500W PA amplifier with Limiter

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#3,363
Hello , i have a question about protect circuit in B500 amplifier circuit .

serial capacitor and parallel resistor - It is a high pass filter

100k and 10nF - is around 160 Hz.

Does this mean that if I use the amplifier for subwoofer up to 120Hz the protection will not work?

Regards !
 
#3,364
Hello, Ive been slowly building a stereo version of this amp but my power supply works out to be +/- 86volts so it won't quite make the 500watts. My question for people with more knowledge than myself is to do the protect circuit that Apex posted on page 12 of this thread.
I have built 1 for each channel as close as I could to the design but I can't get the protection relays to come on. Only thing I have come up with after a day of checking and re-checking is the voltage regulators seem to be off. I'm getting +14.85 and -15.85. The regs are labeled 7815 and 7915 but I thought almost 1 volt over is to much. With the protect boards only powered up the fan control seems to work as it should but I notice a faint glow from the protect LED that goes solid if the BD241C is disconnected. Can the neg regulator be causing this problem?

I'm at a point where I ready to test the amps but want to sort the protect boards first although I have powered the amp boards without any smoke and there is 0 volts on the outputs without an input signal so I feel it should be ok. I'll connect a large 8 ohm resistor and scope to test before I connect a speaker.
 
#3,365
I found the issue with the protect boards. It was the the regulation and I fixed it by adding 22uf elctros on the output of the regs. There are already .1uf ceramics there so I just added the electros and the voltages ended at +14.95 and - 15.05. That fixed all the issues with those.

Big problem testing amp though with smoke and flames. I was testing with input from a signal generator at 1k Hz with an oscilloscope connected to my 8 ohm dummy load resistors. With the input slowly increased whilst watching the scope to around 120v peak to peak R22 went up in smoke and then flames. I didn't notice any clipping or limiting on the scope. The other channel which I tested first blew up Q3,4&5 I though because the input level was way to high when I turned on the signal generator.
Any help in working out what went wrong would be greatly appreciated.
Am I testing incorrectly? I have tested amps like this before with the same gear and I've never seen flames before, always be able to push them up to clipping without problems.
 
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#3,367
apexaudio said:
Yes with proper cooling.
Click to expand...

please correct mr Mile .
🙂
7j38M
 
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#3,370
Got my 2 ch B500 built at last. Pretty happy with the power, my test at 1k hz and 4 ohm load gets 575 watts one channel driven and 360 watts into 8 ohms. This is with the limiter switched off(I put a switch in the limiter circuit).
Had a lot of trouble with hum/noise but after a lot of trial and error I have it quite good. I can list what I did/capacitor added to get it to where I'm happy.
Amp is using Apex's protect circuits and soft start with 4 x 300va 60volt toroids and 6 10k uf 100v caps. Rail voltage ended up at +-86 Volts with no load. Fitted into a stock 3U case which was quite a challenge with the 4 transformers.
Haven't had a chance to drive it hard outdoors but with some 12" fold backs it sounds very clean.

IMG_20180422_181813_1.jpg
IMG_20180422_181834.jpg
An externally hosted image should be here but it was not working when we last tested it.
 
#3,372
Hi g. Mile, i have asked on our local forum about B500. I have builded B500 with 9 pairs NJW0281G/0302G (+-98~100VDC), but i run it only with 6 pairs. After i added 3 pairs i didn't run it becouse i have doubt about driver transistor. Can MJE transistors drive 9 pairs, and how many pairs is maximum? I used standard version, non TEF.
 
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