LME49810/STD03 parallel pairs

[Sebastiaan]

Dear,

Just a question.

The LME49810 has a (typ) output current capacity of 60mA. In almost all cases you need a driver transistor with a descent Beta to make a power amplifier. As exception here the STD03 darlingtons which have a hFE of at least 5000 and even more by higher currents.

Does this means I can theoretical parallel as many as STD03's as I want since output current seems endless?

0,060*5000= 300pkA. Let's say I want to stack 12 pairs of STD03's would this be possible?

With kind regards,
Bas

[enzoR]

yes but you need to add resistors so that the Ib current distributes equally over the parrallel transistors.

[Sebastiaan]

Originally posted by enzoR
yes but you need to add resistors so that the Ib current distributes equally over the parrallel transistors.

Thank you enzoR.

I was thinking about a value between 47 and 150 Ohm.

With kind regards,
Bas

[jackinnj]

Each Darlington pair needs it's own 200 ohm potentiometer...and you will probably have to experiment with the resistor across the bias pins to set the current across the diodes at 2.5mA.

[Sebastiaan]

Originally posted by jackinnj
Each Darlington pair needs it's own 200 ohm potentiometer...and you will probably have to experiment with the resistor across the bias pins to set the current across the diodes at 2.5mA.

Dear Jackinnj,

Thanks for responding. Yes that is the next concern. 12 bias pot's is not fun...

However I saw in Musical Fidelity and Arcam design that they just tied all diode strings together to one pot. I don't believe this gives the best sound solution since there will be always differences between hFE's

With kind regards,
Bas

[jackinnj]

Originally posted by Sebastiaan



Dear Jackinnj,

Thanks for responding. Yes that is the next concern. 12 bias pot's is not fun...

However I saw in Musical Fidelity and Arcam design that they just tied all diode strings together to one pot. I don't believe this gives the best sound solution since there will be always differences between hFE's

With kind regards,
Bas

Ask Janneman -- he used individual bias pots in his PAX amplifier -- (Elektor April 08) and Sanken recommends the same thing...I believe it is due to the possilibity that the betas of the Darlington's might not be the same.

[Sebastiaan]

Originally posted by jackinnj


Ask Janneman -- he used individual bias pots in his PAX amplifier -- (Elektor April 08) and Sanken recommends the same thing...I believe it is due to the possilibity that the betas of the Darlington's might not be the same.

Dear jackinnj,

I am agree with you and Jan that this is the best way. Also Sanken's application sheet advice a pot per pair.

However, this is how Arcam does it.

With kind regards,
Bas

[minhtriet]

Dear All!
I want to buy an amplifier with LME489xx driver one or two pair SAP15s. What LME chip I will choose? LME49810 or 49811?
Thanks.

[Dxvideo]

I am currently working on a project with SAP15s and LME49811. I think 49811 is the best solution for SAPs. Because they already have a biasing systems and do not need Vbe multipliers. So if you consider 49810 and 49830 has bias pins then 49811 (or LM4702) is the best for SAPs. Another point is 49811 has Class A driving stages..

[klewis]

Dxvideo,

I'm working on the same thing. Can you post your schematic? have you mocked it up yet?

Ken