Which is Beter Quasi Or Non Quasi

[nigelwright7557]

I found with a single ouput pair quasi I got a better sound because of the extra driver stage. I found a tendency to just use a VAS to drive the output stage in a complimentary output stage.

I found the quasi to have a little more depth to the sound.

I run a mobile disco and use a complimentary output amp with 3 pairs of MOSFETs.

I found the quasi amp a bit more sensitive to bias than the complimentary amp.
The quasi tended to drift more thermally.

 

[richie00boy]

That is called a speed-up capacitor Shaan, it is one of the things you need to try in real life and see if it helps really. It allows charge to be removed from the bases faster, but also affects bias at high frequencies.

 

[shaan]

i see... any value suggestions please?

thanks

 

[Mooly]

It's not critical, 47 or 100 uf is usual.

 

[homemodder]

It's not critical, 47 or 100 uf is usual.

That large for a suckout cap ??? I use max 1uf on EF or triple outputstages, anything larger seems to make matters worse than better.

Mooly can you show an example of a amp with such high suckout cap or just mention one or two, I cant think of any using such high values.

 

[Mooly]

Mine for one, Doug Selfs designs for another. The caps across the vbe multiplier.
Are you thinking of the cap that links the emmiters of quasi drivers when they are cross coupled to allow for reverse biasing the outputs to increase speed ?

 

[homemodder]

Yes I was thinking you meant the cap across the drivers emitter resistors, the cap across the vbe multiplier I agree, between 10 to 47 uf is good, rather to the higher side as this will prevent oscillations especialy if youre using a darlington or cfp type vbe multiplier.

 

[shaan]

Wow! Thanks for the good info people.

Regarding Oscillation...

I ran this sim with a 10kHz squarewave and the output really matches what you guys said. I'm impressed! I will install this cap in the next board as the current board doesn't have enough space even for such a small cap! Once I though of putting it in the solder side. But the Art would die if I did it!!!!!

BIG THANKS.

 

[gorex69ers]

Presently Yamaha RS202 & RN303 amp is using quasi complimentary type of output stage using 2SC4468 as its output transistor.

 

[GEirin]

RN 303

 

[GEirin]

how does this quasi work?