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Old 16th March 2005, 10:34 AM   #1
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Unhappy Leach Super Amp HELP ...

hi all , i m tryin to build the leach super amp , for my sub woofers , but i didn t find mj15003/04 transistors here ... can i use mj15015/16 ??? .. and can reach bout 300w into 8 ohms from them ???
plzz help me ...

...........................
i attached a file , can i use more mj15015/16 as i shown in this picc to gain more power ???
Attached Images
File Type: jpg leach superamp 15015 15016 2.jpg (85.0 KB, 699 views)
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Old 16th March 2005, 11:14 AM   #2
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MJ15003/4 do 250 watts, 140V max.
MJ15015/16 180 watts, 120volts.

On top of eachother that is 240volts, good enough for the Super Leach.
With 8 MJ15003/4 max dissipation of the output stage is 2000 watts.
Means you need 12 of the MJ15015/16.
3 in parallel do 45 Amps, 5 more than the original.
The MJ15015/16 have an Ft of 6 MHz, a lot higher.

You can place a third stacked set next to the original 2, parallel to Q30,Q20,Q21,Q31.
Hfe is somewhat lower, but overall i'd think using MJ15015 and MJ15016 is a better choice, even if you could have the 15003/4.

For the output stage you can go as high as +100Vdc before risking to blow the output devices.
100Vdc is good for more than 300/8.

I dont quite get what you intended with the circled area.
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Old 16th March 2005, 01:09 PM   #3
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hi jacco vermeulen & thnx for help
in the main Leach super amp there s 8 mj15003/4 ( 4*mj15003 & 4*mj15004 )
and in that pic i did as u said , i mean , i placed a third stacked set like original , parralel to q30 & q20 ( and same for q31 & q21) and show it in that image ( transistors ) in the bottom of the original schematic ... i mean i wanna parralel 2 other transistor out of the board on the heatsink and wire them like that .. i just wanna is it ok ??? is it right ? can i do that ?
and the red area ,, i wanna show j1 & j2 that they r jumper from 2 additional transistors that should be wired to j1 & j2 on the board ...
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Old 16th March 2005, 03:26 PM   #4
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If the jumpers J1 and J2 connect to the output with emitter resistors in between, as with the other output devices, sure.

Of course you should use separate base resistors for the added devices, in your picture it seems as if you connected 1 base resistor to the base of 2 devices.
One end of the base resistor attaches to the base of the output device, the other end at the driver emitter.

You should decide yourself if you like to add resistors to connect to the protection rig.
It acts as a combined voltage divider and current sensor, i'd put an extra 470 Ohm on the third row too.

imo, the extra wiring can cause problems, you should be very carefull in placing them.
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Old 16th March 2005, 06:28 PM   #5
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thnx man ..
so u think it will work as i drawn it yeah ?
( o god i don want to waste my money )
and where should i exatcly put the extra resistor u talked bout ?
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Old 16th March 2005, 06:38 PM   #6
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At the crossing of R37 and R39 that connects to the base of Q10, as shown on the circuit diagram.
Same on the other side, at the crossing of R46 and R48 that connects to the base of Q11.
You just duplicate one of the double output stages, with a base resistor for the driver end, an emitter resistor at the output, and before that a 470 Ohm resistor that goes to the base of either Q10 or Q11 that reduce the output of the driver section.

Thermally a setup as you intend with 3 double barrels instead of 2 is better.
With the same heatsink dissipation can be some 6 % higher, means you can drive it harder.
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Old 16th March 2005, 07:51 PM   #7
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hi
yeha i already do that .. puttin a resistor at the crossing of R37 and R39 but i show it on heatsink
and same for othe rresistors .. and i ll do it for the other side man ..
thank u so much ...
so if i do like that ( 3 double barrels ) whit how much voltage i can gain 300 winto 8 ohm .. or at least 250 w ???
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Old 16th March 2005, 10:40 PM   #8
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You can read that info on the Super Leach pages.

With 12 MJ15015/16 total capacity of the output is 7200pF.
With 8 MJ15003/4 its 8000pF.
Means you will not have worse performance than the original.
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Old 16th March 2005, 10:45 PM   #9
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hi , and thank u ..
i m sooooo nnew in electronic :P ... sorry if i askin silly questions :P
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Old 17th March 2005, 06:47 AM   #10
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If you are new at this, take it really slow.
You can read lots of info on diyaudio on the stages in building an amplifier.
I would recommend building and testing each component of the Super Leach instead of building it all at once and find out the expensive way something is wrong.

For instance:
Build the powersupply and test for correct voltage on the output.
test the amplifier first without the output devices.
Mount the MJ devices one at a time and test for insulation.
Check each soldered lead for correctness.
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