NFB on a switch....question

[studiodunn]

What (if any) issue is there putting the NFB on a ON-OFF-ON switch with one ON to 8ohms and one ON to 4ohms?

[sluckey]

No issues unless you mount the switch next to your input jack or some other sensitive area.

[Roe]

just use a resistor in series with a pot, e.g. 22k and 100k respectively

[studiodunn]

just use a resistor in series with a pot, e.g. 22k and 100k respectively

But won't this mean I can't remove the NFB, as opposed to my switches off position?

[pompeiisneaks]

If the switch is 'off' it can't send current so it's definitely off. Series means before or after the pot itself, if there's an open circuit, nothing goes through at all anyway.

[studiodunn]

I assumed he meant using the pot in place of the switch.........

[pompeiisneaks]

Oh then that makes sense You could still use a switch to take it out of the loop I'd guess but you only need a simple switch at that point. Although I think you need to figure out how to make sure the pot doesn't stay in circuit with it 'off' as that can cause problems with the PI (Sluckey told someone about this a day or two ago on some forum somewhere ;P. I don't recall the exact details.

[sluckey]

That was a totally different scenario. The guy was using a 100K presence pot in a circuit that normally expects a 5K pot. He was strangling the LTP PI tube since cathode current has to pass through that pot.

[pompeiisneaks]

Oh that makes sense now that I think about it. a 5 or 10k presence pot won't have a major impact but 100k is a much bigger current throttle.

~Phil

[MakerDP]

A 100k pot with push-pull switch gives you a ton of flexibility with your NFB loop and is my preferred way of doing it.

[Roe]

just use a resistor in series with a pot, e.g. 22k and 100k respectively

But won't this mean I can't remove the NFB, as opposed to my switches off position?

you can remove the NFB with a no load pot. Alternatively, use a 1MA pot, which will remove almost all NFB

[roberto]

This is my favourite for this purpose, together with a 10-33k resistor in series. Better to switch on/off while in stand-by.
https://www.tube-town.net/ttstore/Poten ... :1601.html

[studiodunn]

Thanks for the suggestions!

I put it on a switch since I was already going that direction. It works great on the amp and really helps define the tone I'm going for.

So, is it a bad idea or BAD to switch while engaged?

[RockinRocket]

This is my favourite for this purpose, together with a 10-33k resistor in series. Better to switch on/off while in stand-by.
https://www.tube-town.net/ttstore/Poten ... :1601.html

Better to switch feedback in standby because of the annoying noise it makes or its technically bad for the output transformer, switch ect?
Thanks

[roberto]

Exactly. Switching while engaged will pop.
Not dangerous, but annoying.