JFET input, MOSFET VAS, LATERAL output = Perfect!!

[keantoken]

SWF, for groundplane prototyping why not just use veroboard and rest it on top of a blank PCB covered in masking tape?

- keantoken

[GregH2]

Kean,

The PCB was never meant to be a prototype! It was meant to be my final version.

I left facilities for all sorts of compensation and filters, but now that I have decided I don't want them I think I'll make something more compact. Nice idea with the masking tape though.

[keantoken]

For my prototypes I want to use a PCB covered in masking tape, and then cut out parts of the tape to use as ground connections. This way I can solder the components and wiring very close to the plane. I can even build the same prototype on both sides of the board, for a stereo prototype. However I suspect that having two ground planes right next to each other could cancel the ground plane specific effect of currents "following the path of least inductance". No one has bothered to try and confirm or deny this to me however.

- keantoken

[dadod]

Why do you need .1R source resistors???

[AndrewT]

could this explain why?

JFET input, MOSFET VAS, LATERAL output = Perfect!!

[GregH2]

Hmm,

Was just playing around again, and it turns out 330pf to 500pf of miller capacitance will solve my overshoot problem. Didn't have much of a listen as it is late here, but my hopes aren't very high. This is an order of magnitude greater than I have tried before. Any thoughts on whether this is an obscene amount compared to most amplifiers?

[keantoken]

This is a VERY fast amp, and as a rule the faster the amp, the larger the compensation cap needed.

- keantoken

[mikelm]

A while ago you were forgetting overshoot and celebrating the great sound of your amp.

What happened ?

I guess your ears will decide if it's obscene

but beings you asked, then yes, I think it is obscene !

[GregH2]

Haha,

Yes true! The only thing I am nervous about is I have been tesing with very short leads and I worry about what will happen when I finally get it into the lounge room and have 3m cables.

But yes, you are right. I fiddled with it this morning and all of last night, with both phase lead and lag up to 330pf, and every combination in between. 330pf does tame it, but the life just disappears and it begins to sound like any other amplifier. I dropped the degeneration in the vas to see if that helped get some life back too.

I have to say, my speakers are very flat and rarely sound good, so it is possible I am looking for some artificial life for my music by using an amplifier that is slightly unstable.

As long as I can get away with it in my final listening position I will be using no compensation. I will try some stability tests with 3m leads tonight.

Oh, one more thing I have found.

I am running only 6mA in the vas using the zvp3310a and like the sound. This creates a very asymmetric square wave with a fast rise time and slower (though still 10x faster than audio) fall time. I think this strong asymmetry may increase the 2nd harmonic distortion and perhaps is why I like the sound so much with this little MOSFET.

[AKSA]

SWF,

You got it!! H2 rules, OK?

Hugh