something with LM4702 and Power FET

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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/showthread.php?postid=1081722#post1081722
http://www.diyaudio.com/forums/showthread.php?s=&threadid=65421

Some references:
near the beginning = http://www.diyaudio.com/forums/showthread.php?postid=1079301#post1079301 ...
http://www.diyaudio.com/forums/showthread.php?postid=1081506#post1081506 ...

Resources and DIY references:
http://www.national.com/an/AN/AN-1490.pdf &
http://www.diyaudio.com/forums/attachment.php?s=&postid=1080368&action=thumb&stamp=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

:smash:

"Truth is one, paths are many ..." The Dali Lama
 
More '4702 DIY references:

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

http://www.diyaudio.com/forums/showthread.php?s=&threadid=79322 ... 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/showthread.php?postid=948757#post948757

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

Almost complete: http://www.diyaudio.com/forums/showthread.php?postid=950514#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/showthread.php?postid=952373#post952373 ... and ... http://www.diyaudio.com/forums/showthread.php?postid=953867#post953867

Veteran's Printed Circuit Board Redesign: http://www.diyaudio.com/forums/showthread.php?postid=1030511#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/showthread.php?postid=1058601#post1058601 = 0.004 THD at >> 70 Watts !! ... good show!

another '4702 DIY builder: http://www.diyaudio.com/forums/showthread.php?postid=1033700#post1033700 w/ pictures

:smash:
 
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 said:
Steve_Eddy: " Balanced inputs? One word: Transformers. ..."

Transformers: Very easy to impliment and usually very good sounding ...

But the weight penilty is too great a burden ...

Er, weight penalty? Too great a burden? What, are you going to be schlepping this thing up Annapurna or something?

I've a very nice input transformer here sitting on my postage scale. It's as good as any you'll find out there and it's tipping the scale at a whopping 1.2 ounces.

So you'll forgive me if I'm left wondering exactly what you mean by a weight penalty that's too great a burden. :scratch:

se
 
Steve_Eddy: " ... Er, weight penalty? Too great a burden? What, are you going to be schlepping this thing up Annapurna or something? ..."

Actually that's not too far from the truth. The biggest complaint from professional musicians on the road is schlepping loads of heavy equipment around from city to city. The idea would be to build a light weight two channel pre-amp and/or amp combo for guitar or microphone(s).

Ala: http://www.mesaboogie.com/Product_Info/Rectifier_Series/RectoPreAmps/RectoPreAmp.html ...

Although this fine tube pre-amp has some extra bells and whistles and may be desirous in the studio, it just doesn't make it on the road = too heavy.

With balanced, solid state inputs, front end plus switching mode power supply a comparable pre-amp could weigh in under ten pounds, even with several 12AX7's in the output for that "mellow" sound. FYI: several musicians I have interviewed indicate that they often buy new at a performance destination and just plug in to the house PA ... rather than pay FedEx shipping on a 30 pound pre-amp on a ten city tour ! [Overnight shipping alone can be greater then the costs of new equipment and just try checking through a 30 pound pre-amp as a "carry on"]. And trusting the equipment leasing or audio rental company to supply decent, quality pre-amps & amps at every stop just doesn't cut it.

Would you trust gorrilla handed roadies with your high end microphones, pre-sets and precious, high quality pre-amp arriving setup, pre-set and ready to hit it ... if your income depended on it ??

Why solid state balanced inputs? That's what works and balanced input transformers can weigh >>= 5 pounds, each.

:eek:
 
Hi Surely,:D
I looked up those eight links. What a waste of time.
There is no refence on any of them to a balanced input transformer nor to the weight of said transformer.

I think you are mistaken.

I have data on Jensen and I have just weighed my Cine Mags and we are in the 56gm (less than 2ounces) region.
 
" ... What a waste of time. There is no refence on any of them to a balanced input transformer nor to the weight of said transformer. ..."

Go to the /amplifiers/tubes/ section of DIYAudio and tell those tube guys how crazy you think they are. Many of them roll their own = winding their own power transformers and line input/output impedence balancing transformers = true DIY fashion using heavy gauge wire on what might be depleted uranium cores (not really) ... ( http://www.diyaudio.com/forums/forumdisplay.php?s=&forumid=5 ) ... :smash:

The results often can be amazingly nice sounding amps ... and when coupled with really top quality speakers the results are sometimes light years ahead of average solid state equipment.

The very best listening experience I have ever had was through mono-block tube amps and tube pre-amps from a vinyl turntable ... >>US$100,000 worth of equipment in a custom listening room. I intend to make several trips this year to this place to "refresh" this listening "bench mark". FYI: the balanced / unbalanced and balanced / balanced transformers in this system weigh more than ten pounds each = each mono-block amp weighs in above 45 pounds. ... Speaking of weight, the turntable on the above system weighs more than 80 pounds and sits on a pedistal weighing more than 500 pounds and has shock absorbers for "earth quake protection" = so the rumble of any passing trucks can't feed back through the sound system ...

:bigeyes:
 
Hi Fast,
you are misreading between two completely different concepts.
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..
is a different request from balanced power amplifiers and tube pre-amps.
 
FastEddy said:
Why solid state balanced inputs? That's what works and balanced input transformers can weigh >>= 5 pounds, each.

:eek:

I'm sorry but that's just nonsense. A line level input transformer that weighs 5 pounds isn't an input transformer but someone using large power transformers and calling them "input transformers."

Line level output transformers don't even weigh that much. A line level output transformer that would be more than suitable for what you're looking to do weighs in at just 4 ounces.

The combined weight of input and output transformers for two channels wouldn't even weigh a pound!

se
 
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