Differential stage biasing choice

zigzagflux · 25th April 2008, 02:36 AM

Hello:

See attached. Questions are pretty simple, but feel free to add 'why' reasons, as it's helpful to know the reasons for what we do.

1. Which scheme would you use, top (CCS) or bottom (resistor)? My leaning is for the top.

2. For CCS biasing, is the capacitor necessary? It seems to me, there is absolutely no effect it will have on the circuit.

Thanks !

sawreyrw · 25th April 2008, 03:09 AM

1. In theory the top circuit is better because the current source has a higher impedance (resistance).
2. The cap should be eliminated. For AC purposes "it looks" like it is between the cathode and ground. Thus at higher frequencies it will shunt the cathode to ground impedance. You don't want this.

oldeurope · 25th April 2008, 07:01 AM

Hello zigzagflux,
please have a look here link .
What about a mixture from Western Electric PP and Differential (forced balance) ?!

Kind regards,
Darius

zigzagflux · 26th April 2008, 01:42 AM

Okay, that confirms that I can get rid of the capacitor (a good thing IMO- one less source of coloration and endless part swapping).

I'll have to mull over the forced balance option at Lynn's site. Anyone try this very design? His Amity/Karna designs are a little different from this topology.

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25th April 2008, 03:09 AM	#2
sawreyrw diyAudio Member Join Date: Apr 2006 Location: Minnesota	1. In theory the top circuit is better because the current source has a higher impedance (resistance). 2. The cap should be eliminated. For AC purposes "it looks" like it is between the cathode and ground. Thus at higher frequencies it will shunt the cathode to ground impedance. You don't want this.

25th April 2008, 07:01 AM	#3
oldeurope diyAudio Member Join Date: Mar 2008	Hello zigzagflux, please have a look here link . What about a mixture from Western Electric PP and Differential (forced balance) ?! Kind regards, Darius

26th April 2008, 01:42 AM	#4
zigzagflux diyAudio Member Join Date: Oct 2006	Okay, that confirms that I can get rid of the capacitor (a good thing IMO- one less source of coloration and endless part swapping). I'll have to mull over the forced balance option at Lynn's site. Anyone try this very design? His Amity/Karna designs are a little different from this topology.

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