Vfet thump when power down - I’m confused.

[perkri]

Hi,

I’ve tried to understand how to fix the thump when powering down, but I’m a bit overwhelmed from reading through the thread…

The VFet I have is the second version in the offering, and with my Cornwalls, there is a rather “potent” thump when powering down.

Trying to figure out how to best fix this problem, and and help with this would be greatly appreciated!

Thanks!

Per

 

[techtool]

Sounds like you need a speaker protection relay board with "instant off" functionality, so that the speakers are disconnected from the amp before the power off thump comes along. The soft start or delayed start boards may already include this, but you may want to check before you buy something just to be sure.

 

[rhthatcher]

Have you looked into the Tuba Filter PCB?

https://www.diyaudio.com/community/...-vfet-theseus-chassis-incl-thump-kill.379747/

 

[Zen Mod]

maybe same iteration of amp https://www.diyaudio.com/community/...-pt-2-n-channel-assembly-by-mighty-zm.385977/

 

[Mark Johnson]

Post photographs of your power on/off switch and its connection to your SMPS filter PCB. Are you using a 2-pole switch having four or more terminals?

I have seen at least four possible "turn off thump reduction" techniques for the N-channel VFET amplifier, discussed on these Forums.

1. The one designed by Nelson Pass and included in the N-channel VFET kit, on its SMPS filter PCB​

​

2. The one called "Theseus PSFILT", whose PCB Gerber files are freely downloadable at LINK_1​

​

3. The one called "Tuba", whose PCB Gerber files are freely downloadable at LINK_2​

​

4. The Zen Mod redesign which asks you to modify your existing Nelson Pass PCB (cuts + jumps + new components), discussed at LINK_3​

 

[perkri]

Wow, thank you for the thoughts & links!

Time for some reading, paper and pencil…

Here are some photos of the build.

 

[Zen Mod]

simplest is to do what I did, you'll see all necessary details

though, I'm pretty sure that turn-Off thump is completely harmless, as I explained in linked thread

if you can endure sound of it, just chill

if not, then change what's needed

 

[perkri]

Suppose I could/should leave well enough alone 🙂

I‘ve read, and you are reiterating it now, that it is harmless.

Its just annoying. Plus, the switch that is in the unit/came with it, seems a bit “soft”. By that I mean, it doesn’t click into/out of position with a definite click. So I figured, if the noise is annoying, and as the switch doesn’t feel right and will be replaced anyway, might as well address the thump at the same time if it’s not too big a thing to fix.

From what I understand, the noise is different in intensity with different units? Seems like this one got the pop, and combined w the 102db speakers, is amplified (see what I did there?)

thanks again,

per

 

[Mark Johnson]

It's not a gigantic surprise that you are experiencing turn-on and/or turn-off thumps.


_

 

[perkri]

Thanks Mark!

Yeah, I know, right?

When I built the amp, I remember reading about the switch being changed, and the jumper being removed? Can not for the life of me find that info… I just remember it being a pretty straight forward thing to deal with as far as reducing its impact.

Per

 

[Zen Mod]

well, you got all the facts, now is up to you

🙂

 

[perkri]

🙂

Lunch is packed.

Its gonna be a lonely trip…

Thank you!!!

Per

 

[tunasto]

I can confirm Zen Mod's approach is M2 in its roots.
Simple and elegant.
Oh, yes and it works.
🙂

 

[Zen Mod]

oh, yeah

One M2, to Rule them All!

 

[tunasto]

I'm talking about Zen Mod's MOD for thump off.
😛

 

[perkri]

Thanks!

As soon as I finish with my day job, I’ll indeed be thumping off…

 

[perkri]

Thank you for all your help. Step one will be to replace the switch and wire it in properly. I will re-examine the thump once that’s done.