Vbe Multiplier for LM4702 Output Stage

[Carl_Huff]

Uhhh ...

To quote Jankinnj from three posts up, "very preliminary" which also means "subject to change". To be very specific, I was asking for examples of what people ended up with and the 'tweaks' they went thru to get there.

I am about to start assembling a project of my based on the LM4702 and was looking to learn from the work already done by others.

 

[jackinnj]

Well, I am working on my Beveled THOR's at the moment, so will not play with the LM4702 for a couple weeks.

Reading the review of the new Halcro amp in Stereophile you get an idea why National chose to use the mu-Metal shielding. (and don't get me started on RFI from diode-snubbers, but I think that I am vindicated).

 

[dfdye]

Ah, I see. I don't have all my tweaks done yet, and I don't really know of anybody else who has a FINAL product other than National. They are really happy with the amp in the "new" app note (AN-1490 ), so if you are looking for a final design, I am sure that would work for you.

I am eagerly awaiting a day when I can really get back in my shop and put in some time on this. I hate leaving projects half finished. I will DEFINITELY post when I get a final output stage that I am happy with. Until then, good luck.

David

 

[veteran]

Progress report anyone??

Who has built an amp around LM4702 that is willing to share their experience? What output devices did you use?

Toshiba 2SK/2SJ MOSFETs are rally good for this design I think that this is very good configuration when you wont to make simple and good sounding amplifier.

An externally hosted image should be here but it was not working when we last tested it.

 

[jackinnj]

Toshiba 2SK/2SJ MOSFETs are rally good for this design I think that this is very good configuration when you wont to make simple and good sounding amplifier.

They hint of that in their Application note -- one could make an amplifier of truely stupendous performance with the LM4702 and the '1058/'162 Lateral Mosfet-- now from Renesas, or the competitive product from Exicon. The lateral MOSFETs do not suffer from thermal runaway problems so design is again simplified.

I think that some of the high-end hi-fi equipment magazine reviewers are going to be surprised when they pry open the cases of some kilo-buck amps and find the LM4702 hidden inside. (Perhaps they aren't allowed to do so.)

 

[veteran]

Jackinnj, I designed this one before National released AN-1490 note

I think that this is good alternative for discrete amplifiers. We have got all components working in the same temperature, etc. Somebody will probably use LM4702 in commercial product - this amplifier is really good.

 

[TonyTecson]

just wait till the lm4702A's come out...a bridged amp at +/-85volt rails? were talking big watts here...

 

[jackinnj]

The Vbe multiplier transistor is not critical. Almost any general purpose NPN small signal transistor can be used! Melbourne, Australia

Glen -- I have used both PNP and NPN -- if you are using lateral MOSFETs the VBE multiplier isn't mounted near the output devices or on the heatsink.

Erno Borbely used a PNP device in his 60 Watt MOSFET amplifier in TAA 2/82.