Negative Sziklai

[timH]

Can someone give me the layout of a negative sziklai please. I can only find a positive layout

Thanks

Tim

[Giaime]

Mmm... are you talking about this?

http://www.dself.dsl.pipex.com/ampins/dipa/dipa.htm

Scroll down. The first schematic has a complete CFP output stage

[AndrewT]

fig 1a and fig 13 C show your Sziklai outputs and the other configurations.

For anyone else listening, the Doug Self articles are excellent grounding for learners to the subject of discrete amplifier design.
I'm not suggesting copying whole schematics, but more keeping all those little ideas for when they might be needed, eg, 5.7 distortion 7, where to tap off the NFB loop, this mistake is repeated by the majority of experienced builders but should never be made by a competent designer/builder.

[timH]

Thanks - yes that's what I needed

Tim

[Giaime]

Originally posted by AndrewT
For anyone else listening, the Doug Self articles are excellent grounding for learners to the subject of discrete amplifier design.

A must read

Originally posted by AndrewT
I'm not suggesting copying whole schematics, but more keeping all those little ideas for when they might be needed

I perfectly agree. If you could see those errors made in $$$$ priced amps...

[timH]

I'm actually wanting to use the Sziklai in a VBE (or gyrator or whatever it's called)

This is the circuit I've come up with for a negative version (based on the positive circuit given by teddy-pardo over on pfm) - sorry its a bit larger than necessary





Tim

[Giaime]

Mmm, I think you missed out a resistor. Look at the CFP/Szilaki pair: there is a common collector driver transistor, which has a "current sensing" resistor on its collector, to drive the "bootstrap" power transistor.

So try a resistor between the lower transistor collector, and the upper transistor emitter, of 100ohm - 470ohm, you'll enhance the "cleanup" action of the gyrator.

Edit: Ps depending on the actual transistors, and the spectral content of noise to be removed, you may not need the resistor in series with the lower bjt's base.

[Lumba Ogir]

Giaime bouna sera,
no, your explanation is not quite correct. That "current sensing" resistor is actually current source for the PNP transistor. In this application, a series pass regulator, it can be omitted to avoid the injection of harmful ripple voltages into the sensitive base of the NPN transistor.
In other applications it is used for defined higher standing current.

[jcx]

Originally posted by Lumba Ogir
Giaime bouna sera,
no, your explanation is not quite correct. That "current sensing" resistor is actually current source for the PNP transistor. In this application, a series pass regulator, it can be omitted to avoid the injection of harmful ripple voltages into the sensitive base of the NPN transistor.
In other applications it is used for defined higher standing current.

some value of npn_be resistor is usually better than none, increased bias current in the pnp increases gain of the pnp and the R_be can speed up turn off of the npn - both improving input ripple rejection at dc and higher frequencies - the signifcance of both effects varies with transistor properties and operating conditions

[timH]

Thanks guys - I'm getting outside my understanding envelope with this so I'm gonna go the experimental route and try it without the base to emitter resistor first and then try it with and see if my ears hear a difference


Tim

ps problem is that they're gonna be fitted in a locally regulated pre-amp so there will be 14 of them to add resistors to