Hi trialabc,
             Scratching my head.
Your comment of 12V 17Ah lead acid battery (which i assume, is about the size of a motorbike battery) would NOT have the stamina to run a 70 Watt Amplifier for 3 hours. (hey I could be wrong) but if it was a small 10 to 20 Watt SS amplifier then yes 4 hours is feasable.

I helped setup a small rig like this for a chap who plays at a market and he used a DC converter into a small little amp.

Joe Cool has probably nailed your confusion of Wattage Power.
Your 75 watts is likely what the Amplifier Draws from the mains.

Actual Amplifier Wattage is going to be far less than that.
I checked the make and model and unless I've got the wrong model your amp is 15 Watts. so yes 3 to 4 hours is what you would get.

BTW, A preamp mixer circuit draws little current and could be run on it's own seperate dry cell batteries. probably get 20 hours easy.

It's the powerAmps that chew up the current demands.
Phil.

Hi, Sounds like a dead short if Amp is shutting down.
Check your wiring.
BTW, please draw a simple diagram rather that trying to explain it all.

A 50 Watt Lpad as used for HiFi crossovers is all that is needed for Amps up to about 10 Watts.

Adding more is needless complexity and more chance of mistakes.
Phil.

Yes just search these posts and you will find a few members use Fet circuits with success.

There are pitfalls to these circuits and once you start cascading them all together like that then *Noise* can be a real pain. Also at only 9 Volts I doubt the chances of success.

Why don't you build it and let us know of the outcome,, could be a real monster. :tu:
Cheers Phil.

Yes and I want a 1,000 Watt Amp that runs on a 9Volt battery.

Hi trialabc,

Arrh mate I think you need to do a reality check.

I guess if you don't have much experience with gear then it's understandable that you might think these things are simple to achieve.
I think if it was that simple then it would have been done long ago.
Sorry chum, What you are asking is possible but not practical. :loco
Big power Amps suck up a lot of power and you would go broke buying the truck batteries needed to run it all.

For that system to work you need to look at portable power generators that output mains power then you can use normal mains powered equipment.
That would be the only sane way to approach that situation.
Cheers Phil.

It will depend what you want to amplifiy and do you mean two speaker as in stereo?
Do you want guitar inputs or balanced mic inputs?

You do need to be a little more specific. 8|

Meantime heres a fairly simple circuit,, I own this Amp and I use it for keyboards and guitar.
Obviously simple to add more channels.
Phil.

First,,, Bubbles ,, yes I'm alive and well.

2nd thanks *DJ Phil*. You are quite right the Letter is the Tolerance not the Voltage,,, late at night I get confused. :loco

And thanks All of you for your concern. :tu:

Nambour is about 80 mile north of the Capital of Queensland, Brisbane.

The great Dividing range runs right down the East Coast of Auz and when we get rain in Queensland on both sides of that range not only does it flood on the coastal towns but it also moves inland.

Some ends up in Lake Eyre ( it's a salt lake in the middle below sea level)

The rest ends up in the Murray River and the water from mid land Queensland actually takes 6 to 9 months to reach the mouth of the Murray River in South Australia.

When all the rivers from the middle of Qland join up, The Condermine, Darling,(to name 2 of many) they ultimately join into the Murray River.
That basin *is then* very close to the same size as the Missisippi. Of course nowhere near as much water flows but it is a very big system none the less.

Australia being so boring and flat in the middle the water just runs outwards and hence town after town gets flooded out.

By now some of you will know the Town of Towoomba because of that freak wave.
Well it's about 80mile west of Brisbane right on the very edge of the great diving range.

Yes I 've driven through that town many times,, that very street that you may have seen on TV.

My Father lived through the bad Floods of 1954 in my home town of Rockhampton which has also been Flooded again.
So yes you could say The East coast of Queensland is really behind the 8 ball.

I lived through the Brisbane flood 1974 so I know what they are in for. I helped many elderly folks in my area clean out the mess afterwards, The smell afterwards is horendous. I will never forget it.

Nambour got away with only some carpark being ripped away and 4 feet of mud in the main shops.  This town is very hilly up and down so water gets away fast.

It has been observed that this Flood may well be Australia's worst natural disaster and It is certainly starting to look that way.

Having witnessed the 74 floods,,, I make a point of living on top of hills rather than low lying areas. 8|
Phil.

Yep I'd say so,
M is the voltage rating of the device.
Can't remember them all off hand but I think *J* means a 100volt rating.

Some makers use different codes but after a while you catch on to the tricks.
Phil.

Ed;
the code Works like this;

uF  nF  pF
000,000,000

So a 100nF would read 104,, that's 10 and just add 4 zeros

Yep a pain until you get how it works,, and darn I still get tricked some times.  :loco
223 would most likely mean, 22nF or .022uF or 22,000 pF all the same.

First two numbers are the *Value* 3rd number is the multiplier.
in this case it's 22 now just add 3 zeros and presto it's 22nF

333 same again 33nF
Phil.

You will find heaps of related info on the Jensen pages,
http://www.jensen-transformers.com/

Heaps of stuff under *Aplications > White papers and Schematics.*

Also *Rane* used to have a mass of technical terms all laid out in alphabetical order but I can't seem to find it now.

But look here ;
http://www.rane.com/

Under *Support* > Library,
Heaps of stuff to help broarden your knowledge base.
Phil.

Thanks for the kind words, It is nice to hear that and know that folks like what they find here. <3)
Phil.

Sorry I was not very clear;
*Impedance is the Resistance of a component at a given frequency*
Measure the DC Resistance of a 600 Z Ohm microphone,,, the reading will be quite different.

Try Reading this one,,
http://www.teamrocs.com/technical/pages/resistance_impedance.htm

Or just google it ,, "ac resistance vs dc resistance"

Phil.

they look like this;
http://www.amptone.com/wallmountspeakerattenuator.htm

They should state that they are for an 8 Ohm system and wired correctly yes everything will be fine.

If you wire them the wrong way then yes when you turn down to zero the amp gets a dead short,,, not that a dead short matters to a Valve Amp but it sounds crap.

Note the two rehostats are different values.
this maintains a relitive Z load to Amp.
Remember that DC Ohms is not the same as Z Ohms
*Z is AC resistance* which is freq dependant and DC Ohms is exactly that. Ohms
Phil.

I had another pic but keep getting internal server error
I'll try again later.
Phil.

Surely they sell Lpads in Tandy,, it will make life so much easier as you don't need to mess with any other components. :tu:

5 watts can be done with a simple speaker pot or L pad.
These are *NOT* like a normal pot they are a specialized unit designed specifically for the purpose of attenuation.
Two *Seperate* rehostats with one common wiper.
This might help you to see what goes on inside.
Cheers phil.

Need more info,
Is it a Valve Amp?
If so how many Watts?
Or What type of power Valves? (i.e. 2x EL84)

If so a 50 Watt HiFi L-pad will do that trick you and save a lot of messing about.
Not the best way but does work for small amps.
Phil.