Switchable cascade hi/low input. Does this look ok?

[Gainzilla]

Hi all,


I've seen some other threads on this site about switchable cascade options. I would like to add a switchable cascading gain stage, like plugging into the high gain input on a JCM800, vs the low input. Only with a switch. 


Does this work as drawn? Or at all? Does this look like it will pop?






Thanks in advance!

[John]

Seems like it should. I *think* you need a path to ground for the unused grid though, like a 1M resistor. It might would pop, but a 470k to 1M resistor across the switch should fix that too.

[HotBluePlates]

Agreed. I'd move the resistor to ground at the input jack over to the grid of the tube which doesn't have a resistor to ground. That way, both preamp tube sections have a resistor from grid to ground.

That's because the function of the resistor on the jack (as seen in other amps without input switching) is the same as the resistor which is connected directly at the preamp tube grid. It is just moved to a physically different (but electrically-same) place.

[Gainzilla]

Agreed. I'd move the resistor to ground at the input jack over to the grid of the tube which doesn't have a resistor to ground. That way, both preamp tube sections have a resistor from grid to ground.

Like so?

[John]

That should do it.

[Gainzilla]

Great, thanks! I've got the tube sockets/power supply wired up. I'll post back with pics/sound clips when I get the rest wired in.


Cheers!


BTW, HotBluePlates: Following our previous thread (Lonestar SE), this is the topology I plan on building. Naylor Super Drive preamp (but I'll be using a mosfet as cathode follower), tube effects loop, Cathodyne PI, P/P EL84 power amp. As per this thread, switchable cascade stage. On paper, should be a fun amp.

[lego4040]

Look at my thread" Legos ac15" thread. Last page reply #627 has Sluckey's picture diagram of it