VSSA Lateral MosFet Amplifier

[PMI]

Less than 50ns 10V P-P into 50Ω http://www.teknetelectronics.com/DataSheet/WAVETEK/WAVET_182A_188110658.pdf

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.

 

[Salas]

Hmmm surely good for up to 200kHZ squares for adding no own limit.

 

[PMI]

Hmmm surely good for up to 200kHZ squares for adding no own limit.

At least, although for my own purposes, testing at over 50KHz square wave was not needed.

If you would care to suggest some test conditions, I will be happy to run some tests later this week, as long as I can do them with the same o-scope etc.

 

[Salas]

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.

 

[Salas]

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?

 

[PMI]

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.

 

[Salas]

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.

 

[Salas]

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.

 

[DuffyDawg]

Tune-up of SMPS400A180 as follows:
- 820 uF/200 V SAMWHA replaced with 1500 uF/200 V Panasonic EE
- 100 uF/100 V SAMWHA replaced with 220 uF/50 V Panasonic FR
- 10 uF/100 V SAMWHA replaced with 47 uF/63 V Panasonic FC
.

Hi LC,

Could you provide the quantity of each capacitor required to modify 1 SMPS?

Thanks, Mark

 

[PMI]

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.

 

[jambul]

Hi lazy cat,

One quick question, can you help me to build the cute little headphone amp base on vssa topology?

Thanks in advance

 

[jambul]

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

 

[Lazy Cat]

Hi lazy cat,

One quick question, can you help me to build the cute little headphone amp base on vssa topology?

Thanks in advance

The best would be exactly the same VSSA PCB as it is now, only with +/-20 V PSU and a little serial output resistance, 22 Ohm or so to suit your type of headphones. The good thing would be pure class-A and still small heatsink.

 

[Lazy Cat]

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.

 

[Lazy Cat]

Hi LC,

Could you provide the quantity of each capacitor required to modify 1 SMPS?

Thanks, Mark

- 2 x 1500 uF/200 V, 105°C, EE series, 5,22 A ripple
- 6 x 220 uF/50 V, 105°C, FR series, 1,6 A ripple
- 2 x 47 uF/50 V, 105°C, FR series

For one SMPS400A180

 

[tinitus]

The best would be exactly the same VSSA PCB as it is now, only with +/-20 V PSU and a little serial output resistance, 22 Ohm or so to suit your type of headphones. The good thing would be pure class-A and still small heatsink.

or output trafo ?

 

[Lazy Cat]

or output trafo ?

Yes some Lundahl for ultimate galvanic isolation, can be step down too

 

[AKN]

Hi,

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



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

Looking forward to this build

 

[Salas]

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.

 

[BenY]

- 2 x 1500 uF/200 V, 105°C, EE series, 5,22 A ripple

For one SMPS400A180

I`ve been searching both Mouser and digikey for this capacitor and didn`t find anything close..
What size capacitor it is???
Thanks.