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Old 22nd June 2013, 08:53 AM   #11
brlmat is offline brlmat  Romania
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I wanted to edit my last post, but i couldn't. AndrewT, my caps are 160Vdc (6X10.000uf) with 22k drain resistors across the rails.

Now back to the modules). Which should i build? Leach Superamp? FET400? GX400 rev1? Any other one? Please, answer this question as i have been stuck with this amplifier open on my desk for a month.

Thank you!
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Old 22nd June 2013, 11:43 AM   #12
amptech is offline amptech  Scotland
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Agree with T Andrew on the psu rails, also some designs push things far to close for caps take the pro sound amps that used 80 volt rails and the poor caps was 6800uf at 80v the top of it was ready to pop with bad hum in the sound... Always use higher Dc rated caps to stop this kind of thing happening.
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Old 22nd June 2013, 04:29 PM   #13
brlmat is offline brlmat  Romania
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People, I know about this. I'll ask again, can you recommend me an amplifier schematic?
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Old 22nd June 2013, 05:33 PM   #14
Bigun is offline Bigun  Canada
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Sorry, I have no experience at those power levels. Did you try looking at some of the many amps posted on this forum though - I'm sure a little searching would turn up some interesting options that you can ask their builders about.
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Old 22nd June 2013, 06:12 PM   #15
brlmat is offline brlmat  Romania
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I have actually been looking for amps but unfortunatelly, they all say the best is theirs. That's why I asked you guys which you think it's the best one.
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Old 22nd June 2013, 06:28 PM   #16
AndrewT is offline AndrewT  Scotland
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A clue will be the output stage.
For 250W you need 5 to 6 times that of device maximum dissipation.

eg.
2 pair of MJ15003/4 = 1000W. Too small.
3pair of 2sa1943/c5200 = 900W. Too small.
3pair of MJL4281/4302 = 1380W. About right
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Old 22nd June 2013, 06:44 PM   #17
amptech is offline amptech  Scotland
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Some diyer's might say they like the sound of brand 'A' amp but you might say brand 'b' amp sounds better so its each to there own of what amp suits them..
Just try a few amps and compare them whether it's mosfet or bipolar amp circuit it's down to you.
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Old 22nd June 2013, 07:36 PM   #18
brlmat is offline brlmat  Romania
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Thank yo. Tho' the problem is I can't listen to many good amps round here. What I can relate to is a Technics sa-ex310 home amplifier and in my opinion it sounds good, not excelent, alittle distorted in the mids and a little bit unnatural, but ok. Also, I think that an MC Crypt Pa-5000mkii sounds like ****.
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Old 22nd June 2013, 08:46 PM   #19
ATAUDIO is offline ATAUDIO  Austria
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Quote:
Originally Posted by AndrewT View Post
A clue will be the output stage.
For 250W you need 5 to 6 times that of device maximum dissipation.

eg.
2 pair of MJ15003/4 = 1000W. Too small.
3pair of 2sa1943/c5200 = 900W. Too small.
3pair of MJL4281/4302 = 1380W. About right
I tend to agree instinctively with your rule. I normally think it in the very simplified way you need a pair of the best SOA BJTs (like the 1st an the 3rd you mentioned) every 100 watts on 8 Ohm.
BUT... Is that rule of the thumb always valid or can it be scaled down with forced ventilation? I am wishing to put some trust on 2 pairs of 15003/4 doing 250W/8 with letīs say a Papst 5" blower in front of the H/S.

And a side note. Unfortunately the rule does not scale well. Going up with the pair numebers (more than 5-6 IMO) the differences in temperature zone on the H/S and/or hfe matching demand even more conservative approaches.
For those that really like to go so up in the OP count in a class AB design.
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Old 24th June 2013, 04:43 PM   #20
brlmat is offline brlmat  Romania
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So guys? Any other thoughts? Best amp schematic? Or can I call this thread dead? Thank you.
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