Serious P.S. question - Driving 2 x 350w amps @ 4 ohm

[mr_squeegs]

hello i have a question for some power supply gurus.

i built a kit amp that drives 200 watts into 8 ohms and 350 watts into 4 ohms

it was running a dual voice coil carbon 12 inch sub with the voice coil in series (8 ohm mode 200 watts peak power)

a lightning strike killed the amp and i ended up just buying a new board module. Using the values i obtained from the new kit i managaed to repair the first board

So right now i have 2 servicable amp modules that can drive 350 watts into 4ohms and just one power supply from the first amp

the original power supply consited of +/- 70 volt rails and used 3 x 8000uf caps for each side of the rail.

i want to place the 2 amps boards in the one enclosure and run them off a single power supply

the dual voice coils of the sub are rated at 250 watts each

so the question i am asking is will my existing power supply be able to cope with 2 amps driving 250watts into 4 ohms ? remembering they are mechanically coupled to the same speaker ?

if not can anyone suggest a suitable supply ?

many thanks - i cant figure this one on my own guys

[The Saint]

It Should work just fine

[Pbassred]

I'm haveing a bad week and I'm too tired to comment on anything that needs more than one sentence.

[djQUAN]

from my experience, it is not a good idea to drive a dual coil sub with two amp channels....

it either results to blowing the amp output stage or burning the coil....

might have done something wrong but either way, I would no longer do it.

[mr_squeegs]

ok so now i have one person that says its ok

one person thats really tired

and one person that says bad things usually happen =)

im going to need some solid maths so i can sleep at night

i was thinking along the lines of that if the amps are in parralell then the impedence of the powersupply would half therefore i might need extra caps on each rail at least to handle the current drain. This theory would be fairly straight foward with the two amps driving seperate speakers.

the question it apears is the work required for one amp to displace a speaker cone Xcm the same

as it is for two amps to displace a speaker cone Xcm ?

I am thinking that having 2 amps driving a dual voice coil could even be more efficient than one. The speaker cone would have a faster impulse responce and be able to accelerate quicker with a parralell push from 2 amps reducing power supply load. Though this gain would mostlly be negated due to the fact 2 amps are being powered.

MY BRAIN HURTS ...... many thanks guys

[Pbassred]

I don't know anything about dual voice coils, though at first guess I'd say that driving the same mechanical assembly from 2 sources of energy requires that they be perfectly in sinc'. Interesting party trick ...... but thats one for the experts. not me.

Its the driving 2 amps off one PSU that alarms me. You have not said what the power pating of the supply is. Driving 2 amps needs a PSU twice as big as driving one amp. The big caps are an energy store, rather than an energy supply. I don't think that impeadance matters as much as 2 amps sucking off a supply designed for one.

Its like filling a bath with the plug out. With a big enough tap you can do it, but you put another plug hole in it you have no chance. It doesn't matter how big and shiney the bath tub is.

Voltage rail drop when you need power, distortion, over heat, fear pain, uglyness, smoke, complete system failure, party collapse, whithering look from that girl to we hoping to get off with, who believed that you were the big dog but now you just a mutt.

'bout covers it.

Separate amps,

[AndrewT]

Hi,
forget about the acceleration thing. Judging by the other thread that discussed but never resolved this topic it causes everyone's brains to hurt or just leave the room if some comments are to be believed.

Two channels each dedicated to a VC is OK. Use a polarised speaker plug and socket to ensure you never connect the VC out of phase.

The amplifier modules will work off the one supply but I suspect they will not perform well due to modulation of the PSU supply voltage.

I have a suggestion.

Most transformers cope well with short term overload.
Most capacitors do transients well.
Rectifiers are cheap.

Keep the existing rectifier and smoothing bank to supply one channel.

Build a second rectifier and smoothing bank to duplicate the original (exact make and type are not that important).
Connect the ~ & ~ of the new rectifier to the secondaries of the transformer.
Connect the + & - of the rectifier to the +ve and -ve of the series connected smoothing caps.
Connect the 0volt common from the transformer to both amplifiers.

Everthing is duplicated except the transformer.
The extra caps are the most expensive item. 6*8mF if you can find them economically.
They provided +-24mF/channel. This is a little light for 4ohm duty.
I would increase this to +-30mF or even +-40mF/channel if you have room and the money. Split the new type and the old type evenly between channels. Can you recover any good electrolytics from the damaged amplifier? There are many 10mF and 15mF available at sensible prices.

[Pbassred]

Why not just repair the old supply? ( he said - stupidly)

[mr_squeegs]

let me reliterate

the original power supply was never damaged and i now have two amp modules instead of one.

The power supply was rated to handle 350 watts into 4 ohms

and i just want to know if 2 amp modules could run off the same supply pushing 250watts into 4 ohm (this being as loud as they ever would be driven. most use would be between 50-200watts)

i am asking this question as with the two modules and p.s. there is no more room left in my enclosure except for maybe an extra 8000uf cap on each rail.

logic says just build another supply if you are using another amp, but remember it is driving the same mechanical speaker. and buying 6 x 8000uf caps new is just over kill i think

best regards..... k

[AndrewT]

do you want mediocre performance or good performance?