help to find mosfet

[theqwerty74]

Hi all,

I would like to try building my first audio power amplifier “push/pull”.

Could you recommend a “good” pair of Mosfet endings (channel p and channel n)? (where “good” = easily available, not oversized and with (LT)Spice model).

The amplifier will look like this: P=25Wrms, load 8ohm and Vpwr = +/- 35V.

Thank you all!,
Marco.

 

[Mooly]

Welcome to diyAudio Marco

You are going to get lots of different opinions over this.

Size isn't really negotiable since you will be looking at either flat packaged devices (TO247 outline) or round TO3 outline. Flat is easier to work with as they only need one hole drilling.

If you choose the common vertical HEXFET then you are looking at the IRFP9240 and IRFP240 type or there derivatives. LT spice has models built in for those.

My favourite devices for a small amplifier would be the less common Lateral FET which are available from certain suppliers. LTspice models are available on this forum from Bob Cordell and Ian Hegglun. A quick search will bring them up.

 

[TungstenAudio]

You might also take a look at some of the projects in the Pass Labs forum. The M2x and F5 are both push-pull type, 25 Watts Class A operation. They will sound better than amps with much higher specifications, and use the IRFP240 and IRFP9240 Mosfets in their output stage.

 

[nigelwright7557]

Welcome to diyAudio Marco

You are going to get lots of different opinions over this.

Size isn't really negotiable since you will be looking at either flat packaged devices (TO247 outline) or round TO3 outline. Flat is easier to work with as they only need one hole drilling.

If you choose the common vertical HEXFET then you are looking at the IRFP9240 and IRFP240 type or there derivatives. LT spice has models built in for those.

My favourite devices for a small amplifier would be the less common Lateral FET which are available from certain suppliers. LTspice models are available on this forum from Bob Cordell and Ian Hegglun. A quick search will bring them up.

I have used irfp240/9240 with good results.

Exicon and Profusion do lateral mosfets but expect to pay through the nose for them compared to irfp240/9240.

 

[theqwerty74]

thank you all for the answers!

I believe that, in the end, I will use the pair 9240/240!

Marco.

 

[U130421]

IRF640,IRF9640 , Stochino uses them in his high performance amplifier. Much much cheaper than IRFP240/9240.

 

[Ian Finch]

I believe that the die is the same in both types too. Can anyone verify that?

 

[IanHegglun]

Yes. My LTspice models turned out to be almost identical using the same manufacturers datasheets. The thermal values are different, obviously, due to their cases.

For TO-220's adding an Al spreader plate of slightly more area than the TO-247 will help somewhat (otherwise you will need more heatsink with TO-220's else reduce the amps power). Use thermal pasted between the TO-220's and the plate with no thermal washer. Then use the larger thermal washers between plates and HS ..

BTW If there are paralleled devices with common drains then a common spreader can be used for the N's and another for the P's. Then cut your own massive washers from sheet. I think it's still available from the DIYaudio store.