My project

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I haven't posted in awhile and I figured I'd better say something.

I now have the cooling system for my 7200W amp all done. If only I had an 8x900W into 12ohm double-barreled MOSFET hifi amp to go with it! I guess now I've got a lot of thinking and a lot of prototyping to do. (no way I can afford Electronics Workbech:( )The OPS will be a lot like the Leach Superamp, and I suppose my first prototypes will be a lot like it all the way through. Unless of course someone has a better idea, I'd be really glad to hear about it. These channels will have something like 3 times the power and nearly twice the supply voltage of the Superamp, so It will be a challenge for stability and performance, I'm sure, and slew rate may well limit it's high freq. performance, but I might be able to pull it off anyway. It'll probably be frustrating as hell, hopefully I'll have the patience to finish the project! (I'd better, I've put a lot of time and money into it already.)

I figure for testing I can bring the voltage up slowly with a large generator, which I might be able to get.

P.S. I almost have a channel of my Leach Amp done, I'm just waiting for a few back-ordered capacitors. I'll keep you updated and should have pictures of it before too long.
I have some small hints for Switchercad:

For FFT:

Resolution = 1/simulation time
5mSec => 200Hz resolution

FFT frequency span = FFTpoints * resolution * 0.5
16384 * 200Hz * .5 => 0 - 1.6384MHz

simulation time / (1/(signal source frequency) should never include decimal values.

Simulation resolution:

Menu : Tools -> ControlPanel -> page - Compression : All compression off

Menu : Tools -> ControlPanel -> page - Spice : Max time step - set to 1e-8 or lower => fine resolution but make simulation longer.

PS : One good thing about switchercad - It checks for updates!

I hope this is usefull?



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Kilowatt said:
I'll try it, but most free CAD programs aren't suitable for high end audio. People have recommended Electronics Workbench, it has everything, but it starts at over $1000 and the Power Pro version of Multisim 2001 is almost $6000.

Get the student version of Workbench. $89 bucks for the simulator and $89 for the PCB layout with all the goodies. I tried the pro edition and it wasn't much different -- just more parts. You can always add and create parts yourself, but for audio design you would have to add the power bjt's to either version.

For some reason when I ordered both Simulator and PCB at once i only got billed $89. hehe
I just had a thought

My big amp won't be isolated, it will have direct line rectification, and this has caused MAJOR concern among everyone. But... car amps aren't isolated, if you measure between the speaker terminals and gnd, you get a big voltage (I'm talking about big car amps), so why is it that they should do this and I shouldn't?! Not only that, but in a car, there is conductive grounded material everywhere, and with my big amp, there won't be.
Yea all big car amps have a transformer. The primary is driven by a MOSFET H-bridge, and the center tapped secondary hooked up to a bridge rectifier (using fast recovery diodes) and capacitor bank just like any normal amp -- and they get away with tiny toroids because of the high switching frequency. Ground is nearly always common between speaker outs and vehicle/chassis.
Why do you ..

Why do you need so much power are you like ritch to power this thing to listen to it what is wrong with a 100watt class a amp rinnning some realy efficiant towers or Satelite speakers.. or are you just doing it because you can and want to see the results that is insane man there is like no speaker out there that can handle that power any way..

the problem is u aren't isolating your power rails from the AC line...from an electrical inspector's point of view. switching power supplies in computers do this. ground coupling is no big deal but usually ac line powered amps only ground the chassis to earth and speaker outputs are connected only to the amp's signal ground ground from the centertap of the transformer. i read your earlier posts about direct line rectification so i'm not gonna try to convince you to do otherwise =)


Kilowatt said:
Hmmmm, in a car amp, chassis ground and speaker ground are common. In my amp, chassis ground and speaker ground are common. What's the difference from an electrical inspector's point of view?
Jason, there are definately speaker systems that can handle 7200W. I'll just use lots of smaller speakers, and the total system will be very efficient. A 7200W amp is always louder than a 100W amp if you use speakers of optimal efficiency for both systems (duh). There are may systems (PA systems) that have this much SPL capability, so what is your argument?

From an electrical inpector's point of view, why should my power rails be isolated from mains? I always thought it was because of shock hazard, but it doesn't increase risk of electric shock or fire compared to ground coupled systems, so what's the difference? You have 300V across the rails and 150V between rails and gnd either way. I know it's surprising that I would still need to ask this, but it hasn't been covered in any of my previous threads. -Just wondering

P.S. I'm far from rich. I live in Montana, where everyone is poor, and it will take me a long time to finish the system, and I'll be limited mainly by funds.
Kilowatt said:
P.S. I'm far from rich. I live in Montana, where everyone is poor, and it will take me a long time to finish the system, and I'll be limited mainly by funds.

Hey Kilowatt,

Wouldn't hurt to benchmark yourself against what a decent PA amp costs. The street price for a new 3400 Watt QSC PLX amp is around $1200, Ive seen them used for around $900. How much less than that do you expect to end up spending?

Are there any sound reinforcement companies in your neck of the woods? It would be worth your time to try and get a part time job with one just for the learning experiance. Plus if you hang around a while you will probably get a chance to pick up some decent used gear at a good price.

It kind of sounds like you want to get into the PA provider business, gentle warning, success is not about having the gear. Lots of people go spend $50K - $100K on gear and end up going bust. You should checkout and find out what people that do this for a living have to say.

Phil Ouellette
Killerwatt Amplifier

Kilowatt, errr, should that be Killerwatt,

The only devices that I am aware of that are directly coupled to the mains are some live chassis televisions.
However these have dc isolated signal connections, and NO conductive user touchable parts or controls.

In Australia, we use MEN (mains earthed neutral) system, where the neutral wire is grounded at the local street distribution transformer - ie unbalanced power distribution.
I'm not sure about US Montanna standards.

If you were to directly couple to the mains, you are likely to end up with unequal rectified DC rails because of (other) DC loads on the power circuit that you are drawing from.

Also likely to suffer earth jacking for same reasons.

Also, you are exposing your amp to every bit of noise on the line and spiking due to large loads turning off/on. (refrigerators etc)

I have a couple of large (3000VA) constant voltage transformer power conditioner units that I got from a salvage yard cheap, and these give DC isolation, in addition to constant AC voltage output.

If your amp is for hire/Pa usage you are usually running in a dirty mains supply environment, with refrigerators, stage dimmers, and all sorts of other noise generators.

There is good reason for commercial items to be DC isolated.
Probably a major one is BIG litigation if something goes wrong !.

Also, musos get pretty narky about getting a tingle (or boot) from their microphone golfball covers, or guitar strings.
Indeed musos have been killed this way.

If word was to get out that your amp/system is DC mains coupled, you aint going to get any hires anywhere - period !.

These are intended as words of advice, and not discouragement.
I also suggest that you go and do some study regarding electrical standards and laws, for your own safetys sake.

Regards, Eric.

PS - I also advise, that for your legal safety, you have any hireable equipment examined and certified by a qualified electrician, or suitable approval body, or else you are leaving yourself wide open to paying for any mistake for the rest of your life !.
Tossing Off In Public

Thanks Helix, for your advice.

From his posts on this thread, it seems to me that this KILLERWATT guy does not really have any proper idea of what he is talking about.
Out of concern I felt that he needed some timely advice on electrical safety and public liability issues.

Did anybody notice that he only uses his alias name ?.

On further reflection, IMO this guy is a BIG TOSSER !.

You are correct Helix, I'm not going to bother with this clown any further.

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