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Old 8th July 2005, 12:36 PM   #11
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bowdown,

just run your amps bridged,

with your said power supply power outputs,

I think its not impossible to drive it 2000 watts at 8 ohms.

rgds,

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Old 8th July 2005, 12:43 PM   #12
Villaw is offline Villaw  Cyprus
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then again you can get a behringer pro amp for 300 US and bridge it. you will be done in 2 minutes and have your neighbours start complaining earlier.
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Old 8th July 2005, 01:13 PM   #13
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Hi bowdown...

The Bipolar Transistor amps are not suitable for driving ultra low impedance loads....because their SOA is extremely small at high voltages and they also suffer from Second breakdown voltages....they are poor performers when you are in need of large voltage signal along with the same magnitude of current rating..
Ultra low impedance load driving capability falls under the kingdom of only N-channel large die mosfets.... BJT just sags the power even if you parallel them in great numbers...

We had a similar situation like yours but our customer wants to drive his 4 X 800W 18" Selenium 8 ohm Subwoofers in parallel resulting in 3200WRMS@2ohms and it needs at least 4000WRMS of sheer power to do the right justice for the Ricter scale to move upwards.
We implemented 2 bridge amplifiers comprising 8 pairs of APT20M18LVR large die mosfets from APT with + - 90 Volt rails and 4 toroids transformer of 755VA each with total of 16 X 10000MFD/100V Filter caps.....8 X 1000V/35A Bridge Rectifiers
Some specs...
Power output....4000WRMS at 2 ohms
Frequency response....10hz to 50khz
Slew rate.....85V/us
Damping Factor >1000 @ 4 OHMS


bowdown you have so much stock under your command, beefing a leach amp is not worth because they are not designed to handle these type of ultra low impedances...try to find some other bipolar design on this forum ......

K a n w a r
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Old 8th July 2005, 01:54 PM   #14
bocka is offline bocka  Germany
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Quote:
The Bipolar Transistor amps are not suitable for driving ultra low impedance loads....because their SOA is extremely small at high voltages
Hi Kanwar,

this is not true, look to the MJL21193 datasheet. 150 watts @100 volts is not so bad for a TO247 package. It's true that bipolars have a second breakdown. You have to take this into account when using them.

About 50-100 watts output power for each transistor on a bank is a typical rating for high-power bipolars. Not neccessarilly every design needs to be a (N)MOSFET design.

Because bowdown has the MJL21193/MJL21194 on the hand he can use them when he designs his amp carefully. And the MJL21193/21194 is cheap.

Quote:
4 toroids transformer of 755VA each
This is definitely not enough for 4000 watts continous power. Look to my calculations.

Quote:
beefing a leach amp is not worth because they are not designed to handle these type of ultra low impedances...try to find some other bipolar design on this forum
No, just parallel enough output transistors for low impedances and use a BIG BIG heatsink. The leach amp is intentionally designed or 8 ohms. For 2 ohms the number of output devices is simply 4 times higher. The problem is, that the leach amp is designed for a +/- 58V power supply, not for +/-100V. The leach amps needs to be modified carefully in this case.

Quote:
just run your amps bridged, [snip]

I think its not impossible to drive it 2000 watts at 8 ohms
Bridging and modifiing the leach amp for 2000 watts @ 8 ohms is nearly the same as modifiing the leach amp to 2000 watts @ 2 ohms. Same number of ouput devices, same power supply...
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Old 8th July 2005, 05:30 PM   #15
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Hello BOCKA......,

Quote:
this is not true, look to the MJL21193 datasheet. 150 watts @100 volts is not so bad for a TO247 package. It's true that bipolars have a second breakdown. You have to take this into account when using them.
Why not you take a look at the datasheet of APT20M18LVR [www.advancedpower.com] and feel the massive SOA under your command......and imagine what type of amp could be constructed by using these monsters....

Quote:
About 50-100 watts output power for each transistor on a bank is a typical rating for high-power bipolars. Not neccessarilly every design needs to be a (N)MOSFET design.
Yeah its not necessary for every design to be n-channel mosfet one...but if you want real ++KW of power levels only N-channel mosfet Rules...... that domain

Quote:
This is definitely not enough for 4000 watts continous power. Look to my calculations.
Do you listen to continuous subsonic Music content on subwoofers or just listen to 10Hz---20HZ continuous Sinewaves only......meanwhile hefty Capacitor bank takes great care of musical dynamics....

Quote:
No, just parallel enough output transistors for low impedances and use a BIG BIG heatsink.
These would consume lot and lots of space on PCB as well as heatsink and still what you get is power SAG when drving reactive loads... why not use high power devices and force cooling .....

K a n w a r
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Old 8th July 2005, 06:08 PM   #16
Mikett is offline Mikett  Canada
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The Leach Super Amp was once called the Double Barrel Amp.

I believe the reason was that the design called for Paralleled as well as SERIES connected output devices. This halves the voltage the ouput transistors sees thus allowing it to operate well within it's SOAR even at higher current and rail voltages.
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Old 8th July 2005, 06:14 PM   #17
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Quote:
Originally posted by Mikett
The Leach Super Amp was once called the Double Barrel Amp.
So, use the normal Leach voltage, bridge the amplifiers, stack the MJ15003/4 and run as many as possible in parallel.
With 200 pairs available that sounds like fun to me.
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Old 9th July 2005, 04:02 AM   #18
bowdown is offline bowdown  Australia
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Gees guys thank you all so much for all your help and info.

Bocka, so your saying that the mj15003/4 to be changed to mjl21193/4 but 4 times as many(16 pairs)
the MJE150031/32 to be changed to mjl21193/4
and the mpsa06/56 to be changed to MJE15032/33
is this correct???

the 2n3439/5416 have a Vceo of 350V

http://www.semelab.co.uk/pdf/bipolar/2N3439_40.pdf

http://perso.wanadoo.fr/jm.plantefeve/2N5416.pdf


Cant i use the double barreled (super amp) version of this amp but use mjl21193/4 outputs x 4 and change the mje150031/32 to mjl21193/4. i currently have a double barrelled amp running on +/-96 Vdc and has been running beautifully for just over a year now. Obviously id have to make a new pcb layout, but shouldnt be too much of a hassle i think.

http://users.ece.gatech.edu/~mleach/superamp/
Thanx workhorse for your input, but id rather try and build a leach super amp on steroids as i dont want all or most of the stuff i have on hand to go to waste especially the mjl21193/4 and the mj15003/4(cant really use em for this project anyway unless i want to series them.)
It would be a real pity to see so much good gear go to waste thats all.

Gees guys i really appreciate all your help.

Thanx again

Bowdown
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Old 9th July 2005, 04:10 AM   #19
Mikett is offline Mikett  Canada
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for woofin the 15003/4 are probably the best use of them.
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Old 9th July 2005, 10:55 AM   #20
AndrewT is offline AndrewT  Scotland
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Hi,
you have two 4ohm voice coils.
I see three options
1. Run them in parallel requiring 2000W into 2ohms. Ultra currents!
2. Run them in series requiring 2000w into 8ohms. High volts even when bridged .
3. Two amps into separate voice coils requiring 1000W + 1000w into 4ohms. 4 core speaker cable. Two bridged amps avoids High volts.
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