National Semi Chip to drive p-p KT88 UL

[Tube Noob]

Hello Gentlemen!

I wasn't sure where to post this being a hybrid, but you all seem to have great knowledge of the LM/LME chips. I am trying to build a push pull ultra linear kt-88 with a solid state driver section (attached Rev1 schematic)

I am just getting started in electronics, so I think that there are a lot of things I may be overlooking. What little experience I do have has been more with tubes; I have done very little with solid state. I am wondering what chip would be a good driver for this amplifier? I have looked at the LME49710, LME49810, LM4780, etc. I know that the LM4780 is a completely different chip, but I am not sure which would be more appropriate (or even necessary) for this situation.

Also in regards to global negative feedback, if this were a tube input stage, I would make a connection from the positive speaker output to the cathode of the driver stage (through a Rf). In this case would I tie it to the inverting input of the first stage? Through a feedback resistor? Will that interfere with the R1/R2 gain setting?

Thank you all in advance for the assistance!

[peterball]

Hi from Australia! I am also contemplating a similar solid state driver and P/I to drive KT88's. You may find information at Lenard Audio - Education - Valve Amps interesting. This site does not give exact information on the opamps (which are discreetly made - not chip) as he obviously makes a lot of money selling amplifiers that use this method. I have found his site to be very interesting. I am also fairly new to all of this and would be keen to share anything I find out with you.

[pacificblue]

The LME49710 is an op amp. The output voltage swing is too limited for what you have in mind.

The LME49810 is a driver IC. It provides two outputs that work in phase with adjustable bias in between them for complementary transistor output stages. It is not suitable to the task. You can probably tweak it to suit, but that is not a task for a starter.

The LM4780 is a chip amp able to provide the same output power as two KT88s, so you surely get enough voltage swing. It is however not optimised to work into high impedance and its performance in such a setup may leave a lot to be desired. Comparable to using a tractor engine in a sports car which may have the right amount of horsepower and torque, but nothing else really fits, because it's too heavy, too big, the useful range of rotational speed is too small, it uses the wrong fuel, etc.