Sub amp for car

kasiss · 10th July 2006, 09:53 PM

I had built some amps like this (with other output transistors).
I have idea to build amp based on Marcus schematic, what would be able to drive 2 Ohm load. Can i do it like this? I expect to get 250w into 4 ohms and 500w into 2 ohms.
Suggestions?

kasiss · 11th July 2006, 02:55 PM

Anybody?

richie00boy · 11th July 2006, 03:06 PM

In my opinion the design already includes enough output devices to happily run 500 watts. Just make sure your heatsink is massive, like 0.15 deg C/W or better.

kasiss · 11th July 2006, 03:10 PM

Originaly there is mje15030/31 drivers and 4 pairs that worked for 300w.
I would like to know, can i use for drivers same as outputs - 2sc5200/2sa1943 ? Shuld i change some rezistor values?

jaycee · 11th July 2006, 04:12 PM

Those transistors are much faster than the originally specced transistors. The circuit might not be stable with them.

Using high power devices as drivers generally isn't a good idea unless you have pre-drivers to drive them. The original driver transistors specified are up to the task of driving that many pairs, so why replace them?

If you really want to use flat pack devices, use the MJL21193/4 pairs. They are similar spec to the original MJ15024/5 devices.

kasiss · 11th July 2006, 05:31 PM

Maby one simple question for you: ho to calculate that mje15030/31 is enouth to drive 6 pairs? is it possible to drive 8 pairs?
MJL21193/4 pairs are 2.5 times expensiver, that 2sc5200/2sa1943 are in my country.

richie00boy · 11th July 2006, 05:37 PM

Check that the 2SC/SA devices aren't fake, there's a lot of fakes about. Search on here...

kasiss · 11th July 2006, 05:45 PM

thees are original for shure. tested - worked, also i had seen fake too.

darkfenriz · 11th July 2006, 05:47 PM

Change emitter resistors of power transistors to lower value, so that short circuit protection allow higher current. 0.15 Ohm should be better. 2sa1943/2sc5200 should be ok for drivers in my opinion.

regards
Adam

P.S. 6 pairs of these output transistors is much more than enough with this power. Heatsinking is crucial.

MikeB · 11th July 2006, 06:45 PM

As jaycee said, it's risky to use that much faster output devices, also if you really intend to drive 2ohms you might want the toughest devices available. These are for example the MJ15024/25.
The sc5200 has only 3A at 50v, the mj15024 has 5A.
Adams hint to change output protection is mandatory, otherwise you will never reach 500watts into 2ohm.
The mje15030/31 should do the job to drive the 6 pairs, if they are genuine. But it will be necessary to increase vas current, 6ma is too low to drive that high currents.
You might look for another amp that is already designed for 2ohms...

Mike

11th July 2006, 03:06 PM	#3
richie00boy Did it Himself diyAudio Member Join Date: Nov 2003 Location: Gloucestershire, England, UK	In my opinion the design already includes enough output devices to happily run 500 watts. Just make sure your heatsink is massive, like 0.15 deg C/W or better. __________________ www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more

11th July 2006, 05:37 PM	#7
richie00boy Did it Himself diyAudio Member Join Date: Nov 2003 Location: Gloucestershire, England, UK	Check that the 2SC/SA devices aren't fake, there's a lot of fakes about. Search on here... __________________ www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more

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11th July 2006, 02:55 PM	#2
kasiss diyAudio Member Join Date: May 2003 Location: LV	Anybody?

11th July 2006, 03:10 PM	#4
kasiss diyAudio Member Join Date: May 2003 Location: LV	Originaly there is mje15030/31 drivers and 4 pairs that worked for 300w. I would like to know, can i use for drivers same as outputs - 2sc5200/2sa1943 ? Shuld i change some rezistor values?

11th July 2006, 04:12 PM	#5
jaycee diyAudio Member Join Date: Apr 2004 Location: Norwich, UK	Those transistors are much faster than the originally specced transistors. The circuit might not be stable with them. Using high power devices as drivers generally isn't a good idea unless you have pre-drivers to drive them. The original driver transistors specified are up to the task of driving that many pairs, so why replace them? If you really want to use flat pack devices, use the MJL21193/4 pairs. They are similar spec to the original MJ15024/5 devices.

11th July 2006, 05:31 PM	#6
kasiss diyAudio Member Join Date: May 2003 Location: LV	Maby one simple question for you: ho to calculate that mje15030/31 is enouth to drive 6 pairs? is it possible to drive 8 pairs? MJL21193/4 pairs are 2.5 times expensiver, that 2sc5200/2sa1943 are in my country.

11th July 2006, 05:45 PM	#8
kasiss diyAudio Member Join Date: May 2003 Location: LV	thees are original for shure. tested - worked, also i had seen fake too.

11th July 2006, 05:47 PM	#9
darkfenriz diyAudio Member Join Date: Jun 2004 Location: Warsaw	Change emitter resistors of power transistors to lower value, so that short circuit protection allow higher current. 0.15 Ohm should be better. 2sa1943/2sc5200 should be ok for drivers in my opinion. regards Adam P.S. 6 pairs of these output transistors is much more than enough with this power. Heatsinking is crucial.

11th July 2006, 06:45 PM	#10
MikeB diyAudio Member Join Date: Apr 2004 Location: Gütersloh	As jaycee said, it's risky to use that much faster output devices, also if you really intend to drive 2ohms you might want the toughest devices available. These are for example the MJ15024/25. The sc5200 has only 3A at 50v, the mj15024 has 5A. Adams hint to change output protection is mandatory, otherwise you will never reach 500watts into 2ohm. The mje15030/31 should do the job to drive the 6 pairs, if they are genuine. But it will be necessary to increase vas current, 6ma is too low to drive that high currents. You might look for another amp that is already designed for 2ohms... Mike

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