500W PA amplifier with Limiter

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#3,041
AndrewT said:
70Vpk (from +-80Vdc supplies) into 2r0 resistor test load is equivalent to 35Apk.
Click to expand...

Please note the rail sagging. The Mackie amp has the following specification:

300W/8ohm approx.70Vpeak
500W/4ohm approx. 63Vpeak
700W/2ohm approx. 53Vpeak

This means about 26A peak output. Peak output current can be 39-130A. Count with the 20A/output device the gain of the MJL21193/4 is minimum gain about 10. This gives 8A totalbace current. The driver has the gain about 30, which menas 270mA base current for the driver. It's not impossible, I guess.

Anyway the overcurrent protection should trigger earlier...

Sajti
 
#3,042
53Vpk from +-80Vdc supply rails is abominable performance.
I would recommend that no buyer goes near a specification as bad as that.

Even the 4r0 spec is bad @ 63Vpk from +-80Vdc

And the clue is in the 8r0 spec where 10V has been lost into a very gentle load.
 
#3,044
AndrewT said:
70Vpk (from +-80Vdc supplies) into 2r0 resistor test load is equivalent to 35Apk.

When driving a reactive speaker load the current demand on transients can be anywhere from 150% to 500% of the resistive test current.

Expect peak transient currents of 52.5Apk to 175Apk
A 4pair output stage will have to pass upto 20Apk regularly through each output device.
One needs to look at the transistor gain for 20Apk and determine the peak transient base current.
Then work through the stages to determine the pre-driver and VAS peak currents.

Working in ClassG & H does not provide any solution for this peak current demand made by reactive speakers.
Click to expand...


sir I m talking about the TEF version of APEX B500 which has 7 pair output transistors,,.
1799945_1379108819027119_1017409264_o.jpg


.and I want to use 50 v ac i.e 70v dc...and yes it is not possible to connect a 2 ohms speaker ...it burns everything...thank u for ur valuable answer....I just built it for 500watt rms PA amplifier..in 4 ohms speaker..
 
#3,045
4r0 is different from 2r0 and different from 2ohms and different from 4ohms.

One must decide what speaker needs to be driven.

Then design the output stages to drive that reactive impedance.

One does not look at a possible project and just guess at what speaker impedance could be used.
It is a DESIGN exercise.
 
#3,046
AndrewT said:
4r0 is different from 2r0 and different from 2ohms and different from 4ohms.

One must decide what speaker needs to be driven.

Then design the output stages to drive that reactive impedance.

One does not look at a possible project and just guess at what speaker impedance could be used.
It is a DESIGN exercise.
Click to expand...

sir,look at this design.
B]

this is famous Rod Elliot subwoofer amplifier...out put is 150w in 8 ohms load..input rail +-56 volt.
and look at the image.

B]

2 pair extra output transistor....gives 240w in 4 ohms load....but..here driver stage is very powerful...thats very important....😀.
 
Last edited by a moderator:
#3,047
What point are you trying to make?

You are posting info on 8ohms and 4ohms loading on an amp with less than 40-0-40Vac transformer.

We seem to have moved away from the enquiry about a 2ohms speaker load on an amp with a 50-0-50Vac transformer.
 
Last edited:
#3,048
pallab said:
sir,look at this design.
B]

this is famous Rod Elliot subwoofer amplifier...out put is 150w in 8 ohms load..input rail +-56 volt.
and look at the image.

B]

2 pair extra output transistor....gives 240w in 4 ohms load....but..here driver stage is very powerful...thats very important....😀.
Click to expand...

:cop:

Please read the notes toward the end of this page,
Elliott Sound Products - The Audio Pages (Main Index)

In particular "Links"
 
#3,050
I'm so confused, about the posting of esp pictures.
It's ONLY esp that I'm aware of that protests like this.
But the site and it's members have the utmost respect for Mr Elliot, so I guess we'll jump through the hoops required.
Maybe its just easier not to link/refer to his pages at all.
The he will never get traffic from this site to his.
 
#3,052
Hello to all
please
can anyone tell that
I want to use b500 tef with 2x60vac trafo on 2 ohms
its a must need for me because i want it be more than stable on 4 ohms
please tell me the no of output tranees to be used as i have plenty of 2sc5200 pairs and transformer ratings
 
#3,053
If you have a 4ohms speaker then you design the amplifier to drive a 4ohms load.

One criteria I use is that the amplifier MUST BE ABLE to drive a resistor test load that is half the nominal speaker impedance. This is not a stability requirement. It's about current capability into reactive loads.
I now design to drive 1/3rd nominal load resistance for a very short period. Just long enough to see the sinewave on the scope. This would be the equivalent to driving a 1r3 test resistor for a 4ohms amplifier.
 
#3,055
The total Pmax of the output devices should be ~ F times the maximum power output of the amplifier.

F = 4 for mosFET devices
F = 5 to 6 for BJT devices.

eg using 2pair of 250W devices (MJ15003/4) total Pmax = 4 * 250W = 1000W
For BJTs F= 5 to 6.
Max Power = 1000 / 5 = 200W

This depends very much on the temperature de-rated SOA of the devices and the temperature of the heatsink that you will typically use, as well as how severe the speaker is in stressing the output stage.
 
#3,056
new design apex b500tef...work..tanks apex audio
and h900tef on trial.
 

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