500 watts into 1ohm SS amplifier design

[tony]

I have often wondered why i have not seen such kind of an amplifier on a daily basis.....
let's find out......the calculations i will present here, you can apply to any existing topology....normally what we see here is that when a circuit is presented, there is always that clamor to raise the rail voltage, reason being is to increase power output....so why not do it the other way, lower the load resistance capability of the amp? this can be as challenging and as enjoyable....

so....

500 watts into 1 ohms means that in terms of ac output at midband,

Eo = sqrt(500x1) = 22.36volts, let us just say 23volts rms....

Eo peak = 23 x 1.4 = 32.2 volts  

Eo peak to peak = 64.4 volts  

Io = 23A rms

Io peak = 32A

Calculation of rail voltages,
assumptions taken:
1. allowing near saturation voltages of 1.5 volts for the output trannies.....
2. allowing voltage drops of 1volt for the emmiter degeneration resistances of the output trannies.....

so +Vcc = 32.2 + 1.5 + 1 = 34.7, or simply say 35volts dc...

our rails at full power of 500watts into 1 ohm then is +/-35 volts,

next post we will look at the power transformer requirements for this power amp....stay tuned folks....

[j a y k e z]

wow subscribing sir

[???]

subcribing....


baka simula na naman ito ng mahabang talakayan.   

[tony]

subcribing....


baka simula na naman ito ng mahabang talakayan.  

  some people want to learn the hard way, i'll let them, there are better things to do... wag lang makuryente......

[tony]

let us proceed.....

let me lay the premise for discussions, sine waves ang signal natin, hindi pa music, kasi for purposes of analysis, mas convinient ang sines.....ito rin ang gagamitin sa full power testing.....

500watts into 1 ohm, this is a class AB power amp....
how much is the total power drawn from the power transformer? (at full power and 2 channels are driven near clipping....)

for stereo, this is 1000 watts into 1 ohm...

classAB efficiency ranges from 64% to about 72%, let us assume that it is 64%.......

so then our total power draw becomes 1000/64% = 1562.5 watts, i will specify a 2kW traffo? why? gusto ko eh.... i will post a detailed design of this traffo in my other thread about traffos...

here you will see that 562.5 watts is lost as heat at the collectors of the output trannies.....

our power transformer then needs to supply this amount of power at its secondary terminals.....

more to come later.......

[TinTopHack]

Hohoho .... Challenging indeed. For one, dealing with resistive losses will be one BIG challenge.

[tony]

Hohoho .... Challenging indeed. For one, dealing with resistive losses will be one BIG challenge.

indeed.....

[SexyPaint]

pa sub din

[Disabled]

sub.

[tony]

What about the output power trannies, how do we spec them?

let us see... our rails at full power is +/-35 volts, assume that our unloaded rails are +/- 50 volts,

therefore for Vceo spec we want a trannie with a rating of at least 100 volts, and  here the TIP35C/TIP36C comes to mind.....

but there is nothing stopping us from using trannies with Vceo ratings greater than 100volts.....

we want trannies that do not suffer from beta droop at higher currents......

start looking for trannies with these qualities and you can recommend me one....

later......meanwhile, this is a good read: http://www.electronics-tutorials.ws/transistor/tran_2.html ; http://www.diyaudio.com/forums/solid-state/89063-need-low-power-high-beta-transistors-please-drop-me-few-part-numbers.html

[sp0c0]

thanks for sharing this master tony..

good karma for you..

[labgruppen]

users of this amp will need monster cables for speakers..

nope, not the monster cable brand, that monstrous welding cable one!!  

[tony]

users of this amp will need monster cables for speakers..

nope, not the monster cable brand, that monstrous welding cable one!!  

thanks for reminding me, actually i have seen one setup using welding cables for speaker wires, somewhere along welcome rotonda in QC....

[jiggins20]

pa sub din..pogi points for you master tony...

[TinTopHack]

users of this amp will need monster cables for speakers..

nope, not the monster cable brand, that monstrous welding cable one!! 

thanks for reminding me, actually i have seen one setup using welding cables for speaker wires, somewhere along welcome rotonda in QC....

It's not just wire size. Even the way you connect the wires (cables) matters a lot.  Every fraction of an ohm due to poor contacts means several watts of wasted power.

[labgruppen]

^agreed sir.. cam-lok connectors may be used, nice match to those welding cables.    may not conform to local electrical codes, though..

[Born2BeWired]

It's not just wire size. Even the way you connect the wires (cables) matters a lot.  Every fraction of an ohm due to poor contacts means several watts of wasted power.

That made this topic even more interesting. These will teach the readers how good engineering, solid foundation, and attention to details, can overcome difficult engineering problems.

[zrehtiek/keitherz]

wait a sec. 23A? arc welding machine?

[Born2BeWired]

In addition to power loses due to ohmic drop, another amplifier system parameters that will suffer when wire resistance comes into play is the Damping Factor. How this affect the sonic quality may spark another heated debate, and if it does, lets do it in separate thread para di magulo itong main topic .

One appealing application that comes to mind when toying with amplifiers driving low impedance load is speaker box where the amplifier is housed right inside the speaker box. Powered speaker ba ang tawag duon? Short wire runs, soldered joints, and elimination of connectors solves some of the problem raised my master tintop.

[labgruppen]

^right on sir..  this amp should be used as near to the speaker as possible to avoid losses while maintaining a reasonable amount of DF.. it also calls for tons of NFB to have an equivalent internal impedance as low as possible..
hmm, how about using a "sense lead" (ala laboratory power supplies)? it might cause instabilities at high frequencies, but if there is a way to apply it to low frequencies only, where DF really matters, then it could help.. some integrated amps have a feature like this, kenwood is one iirc, but i have not seen one in action.