Car amps with seperate PCBs

seperate SMPS

old Magnat Classic 360 models (without the Dog-Logo) have a seperate SMPS providing 2x32V . Problrem is, the pulse generator is not a TL494 , it´s a NE555 . Nut very luxuriously , but it works.


If you want to try the standard SMPS that is built into almost all korean amplifiers you might find this schematic helpful.


That 555 pulse generator sound simple, any ideas on how to build one? I'm only looking for about 200-250W and don't feel confident enough to mess with complicated SMPS's such as Rod Elliots without a pcb layout by somebody who really understands PSU's. I've got the parts so I may make an attempt at it just for fun, but I'm not sure. Would somebody mind telling me how safe it is to play with this stuff? I'm sure the 12V supply is a much safer voltage than a house SMPS, but not the hundreds of amps that that battery stores. And once it is built how reliable are these things assuming it's built correctly?

With that NE555 curcuit you will not be able to get more than 5-10W total. That is because the capacitor (BTW 2700µF is not a common value) powers the transformer during the negative pulse of the NE555. Another problem is, that there is no dead-time that would allow the transformer coil to shut down. If a coil is driven magnetic energy is stored in it, if the voltage is releasedf, the magnetic field that stays inside the coil will generate a high voltage. In the case of this curcuit, the transistors always get a "smack" when the NE555 output is switching. The NE555 used in the old Magnat curcuits is already a small PWM-controller. Not as powerful as the TL494 , of course, but it acts as a real fixed frequency PWM - controller.

Try to build the the SMPS with the above schematic / picture. You should be able to get all parts in the USA. If you cannot get the 2SA1266 (multipurpose transistor) you can use BC-types , like BC557 or anything similar. All transistors in the curcuit are working fully opened / fully closed.

instead of the IRFZ44 you can use SSP50N06 or similar, but then use smaller gate resistors like 47Ohms for those.

IC301 is a 4558 Operational Amplifier. You can also use something else. The IC301 is used for the protection curcuits. The lower part in the schematic is controlled by the thermal resistor.

the upper part is activated by the protection curcuits (music amplifier section) If I remember right, this must be a "low-signal" to activate the protection.

The transformer core is a 50-60mm with a 1: 2,5 turn ratio. I can check the exact windings as soon as I get a broken amplifier again.

another SMPS

Sony has an amplifier with a seperated SMPS. This is the board of a
Sony XM-5540, quite usable amplifier BTW.

It uses 2x30A and should be able to handle around 400-500W

This is what the orig. specs are. You should be able to find this amp in
the USA. If you are lucky, you get one with a broken amplifier board.

Consider that there is no protection on this board. Protect-curcuits are
all on the amplifier board, so you would have to think about the
protect curcuits.

Measurements are aprox: 7x5.5 inches



2004-10-11 5:21 pm
try looking for a 'Phase Linear Modular system' amp. they put the PSU and amplifiers in different cases! you feed +12V (80A fuse on the input) to the psu then get I think + and - 36V out of the PSU which you feed into the slave amps, depending on what impedance speakers you are driving (I believe the slave amps are 1 or maybe even 0.5Ohm stable per channel) you can run multiple slave amps off one PSU.
I snapped a Pyramid amplifier board in half.
A friend gave me the amp,and it wouldn't turn on,so assuming the PSU was toast (after going over it,I couldn't figure out what was wrong) I scored the board with a razor knife several times,and got a nice groove in it,then snapped it right in half.
I connected the amp to a conventional +/-30V Linear supply for use in the great.
Then later I found the fault on the SMPS section, a cold solder joint on a diode! Doh!

Oh well,the PSU section is now my driver for SMPS experiments.
And a seperate 100Wx2 bridgeable amp for the workbench.