So let me get this right - 811 with external driver will have better performance than 830 with internal matched drivers?
Just asking....not being sarcastic.
You can probably get away with the 811 driving a single output pair. It can do up to 7mA. I have a similar app and I'm using the 830.
Just asking....not being sarcastic.
You can probably get away with the 811 driving a single output pair. It can do up to 7mA. I have a similar app and I'm using the 830.
Dude. Just build them according to the application notes. You won't be disappointed.
My LME49811 + STD03 amp sounds better than the Parasound A23 it was replacing. And the Parasound is a damn good amp.
Yeah, there might be a mathematical difference in THD between the LME49811 and '830, but the difference in slew rate is much more likely to be audible than the difference in THD. If you want to use FETs in the output, use the driver designed for FETs.
~Tom
My LME49811 + STD03 amp sounds better than the Parasound A23 it was replacing. And the Parasound is a damn good amp.
Yeah, there might be a mathematical difference in THD between the LME49811 and '830, but the difference in slew rate is much more likely to be audible than the difference in THD. If you want to use FETs in the output, use the driver designed for FETs.
~Tom
So let me get this right - 811 with external driver will have better performance than 830 with internal matched drivers?
Just asking....not being sarcastic.
You can probably get away with the 811 driving a single output pair. It can do up to 7mA. I have a similar app and I'm using the 830.
Yes, the external drivers can be biased to higher current to overcome the gate capacitances of the fets. Not only will THD be better but the speed too.
Im not advocating one opamp for the other as in both cases I would probably use external drivers on both versions. If I remember correctly in one of the application notes National shows speed and THD tests done with external driver and no driver, its no surprise the driver type is superior.
Ok, got it. So LME49811 + STD03 seems to be better couple.
Next step is to find amp case and transformer.
As for transformer I am thinking on this one MCTA100/18 - MULTICOMP - TRANSFORMER, 100VA, 2 X 18V | Farnell België. But it will be very close to LME49811 minimum voltage. Is it an issue?
Any ideas for nice case around Europe? With 50-60mm height?
Next step is to find amp case and transformer.
As for transformer I am thinking on this one MCTA100/18 - MULTICOMP - TRANSFORMER, 100VA, 2 X 18V | Farnell België. But it will be very close to LME49811 minimum voltage. Is it an issue?
Any ideas for nice case around Europe? With 50-60mm height?
But there is a voltage issue.
BJTs need low base to base voltage.
Both Vertical FETs and Lateral FETs need higher voltage gate to gate.
830 is designed for FETs
True. The bias voltage parameter for this chip is not given ....??
True. The bias voltage parameter for this chip is not given ....??
It's all in the LME49811 datasheet
Another quick look and Vbias not stated on datasheet. For 49830 it is. Offcourse it can be calculated but Im lazy.
Maybe a bit slower look?
It's really there, even with different + and - supply voltages.
But as you are lazy: output swing is 33 VRMS with +/- 50 volt rails, and 68 VRMS with +/- 100 volt rails.
Where's SpittinLama when you need him? There's a chart of THD% vs bias current in the LME49830 data sheet. Best advice I can give is that the lateral MOSFETs don't need thermal compensation which is a big design simplification, secondly -- if you tweak the values of the gate stoppers on the MOSFETs you can reduce the THD% (which is already quite good.) This is illustrated in AN-1645. There was going to be another paper/application note on the compensation techniques for this series of drivers, but National decided to channel their resources toward solar power/alternative energy chips before that bubble blew up, and they got swallowed by Texas Instruments in the interim.
The base to base, or gate to gate, bias voltage is not the same as the output swing.
I know Andrew; I guess that homemodder should look at bias voltages required for the output transistors. That has not so much to do with voltage swing of the driver. Important though is output current of the driver (is the driver capable of driving the input capacitance of the output device, where fets generally show higher input capacitance than BJT's - hence the LME49830 with it's much higher output current meant to drive fets).
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