something with LM4702 and Power FET

FastEddy · 14th December 2006, 04:39 PM

The suggestion is for a new thread for the National LM4702. My choices would be to use power MOSFET or HEXFET drivers, rather than Darlington pairs or other scenarios.

The LM4702 would make a most excellent ~ 4 to 6 watt stereo headphone amplifier from +/- 12 to +/- 20 VDC rails !!

This chip amp can have some really excellent THD specs (as low as 0.0006% !) with careful attention to details, ground loop questions, etc., etc.:

" ... At 10 Volts RMS output, THD+N is about 0.005% across a 20 Hz to 20 KHz bandwidth ... It steadily drops to about 0.0015% at maximum output voltage. ..." (error ?) " ... At very low output voltages the data sheet shows that THD+N rises to over 0.1% ..."

Personally, I am also interested in balanced inputs for "pro audio", better quality connectivity between pre-amps and remotely powered and bi-amped speakers (power supply, EQs and LM4702 + drivers in each speaker), etc..

Some origins:
http://www.diyaudio.com/forums/showt...22#post1081722
Lm4702

Some references:
near the beginning = http://www.diyaudio.com/forums/showt...01#post1079301 ...
http://www.diyaudio.com/forums/showt...06#post1081506 ...

Resources and DIY references:
http://www.national.com/an/AN/AN-1490.pdf &
http://www.diyaudio.com/forums/attac...amp=1165969434
http://www.chip-pcb.cn./ = recent kits & modules
http://www.tech-diy.com/Amplifiers/LM4702_Sanken.htm = very good DIY board
http://www.werple.net.au/~gnb/audio/lm4702.html = indepth w/ pics and suggestions

"Truth is one, paths are many ..." The Dali Lama

AndrewT · 14th December 2006, 04:45 PM

Hi,
with just 6V to play with you will be restricted to Lateral Fets. With low Gm you may even run out of drive for these as well.

FastEddy · 14th December 2006, 04:53 PM

Like these: "Next Generation Hexfet / Lateral MOSFET ..." ( from: http://aussieamplifiers.com/nx150.htm ) ...?

FastEddy · 14th December 2006, 06:08 PM

Completed group buys and documantation for a very good LM4702 power amp:

Fast GB: LM4702 high power amp test board ;) ... links for group buy of Veteran's '4702 project = looks good! (board layout: http://www.audio.webd.pl/images/lm4702_pcb.gif ) ... power MOSFET drivers ... oh boy!

Partially assembled: http://www.audio.webd.pl/images/lm4780_pcb_5.jpg ... http://www.audio.webd.pl/images/lm4702_pcb.jpg ... http://www.audio.webd.pl/images/lm4702_assemb.jpg ...

" ... I do feel the chip should be on a small heatsink it runs pretty warm. ..." http://www.diyaudio.com/forums/showt...757#post948757

Origins of the National design?: http://www.ampslab.com/c200cfp.htm

Almost complete: http://www.diyaudio.com/forums/showt...514#post950514 ( http://www.audio.webd.pl/images/lm_amp.JPG & http://audio.webd.pl/images/lm4702_amp_test_1.jpg )

Further circuit improvements: http://www.audio.webd.pl/pdf/monster_amp.pdf

Almost there: http://www.diyaudio.com/forums/showt...373#post952373 ... and ... http://www.diyaudio.com/forums/showt...867#post953867

Veteran's Printed Circuit Board Redesign: http://www.diyaudio.com/forums/showt...11#post1030511 ... newer schematic: http://www.unisonus.com/pdf/monster_amp.pdf ( http://www.unisonus.com/projects/lm4702_amp.html ) ... technical results: http://www.diyaudio.com/forums/showt...01#post1058601 = 0.004 THD at >> 70 Watts !! ... good show!

another '4702 DIY builder: http://www.diyaudio.com/forums/showt...00#post1033700 w/ pictures

SpittinLLama · 14th December 2006, 10:12 PM

Read that LM4702 group buy thread by Veteran. I tested his first board and put some info in there about it. Although THD didn't get below 0.005% the stability is very good and the comp caps can probably be reduced for higher slew rate. They were 30pF but may be able to go down to 15pF. It sounds great to me but I am no listening expert so that means little. I am working on a board more like his monster amp schematic, more devices on each side for higher power. I have only use the 1530/201 pair but am going to try the 1058/162 pair also. Biggest contrionutor to THD on the board I tested is the 2nd harmonic. Others are down really low.

For low power I would think the LM4562 with a buffer output stage might be a better ideal. No reason to use at +/-12V when maximum is like +/-75V.

-SL

FastEddy · 14th December 2006, 11:36 PM

" ... No reason to use at +/-12V when maximum is like +/-75V. ..."

Yes, the lower the rail voltage, the poorer specs like THD, etc. My thoughts os this as a headphone amp (only) may be amiss ...

FastEddy · 14th December 2006, 11:41 PM

" ... I am also interested in balanced inputs for "pro audio", better quality connectivity between pre-amps and remotely powered and bi-amped speakers ..."

Anyone have thoughts about this?

FastEddy · 16th December 2006, 05:02 PM

... more ...

http://www.diyaudio.com/forums/showt...43#post1083343

http://www.diyaudio.com/forums/showt...03#post1083403

http://www.diyaudio.com/forums/showt...06#post1083406

Steve Eddy · 17th December 2006, 01:53 AM

Quote:

Originally posted by FastEddy
" ... I am also interested in balanced inputs for "pro audio", better quality connectivity between pre-amps and remotely powered and bi-amped speakers ..."

Anyone have thoughts about this?

Balanced inputs? One word: Transformers.

se

jackinnj · 17th December 2006, 03:20 AM

Quote:

Originally posted by AndrewT
Hi,
with just 6V to play with you will be restricted to Lateral Fets. With low Gm you may even run out of drive for these as well.

Transconductance for one Latfet is 1 S.

14th December 2006, 04:39 PM	#1
FastEddy diyAudio Member Join Date: Jun 2006 Location: North Californie	something with LM4702 and Power FET The suggestion is for a new thread for the National LM4702. My choices would be to use power MOSFET or HEXFET drivers, rather than Darlington pairs or other scenarios. The LM4702 would make a most excellent ~ 4 to 6 watt stereo headphone amplifier from +/- 12 to +/- 20 VDC rails !! This chip amp can have some really excellent THD specs (as low as 0.0006% !) with careful attention to details, ground loop questions, etc., etc.: " ... At 10 Volts RMS output, THD+N is about 0.005% across a 20 Hz to 20 KHz bandwidth ... It steadily drops to about 0.0015% at maximum output voltage. ..." (error ?) " ... At very low output voltages the data sheet shows that THD+N rises to over 0.1% ..." Personally, I am also interested in balanced inputs for "pro audio", better quality connectivity between pre-amps and remotely powered and bi-amped speakers (power supply, EQs and LM4702 + drivers in each speaker), etc.. Some origins: http://www.diyaudio.com/forums/showt...22#post1081722 Lm4702 Some references: near the beginning = http://www.diyaudio.com/forums/showt...01#post1079301 ... http://www.diyaudio.com/forums/showt...06#post1081506 ... Resources and DIY references: http://www.national.com/an/AN/AN-1490.pdf & http://www.diyaudio.com/forums/attac...amp=1165969434 http://www.chip-pcb.cn./ = recent kits & modules http://www.tech-diy.com/Amplifiers/LM4702_Sanken.htm = very good DIY board http://www.werple.net.au/~gnb/audio/lm4702.html = indepth w/ pics and suggestions "Truth is one, paths are many ..." The Dali Lama

14th December 2006, 04:45 PM	#2
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, with just 6V to play with you will be restricted to Lateral Fets. With low Gm you may even run out of drive for these as well. __________________ regards Andrew T.

14th December 2006, 06:08 PM	#4
FastEddy diyAudio Member Join Date: Jun 2006 Location: North Californie	More '4702 DIY references: Completed group buys and documantation for a very good LM4702 power amp: Fast GB: LM4702 high power amp test board ;) ... links for group buy of Veteran's '4702 project = looks good! (board layout: http://www.audio.webd.pl/images/lm4702_pcb.gif ) ... power MOSFET drivers ... oh boy! Partially assembled: http://www.audio.webd.pl/images/lm4780_pcb_5.jpg ... http://www.audio.webd.pl/images/lm4702_pcb.jpg ... http://www.audio.webd.pl/images/lm4702_assemb.jpg ... " ... I do feel the chip should be on a small heatsink it runs pretty warm. ..." http://www.diyaudio.com/forums/showt...757#post948757 Origins of the National design?: http://www.ampslab.com/c200cfp.htm Almost complete: http://www.diyaudio.com/forums/showt...514#post950514 ( http://www.audio.webd.pl/images/lm_amp.JPG & http://audio.webd.pl/images/lm4702_amp_test_1.jpg ) Further circuit improvements: http://www.audio.webd.pl/pdf/monster_amp.pdf Almost there: http://www.diyaudio.com/forums/showt...373#post952373 ... and ... http://www.diyaudio.com/forums/showt...867#post953867 Veteran's Printed Circuit Board Redesign: http://www.diyaudio.com/forums/showt...11#post1030511 ... newer schematic: http://www.unisonus.com/pdf/monster_amp.pdf ( http://www.unisonus.com/projects/lm4702_amp.html ) ... technical results: http://www.diyaudio.com/forums/showt...01#post1058601 = 0.004 THD at >> 70 Watts !! ... good show! another '4702 DIY builder: http://www.diyaudio.com/forums/showt...00#post1033700 w/ pictures

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14th December 2006, 04:53 PM	#3
FastEddy diyAudio Member Join Date: Jun 2006 Location: North Californie	Like these: "Next Generation Hexfet / Lateral MOSFET ..." ( from: http://aussieamplifiers.com/nx150.htm ) ...?

14th December 2006, 10:12 PM	#5
SpittinLLama diyAudio Member Join Date: Apr 2005 Location: In the Wild, Wild West	Read that LM4702 group buy thread by Veteran. I tested his first board and put some info in there about it. Although THD didn't get below 0.005% the stability is very good and the comp caps can probably be reduced for higher slew rate. They were 30pF but may be able to go down to 15pF. It sounds great to me but I am no listening expert so that means little. I am working on a board more like his monster amp schematic, more devices on each side for higher power. I have only use the 1530/201 pair but am going to try the 1058/162 pair also. Biggest contrionutor to THD on the board I tested is the 2nd harmonic. Others are down really low. For low power I would think the LM4562 with a buffer output stage might be a better ideal. No reason to use at +/-12V when maximum is like +/-75V. -SL

14th December 2006, 11:36 PM	#6
FastEddy diyAudio Member Join Date: Jun 2006 Location: North Californie	" ... No reason to use at +/-12V when maximum is like +/-75V. ..." Yes, the lower the rail voltage, the poorer specs like THD, etc. My thoughts os this as a headphone amp (only) may be amiss ...

14th December 2006, 11:41 PM	#7
FastEddy diyAudio Member Join Date: Jun 2006 Location: North Californie	" ... I am also interested in balanced inputs for "pro audio", better quality connectivity between pre-amps and remotely powered and bi-amped speakers ..." Anyone have thoughts about this?

16th December 2006, 05:02 PM	#8
FastEddy diyAudio Member Join Date: Jun 2006 Location: North Californie	... more ... http://www.diyaudio.com/forums/showt...43#post1083343 http://www.diyaudio.com/forums/showt...03#post1083403 http://www.diyaudio.com/forums/showt...06#post1083406

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