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VSSA Lateral MosFet Amplifier

Correct... Square wave rise/fall time is rated at less than 50 ns 10V peak-to-peak under ideal conditions. But it is not as simple as that, because from past experience I noticed there seemed to be some dependency on the selected frequency range, too.

Can't say I ever verified the fine print, but I can take a look next time I use it. Never really been an issue for audio before.
 
If you had an arb gen maybe you could design a combo signal with a fast edge, then a ramp down, a ramp up and some pulses full scale and runt so to push stability checks. Still a non ringing 50kHZ square pass you did is a very good health indicator.
 
P.S. The small edge you had might just be the amp input had no 50 Ohm feedthru. What was the LPF freq you used at its input?
That is possible, I used a piece of coax attached to a few inches of audio cable, hardly ideal.

The input filter is exactly (same values) as shown in Shaan's schematic. In addition to that, 47pf at the VAS transistors (none shown on that schematic), 100R and 130R gate resistors at the SK1058/SJ162 no Zobel installed on the board at the time of test.
 
This topology if CCSed can do 2.5-3MHZ even, but its better be limited for all practical intends and purposes to what it can do safely on any given layout. Lazy Cat had surely done that. The tiniest the safest for fastest.
 
What is the -3dB of the working closed loop amp? You can check that point for a sinewave going from 6 graticules down to 4.25 since you got 4MHZ gen capability. Shaan's 1k 100pF input LPF should kick in for about -3dB @ 1.6MHZ anyway.
 
What is the -3dB of the working closed loop amp? You can check that point for a sinewave going from 6 graticules down to 4.25 since you got 4MHZ gen capability. Shaan's 1k 100pF input LPF should kick in for about -3dB @ 1.6MHZ anyway.
I can read the scope, and calculate the corner frequency, n/p there. I intend to repeat some of the tests anyway, and I will make a note of 3 db freq at the high end. At the moment I just remember it was well above what I was interested in at the time.

If I am going to test above 100K, we should also decide on what kind of load to use for the test, if any.
 
Aha,

I need to drive 20 - 60 ohm in ear monitor and headphone, and my stax lambda as well with the equalizer.

Thank lazy cat

You have to know the ALF double mosfet is a very good device and small VSSA layout has very low noise, ideal for headphones. Serial resistance value have to be tested to find most suitable. Also serves as a protection against full output, short circuit etc.
 
Hi,

Heatsink testing in forthcoming VSSA home (old Rotel amp).

VSSA_home.JPG

Heat sinks not so big but still manages about 20C above ambient at ~14W (VSSA bias).

Looking forward to this build 🙂
 
I can read the scope, and calculate the corner frequency, n/p there. I intend to repeat some of the tests anyway, and I will make a note of 3 db freq at the high end. At the moment I just remember it was well above what I was interested in at the time.

If I am going to test above 100K, we should also decide on what kind of load to use for the test, if any.

Just nominal Ohmic.