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Old 20th June 2010, 11:42 PM   #41
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Nice bit of rendering for the board layout

IMHO while the output stage maybe be capable of the power out
The input and driver stage leave a lot to be desired for this kind
of power level and the number of output devices that is is expected to drive.
A VAS driver stage for 20 o/p devices would only give you a bandwidth of less
than 35khz at best... The gate charge just has no where to go.
Also the o/p devices are way to close to each other, just not enough thermal
mass around each device for this power level.

The diode in the emitter in the Vbe multiplier will help a small amount for compensation, but what you will find is it will not compensate correctly under load and under compensate, this type of biasing scheme is not suitable for such high power.

There are a number of other design errors in the input and driver stage.

Great job on the PCB layout, it looks OK, juts need to fix some design issues
and I think it will be OK.

Cheers

Anthony
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Old 21st June 2010, 03:13 PM   #42
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2SA968B/2SC2238B (25W,100MHz) 35mA, 4xIRFP240/9240
Bandwidth -3dB = 1,8Hz370kHz
Bandwidth -1dB = 3,2Hz200kHz
Bandwidth -0,1dB = 10Hz70kHz
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Old 21st June 2010, 07:02 PM   #43
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in a professional amplifier and in levels of power by far lower than 400-500 W a wining design is not the amp it shelf ..... strip down the circuit ( of a typical AB design ) and you will realize that most amplifiers are based more or less on the same idea .

now what makes one amplifier better than one other is neither the schematic nor the pcb ...what makes the amplifier better is the supportive circuits that control and secure various stages of the amplifier .....

we have units doing that in many many ways and not always with succes ...either they protect the amplifier too much and kill all the sonics but at least poreserve stability or provide protection that fails under a few conditions ...

Using Dr Bora's sayings at this level of power the amplifier should be designed as idiot proof from every aspect ....

regards sakis
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Old 21st June 2010, 09:31 PM   #44
PMA is offline PMA  Europe
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Quote:
Originally Posted by Federmann View Post

2SA968B/2SC2238B (25W,100MHz) 35mA, 4xIRFP240/9240
Bandwidth -3dB = 1,8Hz370kHz
Bandwidth -1dB = 3,2Hz200kHz
Bandwidth -0,1dB = 10Hz70kHz
This amp has no driver transistors, just VAS and paralleled output devices. It would be nice to see not the small signal frequency response, but power bandwidth, frequency response measured somewhere at -3dB of full output power.
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Old 21st June 2010, 09:50 PM   #45
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Quote:
Originally Posted by PMA View Post
This amp has no driver transistors, just VAS and paralleled output devices. It would be nice to see not the small signal frequency response, but power bandwidth, frequency response measured somewhere at -3dB of full output power.
Measured:
2Hz-3MHz
Input voltage 1V
Output voltage 10,9V/4Ω/1kHz (30W)
Is not practical to measure 60V/3MHz!!!

Last edited by Federmann; 21st June 2010 at 09:53 PM.
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Old 29th June 2010, 04:10 PM   #46
XGAS is offline XGAS  Germany
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Quote:
Originally Posted by Federmann View Post
Click the image to open in full size.
Click the image to open in full size.

8 pairs and 2x500W
I am in doubt if any prototype of this amp exist, 'cause I think this photo is a Photoshop or Corel image done by inserting of CAD image to it. You can strong view it on superscription "M2K" and "Volume A, B".
There is no heavy cooler. And all your scheme is tricksy. I can only pressupose that it will explode by heat caused by performer transistors.
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Old 29th June 2010, 04:30 PM   #47
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I like your soldering iron
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Old 29th June 2010, 05:07 PM   #48
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You need to get realistic here , 1 - 2kw with small heatsinks , cramped layout , and a very simple driverless LPT/VAS..... BURNING AMP...

Below (attachment 1) , you will see what just 4 pair IRFP240/9240's needs for 800W dissipation. The 4 pair were spread out across the whole 17" of that monster and hit 50C with convective cooling only. If one was to use forced air ,more wattage could be successfully dissipated.

For 3-6 pair , at a minimum , a mje340/350 driver pair would suffice. I use 2sa1837 / 2sc4793 (much faster) or mje15032/33's (cheap , but stronger).
For 10 pair , wow ... definitely the mje15032/33's , gate protection diodes , 2 transistor precision VBE , and a proven LPT/VAS.

OS
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Old 29th June 2010, 07:14 PM   #49
Xoc1 is offline Xoc1  United Kingdom
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Federmann
Many members have commented on your amplifier design.
Many have complimented the work that you have done.
Others have made suggestions to improve the amp.
Their suggestions are based on a wealth of experience and knowlege of amplifier design.
So far all you seem to have done is defended your design as is.
Are you interested in improving this amplifier with the help and support of the members of this forum?
I feel that your stance is alienating other members if the last few posts are anything to go by!
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Old 30th June 2010, 03:56 AM   #50
Eva is offline Eva  Spain
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Hi Federmann

I like your work, don't take them too serious. They enjoy heavy inefficient overbuilt amplifiers with $$$ exotic parts, while our tastes are probably the opposite (seeking something small, light weight, low cost, and still capable of doing the job properly from the electrical point of view).

Also, at first glance, your PCB layout looks much better than the traditional ones with the power supply tracks on the sides, the small signal circuits in the middle, no ground plane, useless decoupling capacitors due to long PCB traces, and overlooked parasitic inductances everywhere.
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Last edited by Eva; 30th June 2010 at 03:59 AM.
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