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Old 26th February 2010, 09:59 PM   #31
81bas is offline 81bas  Germany
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Originally Posted by vogor View Post
Question: whether If to do a bridge exit and a unipolar power supply that it will be necessary levelshifter stage?
it is better to use a bipolar power supply here
Otherwise you will need to have some reference voltage at the input integrator (TL081), you will get a big CLICK/POP at startup, maybe it will not start to oscillate at all, you will get the problems with non symmetrical clipping and so on...
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Old 26th February 2010, 10:29 PM   #32
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CMOS can work great as a comparator
I chose the CD 4049 using 2 stages
before this the audio feeds into an LF353 (fantastic stability)
The output drives the low side MOSFET with an NPN PNP totem pole pair
The high side is also discrete
12v supply 15ns switching time (at first stage output)

My amp runs +- 42 Volts , 1.25 Mhz, 3 channels Left - Sub - Right
The topology is DC coupled except for signal input capacitor
Audio gain 25 db Dc offset 2.5 Millivolts
I have yet to do a distortion test, but there are no audible artifacts
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Old 27th February 2010, 07:06 AM   #33
AP2 is offline AP2  Italy
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Hi,
maybe it's better that you have not measured IMD, THD and efficiency.
LF353 has a linear behavior (used as a comparator) up to 150 kHz.
this low frequency and slow switching time are not adequate for medium-good result of audio.
I'm curious to see the signal at the gate mosfet your amplifier at 1.2 Mhz.
totem-pole(NPN-PNP) for drive mosfet is good.
is possible see partial of you scheme?
If you want, I can illustrate with waveform, why not very good LF353.
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Old 27th February 2010, 07:37 AM   #34
AP2 is offline AP2  Italy
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Originally Posted by AP2 View Post
Hi,
maybe it's better that you have not measured IMD, THD and efficiency.
LF353 has a linear behavior (used as a comparator) up to 150 kHz.
this low frequency and slow switching time are not adequate for medium-good result of audio.
I'm curious to see the signal at the gate mosfet your amplifier at 1.2 Mhz.
totem-pole(NPN-PNP) for drive mosfet is good.
is possible see partial of you scheme?
If you want, I can illustrate with waveform, why not very good LF353.
----------------------------------------------------
I'm sorry, I have not read the first part of your post.
Moon are... sometimes.
then very interesting your project.(if you put a primary FB post LF353)

Last edited by AP2; 27th February 2010 at 07:46 AM.
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Old 27th February 2010, 07:03 PM   #35
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The oscillation is controlled by the HEF4049 (4050 can be used as well)
and the Mosfet output stage. The 2n4401 feeds a 27ohm resistor to the gate
A 2N5401 sinks the gate current through a 3.3 ohm resistor.
This provides proper dead time in the Turn on phase of operation
there is about 500mv of Near sinusoidal output voltage on the 353 feeding a
level shifting 2N5401. I still need to design an over-current shutdown circuit
I am thinking of selling a board for this amp.
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Old 1st March 2010, 03:23 AM   #36
vogor is offline vogor  Russian Federation
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The amplifier is work! But there is a problem: at inclusion sometimes there is a constant pressure (already 3 dynamics has burnt), and at deenergizing of races of 2 volts. What can it be and how to cure, it would be desirable to make stable smooth start and amplifier deenergizing, whether there was at you a similar problem? Output mosfets - irfp260, the driver ir2110.
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Old 1st March 2010, 04:52 AM   #37
Baldin is offline Baldin  Denmark
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Hi Vogor

Is it the same schematic as in post #1????
What supply voltage are you running?

Not, sure I understand; at start up the amplifier is butning your speakers??

Are you sure it actually starts up (oscillate) every time?? Or does the output just swing to one of the rails (high DC)
(Yes I have had a lot of trouble not getting the amp tor start oscillating ...... not totally sure how tohelp this in your design though ... will think it over)

Do you use any fuses in the rails? (I use polyfuses for prototyping ... as I wrote some messages ago)

Use a dummy load of 8 ohm, until you are sure it starts up properly.
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Old 1st March 2010, 05:26 AM   #38
vogor is offline vogor  Russian Federation
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Quote:
Originally Posted by Baldin View Post
Hi Vogor

Is it the same schematic as in post #1????
What supply voltage are you running?

Not, sure I understand; at start up the amplifier is butning your speakers??

Are you sure it actually starts up (oscillate) every time?? Or does the output just swing to one of the rails (high DC)
(Yes I have had a lot of trouble not getting the amp tor start oscillating ...... not totally sure how tohelp this in your design though ... will think it over)

Do you use any fuses in the rails? (I use polyfuses for prototyping ... as I wrote some messages ago)
Hi!

Use a dummy load of 8 ohm, until you are sure it starts up properly.
Yes, scheme that I have resulted in the thread beginning, a power supply voltage +/- 65V
I have really burnt three dynamics from for constant voltage which appears and then at repeated inclusion it is not present also the amplifier normally works, I think that a problem in transient at start but I do not know as it to eliminate. Fuse did not use.
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Old 1st March 2010, 11:26 AM   #39
81bas is offline 81bas  Germany
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Originally Posted by vogor View Post
Yes, scheme that I have resulted in the thread beginning, a power supply voltage +/- 65V
I have really burnt three dynamics from for constant voltage which appears and then at repeated inclusion it is not present also the amplifier normally works, I think that a problem in transient at start but I do not know as it to eliminate. Fuse did not use.
+/-65V without fuses - you are crazy! Use it at least at the output!
Did you followed your schematics precisely or you have skipped some parts from it? Please post the photos of your prototype here (both pcb sides) and I can try to give some recommendations for you then

I think it is almost impossible to remove the POP at startup in this schematic. Look at the startup circuit on T2, this is intended to generate a long negative output impulse at startup, to charge the driver bootstrap cap and to initiate the oscillation. In original IRAUDAMP1 they have used an output relay, which was intended to block this POP from speaker.

Also, I recommend to use some emitter followers to generate +/-5V voltage for input stage, because R11 and R12 with 4.7K can produce too low current to power up the input stage (at +/-65V this gives only 12mA).

Last edited by 81bas; 1st March 2010 at 11:43 AM.
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Old 1st March 2010, 11:26 AM   #40
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This is the original circuit from IR, i dont know where the author got hes design from no wonder NO "design" or implmentation detail is given(typical when you copy and paste other peoples work.)

see below for the orignal design, the one posted here has some addtional changes supply changes and active component changes ect.. without reason behind it.

http://www.irf.com/product-info/audi...sdtutorial.pdf

note the orignal doesnt give design detail just high level notes on how to go about designing a class d amp usefull for "us" newbies
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Last edited by Reactance; 1st March 2010 at 11:33 AM.
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