Diezel VH4 Negative Feedback switch - how much voltage?


Active member
My goal is to wire up a SPDT on-on switch between the 4 ohm and 8 ohm speaker jacks on my VH4, which then connects to the NFB circuit (white wire). This would allow me to switch between the stock NFB and about half of the NFB. I first learned about this from @fusedbrain in this post.

I've done this mod before by just moving the wire over to the 4 ohm jack, but I'd like to be able to switch between the two values as a fun experiment. After this, I'd like to try connecting the NFB to a pot to adjust it to a greater range and see what I prefer. Anyway, these are my questions:

1) Would the voltage going across the 4 ohm and 8 ohm speaker jacks from the output transformer possibly fry the switch? The one I'm looking at is rated 5A 120VAC / 2A 250VAC. I haven't measured the voltage on the wires yet, so I'm just brainstorming here to avoid possible mistakes.

2) Reducing an amp's NFB by too much could introduce excess noise/distortion, depending on how the circuit is designed, correct?


Well-known member
NFB is low current high voltage, so your switch is fine.

Less NFB means more distortion and less of a flat frequency response, so some notes will be louder than others volume wise.

You should be good!


Well-known member
I’ve used Carling and Taiway mini toggles for NFB switches for years with not one issue. I make them 3 way, 4, 8, 16 ohm AND add a NFB pot.

Some people say 8 ohm with more NFB resistance is equal to say 4 ohm with less resistance. Example 4ohm/47k vs 8ohm/68k. But I don’t agree and I still hear a difference.