what poweramp is realy the best to build?

[lineup]

.


Have a look at this website:
LM4702 Audio Power Amplifier Driver
plenty plenty of good info about LM4702 and how to use it


among all info at ....
Glenn Baddeley - Audio and Hi-Fi (australia) http://www.werple.net.au/~gnb/audio/
.... one link to this diy project (actually to a diyaudio.com member site!)

In 2005 National Semiconductor introduced the LM4702 device driver.
This chip provides the input and drive functions
for either bipolar junction transistors, or MOSFET's.
....................................

I chose instead to use the Sanken SAP16N and SAP16P power Darlingtons which were obtained from Profusion in the U.K.

Profusion got the transistors to me in just a few days with their webstore and Royal Mail.

Importantly, the Sanken devices with their built in temperature sensing diodes make it unnecessary to use a Vbe multiplier to prevent thermal runaway.

LM4702 prototype with Sanken SAP16P and SAP16N

DIY Amplifiers -- The LM4702 meets Sanken SAP16


My lineup comment:
Sanken makes high class transistors.
Many of which are excellent for use in Audio Power Amplifier.
For example wellknown: 2SC2922 + 2SA1216 !!!!


lineup

[FastEddy]

Lineup & AndrewT"
L " ... Such a BIG Power chip and only drive like max ~5mA ..."
A " ... using the maximum 30mA quiescent current and +-100Vdc then dissipation is 6W ..."
L " ... of course, as it has got option to use 200 volt this means power and heat. ..."
L " ... chip ground lead has a dirty return current implying something other than pure ClassA inside ... "
From link(s) below: " ... Do I need a heat sink for the LM4702?
You do not need a heat sink on the LM4702 itself. However, it is necessary to use a heat sink on the output stage. The LM4702 does have internal thermal protection, but this does not monitor the output stage. ..."

I'm speculating a little bit here: National would, of course, like to build a "one size fits all" type of power amp / pre-amp input stage chip and I bet there are plenty of mass market manufacturing customers who will want it that way (for reduced inventory headaches, etc.). The "BIG" heat sink (as AndrewT points out) is certainly needed for those cases of very significant rail voltage and power output, ~=> +/- 50 VDC or more, and if (as most manufacturers will probably want to do) there is one single power supply for a whole mass market production device (for cost savings, low parts count), then mounting the die on a extra "BIG" heat sink will fulfill the requirement. Additionally, the manufacturers will also want a common heat sink for the '4702 and any output drivers, and that "BIG" heat sink tab will thermaly stablize (and thermaly lock) the input parts and output parts together = more accurate voltage following and better over all specs like THD, popcorn noise rejection, CMRR, etc.

Good eyes, Lineup: This is very interesting: http://www.werple.net.au/~gnb/audio/lm4702.html >> " ... 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. ..." (It would seem that there is a decimal place error: /=/ 0.015% ?) " ... At very low output voltages the data sheet shows that THD+N rises to over 0.1% ..." (this is more likely National's reality than the author's).

Interesting design & build suggestions all over this web page like: http://www.werple.net.au/~gnb/audio/...inConn2d30.jpg (& http://www.werple.net.au/~gnb/audio/...urrent1b10.jpg ), http://www.werple.net.au/~gnb/audio/...inking1e20.jpg ... setting the "mute function": http://www.werple.net.au/~gnb/audio/...esistor1d5.jpg

So, best advise to DIY designers using the /4702: use a common heat sink for this chip and the output drivers, if possible, and pay close attention to your star ground scenarios.

Thanks should be given to Glenn Baddeley (glennb) for the research and web pages above. This page had been hit 5000+ times so there is a lot of interest in this chip besides us here at DIYAudio ...

(Should we start a new thread or update and otherwise follow through on these LM4702 DIY pages? ... I still want balanced inputs and power MOSFET outputs on mine.)

[FastEddy]

... more ...

From Lineup's second link above = http://www.tech-diy.com/Amplifiers/LM4702_Sanken.htm : " ... National recommends that you use 2 toroidal transformers and full wave bridges for the positive and negative supply rails and I won't quibble with them. ..."

National recommends?? I would have said "suggests" instead as trying to reduce CMRR (crosstalk) inside the chip, externally, is a serious mis-use of resources. Also having common ground references between the two bridge/filters of the twio supplies might lead to ground loop questions, defeating the purpose of dual supplies : http://www.tech-diy.com/Amplifiers/LM4702_Power.gif ...

Better to have seperate, isolated mono-block amp chips than multiple transformers and multiple diodes sets of two power supplies if the effort is to reduce or improve crosstalk specs. Also tying two supply sources together at the ground(s) for alternate voltage sources (for other boards & equipment?) is more easily resolved with simple linear voltage regulation (LM317, etc.) = better specs ... No?

Interesting as well: " ... he Sanken devices with their built in temperature sensing diodes make it unnecessary to use a Vbe multiplier to prevent thermal runaway. ..." Is this more justification for using a common heat sink for the '4702 and the output drivers ?

Very nice job BTW, Lineup !! A mighty fine "one off" DIY board and layout ...

[lineup]

Originally posted by FastEddy

Good eyes, Lineup: This is very interesting: http://www.werple.net.au/~gnb/audio/lm4702.html
----------------
Thanks should be given to Glenn Baddeley (glennb) for the research and web pages above. This page had been hit 5000+ times so there is a lot of interest in this chip besides us here at DIYAudio ...

Should we start a new thread or update and otherwise follow through on these LM4702 DIY pages?
I still want balanced inputs and power MOSFET outputs on mine.
.

I suggest you start a new LM4702 topic in Chip Amps.
something with LM4702 and Power FET in subject.

There are many many, as you know, that are interested in
New Chip Projects as well as very many Interested in MOSFET.
So this strategy might generate some posters!

The LM4702 + MOSFET twist
would add something new as complement to those several 'old' LM4702 topics.
Besides, those old topics, some of them are so long topics (many posts to read).

There are ways to use LM4702 with MOSFETs.
No doubt in my mind.
Member: jackinnj - the owner of http://www.tech-diy.com/ sure would know.
He might have tried Lateral MOSFET and they could possibly be used,
if not the IRFXXXX HEXFET can be used.


If you find this better,
you could hang on at some other LM4702 topic,
I have seen at least ONE new topic about LM4702 in 'Chip Amps'
and several new posts in older LM4702 topics. With images of builds.



I myself has got many other things to focus at, for now.
But I may jump in again,
if I think I have any useful idea or comment.
About LM4702 - an interesting and intriguing Chip

[FastEddy]

Like this? http://www.diyaudio.com/forums/showt...41#post1081741

[spind]

Have you checked this thread? Towards pg 4 or pg 5 'veteran' uses and is quite happy with output Fets with the 4702.

Fast GB: LM4702 high power amp test board ;)

[redjr]

Hi all. Relatively new member here. I know this is an old thread, but is the LM4702 chip still a good module to build a 100wpc amp around? I'm getting ready to build a 'audio grade' amp and want to pick the best all-around chipamp for doing this. I may also consider some of the DIY choices for class D modules too.

I'm reading a lot here on DIYAudio and appreciate everyone's take and experience on the topic. I am confused a bit on whether or not you need to use additional transistors (as in Darlington pair) to get the level of output I want, or can you just use the module? Perhaps more reading is necessary. I've seen some cool Class D amps on eBay that look intriguing. I'm an expert at using a soldering pencil and have put numerous kits together. Even DIY'd a few amps over the years.

Thots?

redjr

[godfrey]

You do need to add Darlington output transistors. There's more technical details in the datasheet here. I've no idea how good it is. Follow the links in the 2 posts above yours. Maybe there's useful info there.

[jacco vermeulen]

Originally Posted by redjr

LM4702 chip good module to build a 100wpc amp around?

sure is : http://www.ti.com/lit/an/snaa045/snaa045.pdf (with 2 pairs per channel)

[AndrewT]

Look at the lme49810, 49811, 49830
Similar but newer production.