LM4702
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BradAvenson
Well-known member
http://cache.national.com/ds/LM/LM4702.pdf
A link to datasheet.
A link to datasheet.
Svart
Well-known member
now you tell me.. i just built mine with 3886s
dale116dot7
Well-known member
I built an amp without protection. Sounded good. It blew up very convincingly though...
> Check the NS LM4702
Saw that. As Daledot says: zero protection. Short and die. Interestingly the 4702 may survive, the external transistors will burst. It is probably meant for internal use in powered speakers, no user-muckable output connections.
I don't believe un-protected amps are a good thing. I believe that hitting protection in normal operation is a Bad Thing; the answer is to build an amp so beefy that it just won't ever go into the danger zone when working properly, the protection is just there to save you whan things get very abnormal. Since transistor amps came into mass production, any major amp failure costs almost as much to repair as to buy new: it may be cost-effective to put more in at the beginning than to live at the edge and keep replacing parts or amps.
Years ago there was a chip, SE540? Also one from NS. These had the basics of the output protection system on-chip. You could go nuts calculating several resistor and diode values, but at least they tried.
The SE540 would deliver real current, and could be used without transistors as a line amp. The 4702 seems very lame, just a couple mA IIRC. Might be good for driving big-tube grids, if you don't think that sort of thing is a sin.
Saw that. As Daledot says: zero protection. Short and die. Interestingly the 4702 may survive, the external transistors will burst. It is probably meant for internal use in powered speakers, no user-muckable output connections.
I don't believe un-protected amps are a good thing. I believe that hitting protection in normal operation is a Bad Thing; the answer is to build an amp so beefy that it just won't ever go into the danger zone when working properly, the protection is just there to save you whan things get very abnormal. Since transistor amps came into mass production, any major amp failure costs almost as much to repair as to buy new: it may be cost-effective to put more in at the beginning than to live at the edge and keep replacing parts or amps.
Years ago there was a chip, SE540? Also one from NS. These had the basics of the output protection system on-chip. You could go nuts calculating several resistor and diode values, but at least they tried.
The SE540 would deliver real current, and could be used without transistors as a line amp. The 4702 seems very lame, just a couple mA IIRC. Might be good for driving big-tube grids, if you don't think that sort of thing is a sin.
I have dh200s from the late 70's? I like that amp, one has been in the hifi system since I built it from a kit(it has polystyrenes for some of the stock ceramics it came with and some other caps changes). No output protection but a fuse, it does use lateral mosfets as output devices IIRC.
I like the DH200 better than tube amps for hifi. The hifi world does make to much of the amps used, speakers are the problem IMO.
This chip even with BJTs might make a good amp for homemade speaker monitors where you know what the speaker load is.
like PRR posted
"It is probably meant for internal use in powered speakers"
I like the DH200 better than tube amps for hifi. The hifi world does make to much of the amps used, speakers are the problem IMO.
This chip even with BJTs might make a good amp for homemade speaker monitors where you know what the speaker load is.
like PRR posted
"It is probably meant for internal use in powered speakers"
Kev
Well-known member
[quote author="PRR"] ... the answer is to build an amp so beefy that it just won't ever go into the danger zone when working properly, the protection is just there to save you when things get very abnormal. [/quote] that's so old school
:green:
AND I love it
am I ... we ... :roll: ... just plain dinosaurs ?
today people seem to do things with less
then add all this protection. undo sort of stuff
don't get me wrong as I love some of the modern stuff, finger sized MP3 players and IEM etc
BUR when it comes to the 8 ohm Speaker world the maths hasn't changed since the begining and V still = IR
and Power still = VI ...
and current is still current
more current needs bigger, thicker, heavier etc
yeah yeah switch mode ... but a good switch mode !!
no free lunches
if the amp clips ... get a bigger amp
yeah
one that actually have a power supply in it.
shut up Kev
before you start raving
Paul is right ... he always is :thumb:
you guys are lucky to have him put such a good proportion of his time in here.
:green:
AND I love it
am I ... we ... :roll: ... just plain dinosaurs ?
today people seem to do things with less
then add all this protection. undo sort of stuff
don't get me wrong as I love some of the modern stuff, finger sized MP3 players and IEM etc
BUR when it comes to the 8 ohm Speaker world the maths hasn't changed since the begining and V still = IR
and Power still = VI ...
and current is still current
more current needs bigger, thicker, heavier etc
yeah yeah switch mode ... but a good switch mode !!
no free lunches
if the amp clips ... get a bigger amp
yeah
one that actually have a power supply in it.
shut up Kev
before you start raving
Paul is right ... he always is :thumb:
you guys are lucky to have him put such a good proportion of his time in here.
> that's so old school
Huh?
If you were old enough, you'd remember that you "can" make 100 Watts with a pair of TO-3. At least, as long as the load is resistive and no strong signal above 2KHz.
"New school" is to use many-many transistors. Oh, no more than really needed, but a lot more than we ever did in the late 1960s. They may be plastic, but often have more SOA each than the old jobs, which means LOTS more SOA in the whole amp. (And we know SOA much better than in the Dawn.) That means reactive and kicky loads stay inside safe lines. It also means the heatsink changes from a HUGE CHUNK to spread the heat of two devices into a lot of air, into an extruded rail because no single device has great heat.
And this came about because transistors changed from $7 each (in days of $0.75 cigarettes) to $2 (in days of $6 cigarettes). 30:1 reduction in real cost! Even if buyers expected the amps to go down 10:1 in real cost, that suggests 3 times the transistors will fit in the budget. (In fact amps have centered on $1/Watt since the Phase Linear 400, while all non-tech prices have risen.)
Huh?
If you were old enough, you'd remember that you "can" make 100 Watts with a pair of TO-3. At least, as long as the load is resistive and no strong signal above 2KHz.
"New school" is to use many-many transistors. Oh, no more than really needed, but a lot more than we ever did in the late 1960s. They may be plastic, but often have more SOA each than the old jobs, which means LOTS more SOA in the whole amp. (And we know SOA much better than in the Dawn.) That means reactive and kicky loads stay inside safe lines. It also means the heatsink changes from a HUGE CHUNK to spread the heat of two devices into a lot of air, into an extruded rail because no single device has great heat.
And this came about because transistors changed from $7 each (in days of $0.75 cigarettes) to $2 (in days of $6 cigarettes). 30:1 reduction in real cost! Even if buyers expected the amps to go down 10:1 in real cost, that suggests 3 times the transistors will fit in the budget. (In fact amps have centered on $1/Watt since the Phase Linear 400, while all non-tech prices have risen.)
Kev
Well-known member
[quote author="PRR"]... It also means the heatsink changes from a HUGE CHUNK to spread the heat of two devices into a lot of air, into an extruded rail because no single device has great heat. [/quote]
oh the heatsinks
no
I don't miss them
ah yes
Phase Linear
great to look at BUT bad to lift and move
" oh my aching back "
some of those electronic componets are now $1 and the cigarettes are now $10 plus
things change ... probably for the better
but sometimes I like to remember things ... my way
:roll:
oh the heatsinks
no
I don't miss them
ah yes
Phase Linear
great to look at BUT bad to lift and move
" oh my aching back "
some of those electronic componets are now $1 and the cigarettes are now $10 plus
things change ... probably for the better
but sometimes I like to remember things ... my way
:roll:
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