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Old 9th March 2012, 09:59 AM   #1
Buslik is offline Buslik  Belgium
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Default LME49811 + 2SK1058/2SJ162

I would like to build 50W 8Ohm amplifier based on LME49811 + 2SK1058/2SJ162 pair.
Does it worth to add BD140/BD139 stage?
Or it will be even better to use LME49830 and connect FETs directly?
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Old 9th March 2012, 12:53 PM   #2
AndrewT is offline AndrewT  Scotland
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National released the 830 specifically for mosFET output devices.
Why choose an 811 when it is intended for BJT output devices?

If you or other Members come up with a list of good reasons for choosing the 811 then go ahead.
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Old 9th March 2012, 01:21 PM   #3
Buslik is offline Buslik  Belgium
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THD of 811 is smaller. So I think that 811+BD140/139 will result in better slew rate and smaller THD than just 830.
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Old 9th March 2012, 06:29 PM   #4
Arius is offline Arius  United States
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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.
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Old 9th March 2012, 06:35 PM   #5
tomchr is offline tomchr  United States
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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
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Old 10th March 2012, 10:21 AM   #6
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Quote:
Originally Posted by Arius View Post
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.
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Old 10th March 2012, 11:29 AM   #7
AndrewT is offline AndrewT  Scotland
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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
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Old 13th March 2012, 11:26 AM   #8
Buslik is offline Buslik  Belgium
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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 BelgiŽ. 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?
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Old 13th March 2012, 11:46 AM   #9
AndrewT is offline AndrewT  Scotland
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A 100VA transformer would normally be paired up with a 50W to 100W amplifier.
Or you could pair it up with a stereo amplifier of 25W+25W to 50W+50W.
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Old 13th March 2012, 12:04 PM   #10
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Quote:
Originally Posted by AndrewT View Post
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 ....??
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