Build This MoFo!

[plasnu]

Installed it into the system....and no output.
Re checked bias and it reads zero.

If it was working fine before installing, I would check if C1 installed correctly.

 

[Michael Rothacher]

Quick questions: What FET are you using? Have you installed the Zener diode?

🙂

 

[Dennis Hui]

When you powered down the mofo, did you just disconnect the DC or AC?

There has been some discussion that disconnecting the DC plug can cause an
inductor 'kick' that can damage the mosfet.

For my build, I have the protection zener installed, along with a small cap in
front of the amp PCB so that if the DC connection is cut, the discharge from the
cap should still control the inductor kick. And finally, I always disconnect at the
AC side.

 

[Nelson Pass]

yes
for example this design HP-REN-OS - Solid state Hi-end current amplifier by Bartolomeo Aloia with an innovative circuit to avoid the switching off of the transistors (here the simplified schematic)

but this is another thread so we shouldn't talk about it here

Sure we can.

Looks like the circuit I did in '73 (not the one we used at Threshold) and which Technics did around '78.

You can replace those current sources with resistors and it works fine.

 

[audiodesignguide3]

Sure we can.

Looks like the circuit I did in '73 (not the one we used at Threshold) and which Technics did around '78.

You can replace those current sources with resistors and it works fine.

After some simulations I verified that using a resistor instead of the current generator the result is worse, do you remember the models of the amplifiers mentioned?

 

[yaduck9]

If it was working fine before installing, I would check if C1 installed correctly.

Yes I did check. The black stripe on the CAP is toward the outside edge of the board.

 

[yaduck9]

Quick questions: What FET are you using? Have you installed the Zener diode?

🙂

I am using the one listed in the BOM Infineion IRFP250NPBF from Allied electonics


No, I did not install the zener diode

 

[yaduck9]

When you powered down the mofo, did you just disconnect the DC or AC?

There has been some discussion that disconnecting the DC plug can cause an
inductor 'kick' that can damage the mosfet.

For my build, I have the protection zener installed, along with a small cap in
front of the amp PCB so that if the DC connection is cut, the discharge from the
cap should still control the inductor kick. And finally, I always disconnect at the
AC side.

Well..after performing the bias adjustment I did disconnect the power both times by disconnecting the plug on the DC side.


So that and the lack of a zener diode could be the issue.


I will have to go and obtain a few more transistors and try again.


Thanks to all for sharing and taking the time to reply. 🙂

 

[yaduck9]

Unless the Rolls is malfunctioning, there is no reason you shouldn’t be getting some output.

Drive the MoFo from your phone to test. Or a CD player. Anything that has a line-level signal.

Zero bias measured is indicative of an error in MoFo itself.

That is good to hear that the CD player has enough power to get some output. I do have a diy passive preamp I can use in the future for testing.


Thanks.
Gotta get those transistors first.

 

[Michael Rothacher]

I think that will fix your issue.

The Zener was upgraded to "mandatory" some time ago, but I'm afraid that info is somewhat buried in lots of other information. It is especially important when using other MOSFETs (which may have even lower maximum Vgs) or other inductors (which might have a lot more "kick")

Let us know how you fare. 🙂

 

[tunasto]

@Michael,
maybe you can put that info(zener mandatiories ((thoes this word exist?)) ) in doc we are downloading, even I already have 8 versions in the download folder, I download it again and again.

Or/And to put in the first post as Note, or it is not possible after some time...

 

[tunasto]

And may I ask you, always forgot.
What are speakers in the post #2 of this thread

 

[woody]

I do believe these are the speakers you are talking about But I think the company went out of business well over a year ago. Oh the store list them as sold out but realy that company went out of business well over a year ago. Scandinavian Audio Labs SAL 08C08 (Pair) – diyAudio Store

 

[Michael Rothacher]

@Michael,
maybe you can put that info(zener mandatiories ((thoes this word exist?)) ) in doc we are downloading, even I already have 8 versions in the download folder, I download it again and again.

Or/And to put in the first post as Note, or it is not possible after some time...

Yes, certainly. I updated it in the version printed in AudioXpress this past year, and I'll post an updated copy of that text on my website shortly. I'll also see if I can edit the first post. 🙂

Also, an update to MoFo has been on the bench, but there are a couple of projects coming ahead of it.

 

[Dennis Hui]

MoreMoFo? 🙂

I really love the Mofo, so I'll definitely be looking forward to the update.

Cheers,
Dennis

 

[dliscomb]

That is good to hear that the CD player has enough power to get some output.

As others have said, yaduck, I use my MOFOs daily driven with my Samsung smartphone, and it works well enough for music whilst working.

(I have yet to finish my AKSA-Lender preamp, but for a crimp tool.)

Kind regards,
Drew

 

[audiodesignguide3]

Mofo/Inpol with 195T5

Here the first photos of my Mofo/Inpol with 195T5

 

[Michael Rothacher]

Handsome! 🙂

 

[Michael Rothacher]

MoreMoFo? 🙂

I really love the Mofo, so I'll definitely be looking forward to the update.

Cheers,
Dennis

I like that, Dennis!

Let's call it Mo' Better MoFo after the Spike Lee film.

Coming this Spring.

 

[Dennis Hui]

Most excellent. Looking forward to it.