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-   -   VFET amp Bourns trimmer exchange (https://www.diyaudio.com/forums/pass-labs/373208-vfet-amp-bourns-trimmer-exchange.html)

MEPER 5th July 2021 12:59 PM

No, not sure about this but want to give the VFET a "last chance".
I did not see anything unusual using lab-supply and I did see some strange noise on Meanwell supply so new supply will be an upgrade to the amp.

If one VFET is noisy I must decide to either live with it, try to get a new pair (is that possible?) or "upgrade" to THF-51 (I got some of these). There will be such an output stage in the future for this amp? .....also running at 36 VDC? :-)

PKI 5th July 2021 06:19 PM

Maybe sell the amp to someone who will use it as is? Those are kinda collector items. I closed mine the moment I finished it and have no intention to change anything. Nelson gave us so many other ideas and projects to toy with.

MEPER 5th July 2021 07:43 PM

It has no. 33.....same no. as Max Verstappen in Formula 1 :-)

I assume/hope the new SMPS PSU will solve the problem. Until then I have the fun "building" the PSU. I may add small bank of caps if space inside the chassis allows it. The quite powerful PSU can probably handle a "few" uF at the output.

Soundhappy 15th August 2021 07:17 AM

@ Meper

Any news ?

MEPER 14th September 2021 10:14 AM

2 Attachment(s)
I did not see the "request for news" until now where there is a little bit of "news".

The new SMPS module arrived after two months last week and I then built the module into a chassis and added a couple of filter caps at the output (4-poles) as you can see. It reduced the ripple noise a bit (from 9 to 6 mV when just measured using a DMM).

Also added an output fuse (4A F) and in IEC inlet there is a 1A T fuse to avoid any disaster from the 2 kW module. Without additional heatsinking it run about 62 C where it is hottest (when loading amp (3.2A)). The thermal fuse kicks-in at about 90C according to spec. So I think it is ok to let it run "as is". When chassis is closed it will probably be a little "hotter". I guess it is ok as I measured the temp direct at component side. Heatsink is a bit cooler. Module has soft start both at input and output and has no problems with the filter caps.

But noise problem is still there. I get these "noise bursts" from time to time (20 mV when it peaks) at speaker out. Other times it is 0.0 mV and can be that for at long time. Other channel is always 0.0 mV AC.

I made the big decision to de-solder VFETs and swap them. Until now only de-soldered and as you can see three solder pads also came off. But I assume these are "stand-alone" and it will only make it easier to de-solder next time :-) ...still one pad in place....

I need to clean the TO-3 PINs and insert again. I have marked the "suspicious" one :-)

MEPER 14th September 2021 10:32 AM

Correction.....it was solder only on pins (no pads). So it was easy to clean.
I used hot-air to de-solder and it went rather smooth.

Soundhappy 14th September 2021 11:38 AM

@ Meper

Such courage!
Fantastic you don't give up and make your all possible efforts.
Good luck for perfectly perfect amplifier :treasure: Cheers

MEPER 14th September 2021 11:40 AM

Noise problem has now moved from right to left channel. So one of the VFETs makes these "noise bursts" from time to time.

Is there any source somewhere of these?
In principle I only need one.....(measured to "84") ....what that number means I don't know? Vgs figure?

MEPER 14th September 2021 11:49 AM

Quote:

Originally Posted by Soundhappy (https://www.diyaudio.com/forums/pass-labs/373208-vfet-amp-bourns-trimmer-exchange-post6785304.html#post6785304)
@ Meper

Such courage!
Fantastic you don't give up and make your all possible efforts.
Good luck for perfectly perfect amplifier :treasure: Cheers

Yes, let us see if I end up with a perfect amp :-)

You often show pictures of boxes full of these devices?
Do you need them all? :-)

Soundhappy 14th September 2021 12:11 PM

@ MEPER

More plenty in the past because I have ready sold , change many Vfet pairs to Diyers..
I wait for round 3 to build this amp and finalise others , lottery kit was not for me but for one friend as well..


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