What would a Sziklai pair do in an effect?

[Marc.yo]

Has anyone ever used a Sziklai pair in a guitar pedal? Can you show a configuration and it's use?

If you're wondering what it is, it's right here.


Thanks

[mattpocket]

So its like a PNP and an NPN...

Sounds really interesting, does anyone know any part numbers for trannies of this orientation?

Matt

[Sir H C]

Sziklai pairs were used in the "old days" when high power, fast PNP devices didn't exist.  So you would have a PNP driving an NPN - collector of the PNP to the base of the NPN, and the emitter of the PNP to the collector of the NPN, and this would look like a PNP but you lose about 1 volt of headroom.

Use in a pedal?  I guess you could make a fuzzface wtih these, it might do some interesting things, might work well with silicon NPNs and leaky germanium PNPs.

[Marc.yo]

I'll go try 2 silicons. I'll report back

[R.G.]

The Sziklai pair is comparable but slightly different to a darlington pair. It gives you hfe squared current gain, generally high linearity and high frequency response, and allows you to fake a power PNP from a PNP and a power NPN.

It is a 100% feedback setup, and as such it will wipe out many of the little oddities that make transistors desireable for effects. It should be very clean and high gain until it bangs into a power supply limit. When that happens, it limits sharply.

[Marc.yo]

You're exactly right. It's amazingly clean and warm. Holy cow! I'm not using any caps. I'm using a crappy SS amp (for now). Just one resistor and a LED. It's set up like a Bazz fuzz. No distortion at all. None. I'm also using a strat with a maple board with the bridge pickup. Normally it's pretty ice-picky. Now it's crazy. This a crazy clean boost!

[sfx1999]

Then design a booster around it!

[Marc.yo]

will do. I'm working on it!

[markm]

Then design a booster around it!

This is quite an interesting configuration indeed! 

[Dragonfly]

http://www.diystompboxes.com/smfforum/index.php?topic=56651.0

http://www.diystompboxes.com/smfforum/index.php?topic=38394.0

http://www.diystompboxes.com/smfforum/index.php?topic=52271.0

http://www.diystompboxes.com/smfforum/index.php?topic=38578.0

[Marc.yo]

I'm thinking the LED needs to be across the base and the collector. If it's not you get this horribly farty distortion.

[brett]

For some inresting uses of this setup in simple guitar amps, check out Rod Elliott's (?) ESP pages.
All of his guitar-related pages are excellent reading for any medium-level DIYer in the forum.
cheers

PS besides this configuration, there's another, related system that's very handy.  You can see it in the Bosstone.  I don't know if it has a name.  Instead of the second device giving a multiplying effect on gain, it adds a smaller multiple, and lowers the output impedance.  In the Bosstone, Q2 is used to double the gain available from Q1, but it could easily be adapted for other increases, such as 3, 5 or 10.  If someone smarter than me could work out a feedback system, you could replace many op-amps with these little monkeys.   

[R.G.]

There are quite a number of the two-transistor feedback pairs. They do have quite a wide range of applications and in fact they were used in many of the places we would use an opamp - until opamps became affordable.

They were dumped because they don't have quite the linearizing gain, they don't have quite the predictability, and they are not quite as flexible. They take the same number of components or more to do the same job and more PCB space. And for the electronics industry, that was enough.

There is a feedback system in each of them, and it varies with the exact circuit as to how to set it up. That's another reason opamps replaced them - they were more complicated.