LME49810 with STD03N/P

[Sebastiaan]

Dear All,

To make a very compact and easy design I want to use the LME49810 driver with STN03N/P darlington output devices. These have integrated temperature compensation diodes for biasing. So no need for a VBE multiplier. How to do that with the LME49810 which has dedicated bias pins. Let them unconnected?

With kind regards,
Bas

[ttan98]

There were some discussions on LME49810 under Chipamp section.

Do a serach you may get what you want.

[janneman]

Originally posted by Sebastiaan
Dear All,

To make a very compact and easy design I want to use the LME49810 driver with STN03N/P darlington output devices. These have integrated temperature compensation diodes for biasing. So no need for a VBE multiplier. How to do that with the LME49810 which has dedicated bias pins. Let them unconnected?

With kind regards,
Bas

Nice idea. If you want to benefit from the bias diodes in the Sankens, you need to bias them with current - 2.5mA of it. Does the 49810 provide those current sources? See my Elektuur article (paX amplifier) for more details.

Jan Didden

[SpittinLLama]

According to the LME49810 datasheet, the bias current from the bias pins is about 2.8mA. Sounds like it may work but might need some resistor divider or something to adjust the current through the bias diodes.

-SL

[janneman]

Originally posted by SpittinLLama
According to the LME49810 datasheet, the bias current from the bias pins is about 2.8mA. Sounds like it may work but might need some resistor divider or something to adjust the current through the bias diodes.

-SL

2.8mA sounds close enough. Worth a try. Please keep us informed, I find this quite interesting.

Jan Didden

[Sebastiaan]

Dear,

Thanks for the responses. I did read your very interesting article about your PAX amplifier Janneman. In fact it was your article which inspire me to go with the STD03 devices. The point is, this design have to be extremely compact, nearby the dimensions of a class D amplifier. that is why the choice for a all in one driver chip, and darlingtons with integrated diodes. This way I safe a discrete driver stage. With using Darlingtons I safe space for driver transistors after the LME49819.

But I still wondering how to implement the LME49810. How to use the bias pins? Since biasing is doing direct at the didoes of the STD03 with a resistor (variable pot in this case)

Should i short the bias pins so maximum current is flowing? There must be a way to include the internal diodes of the STD03 in the bias pins circuit as replacement for the VBE multiplier.

I keep you informed, but 'm still not out of this.

With kind regards,
Bas

[Sebastiaan]

Dear,

I wanted to post some results about my experiments with the LME49810 chip and the Sanken STD03 darlingtons.

I end up with shorting the BIAS pins of the LME49810, and that gives a forward current flowing of +/- 2,8mA over the diodes in the STD03 die. I'm experimenting with the idle current bias settings. Unlike the older SAP devices the new STD darlingtons don't have the built in emitter resistor anymore (with the risk of blow them) so now it is possible to experiment with higher biasing (In the older SAP devices this higher current will blow up the internal emitter resistor). I found the amplifier sound better with idle current of 50mA.

The sound of this combination is incredible!! It is the most compact amplifier I ever designed and the PCB dimensions can equal an B&O ICE 250A class D module. No longer is class D the only alternative if the circuit have to be very compact.

Hence... The output power is less then a class D design but more then sufficient for the target I design it for. The STD03 devices are very powerful though.

With an idle biasing of 60mA the amplifiers sounds extremely transparent, fast and musical. I could not believe such a simple and compact design can sound so smooth, musical and powerful. the LME chip have some smoothness and classy sound I truly like.

I only use one pair of STD03's.

I will experiment with two pairs in parallel like Jan Didden's PAX design. I know the SAP papers advice a variable resistor per pair when u use more then one pair of darlingtons. But it should be possible to combine the diodes and use only one variable resistor. I know Arcam and Musical Fidelity do it that way also. (this for ease of manufacture process, only one adjusting point)

I will keep u informed and post schematics once the circuit is finalized. I think this is the perfect compromise between the LM3886 chip amps and total discrete. This approach gives just a little bit more freedom in design then the LM3886 chips. Especially in biasing techniques and the freedom to bias the output stage further in class A (what I prefer judging by my ears)

With kind regards,
Bas

[janneman]

Hello Bas,

My experience with the Sankens is exactly the same - just about 50-60mA bias per pair sounds best. That's a bit more than the 40mA recommended for zero tempco, but I have never had any problems with thermal runaway anyway.

I am a bit sceptic about 'combining the diodes for a single bias pot', unless you match the output pairs wrt Vbias. You can set the bias that way for two pairs to 120mA, but it will most probably not divide evenly between the two.
But maybe I'm wrong, I haven't tried it yet.

Jan Didden

[Sebastiaan]

Dear Jan,

In first instance I also though it would be impossible (and I didn't tried it myself yet) but then I saw it happened in the Arcam FLM monoblocks and almost al former Musical Fidelity stuff. If you want to I have the scmematics of the Arcam FJM P1 who use the same Sanken Darlingtons. They do something very neat with a opamp configured in a current feedback loop with using the V+ and V- pins.

With kind regards,
Bas

[Sebastiaan]

Dear,

Today some new experiments. I raise the bias level even more. As an matter of fact. I made a relais switch between the diodes with an extra bypass resistor. This way I can switch between high idle bias and low idle bias. The high bias sounds much better. I'm much higher then advised with around a current 70mA, but it sounds incredible smooth and with so much ambiance and depth.

With kind regards,
Bas