Lm4702

[jackinnj]

Originally posted by glennb
You Hooking up a SAP-15N/P or SAP-16N/P pair of darlingtons is actually quite easy. I make no apologies for the blunders of people who don't actually know what they are doing, but learning by practical experience is a great tool.

The article from Elektor last summer points the way. ("Compact 200W Output Stage", Elektor, July-August 2005). If you don't subscribe to Elektor (you should) , you can purchase a PDF of the article from their website.

[dshortt9]

You have made some very good points.

So what is considered the best output configuration?

[Mark St. Denis]

Hi,

Just a simple minded idea. According to Peavey at

http://www.peavey.com/support/techno...s/classact.cfm

there is also design philosophy quoted from page 2 MOSFETS

"properly designed and used within design parameters, an amplifier will not have a characteristic sound -- the positive sound qualities attributed to vacuum tubes are actually artifacts of non-ideal preformance and musical sounding overload beyond electrical clipping".

With this design philosophy in mind

http://www.genzbenz.com/?fa=detail&m...sid=422&cid=95

states "with seperate FET and 12AX7 tube channels that can be selected independently or mixed togeather creating endless tonal possibilities".

So just the rigid topologies of A, B, AB et all and rigid electronics

theory and application, can still leave room for design philosophy

while investigating output stages, even odd FET and TUBE

parallel output stages philosophy.

Mark

[Mark St. Denis]

Hi,

Written by Nelson Pass of Pass Labs

www.passlabs.com/downloads/articles/seclassa.pdf

We've heard Triodes, Pentodes, Bipolars, VFMET, MOSFET, IGBT ...

and appreciation of audio is a completely subjective human

experience ... we should no more let numbers define audio

quality than we would let chemical anaylsis be the arbiter of fine

wines ... why are we looking to reduce subjective experience to

objective criteria anyway?

Mark

[Mark St. Denis]

Hi,

With a GN X 3000 from www.digitech.com a musician can

simulate 40 amp models and 25 speaker cabinets and with a POD

X Live from www.line6.com a musician can simulate 36 amp

models and 24 speaker cabinets. So why should the LM4702

driver be limited to the subjective sound of 1 output stage,

expecially calling this 1 output stage the "best"? Some like TUBE

flavor. Some like BIPOLAR flavor. Some like MOSFET flavor. Some

like hybrid flavors. So why 1 "best" ouput stage for all subjective

human listening experience?

Mark

[Mark St. Denis]

Hi,

National Semiconductor writes some philosophy on LM4702:

"Sound quality can be a very heated and subjective debate.

However, some feel that there are differences that can be heard

between different pieces of equipment and that almost all of

these can be quantified ... a significant amount has been written

in the audiophile press about how different types of passive

components affect perceived sound quality ... [in our prototype]

all of the passive components used in the demo amplifier are

standard".

www.national.com/an/AN/AN-1490.pdf#page=7

at topical subdivisions sound quality and parts selection.


So I guess one philosopy of ouput design, is to start with the

stardard parts and then evolve into the more esoteric parts,

while always listening to the subjective sound output and then

double checking the subjective with the objective quantified.

Mark

[Mark St. Denis]

Hi,

NS has already made an output stage philosophy at the FAQ

question entitled "How do I get an ouput power of 300 watts or

more per channel for the LM4702".


NS's answer: The output stage will need to be composed of 3

NPN/PNP output pairs.


It is also possible to get 100 watts with 1 output pair and 100-

200 watts with 2 NPN/PNP output pairs.


This philosophy is 1 pair then 2 pair then 3 pair or 2 transistors

per channel then 4 transistors per channel then 6 transistors per

channel, which is a standard design philosophy.

http://search.national.com/iphrase/q...gories=1phrase

Mark

[Mark St. Denis]

Hi,

Alan Blumlein earned 128 patents including British 394325 for

stereo audio by the time he died at age 39.

What would AB do with LM4702, just another conventional 2

channel stereo circuit?

http://www.ieee-virtual-museum.org/c...=1234681&lid=1

Mark

[Mark St. Denis]

Hi,

This old May 1992 Electronics World image showing part of

Tosbiba's application note X3504 may be one of the first DIY

notes available for use of IGBT in audio output stages citing use

with a GT20D101.

Does anyone have any newer IGBT audio ampflier output stage

schematics?

www.audiodesignguide.com/tra/igbtsch.jpg

Mark

[Mark St. Denis]

Hi,

UNETTO minimal power amplifier uses class A driver (which

LM4702 is) and class AB push pull output stage.

Note says IGBTs are voltage sensitive devices and a small change

in the input voltage generates a large change in the output

current. This would be an odd mixture with LM4702 semi-constant

current (for low noise) with large voltage change to next drive

a low voltage sensitive IGBT output stage with a high current out

put swing. The "odd couple amp".

http://digilander.libero.it/essentia...netto_home.htm

Mark