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About a simple class D amp

J

Jean Parent

Hello

Here is a very very simple class D PA amp.

http://img516.imageshack.us/img516/3319/classdpaamp.jpg

For sure this amp would have a high distortion. This is my first class D
amp, but it is only for 100 to 300 w for PA only.

Is there any errors in this schematic, and is there any suggestions of
simples modifications to made it a bit better ?

For Q3 I would use MJ2955 or for higher power MJ15004

How about a power mosfet for Q3 ?

Thank you

Bye

Jean
 
V

Vladimir Vassilevsky

Jean said:
Hello

Here is a very very simple class D PA amp.

http://img516.imageshack.us/img516/3319/classdpaamp.jpg

For sure this amp would have a high distortion. This is my first class D
amp, but it is only for 100 to 300 w for PA only.
Click to expand...

No way this schematics is going to make 100 to 300W.
Is there any errors in this schematic, and is there any suggestions of
simples modifications to made it a bit better ?
Click to expand...

The first improvement is use the half bridge output stage instead of the
single ended.
For Q3 I would use MJ2955 or for higher power MJ15004

How about a power mosfet for Q3 ?
Click to expand...

If you need a simple class D amplifier which really works, there is a
bunch of single IC solutions from TI, NXP, ST, Freescale. If this is
about the minimalist contest, a class D amplifier can be built using
just one FET and few resistors and caps.

Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com
 
E

Eeyore

Jean said:
Hello

Here is a very very simple class D PA amp.

http://img516.imageshack.us/img516/3319/classdpaamp.jpg

For sure this amp would have a high distortion. This is my first class D
amp, but it is only for 100 to 300 w for PA only.
Click to expand...

And that makes distortion OK ?

Is there any errors in this schematic, and is there any suggestions of
simples modifications to made it a bit better ?
Click to expand...

It's a heap of crap if that's what you wanted to know.

For Q3 I would use MJ2955 or for higher power MJ15004

How about a power mosfet for Q3 ?
Click to expand...

Go to I.R. ( irf.com) and use one of their application circuits.

Graham
 
J

Jean Parent

Vladimir said:
No way this schematics is going to make 100 to 300W.


The first improvement is use the half bridge output stage instead of the
single ended.


If you need a simple class D amplifier which really works, there is a
bunch of single IC solutions from TI, NXP, ST, Freescale. If this is
about the minimalist contest, a class D amplifier can be built using
just one FET and few resistors and caps.

Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com
Click to expand...


Hello

Yes, a minimalist, any diagrams of that class D amp using one fet and few
resistors and caps ?

Thank

Jean
 
V

Vladimir Vassilevsky

John said:
On Sun, 08 Mar 2009 12:39:11 -0500, Vladimir Vassilevsky



That sounds cute. How?
Click to expand...

A basic oscillator circuit with hipass RC-RC-RC in the feedback from
drain to gate. The speaker is the load in the drain. The hint is that at
high frequencies the speaker inductance makes the resonance with the FET
stray capacitance. The typical parameters make the resonance exactly
where it is needed. So, the whole thing oscillates in the nonlinear
mode, and the FET is switching. If the audio frequency is applied to the
gate, that pulse width modulates the drain current. There is also the
bias circuit to keep the operating point.

As simple as that: FET, speaker, 4 resistors and 3 caps.


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com
 
T

Tim Williams

As simple as that: FET, speaker, 4 resistors and 3 caps.

Vladimir Vassilevsky
DSP and Mixed Signal Design Consultanthttp://www.abvolt.com
Click to expand...

Here's a fairly minimal circuit, a lot more parts than under
discussion but a lot fewer actives than anything using an IC. Class
DA, the circuit itself has good efficiency but the output network
ruins things. Excellent linearity though -- less than 0.1% THD!

http://webpages.charter.net/dawill/tmoranwms/Elec_Compound3.gif

Tim
 
E

Eeyore

Tim said:
Here's a fairly minimal circuit, a lot more parts than under
discussion but a lot fewer actives than anything using an IC. Class
DA, the circuit itself has good efficiency but the output network
ruins things. Excellent linearity though -- less than 0.1% THD!

http://webpages.charter.net/dawill/tmoranwms/Elec_Compound3.gif
Click to expand...

It scares me when people talk about excellent audio linearity being 0.1%
THD.

Just ordered some Nat Semi samples of some op-amps with so many zeroes
in the THD figure that it's simpler to quote it as SINAD instead. It's
-130dB.

Graham
 
G

Gaetan Mailloux

Hi

I was, since few months, looking for an easy to build PWM inverter, and
without any PIC programing.

Looking again at the 555 PWM amp circuit, I have an ideas, by merging a
500 w sine inverter with the PWM section of the 555 PWM amp circuit it
made a PWM inverter.

Here is the final circuit.

http://img205.imageshack.us/img205/4066/invertersine500wccpwm.jpg

It should work... I think...

Thanx

Cheer

Gaetan
 
F

Fred_Bartoli

Eeyore said:
It scares me when people talk about excellent audio linearity being 0.1%
THD.

Just ordered some Nat Semi samples of some op-amps with so many zeroes
in the THD figure that it's simpler to quote it as SINAD instead. It's
-130dB.
Click to expand...

Huh... Did you actually look at the drawing? It's a full toobs switching amp
and 0.1% is not bad at all considering the stuff involved and that it's an
open loop design.

And building such a bizarre amp shows some sense of humor and derision I
like.

I thought the brits could easily understand this. Apparently not all of
them.
 
E

Eeyore

Fred_Bartoli said:
Huh... Did you actually look at the drawing? It's a full toobs switching amp
and 0.1% is not bad at all considering the stuff involved and that it's an
open loop design.
Click to expand...

Now that IS impressive.

And building such a bizarre amp shows some sense of humor and derision I
like.
Click to expand...

I'll have to get to understand you better

I thought the brits could easily understand this. Apparently not all of
them.
Click to expand...

Had I looked I would have done. My sense of humour is somewhat dry at times so I
would have apreciated it. None the less, it goes to show just how far some
devices have gone now.

On the subject of tube amps, anyone here heard of the 'circlotron' amplifier ?
It was an EV design and I still haven't fully fathomed it. Google will find it.

Graham
 
T

Tim Williams

http://www.tubecad.com/2008/03/blog0137.htm

Ye Gawds.

My brain hurts now....

Bob M.
Click to expand...

Meh, it's just two cathode followers in series. What gets me is, I've
seen at least one 10kW shaker table amp (the manufacturer escapes me,
but shaker tables is basically all they do...) which was built with
about 50 x stud-type NPNs (rated about 200V 2A each) per water-cooled
rail. A three-phase transformer sitting in the bottom provided
isolated power to the two halves. It ran class AB or so. The whole
thing (including signal generation) occupied three full racks.

Tim
 
T

Tim Williams

Here is the final circuit.

http://img205.imageshack.us/img205/4066/invertersine500wccpwm.jpg

It should work... I think...
Click to expand...

Much better to completely ignore the 555 altogether. The 555 isn't
bad in and of itself, it's a fine switching device and oscillator
building block. However, using pin 5 to control it is essentially
stupid. You can linearize it, principally by controlling charge and
discharge currents, but that's extra circuit. You can also use two,
one as a clock generator and the other as a variable delay, but that's
still more circuitry. You might as well start over with another
general-purpose 8-pin chip, like so:
http://webpages.charter.net/dawill/Images/Pulse_Width_Modulator.gif
Scrunched together on a bit of perfboard, this circuit hardly occupies
a square inch, it's quite easy to build. Couple the logic-level
signal into whatever output stage you want.

Or for that matter, if you're adventerous, you can use the LM311's
beefier output stage directly for maybe 1W total output. ;-)

Tim
 
M

MooseFET

Hello

Here is a very very simple class D PA amp.

http://img516.imageshack.us/img516/3319/classdpaamp.jpg

For sure this amp would have a high distortion. This is my first class D
amp, but it is only for 100 to 300 w for PA only.

Is there any errors in this schematic, and is there any suggestions of
simples modifications to made it a bit better ?

For Q3 I would use MJ2955 or for higher power MJ15004

How about a power mosfet for Q3 ?

Thank you

Bye

Jean
Click to expand...

Another idea:


in ---!!---/\/\--+------/\/\-----+---))))---!!--- Out
! !
! !\ HC14 !
+---! >O--------
! !/
 
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