F5 components, parts you use

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#41
captain pugwash said:
I built the bog standard F5 as per the PASS instructions so by a pair I meant 2 x N and similarly 2 x P mosfets for a stereo amp. I had always read/assumed that the 2 x N's had to be matched and the same for the 2 x P's. I seem to remember that it was a bloke called Nelson Pass who opted against the IR P channels as they introduced an element of distortion (despite them being in the original schematic). I had always intended to go for matched mosfets after the initial build but this was so good in the first place that I haven't really felt the need. But things can always get better...
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NP did have a comment on the IRFP parts in this thread (post 678):
http://www.diyaudio.com/forums/pass...ng-impressions-discussion-68.html#post2226997
 
#42
hey
I have these Lateral Renesas, 8pairs, selected
and know what they say about them, in F5
then thought I would save them for other project

been thinking about multiple TO-220
but seems unnecessarily tedious :smash:

now, I have a nasty plan with them Laterals, again
one pair, and give them hell
monos, and each output transistor on its own heatsink, 300x200 x40
running on 2x 22V trafos
cascoded Jfets, ofcourse

I consider this as experimental :flame:
and needless to say, I have no plans of driving 1ohm speakes with these 🙂
 
#44
juma said:
capt. pugwash,
I've built a few F5s for my friends and all of them liked the sound of IRFP parts better although I told them about IRFP P-channel part flaw. Go figure...
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Nelson said something similar, a long time ago 😉

I think suiteable words could a bit like, slightly softer more pleasing sound with IR parts

thats said, I have not heard a NelsonPass design, yet
 
#46
vdi_nenna said:
Can any of the available Toshiba power mosfet replace the IRF mosfets directly?
Looking to build a standard F5 using only one N and P channel; not a X'ed or paralled output.

Thanks,

Vince
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The answer is yes, for 1530s and 201s. But, do to the lower threshold voltage of the Toshiba's you will be adjusting the pots to a lower value than if IR devices were used. There is the possiblity that a slight shift in the output spectra will result(sound will possibly be slightly different). It appears to be 6 of one and a 1/2 dozen of the other as to the actual sound difference between the two though.
:Pawprint:
 
#47
Thanks for the reply, flg.

Toshiba's you will be adjusting the pots to a lower value than if IR devices
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This doesn't mean a change in pot value, but only in adjustment value, correct?

It appears to be 6 of one and a 1/2 dozen of the other as to the actual sound difference between the two though.
Click to expand...
I wonder if it's worth the expense?? I guess I'll either try it or look for other's impressions.

Thx,

Vince
 
#48
capt. pugwash,
I've built a few F5s for my friends and all of them liked the sound of IRFP parts better although I told them about IRFP P-channel part flaw. Go figure...
Click to expand...

Thanks Juma - I'll have to give the IR's a try now, trouble is my de-soldering skills will result in the Fairchilds getting spoilt!!

I'm still not certain about matched mosfets for the standard F5, can anyone explain why you do or don't need matched pairs??
 
#49
I'm still not certain about matched mosfets for the standard F5, can anyone explain why you do or don't need matched pairs??[/
Click to expand...

They are not matched in the standard F5 because there is a single N and P channel mosfet per channel. If you had multiple, parallelled N and P mosfets, you match them so they share the same amount of current or else one might run away with all the current and the other will just sit there doing nothing.

Complimentary mosfets are N and P Channel mosfet made to work together. Some Toshibas are made for audio purposes and are complimentary to each other. IRF made FETs, not so much.
 
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#50
They are not matched in the standard F5 because there is a single N and P channel mosfet per channel. If you had multiple, parallelled N and P mosfets, you match them so they share the same amount of current or else one might run away with all the current and the other will just sit there doing nothing.

Complimentary mosfets are N and P Channel mosfet made to work together. Some Toshibas are made for audio purposes and are complimentary to each other. IRF made FETs, not so much.
Click to expand...

So the 'N' in the left channel doesn't have to match the 'N' in the right channel (and likewise the 'Ps') ??
 
#51
So the 'N' in the left channel doesn't have to match the 'N' in the right channel (and likewise the 'Ps') ??
Click to expand...

That is correct. It's just one of the things that makes this amp so great in my opinion.

In most cases, you wouldn't need to match N or P-ch mosfets to the other channel.
But, I bet some of the perfectionist here do anyway! 😉
 
#56
Thanks for the link, but these are not the original PCB's like in FW's amp. The original are even longer, id say.
 

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