An amp with 2 separate PI's

[macula56]

this morning i saw a schematic for an Orange AD30, i believe, that had 2 separate PI's. it used switching to run them into the power section. if i wanted to build something with 2 different PI's and run them into the same power amp section, what would i need to do? would i have to switch them in and out so that one was in the path while the other was out of the path? could i use mixing resistors like we do to combine channels before going into a PI? could i run both of them straight into the power section without worrying? any ideas ot thoughts would be greatly appreciated.  thanks, JMac.

[sluckey]

I would think you could just simply parallel the 2 PI inputs but would need to use a DPDT switch between the PI outputs and the PA grids. Exactly how did the Orange switch?

EDIT... I've just looked at the AD30 schematic and don't see dual PIs. Can you provide a link to the schematic you saw?

[macula56]

see if this works.
http://users.telenet.be/orangefg/OFG_SCHEM/AD30TC_mainpcb1.pdf

[FYL]

this morning i saw a schematic for an Orange AD30, i believe, that had 2 separate PI's. it used switching to run them into the power section.

It's the Twin Channel version, supposed to offer different preamp distos : two full preamps and PIs with PPIMVs switch-selectable. The standard AD30 uses a more classic architecture.

if i wanted to build something with 2 different PI's and run them into the same power amp section, what would i need to do? would i have to switch them in and out so that one was in the path while the other was out of the path? could i use mixing resistors like we do to combine channels before going into a PI? could i run both of them straight into the power section without worrying?

You may use mixing R's or pots if the signals are in phase, or a switch or...


(Edit: corrected a couple of typos)

[macula56]

FYL said,
You may use mixing R's or pots if the signals are in phase, or a switch or...

by in phase you mean the same numbers of stages, correct? or does that mean both channels have either odd or even numbers of stages?
i don't want to switch them. i want them on all the time but switch between inputs so i guess i will try mixing resistors.

[FYL]

Some stages are phase inverting (plate follower), others aren't (cathode follower).

[macula56]

ah, i see. i don't know yet what i am gonna wire up for preamp stages.