in parallel to the serial resistances of the feedback path to tune the phases. I try it .
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Old 9th December 2012, 04:01 PM   #3695
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Quote:
Originally Posted by coolewater View Post
Hello Esperado, a good idea, thank you. A trimming capacitor in parallel to the serial resistances of the feedback path to tune the phases. I try it .
You can tune-it for no overshoot à 1Khz for small signals as well as half the power.
The reason to reduce the miller is to keep the open loop bandwidth as high as possible. It has a direct impact on the quality.
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Old 9th December 2012, 06:11 PM   #3696
shaan is offline shaan  India
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Quote:
Originally Posted by Lazy Cat View Post
Why you never connect output transistors pins directly to PCB?
Hi LC.

The wires are for testing different pair of LATFETs in the same board, with as less mess as possible. Under-board aesthetix.

The gate wires have two 100ohm stoppers at each end, one on-board, another on FET.

The final assembly will not have these ugly wires; what's the meaning of having a peeceebee if putting wires here and there?

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Old 10th December 2012, 06:59 AM   #3697
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Hello Esperado, Hello LC,
I have removed all 47pF Kapacitors. I tuned the phases with a a trimming capacitor in parallel to the serial resistances of the feedback path. I had a perfect rectangular signal. When I switched to a second pair of MOSFET were the oszillations again. I will turn to a driver stage. One more question: What the resistors R8 and R10 effect at 1.2 K? In my opinion, provide the resistors Transisoren the Q1 and Q2 with current when the output signal is 0 volts. Is that correct?
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Old 10th December 2012, 09:16 AM   #3698
Jay is offline Jay  Indonesia
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Hi Gerd,

I think you can do the following to improve the stability of your circuit:
(1) Lower the input resistance. 1K is too high
(2) Add the 2 diodes circuit across the input emitters as in the basic circuit.
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Old 10th December 2012, 05:45 PM   #3699
shaan is offline shaan  India
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I connected the second board and it's working well as well...

Bias almost equal to the first board, 4mA, 18mA, 170mA! I think I've got some decent parts this time. No bad effects.

Soon gonna put them inside a nice case. Probably with a toroid.
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Old 18th December 2012, 04:51 PM   #3700
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Hi,

the final version of my SSA Mosfet. The PCB is in the works. A Question to the Bias:
In my opinion would be 100 mA enough to the end Fets and 15 mA to the Cascodes. What value of Bias would be useful for the driver Fets M9 and M10?
I can change the current through the cascode, by two Ways: First: I change the value of Resistors R9 and R12 (270 Ohm). second: I change the value of the Cascode -Resistors R16 and R18 (10 Ohm). What would be the better way?
Best regards Gerd
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