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bowdown 8th July 2005 06:55 AM

High Current Leach/leach super amp
Hi i was just wandering if anyone has or knows how to modify the leach/leach super amp to run really low impedences like 1 ohm. I was just thinking of adding more output transistors and also changing the protection circuit so it doesnt kick in until about 0.5 ohm or some thing(but dont know exactly what parts i need to change). Please let me know what you guys think.Please help if you can.



amplifierguru 8th July 2005 07:28 AM

Hi Bowdown,

Why you wandering in this direction? This low Z raises many issues especially of quality and sani...

This is not the best amplifier design for low Z as big supply crap will feedthrough to sound.

You don't drive a 4WD by any chance?


bowdown 8th July 2005 07:50 AM

I just wanted a high current amp as i have a sub that needs about 2000wrms and is 2 ohms(dual 4 ohm coils) so i was going to build another pair of leach/superamps as i have heaps and heaps of parts for them(I mean heaps). was going to build 2 high current modules that are stable down to 1 ohm then run them bridged at 2ohm. i dont currently have a 4WD.



amplifierguru 8th July 2005 07:57 AM

Your power supply is the first major problem. Kanwar (Workhorse) can probably advise there. I guess if you have a shi*load of parts.

It's no problem to do, but... what suburb do you live in... I have rellies in Perth who like their p&q.


bowdown 8th July 2005 08:21 AM

Im usually in Bunbury but go to perth(joondalup) every couple of weeks. Yeah see i bought all the stuff in big quantity to get a really good price on the stuff as i was planning on making a few leach amps for my home theater stuff probably end up with 3 or so 6 ch amps and a couple of BIG 1ch amps to run the subs. and i have to build a few amps for my brother too. thats why i didnt worry about over buying. whats p&q mean? sorry. You in Australia? yeah some info on power supply would be good. was thinking of using two or three 2.5-3 kva toroidals per monoblock. but i would have to run 2-3 lots of power sockets to the amps as the sockets can only handle 10 amps. might get a higher current one put in.



jaycee 8th July 2005 08:40 AM

If it's dual 4 ohm coils why not put them in series ?

bocka 8th July 2005 08:50 AM

Hi bowdown,

OK, lets do some engineering for free ;)

2000 watts @ 2 ohms results in a peak current of

sqrt(2 * 2000watts / 2ohms) = 45 amps

as well as an peak voltage of

sqrt(2 * 2000watts * 2 ohms) = 89 volts

With some losses you'll need about 100 volts on the rails. To make this amp save on a phase angle of let's say 45, each transistor bank must handle about

1/sqrt(2) * 100 volts * 45 amps = 3100 watts peak.

I suggest, that the transistors have this SOAR capabilities for at least 10ms. When using a MJL21193/MJL21194 for example one transistor is able to handle about 1.5 amps @ 100V at 25C. Because the junction temperature is higher you'll have to decrease the power handling of each transistor to about 1 amp.

In this case you have to parallel about 30 devices (each bank, positive and negative) for reliable operation.

The efficiency of a power amp is about 65%. This means that you have to dissipate about

0.35 * 2000watts = 700watts.

Although when you don't need this as permanent load requirement, a heatsink of about 0.05K/W is necessary. Forced cooling for this low thermal resistance is mandatory. In this case the heatsing gets about 35C warmer under full load condition.

Power supply:

1 / efficency * output power = power of supplies

1 / 0.65 * 2000watts = 3100 watts is necessary for your power supply. In this case you'll need a transformer, which power rating is about 1.5 timers higher.

A 4500 watts transformer is needed, when permanent load is required.

To obtain an rail voltage of 100 volts under full load condition and about 10% voltage drop from unloaded to loaded condition a transformer with

100volts * 1.1 / sqrt(2) = 78volts

is required.

Although these are only quick calculations, there shouldn't severe mistakes in.

bowdown 8th July 2005 09:34 AM

Gees bocka thanx for all this good info. Hmmm dont know what i should do now. This is what i have at the moment at home. I got approx 130 pairs of mjl21193/94, approx 200 pairs of mj15003/4, 5000 pairs of mpsa06/56,250 pairs of mje15030/1,1000 pairs of 2n5416/2n3439 and all the resistors,diodes and caps in the hundreds, 4 2kva torodals giving me +/- 96Vdc and another 4 on their way. i Have 3 meters of raw heatsink (300mm = about 0.3c/w not fan cooled) i can get it cut into any length. Please advise me what other amps i can build with this stuff.

Jaycee i dont mind running it at 8ohm but dunno how to get 2000watts rms at that impedence.

Gees thanx guys for all your help. i really appreciate it.



jaycee 8th July 2005 09:42 AM

I would look into building one of Anthony Holton's amps, MOSFET output based, if you really want this kind of power. I would say 2kW for a sub is very, very, very overkill when a 400W is enough to make my house shake.

You're definately going to have to have lots of output devices, a high rail voltage, and probably fan cooling for this. This is an ideal application for a Class D amp but these aren't really practical for the DIY constructor unless he has a lot of experience.

bocka 8th July 2005 10:05 AM

I'd build the leach amp. Stick with the MJL21193/21194 as outputs. For the driver I'd recommend another MJL21193/21194. And for the predriver I'll recommend a MJE15032/MJE15033.

The MJ15003/15004, the MJE150031/150032, MPSA05/56 are not applicable for this high power design because of the too low Vce ratings. I haven't a datasheet for the 2n5416/2n3439 on the hand. I'd look for transistors with a Vce of 300V at least. Maybe there are some 2SA/2SC devices that fit these requirements.

The transformers should be sufficiant. Maybe you'll get a little bit less power than 2000 watts.

I think forced cooling with a 0.3K/W heatsink can obtain 0.05K/W. Give it a try. Maybe you measure the temperature under full load conditions.

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