change the SMPS circuit in car amplifiers. + picture

hii all...

i have amplifier in my car that stated (14.4V)

200Wx2 ~ 4 ohm
300Wx2 ~ 2 ohm
600Wx1 ~ 4 ohm bridge.

Class AB
SMPS ~ TL494
2 Channels.
6 transistors per channel. (3-2sc5198 3-2sa1941)
6 transistors per transformer. (IRFZ44)

now... i check the volt inside. if i put a : (in\out)

11.3V the SMPS out 67.3V (33.5V +/-)
12.8V the SMPS out 77V (38.5V +/-)
14.2V the SMPS out 84.8V (42.5V +/-)
14.5V the SMPS out 88V (44V +/-)

what i need to change in the circuit to get 88V all the time?
or to get 88V in 12V. ?? the frequency?

many thanks.
tamir.

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6.jpg

7.jpg
 

edl

Member
2004-10-19 2:35 pm
Hi!

You need to change a resistor near the PWM IC (TL494).
To the non-inverting "leg" goes the voltage reference. To the inverting "leg" goes the output voltage, divided by to resistor. Let's change one of the divider resistor to get 88V output voltage when the input is 12V.
 
just my 2 cents in order to complete confusion: :D

it looks like the SMPS is non regulated and the output voltage
is defined by the transformer ratio only.
...looks like 1:1:3:3 (push:pull:sec1:sec2)
....or 1:1:6 center tapped....

BTW:
Your plan to increase the supply voltage of the amp around 20%
will bring just less than 2db for your ears.
....not worth any effort...
If it does not play loud enough, you need bigger steps.
By far bigger steps.
 

mzzj

Member
2005-07-02 8:17 pm
65N 25E
ChocoHolic said:
just my 2 cents in order to complete confusion: :D

it looks like the SMPS is non regulated and the output voltage
is defined by the transformer ratio only.
...looks like 1:1:3:3 (push:pull:sec1:sec2)
....or 1:1:6 center tapped....

BTW:
Your plan to increase the supply voltage of the amp around 20%
will bring just less than 2db for your ears.
....not worth any effort...
If it does not play loud enough, you need bigger steps.
By far bigger steps.
Yes, looks like unregulated indeed. And there is no easy way to regulate as i told. secondary side inductors are needed for regulation, this kind of "crappy" power supply without inductors is quite popular in car amps.
 
ChocoHolic said:
just my 2 cents in order to complete confusion: :D

it looks like the SMPS is non regulated and the output voltage
is defined by the transformer ratio only.
...looks like 1:1:3:3 (push:pull:sec1:sec2)
....or 1:1:6 center tapped....

BTW:
Your plan to increase the supply voltage of the amp around 20%
will bring just less than 2db for your ears.
....not worth any effort...
If it does not play loud enough, you need bigger steps.
By far bigger steps.

it is 1:1:3:3

2db it is what i need to get to win in the 1_th plase is SPL (CAR AUDIO competition )

thanks....
tamir
 
Unfortunately the output voltage is already at the upper that you
can reach with a 1:1:3:3 transformer.
But be careful a 1:1:4:4 ratio could already blow your amp !


...if you would have needed 2db during the last contest, then you
will need at least 5 db more in the next contest.
The other guys are not sleeping!
So you have several choices:
a)... to loose your girl friend, because you loose the
SPL competition.
b)... to loose her, because you buy a 1kW amp & speaker system
but don't have left any money to invite here for dinner.....
c) ...to loose her because you spend all your time with the
modification of your amp and blow your overloaded system during the next contest..
d) ..forget about SPL competition and become lucky with
a girl friend that does not judge you by your amplifier rating

From my perception c) would be worst.. :smash:
 

anatech

Administrator
Paid Member
2004-06-06 8:31 pm
Georgetown, On
Hi,
ChocoHolic is right, you need way more power. Don't mess with that one or you may blow it up. You can gain 2dB by starting the contest with your voicecoils cold in most cases.

Most car amps I used to work on did have output inductors (small) and they were regulated by a TL494, SG3524 or SG3525. But you should do the math. Assume your amp is, say 85% efficient in the power supply and 65% in the amplifier section - I'm being nice here. How much current do you need to run this thing at full power? What are the IR losses in the wire. Don't forget the little wire that goes from the chassis to the battery return.

-Chris
 
OK....OK....
I have been in a honest mood, when writing my last post.
If you really want to choose option c), then you could try to
add turns on the secondaries.
It is not so easy to count the turns on the picture.
But it looks like 4:4:13:13.
So you have the possibility to increase the secondaries in small steps.

BTW: What's the voltage rating of your electrolytic caps?
Please note that you should not kill them even if your car
decides to deliver 16V battery voltage for a short while...
 
...if you would have needed 2db during the last contest, then you will need at least 5 db more in the next contest.
The other guys are not sleeping!
So you have several choices:
a)... to loose your girl friend, because you loose the
SPL competition.
b)... to loose her, because you buy a 1kW amp & speaker system
but don't have left any money to invite here for dinner.....
c) ...to loose her because you spend all your time with the
modification of your amp and blow your overloaded system during the next contest..
d) ..forget about SPL competition and become lucky with
a girl friend that does not judge you by your amplifier rating

:D :D :D

ChocoHolic, you sure give Astro Power the ultimate answer.

BTW, it is not easy to mod a car amp to have bigger power in stable way. Even in SPL measurement of 5 seconds turn-on. If done correctly you can modify the SMPS transformer, but you will also have to change caps (with higher value), add more wire in the smps, add more mosfet smps, thicken the heavy current rail(s), add more output transistors (if the load is the same, but the rail is higher), add more bias in the driver section, change the heatsink due to more heat will be coming, etc.. etc..., not so easy as rising the voltage only, though.
From what I know, in SPL competition, power amp is #6 (or is it #11?:D) that makes a certain car win.
#1 is to have a very accurate tuning frequency
#2 is to have a very rigid car+minimum body deflection (means you have to thicken your body plate with resins+mat, put tons of damping asphalt or concrete if necessary, put it in car roof, car door, car floor. Thicken all the glass (they can bend in pressure)
#3 is to have NO leakage at all from the car's cabin to outside air. You have to look even the smallest leakage, and fix it.
#4 is to have to have very good woofer
#5 is to have very large energy reservoir (12V batteries)+sufficient cables.
Doing #1 and #2 correctly will give you more dB's than double the amp rating.
 
You should check small-signal transistor and capacitor voltage ratings in order to know wether it will allow for higher rails. Components with not enough voltage rating should be replaced.

Concerning the output devices, the datasheet states [email protected] and [email protected] DC SOA ratings, so operation with +-50..55V rails and 2ohm per channel with music signals may be possible for small amounts of time (there is not enough heatsinking anyway).

Concerning the PSU, due to its MOSFET and unregulated nature, it is also capable of whitstanding higher than expected currents for low periods of time. I've had IRFZ48V TO-220 devices conducting even 50Arms for several hours without blowing (with careful gate drive and heatsinking).

So, by making some clever changes to the circuit, you may rewind the toroids to produce +-50V with 12.8V input ([email protected]) without blowing anything. However, this requires very careful analysis of worst case voltage and power stress for each component in the circuit and probably several parts will have to be replaced (the PSU filter capacitors are the first candidates for replacement).

If you decide to go on, do it at your own risk. It's a complex task.
 
Hi, Astro Power,

in the last contest i got 143dB it is second plase.
and the box is BASS HORN

From your information, I REALLY think that your system can be made more dB without modifying the amp.

I've made SPL vented box, bandpass box, other kind of box, and I think what can reach highest SPL is vented box, especially slotted box (you use square port made from wood, and make it as big as possible, do not use small tubes for port) This slotted port is even louder than using PNR tube port.

The problem with bandpass box or horn box like you use, is that it will shift the tuning frequency when put inside the car. For example, you tune outside you get 43hz. When you put in car the whole system will shift to 47hz. And it is impossible to change the tuning of that kind of box. So in short word, I think you haven't reach the very tuning of your car+subwoofer box.

The key is to tune the box inside the car. You put the box inside the car already, but do not power the subwoofer. You took another speaker+sealed box (10" or 12" single), but in a properly volumed box. You took the RTA, and sweep the bass from 30 to 200hz, and find out which is the tuning of the car with your big subwoofer box inside the car.
When you already find out this, you slightly calculate how much port area and port length you need in your box.
Make the slot length can be adjustable for final tuning.

The final tuning is you adjust the length of the slot port inside the car, and you go to battle with test tone with the frequency of your systems tuning.
 
EVE thanks u.....

but i thing the change the transformer from 1:1:3:3 (4:4:12:12) to 1:1:3.5:3.5 (4:4:14:14)

it will be more easy... dont u thing?
and in the amp i have volt limit... if tha amp will get 16V in the input, the volt is dont get over 50V +/- .

lumanauw.... hello...

the volume of the box is 230 liter (8.122 cubic foot)

and inside i have a 2 15 inch 800W subwoofers

data sheet of the subwoofers

the box is a normal vented box with 2 tube ports diameter of 6 inch.

i plan to change that to a big square port . and add horn.....

it is produce improvement ?!

what u thing i need to do the boxs to get the maximum SPL ?
and what is the slotted box?

i need the tuning the bass box to +/- 50HZ.

thanks for the help.

tamir
 
I don't feel you could get any improvement below 60Hz with horns inside a car, since the reduced volume of the cabin is already strongly loading the drivers at such low frequencies. On the other hand, horns are nice for listening to music since they allow to boost the 60..250Hz 'punch'.

Also, if you decide to add turns to the secondary windings, remember that voltage ratings of most components are reduced with increasing temperature, so pay attention to cooling.