1kW MOSFET amplifier - Page 7

AudioFreak · 22nd January 2002, 04:14 AM

ripple @ the output should be well under 5mV so 3.5V ripple on the rails will need an awful good PSRR

even 1mV @ the output of those bass drivers will cause about 75dB of noise @ 1M

and 3.5V is about 2% of the rail

blmn · 22nd January 2002, 04:19 AM

There is something wrong here, because 3.47V is near 2% ripple if you consider, for example 180V per rail. 2% is a reasonable ripple under full load, I think, but, remember, your load is not constant and you might consider your mains capacity too.

It seems to me you can use these values and change it at your tests if you wish. someone above says something about making one or two units first to perform a fine tuning of your design. I think it is a wise advice.

Regards

Jeremy_Wolf · 22nd January 2002, 04:29 AM

Won't there be a huge inrush of current when you turn on the amp? Wont the caps draw a monsterous amount of current without limiting their initial turn on charging because of being directly connected to the mains? Also, what about the fact that a standard U.S. outlet is only capable of supplying 120V at 15 amps? Is that enough to quench your creations thirst? Are you going to have multiple circuits run to where the amp will be living?

What is this frakenstein project going to be powering, a small town? And do you have schematics of the amp you want to build

If you do I want to see them cause I like overkill

Kilowatt · 22nd January 2002, 04:50 AM

The amp will plug into a standard American range outlet, which can supply 240VCT, 50A. Yes, there will be a huge inrush of current at startup, and it wouldn't surprise me if it makes the neighbors' lights dim for a second or so, but I will have 600V, 150A discrete diodes in the power supply, so it ought to handle it.

It will power 8 Audiobahn ALUM12X subwoofers as part of a tri-amped system easily capable of 140+dB @1M.

As for the schematics, I'm still designing it, but the front end will look a lot like the Leach Superamp with 20 MOSFETs instead of 8 BJTs, and the rest will look a lot like one of Randy Sloan's high performance MOSFET amps. I am hoping for a THD of less than 0.1%, and the amp will be capable of driving almost any speaker system you can throw at it. Not to brag, but hopefully, I will end up with one of the best super high-performance, painfully powerful high end class AB,B MOSFET amps that can possibly be built by an ordinary audiophile.

AudioFreak · 22nd January 2002, 04:53 AM

man i want a 50A outlet!!! for my XA based amp!

Kilowatt · 22nd January 2002, 05:00 AM

Huh, I have two in my house, but I don't see how I can give you one.

Almost all American households have at least one, we plug our ovens and arc welders into them. We use very similar 30A outlets for clothes dryers, surely you must have one too. What do you do when you need lots of power?

AudioFreak · 22nd January 2002, 05:15 AM

we have 240V 10A outlets..... not CVT ... for higher power he have 15A outlets... speacial 20A distribution plugs and 3-phase when higher voltage is needed. higer current is generally only available for industrial installations.

Kilowatt · 22nd January 2002, 05:23 AM

Interesting. Anyway, on a different subject, I am finding it a little confusing trying to modify the Randy Sloan type topology to have series-arranged output devices like the Leach Superamp. This is because the Leach design has a predriver stage (Q14 and Q15, here's a link http://users.ece.gatech.edu/~mleach/superamp/ ) that does not exist in Sloan's design. This stage seems rather critical in the double-barelled OPS design of the Superamp, but I'm rather inexperienced with such things.

subwo1 · 22nd January 2002, 06:30 AM

It seems like the Leech Super Amp is practically Class G. It seems like you could add a lower level power supply at 2/3 the level of the highest level. Then you connect diodes to the lower transistors to allow them to withstand reverse bias as the upper ones take over. The trade-off as I understand is some extra distortion as the storage charge on the lower transistors' bases prevents them from switching seamlessly. But the Hitachi amp that was using the technique did not spec with very poor distortion figures. But after the modifications, I doubt the amp could be considered low TIM any more.

Jeremy_Wolf · 22nd January 2002, 06:52 PM

KiloWatt, those audiobahn alum 12's don't need "that" much power to play very loud. I know this because I have 3 of them in a linkwitz transform setup, and as we all know linkwitz transforms need a lot of power. I was using a crown ce1000 to power my three wich was a 4 ohm load (12 ohm each, then all in parrallel). It was a good matchup. I could exceed xmax at 20hz. I still use the same 3 audiobahn alum 12's now, but I use a CE2000 i picked up dirt cheap. The alum 12's are a very effeicent sub. I have been able to hit over 130db in my house at around 50 hz. These subs get way loud. I am also no where near maxing out the amp either. Either way your setup is going to be sweet.

22nd January 2002, 06:30 AM	#69
subwo1 diyAudio Member Join Date: Jan 2002 Location: North American Continent	Kilowatt, convert it to Class G It seems like the Leech Super Amp is practically Class G. It seems like you could add a lower level power supply at 2/3 the level of the highest level. Then you connect diodes to the lower transistors to allow them to withstand reverse bias as the upper ones take over. The trade-off as I understand is some extra distortion as the storage charge on the lower transistors' bases prevents them from switching seamlessly. But the Hitachi amp that was using the technique did not spec with very poor distortion figures. But after the modifications, I doubt the amp could be considered low TIM any more.

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22nd January 2002, 04:14 AM	#61
AudioFreak Warp Engineer On Holiday Join Date: Oct 2001 Location: Queensland, Australia	ripple @ the output should be well under 5mV so 3.5V ripple on the rails will need an awful good PSRR even 1mV @ the output of those bass drivers will cause about 75dB of noise @ 1M and 3.5V is about 2% of the rail

22nd January 2002, 04:19 AM	#62
blmn diyAudio Member Join Date: Feb 2001 Location: .	There is something wrong here, because 3.47V is near 2% ripple if you consider, for example 180V per rail. 2% is a reasonable ripple under full load, I think, but, remember, your load is not constant and you might consider your mains capacity too. It seems to me you can use these values and change it at your tests if you wish. someone above says something about making one or two units first to perform a fine tuning of your design. I think it is a wise advice. Regards

22nd January 2002, 04:29 AM	#63
Jeremy_Wolf diyAudio Member Join Date: Jan 2002	Won't there be a huge inrush of current when you turn on the amp? Wont the caps draw a monsterous amount of current without limiting their initial turn on charging because of being directly connected to the mains? Also, what about the fact that a standard U.S. outlet is only capable of supplying 120V at 15 amps? Is that enough to quench your creations thirst? Are you going to have multiple circuits run to where the amp will be living? What is this frakenstein project going to be powering, a small town? And do you have schematics of the amp you want to build If you do I want to see them cause I like overkill

22nd January 2002, 04:50 AM	#64
Kilowatt diyAudio Member Join Date: Nov 2001 Location: Harlowton, MT, USA	The amp will plug into a standard American range outlet, which can supply 240VCT, 50A. Yes, there will be a huge inrush of current at startup, and it wouldn't surprise me if it makes the neighbors' lights dim for a second or so, but I will have 600V, 150A discrete diodes in the power supply, so it ought to handle it. It will power 8 Audiobahn ALUM12X subwoofers as part of a tri-amped system easily capable of 140+dB @1M. As for the schematics, I'm still designing it, but the front end will look a lot like the Leach Superamp with 20 MOSFETs instead of 8 BJTs, and the rest will look a lot like one of Randy Sloan's high performance MOSFET amps. I am hoping for a THD of less than 0.1%, and the amp will be capable of driving almost any speaker system you can throw at it. Not to brag, but hopefully, I will end up with one of the best super high-performance, painfully powerful high end class AB,B MOSFET amps that can possibly be built by an ordinary audiophile.

22nd January 2002, 04:53 AM	#65
AudioFreak Warp Engineer On Holiday Join Date: Oct 2001 Location: Queensland, Australia	man i want a 50A outlet!!! for my XA based amp!

22nd January 2002, 05:00 AM	#66
Kilowatt diyAudio Member Join Date: Nov 2001 Location: Harlowton, MT, USA	Huh, I have two in my house, but I don't see how I can give you one. Almost all American households have at least one, we plug our ovens and arc welders into them. We use very similar 30A outlets for clothes dryers, surely you must have one too. What do you do when you need lots of power?

22nd January 2002, 05:15 AM	#67
AudioFreak Warp Engineer On Holiday Join Date: Oct 2001 Location: Queensland, Australia	we have 240V 10A outlets..... not CVT ... for higher power he have 15A outlets... speacial 20A distribution plugs and 3-phase when higher voltage is needed. higer current is generally only available for industrial installations.

22nd January 2002, 05:23 AM	#68
Kilowatt diyAudio Member Join Date: Nov 2001 Location: Harlowton, MT, USA	Interesting. Anyway, on a different subject, I am finding it a little confusing trying to modify the Randy Sloan type topology to have series-arranged output devices like the Leach Superamp. This is because the Leach design has a predriver stage (Q14 and Q15, here's a link http://users.ece.gatech.edu/~mleach/superamp/ ) that does not exist in Sloan's design. This stage seems rather critical in the double-barelled OPS design of the Superamp, but I'm rather inexperienced with such things.

22nd January 2002, 06:52 PM	#70
Jeremy_Wolf diyAudio Member Join Date: Jan 2002	KiloWatt, those audiobahn alum 12's don't need "that" much power to play very loud. I know this because I have 3 of them in a linkwitz transform setup, and as we all know linkwitz transforms need a lot of power. I was using a crown ce1000 to power my three wich was a 4 ohm load (12 ohm each, then all in parrallel). It was a good matchup. I could exceed xmax at 20hz. I still use the same 3 audiobahn alum 12's now, but I use a CE2000 i picked up dirt cheap. The alum 12's are a very effeicent sub. I have been able to hit over 130db in my house at around 50 hz. These subs get way loud. I am also no where near maxing out the amp either. Either way your setup is going to be sweet.

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