Mini-Mosfet

[Xandrell]

Hi Folks...

Currently i am trying to build up a new amp. It´s going to be the "Mini-Mosfet" which is presentated @redcircuits(Projekt 123). The ampsection is taken from the schematic on this page with very few modifikations:



Does anyone have build this amplifier and could give me some hints on upgrading this?

[nigelwright7557]

Your link is broken.

[jerluwoo]

Mini-MosFet Audio Amplifier - RED - Page123

[nigelwright7557]

Lacks thermal stability for vertical mosfets.
Also would need source resistors.

[Xandrell]

Sorry for the broken link.

Could someone explain a bit about using source resistors or give me a hint on a similar project using mosfets, small part count and a supply of +-12VAC or 24VAC (i already own two torroids with 2x12VAC/100W)? The fact that this design is C-coupled doesn´t matter (for me). This should be an experimental platform to learn more about using mosfets.

[BobEllis]

Source resistors (connected between the Source pins and the output in your circuit)provide some negative feedback, as current rises the net Gate-Source voltage is decreased. Since vertical mosfets tend to conduct more as they get hotter, this helps turn them down. It probably still won't keep them from running away, unless the Source resistors are large. You should use a Vgs multiplier thermally coupled to the outputs to keep it under control.

For low parts count mosfet amps, see the Zen series at Pass Laboratories. It makes good reading to help understand the concepts. The trouble with Zen is that they really want a bit more voltage than your transformers can supply, though thy will work at lower output.

A slightly higher parts count project that would make good use of your transformers would be a Mini Aleph. It's intended to run on +/-15V rails, a good match for 2x12VAC. You can get boards at DIY Chip Amplifier Kits, PCB's, Components and Information.

Enjoy your project.

[Xandrell]

Thanks for the quick reply on my questions. I´ve googled for about half an hour now for an apropiate (guess that´s the word ^^) schematic on the named Mini-Aleph, but couldn´t find any. I think when trying to search this forum, i can read bout 200+ threads indeed

So anyone got´s a quicklink for me?

[BobEllis]

http://www.chipamp.com/diyaudio/mini...parts_list.xls
http://www.chipamp.com/diyaudio/miniAsch.pdf

The boards can make a mini Aleph or use the output boards to add up to three more output devices. Very few parts change on the main board if you want to go from a mini to a larger version later. The various versions of the Aleph amp primarily differ in the number of output devices, bias setting resistors and AC current gain. All items which can be tweaked to your preference if you don't mind calling your amp an Aleph 3 inspired amp instead of a clone.

[Xandrell]

I think maybe i´ll go with the Mini-Aleph or even with an JLH.