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zigzagflux 25th April 2008 02:36 AM

Differential stage biasing choice
2 Attachment(s)

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,

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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