View Full Version : monoblock 700W rms/2Ω

05-14-2013, 09:56 PM
Hi to everyone.
I will present a car amplifier that i designed two years ago.

Unfortunately for those who are interested in schematics, i will not post any as i try to make a living out of this.

So, please do not ask for schematics.

As in all car amplifiers there are 2 main stages, the step up smps, the audio amplifier.

As a housing i used an old heatsink from a DC to AC inverter.

The smps, the preamplifier, and all auxiliary circuitry are designed by me.

The power amplifier itself is an existing patented design, and i have written permission to use it from the patent .

I have only made some modifications to fit the application.4055




The main problem is to "pass the current" through the circuit.

Up to now, i have been using copper sheets cut on CNC machines to strengthen the underside of the pcb


this time i thought of something else, i used busbars that are already available to electricical shops


The prototype pcbs are shown below

i used photosensitive board, then liquid tin and finally i used a green coat spray




there is an input choke that along with large-high quality-electrolytic capacitors, forms a tuned circuit that stimulates 141,000μF at the 12V input.


this choke is calculated for 150Arms

Now, the control pcb is a small board perpendicular to the main smps board and it is 100% made with smt components.

below you can see how the busbars are used in the pcb


05-14-2013, 10:06 PM
there are two trafos with their secondaries in series to provide the power needed for the amp

and i used a mu sheet on top of them to minimize high frequency noise emission

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the oscillation frequency of the pwm was set to around 210KHz and there is a very special circuit to drive the fets


below, you can see this circuit unloaded. it ensures very fast turn on and off characteristics


05-14-2013, 10:20 PM

as stated above, the amplifier is a mono class AB amp that used 14 output fets (7+7) in TO-220 case.

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two things characterize this amplifier : speed and bandwidth

i did extensive testing to see the capabilities

in some of the tests the idle current was raised

1KHz square wave at 37Vp-p

50KHz square wave

the load is always resistive 4Ω/1%

output at 2/3 of output power

Now, the most interesting part (at least for me)

high frequency tests

05-14-2013, 10:44 PM
and it goes up

as you can see below 400KHz sine is no problem

not 800KHz

the amp goes up to 1MHz

here the entire front end of the amp started to overheat
probably due to the lack of shielding (ground plane)

please not that the idle current is a bit raised for those tests.
the load on all the above is 4Ω resistive

here is the amp set to the final idle current and a triangular signal

the audio amp
you can see the very high quality ROE capacitors (105oC).

since the amp uses fet as outputs, and fets tend to oscillate, there is one more test

the amp is fed with a high frequency square wave signal at full swing, but with no load

if something goes wrong, the fets oscillate and the amp is fried

the following two pics show exactly the same thing

in the first one, you can see the 100KHz square wave

and the second one shows the maximum swing (of the 100KHz signal) is 142Vp-p (on the up right of the scope you can see what it is set to measure)

05-14-2013, 11:29 PM
power output at 445Wrms/4Ω 4100

max output at 475Wrms/4Ω

and clipping at 123Vp-p

with a 2Ω load the amp produced easily 700Wrms/2Ω at soft clipping (just below 3%)

maximum output power was around 40VACrms (800Wrms/2Ω) and the current consumption at 13.5V was 111A

there is one final test to see the stability of the amp
i inserted a 2.2μF capacitor in parallel with the 4Ω resistor
the amp is very steady indeed

05-15-2013, 07:46 AM
Very nice work Ultra, Really nice

Thanks for sharing

05-15-2013, 02:35 PM
very nice ..
looks like you used the IRF640, 9640
as very similar to mono amplifiers "Rockford Fosgate"

05-15-2013, 04:31 PM
thank you

yes, you are right, i used IRF640/9640.

Rockford uses them in class BD amps, not class AB1 like this one.

From what i have found, if i could use more of those, i would have even more power output.

(my driver circuitry is capable of feeding 12 pairs of outputs)

The capabilities of the smps are bigger than the demand of this amp.

Just for proving this, i built another audio amp with 6 pair of 2SA1943/2SC5200 and the max output was around 900Wrms/2Ω.

And i use only 12xIRF3205 in the power supply.

05-15-2013, 11:02 PM
very well.
you could talk more about the topology ..
class AB1 & AB2
good work ..

05-29-2013, 08:06 PM
The amplifier needs 1.1Vrms to produce full power at 4 ohm load, so there is a two stage low distortion preamplifier that is implemented with OP275 chips.