Nipples

[christarak]

Greetings from the land of "Covid-(Almost)-Under-Control".

Have you seen a sine wave with a pronounced "nipple" at the top or bottom of the sine wave? Any ideas as to what is it, and is there a generic cause?

My apologies if I posted this under the wrong forum.

[nickb]

We really need a schematic and to know the conditions of the test.

If I were to guess, just for the fun of it, you are looking at the waveform inside a negative feedback loop and the output is clipping

[christarak]

We really need a schematic and to know the conditions of the test.

If I were to guess, just for the fun of it, you are looking at the waveform inside a negative feedback loop and the output is clipping

Thanks Nick. Its not a specific amp this time, but yes, it does seem to accompany not-nice clipping or other nasty waveforms. I can't recall where I have seen it. I was curious to know if the "nipple" was a symptom well-known to those more experienced than me.

We are hearing horror stories of Covid in the UK. One in 50 households. That's not good. I hope you get your vax soon. The Australian government has the arrogance to make us wait until March. They must think that our tests are better than the EU, UK, USA!!

[Leo_Gnardo]

Have you seen a sine wave with a pronounced "nipple" at the top or bottom of the sine wave? Any ideas as to what is it, and is there a generic cause?

In tube amps, with a the amp driving a resistance/impedance greater than that specified for the output tap. Not just a little bit, say double the intended load, or more.

What's the circumstance of your observation? Tube/transistor? Inquiring minds want to know.

Avoiding covid like the plague in the USA. Mask up, keemo sabay!

[nickb]

When the output clips the feedback boosts the signal to try to fix the problem.

[nickb]

Avoiding covid like the plague in the USA. Mask up, keemo sabay!

Well that seems to be a particularly appropriate idiom

[The Dude]

Damn! I thought it was gonna be a porn thread.

[nickb]

The night is still young!

[trobbins]

Check the PI stage - nipple distortion is known to occur there - Merlin posted some scope plots many years ago to describe the overload results that can occur, and how to alleviate that.

[christarak]

In tube amps, with a the amp driving a resistance/impedance greater than that specified for the output tap.

Thanks Leo. That's good information just there. I'm filing that in my last remaining memory cell.

[christarak]

When the output clips the feedback boosts the signal to try to fix the problem.

That explains it beautifully, Nick.

[Helmholtz]

Check the PI stage - nipple distortion is known to occur there - Merlin posted some scope plots many years ago to describe the overload results that can occur, and how to alleviate that.

That would be a typical cathodyne effect. Only the negative half of the plate output will show the nipples when grid current starts.

[christarak]

Check the PI stage - nipple distortion is known to occur there - Merlin posted some scope plots many years ago to describe the overload results that can occur, and how to alleviate that.

Thank you for that. I think it was in the PI stage, come to think of it. I bought Merlin's book a couple of months ago. I'll see if I can find that. Much appreciated.

[Helmholtz]

Thank you for that. I think it was in the PI stage, come to think of it.

The NFB effect nickb described would also show at the PI outputs.

[christarak]

That would be a typical cathodyne effect. Only the negative half of the plate output will show the nipples when grid current starts.

Vielen dank, Helmholtz. I will stare at a Cathodyne PI until I understand this cause. Do you mean when the grid voltage increases and the plate voltage drops (and the cathode voltage increases)? I hope this effect is explained in Merlin's book.