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Can somebody check over my LME49811 circuit
Can somebody check over my LME49811 circuit
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Old 1st May 2011, 02:14 PM   #1
benproiii is offline benproiii  United States
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Default Can somebody check over my LME49811 circuit

Can somebody check over my circuit of a LME49811 using Bipolar transistors.
Can someone tell different component values to get the best sound quality.
Will this circuit work stable?

http://i764.photobucket.com/albums/x...i/LME49811.jpg
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Old 2nd May 2011, 12:46 AM   #2
benproiii is offline benproiii  United States
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anybody
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Old 13th June 2011, 10:18 AM   #3
shokoladas is offline shokoladas  Lithuania
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I would change something in your schematics.Is this tested circuit before?
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Old 13th June 2011, 10:35 AM   #4
AndrewT is offline AndrewT  Scotland
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This is a two stage EF, 2pair output stage driven by the 49811 chip.

200VR is a bit low in value to ensure you can adjust the output bias down to setting up values.

6 to 7mA of driver bias seems very low.

The base stoppers @ 10r may be a bit high for the output devices. But easy to trim these down with a second parallel resistor tacked on.

Have you investigated the current demand of your proposed speaker load on the 49811 chip? Two stage EF will demand very high peak transient current when driving into moderate 4ohm speakers and similarly into 8ohm severe reactance speakers.
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Last edited by AndrewT; 13th June 2011 at 10:38 AM.
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Old 13th June 2011, 01:40 PM   #5
shokoladas is offline shokoladas  Lithuania
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Quote:
Originally Posted by AndrewT View Post
This is a two stage EF, 2pair output stage driven by the 49811 chip.

200VR is a bit low in value to ensure you can adjust the output bias down to setting up values.

6 to 7mA of driver bias seems very low.

The base stoppers @ 10r may be a bit high for the output devices. But easy to trim these down with a second parallel resistor tacked on.

Have you investigated the current demand of your proposed speaker load on the 49811 chip? Two stage EF will demand very high peak transient current when driving into moderate 4ohm speakers and similarly into 8ohm severe reactance speakers.
Do you get any thd inprovement when using base stoppers for bjt output stage?
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Old 13th June 2011, 03:01 PM   #6
AndrewT is offline AndrewT  Scotland
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Probably not.
But then who wants a broken amp that blew up due to oscillation? I would rather have a tiny bit, if any, of extra distortion that plays reliably.
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Old 13th June 2011, 06:32 PM   #7
shokoladas is offline shokoladas  Lithuania
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Quote:
Originally Posted by AndrewT View Post
Probably not.
But then who wants a broken amp that blew up due to oscillation? I would rather have a tiny bit, if any, of extra distortion that plays reliably.
Interesting...Base stoppers for FET's yes i know,but for BJT i don't know.Never heard that.Have read that they are not nesecary for this reason.I had never oscilations without them,also have no theoretical ideas how stoppers can relate with oscilations. If you know something more please share with me
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Old 13th June 2011, 06:41 PM   #8
AndrewT is offline AndrewT  Scotland
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You show the base stoppers in post1.
I am saying you might need or want to reduce the value to far less than 10r.
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Old 13th June 2011, 06:48 PM   #9
shokoladas is offline shokoladas  Lithuania
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IMHO they can be 0 ohm
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Old 14th June 2011, 05:01 AM   #10
Ian Finch is offline Ian Finch  Australia
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If, as in this circuit, you use high Ft, Hfe transistors for output and drivers, it's quite possible to have oscillation even in a simple EF O/P stage. Make it a triple and that is guaranteed, so it is about gain really - with complications like long tracks or capacitive coupling to other stages. This is treated in any good text on audio amplifiers. Try Randy Slone or Bob Cordell's books. These are inexpensive and excellent works for DIY.

Using old parts usually suggests low gain and no oscillation problems, so sure, no stopper resistors required. Here, not a bad idea at around 3 ohms each. 10 is typical in the driver bases of a triple (pre-driver + driver + output transistors).
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