lateral mosfets vs. bjts in audio amplifier design

[[email protected]]

No-one in their right mind patents circuits that are essentially 'obvious' if
only you're clever / smart enough.


No. It was DOS Orcad remember. Besides I prefer to keep my circuitry to myself
rather than give it away to every copier.

Graham

Oh well. I'll just borrow a copy of Slone's text then.

Douglas Self didn't care for mosfet amps too much. That's why I posed
my original question.

Michael

 

[Eeyore]

What exactly does back-calculate mean?

To do the RMS addition calculation backwards.

I have used the AP system 1. It does quite a few tests automatically,
so I would say it is worth it. The 8903 I got was $250 or $300 (I
don't recall exactly) about 6 years ago. APs were substantially more
at the time.

It was an 8903 I probably used once on one project. Clumsy to use and poorer
residuals than AP. I'd have the AP Portable One any day over that. In fact for
simple bench work I prefer the Portable One over the System One because it's
simple 'press button' stuff, no mice to arse about with and it takes up little
room. No other audio measuring set comes close in terms of performance or
convenience.

Graham

 

[Eeyore]

And it was developed under contract for a client so it's not really mine to give
away.

Oh well. I'll just borrow a copy of Slone's text then.

Douglas Self didn't care for mosfet amps too much. That's why I posed
my original question.

I don't care for Doug Self too much come to that. Long story.

Graham

 

[Eeyore]

Hi Graham,

Is this a good audio amp using HexFET for a starter?

http://users.otenet.gr/~athsam/power_amplifier_45w_hexfet_eng.htm

The driver and output stages use IRF9540 and IRF540 and the opamp is
LF411. THD is 0.2%. Power supply is +/- 30V.

I like it because the PCB design is included.

0.2% THD ? That's hilarious.

No it's shitty.

Graham

 

[Eeyore]

---
Geez, Graham, unlike you, as you well know, over the years I've given
away hundreds, if not thousands, of fully worked out, functional designs
and presented them right here, on these groups, as either formal
drawings roughly conforming to DoD-STD-100C and MIL-HDBK-1006/1 or as
ASCII drawings, when possible.

If some of my designs were commercialized, as I'm sure they were, that
could easily amount to millions of dollars that I've given away.

Are you that mean?

If you knew me in person you'd know otherwise.

I have actually considered putting up some pages online of design tips for audio to help
counter all the shit out there.

---
Strange, that 'cautious' bit, since it seems that even though you get
flamed, for example, for posting gratuitous insults and professing that
you're better than everyone else (which you seem to think are good
deeds) you throw caution to the wind and continually post that kind of
crap.

As far as audio goes I AM better than 99.9% of the competition. I was in a meeting on
Monday regarding a project and sadly had to blow one of the originator's ideas (and he
seemed pretty smart) straight out of the water since he hadn't even properly read a data
sheet it seemed. I'm notorious for finding faults before they get built.

Graham

 

[Kevin Aylward]

Hi Graham,

Is this a good audio amp using HexFET for a starter?

http://users.otenet.gr/~athsam/power_amplifier_45w_hexfet_eng.htm

No.

Kevin Aylward
www.kevinaylward.co.uk
www.blonddee.co.uk

 

[Kevin Aylward]

Everything is worth it.

?

Kevin Aylward
www.kevinaylward.co.uk
www.blonddee.co.uk

 

[Kevin Aylward]

Not with that Radford shit by any chance ?

Indeed it was.

Kevin Aylward
www.kevinaylward.co.uk
www.blonddee.co.uk

 

[[email protected]]

Either needs lots of negative feedback to be really linear, so THD+N
depends on the overall circuit design, not much on the final output
devices. It's generally easier to drive mosfets than bipolars, but in
audio bandwidths it doesn't matter much. Bipolars, lateral fets,
vertical fets, all can be made to work plenty well enough.

I use vertical (conventional power) fets in my NMR gradient amps,
because they are easy to drive fast (directly from a small opamp) and
are (at least some of them are) tough... no second breakdown, easier
to keep biased over temperature.

John

Ah, so with a good enough circuit design, HEXFETs can offer that
0.00...01% THD+N too?

Michael

 

[Eeyore]

Either needs lots of negative feedback to be really linear, so THD+N
depends on the overall circuit design, not much on the final output
devices.

Maybe for full power but NOT in the vital crossover region.

It's generally easier to drive mosfets than bipolars, but in
audio bandwidths it doesn't matter much. Bipolars, lateral fets,
vertical fets, all can be made to work plenty well enough.

Lateral fets are vastly better for audio. Not least because they match
brilliantly to name another of their features.

I use vertical (conventional power) fets in my NMR gradient amps,
because they are easy to drive fast (directly from a small opamp) and
are (at least some of them are) tough... no second breakdown, easier
to keep biased over temperature.

Also laterals are only made in small quantities and cost a lot.

Graham

 

[Eeyore]

?

If only for the technical challenge and personal reward.

Graham

 

[Eeyore]

Indeed it was.

Explains a few things - LOL ! ;~)

Graham

 

[Eeyore]

Ah, so with a good enough circuit design, HEXFETs can offer that
0.00...01% THD+N too?

Yes I expect so but it may be trickier.

Graham

 

[Eeyore]

More audio cargo-cult science.
No.


Bipolars, lateral fets, vertical fets,
all will work as well at audio frequencies if the circuit design is
right. All need negative feedback and sensible bias control.

Matching verticals is a PIG. Laterals do it naturally. Plus biasing them is
kid's stuff.

Graham

 

[[email protected]]

To do the RMS addition calculation backwards.


It was an 8903 I probably used once on one project. Clumsy to use and poorer
residuals than AP. I'd have the AP Portable One any day over that. In fact for
simple bench work I prefer the Portable One over the System One because it's
simple 'press button' stuff, no mice to arse about with and it takes up little
room. No other audio measuring set comes close in terms of performance or
convenience.

Graham

The AP system one came out later than the HP 8903B, so you would
expect it to be better. The portable was later still. The Portable One
has an HP 8903 emulation mode, so I guess you call that clumsy
mode. ;-) Anyway, the HP8903 was good for it's time, but time marches
on.

I really don't like PC based black boxes, so the Portable One would be
my choice for an upgrade. The HP 8903 is a back breaker too.

The applications group at AP is great. The system one has this digital
interface on the back. I couldn't quite get it working, called apps,
and the person asked how many people have access to the box. It turns
out the interface was done with simple gates (TTL I think) and often
people blow them up. The bigger the lab, the more likely someone blows
them up and doesn't own up to it. Well, that was the case, but
fortunately the interface chips are in sockets.

I still have my HP 334A. It is the only THD analyzer I've seen with RF
demod. I can't say the box has seen a power cord in a few years, but
you never know.

 

[Eeyore]

The AP system one came out later than the HP 8903B, so you would
expect it to be better.

Maybe. More to the point is that they were designed by the ex-Tek guys. I'd used
Tek's SG505 and AA501 previously. And they were quite OK too.

The portable was later still. The Portable One
has an HP 8903 emulation mode, so I guess you call that clumsy
mode. ;-) Anyway, the HP8903 was good for it's time, but time marches
on.

It has an IEEE interface option I believe.

I really don't like PC based black boxes, so the Portable One would be
my choice for an upgrade.

They are very nice. For a self-contained unit I think they are simply unbeatable. And
so well built too !

The HP 8903 is a back breaker too.

I agree.

The applications group at AP is great.

Always has been with regular app notes.

The system one has this digital
interface on the back. I couldn't quite get it working, called apps,
and the person asked how many people have access to the box. It turns
out the interface was done with simple gates (TTL I think) and often
people blow them up. The bigger the lab, the more likely someone blows
them up and doesn't own up to it. Well, that was the case, but
fortunately the interface chips are in sockets.

I still have my HP 334A. It is the only THD analyzer I've seen with RF
demod. I can't say the box has seen a power cord in a few years, but
you never know.

Many years ago I bought some used B&K and hardly ever used it. Technology marches on
!

Graham

 

[Eeyore]

But why buy expensive, sole-source, 100 watt fets when you can get
cheap, multisourced, 300 watt fets?

(a) they're not 100 watt - in fact one supplier does a dual die 500W device in
TO-3. With an internal copper heat speader btw.

(b) they match like Vfet's don't.

(c) any more silly comments ?

Graham

 

[Eeyore]

Find fault with them then !

You're a babe in arms in this discipline.

Graham

 

[Eeyore]

---
Really?

You make those claims and then, conveniently, fail to back them up
because of the restrictions you claim are placed upon you by copyright
and contractual limitations.

I understand your frustration, but I don't think you're important.

If you were, you'd have technically relevant articles published in peer
reviewed journals or, at the very least, cogent discourse posted here,
on USENET.

As it is, all you seem to be intent on doing is promoting yourself as
some sort of audio Guru who claims to greatness but who refuses to
submit proof.

Suit yourself. Everything I claim does what it does. All you have to do is
buy one and test it yourself.

I currently have a bit of a quandary. I've been offered 2 serious jobs this
week. And I can't even begin to tell you the background, it's so
complicated.

I've made one decision though. If one outfit wants me it'll be Group
Technical Director.

Graham

 

[Eeyore]

Local joke.

Graham