Negative Sziklai

Status
Not open for further replies.
Jump to Latest
#3
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.
 
#6
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

An externally hosted image should be here but it was not working when we last tested it.




Tim
 
#7
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.
 
#8
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.
 
#9
Lumba Ogir said:
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.
Click to expand...


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
 
#10
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 🙁
 
#15
Hello jcx,

jcx said:
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
Click to expand...

you're perfectly right. The resistor increases the gain of the regulator, giving better ripple rejection: and this gain increase is much stronger than the inevitable ripple "path" to the transistors (of course this effect is mainly at high frequencies).

Lumba Ogir: just try to do a SPICE simulation, you'll see what I mean 😉

An externally hosted image should be here but it was not working when we last tested it.


Red trace, no resistor: green trace, 100ohm resistor 😀
 
#16
timH said:
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 🙁
Click to expand...

Well, that's hard. But I think, honestly, that with a good layout and the accurate choiche of passive components, that a LM317 outperforms this circuit and potentially is smaller in PCB area. Maybe, if the voltages are standar values, even fixed regulators can work in your application.

May I suggest the reading of "Linear & Switching Voltage Regulators Handbook" by OnSemi, I think you can download it for free in their own website.

My :2c:
 
Status
Not open for further replies.
Top Bottom