Use of L-mosfets in source-follower is good though. Overall, it doesn't look like anything special; I can see plenty of potential enhancements.
Reply
I dont agree with RODE as he states that lateral type Mosfets sound good as compared to VERTICAL switching Mosfets.
I am designing N-CHANNEL MOSFETS amps using IRF mosfets and has compared them with ams using lateral mosfets.
The result is somewhat different , the lateral types doesnt drives in professional way and create more distortion than vertical counterparts!
I dont agree with RODE as he states that lateral type Mosfets sound good as compared to VERTICAL switching Mosfets.
I am designing N-CHANNEL MOSFETS amps using IRF mosfets and has compared them with ams using lateral mosfets.
The result is somewhat different , the lateral types doesnt drives in professional way and create more distortion than vertical counterparts!
it is essentially the citation 12 mosfet version. and it shouldn't be that hard to figure out component values.
Incidentially, I am breadboarding a similar design using a mosfet driving two mosfet output devices.
one trick I learnt while simulating mine is that you need to run the vas stage fairly hot (like 10ma or higher) for the irf devices I am using (540/9540). Otherwise, you may have to use a driver section (I used mje15030/15031 configured in a T) which actually improved performance considerably.
i have had great luck with bootstraps so I don't quite know why others are so sick and tired of it.
Incidentially, I am breadboarding a similar design using a mosfet driving two mosfet output devices.
one trick I learnt while simulating mine is that you need to run the vas stage fairly hot (like 10ma or higher) for the irf devices I am using (540/9540). Otherwise, you may have to use a driver section (I used mje15030/15031 configured in a T) which actually improved performance considerably.
i have had great luck with bootstraps so I don't quite know why others are so sick and tired of it.
Mosfet Citation 12
Quite a bit of difference! Quasicomp output stages are making a bit of a comeback lately Since the N channel mosfets are better than the the P channels this might be the way to go. The mosfet Citation 12 could be redesigned with all mosfets ( Zetex and IRF) and would be a very interesting project........
Quite a bit of difference! Quasicomp output stages are making a bit of a comeback lately Since the N channel mosfets are better than the the P channels this might be the way to go. The mosfet Citation 12 could be redesigned with all mosfets ( Zetex and IRF) and would be a very interesting project........
driving irf mosfets
what I found is that you can improve mosfet performance by increasing bias current of their drivers. because of their high gate capacitance, those devices don't behave like true "voltage-driven" devices. Instead, they will have substantial gate current, especially at high frequencies: depending on your set-up, the irf540s will have about 0.5-1ma gate current at 20khz.
so one way to improve mosfet performance is to use high driver current so that any "gate" current wouldn't have a significant impact on their drivers.
I used 40ma on the driver in my mosfet jlh, and in my mosfet citation 12, I am using 10ma for the driver (which itself is a mosfet as well).
mosfet drivers (especially medium power mosfets rated at about 1amp maximum current) do quite well. They can be run very hot (into 100-200ma if you so desire), and because of their small gate capacitance (100-150ph at most), they kind of isolate the VAS from overloading the input stage. I like them a lot.
However, they do give you higher distortion, and are a major pain in the rear to run in cfp configurations.
what I found is that you can improve mosfet performance by increasing bias current of their drivers. because of their high gate capacitance, those devices don't behave like true "voltage-driven" devices. Instead, they will have substantial gate current, especially at high frequencies: depending on your set-up, the irf540s will have about 0.5-1ma gate current at 20khz.
so one way to improve mosfet performance is to use high driver current so that any "gate" current wouldn't have a significant impact on their drivers.
I used 40ma on the driver in my mosfet jlh, and in my mosfet citation 12, I am using 10ma for the driver (which itself is a mosfet as well).
mosfet drivers (especially medium power mosfets rated at about 1amp maximum current) do quite well. They can be run very hot (into 100-200ma if you so desire), and because of their small gate capacitance (100-150ph at most), they kind of isolate the VAS from overloading the input stage. I like them a lot.
However, they do give you higher distortion, and are a major pain in the rear to run in cfp configurations.
Hi!
Why does Rod metions time and again in his articles about this mosfet amp (I have also access to his construction site with the complete circuit), that the layout of the PCB is very important, in fact a lot more important than for all (his) other amps?
Only to boost PCB sales, or are mosfet amps more open for distortions than comparable bipolar amps?
Bye,
Arndt
Why does Rod metions time and again in his articles about this mosfet amp (I have also access to his construction site with the complete circuit), that the layout of the PCB is very important, in fact a lot more important than for all (his) other amps?
Only to boost PCB sales, or are mosfet amps more open for distortions than comparable bipolar amps?
Bye,
Arndt
Other things aside, I don't agree with using a resistor for
the bias voltage when it is not fed by a constant current
source. With the bootstrapped loading, the quiescent current
becomes a function of the supply rails, so anyone building this
should use a well regulated supply.
That said, we welcome yet another designer seeing the light
on Mosfets.
the bias voltage when it is not fed by a constant current
source. With the bootstrapped loading, the quiescent current
becomes a function of the supply rails, so anyone building this
should use a well regulated supply.
That said, we welcome yet another designer seeing the light
on Mosfets.
PMA said:
I think each of points is valid on its own. But if you take tha attitude that no design is without compromise and you may see that those might just be areas where Rod made his compromises (I am guessing here).
I wouldn't go as far to say that the above is the worst of any world, tho.
As to C9, I was curious about it too and quite frankly it is the first time I have seen it done. One possible explanation is to equal out the gate capacitance differences between the upper and lower mosfets: but that assumes the N-channels have lower gate capacitance which usually isn't true.
I suppose there are some raationales for C9. Just we don't know what they are.
c9 is an attempt to make the output devices appear to have similar "effective" gate to source capacitance. Borbely has done this also and talks about it in either a "post project" letter in the Audio Amateur (now Audio Express) or in on of the actual projects that might be on his web site. One can actually write the equations for a source follower and work it out.
I have both used "c9" and not in my projects over the years and haven't noticed any audible difference nor any difference when looking at "symmetricalness" of slew rates. However, I trust Mr. Borbely's judgement on such matters MUCH more than mine (I'm not an idiot all the time ).
mlloyd1
I have both used "c9" and not in my projects over the years and haven't noticed any audible difference nor any difference when looking at "symmetricalness" of slew rates. However, I trust Mr. Borbely's judgement on such matters MUCH more than mine (I'm not an idiot all the time
).mlloyd1
millwood said:
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.