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Old 23rd June 2006, 06:41 AM   #1
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Cool Pa amp

hello all

Im wondering wether or not this amp will work for what i need it to. I wish to make a simple yet powerful amp 400-500watts rms into 4ohms. I intend on using the amp for pa sub usage so THD wont matter much

any comments or thoughtful thinking welcome
the amp isnt anything complicated a cp for the input then the regular vas stage then to the power horse cfb. Of course all this is wishful thinking

http://img233.imageshack.us/my.php?i...oweramp0ry.jpg
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Old 24th June 2006, 03:48 AM   #2
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I'll assume that sence people looked at it and haven't posted means that something is wrong or missing...

I feel confident in this amp thogh id like some one to take a look and comment on what they'd recomend via Kiss approch on inproving the schematic
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Old 24th June 2006, 04:52 AM   #3
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From what I can see on the front end, the two 10k resistors going from the positive supply to ground will set a dc bias point for Q1 of 30V. Same going from the negative supply to ground, so the dc bias point will be -30V for Q2. If you then take a look at the voltage drop across the base to emitter of Q1/Q2, you should drop ~0.65V per transistor. So the emitter of Q1 should be ~29.35V and the emitter of Q2 should be ~-29.35V. The problem comes in that you have the emitters tied together. There is nothing in there to drop the ~60V difference between the two emitters.
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Old 24th June 2006, 07:29 AM   #4
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Ignoring the problems with the front end, you're going to need about 80V from a typical supply to get the power you're expecting to see.

I would suggest a 55-0-55 400VA transformer and a pair of 10,000F caps.

You want a simple front end with a $6 pcb?

http://www.audioxpress.com/bksprods/pcbs/nelsonpass.htm

http://www.passdiy.com/pdf/a40.pdf

~snip~

Post #4
http://www.passlabs.com/images/projects/a40f6.jpg The circuit board for this amp is the deal of the century. Still available for only $6 from Old Colony! Who cares? It's only 40 watts. Not really. Jumper Q11 and change R9 to 27K 1/2W(Pass suggests this for the A40 if you are having trouble finding the fet, only use 10K for his design) http://www.passlabs.com/projects/a40_subs.htm Change Q1,2,3,6 to the MPS8099 or 2N5551. Change Q4 and Q5 to the 2N3440/2N5416 pair. Use a heatsink on these. Change R10 to 68 ohms. Delete R13 and D3. R11 will be selected for bias. C4 will be for high frequency response. R14,15 will be changed to one 220 ohm per ouput device. The outputs are to be two each BUZ900D/905D http://www.semelab.co.uk/magnatec_mosdata.htm This will give 400 watts RMS with a 53V+53V 800VA transformer and only two pair of outputs! Don't forget to add 10V gate zeners and output flyback diodes.

~snip~

Use an EF output stage with 4 pair of MJ21139/94 type outputs, MJE15034/35 type drivers.

Basic plan (4X Q7, Q8):

http://www.diyaudio.com/forums/attac...amp=1040960593
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Old 25th June 2006, 01:02 PM   #5
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Once again you have it.

Mr.DJK designs an amplifier.

I have built this A40 as designed by DJK using MJ15024's and MJ15025's. I beat the living hell out of it without ANY problems.
Well worth the effort in my opinion.
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Old 26th June 2006, 09:25 AM   #6
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Correction:

"Use an EF output stage with 4 pair of MJ21139/94 type outputs, MJE15034/35 type drivers."

Should read MJ21193/94 and MJE15032/33.

The MJE15030/31 will probably work to 80V even though only rated at 150V. The MJE15034/35 will probably work OK too, but the gain starts going down sooner than the lower voltage MJE parts.

The amp burnedfingers built has 6X MJ15024/25 and runs on about 93V for about 600W/4R for his subwoofer.
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