another schematic

[sakis]

this is a schematic that i made some conversion with ....

the particular schematic belongs to greek made amp that worked alot around the late 70's

of course if the topology is a copy of some existing amplifier please let me know since i realy dont know were is it coming from or who was the original designer ....

the original schematic was a quasi so i removed the quasi output and made it an sziklai ....

i havent test it yet ( no time ) but i found time to draw a schematic for people to see and advice me if they see some things wrong ....

i apologize for starts cause i copy the schematic from a pcb so there is a chance or more that i have made mistake ( s)

the original amp is a working amp that actually performs very well but i dont like quasi ......

[darian]

The BD140 lower right is upside down.

[jaycee]

Hmm, it seems like someone took the Hitachi lateral MOSFET demo circuit, and glued a CFP output stage onto it!

[Wavebourn]

It looks like the original designer struggled a lot to make this thingy stable on high frequencies... I think changing something even in layout you'll face oscillations.

[AndrewT]

could someone explain how the Vbe multiplier works?
and does the diode in there give thermal compensation?

[scott wurcer]

Something fishy about that offset pot.

[Wavebourn]

Originally posted by scott wurcer
Something fishy about that offset pot.

It should work, since a current mirror with diode and transistor is not ideal. However, a trimmer between upper 100R resistors (from emitter and from diode) with a wiper to + rail would look better.

[Wavebourn]

Originally posted by AndrewT
could someone explain how the Vbe multiplier works?
and does the diode in there give thermal compensation?

The diode gives additional voltage drop with lesser dynamic resistance than a plain resistor would have. And yes, it is in series with BE junction so will work as well for thermal compensation.

[sakis]

except the output circuit does the rest ring a bell ????

as a quasi this amp used to work very fine

waveburn :
It looks like the original designer struggled a lot to make this thingy stable on high frequencies... I think changing something even in layout you'll face oscillations.

not really ....since this amplifier was made to drive 100v transformers i think that the designer wanted to "keep " amplifier stable at all times

100v systems can be very tricky some times

what atracted me to this amp is that no matter these aditions for keeping it stable it really works fine .....meaning that less is better but when you add carefully then its ok .....you gain safety without loosing quality ....

will see needs more study arround it