High input level LM3886 amp ?

bibster · 11th October 2006, 07:07 PM

Hi all,

I've about completed my 5687 based linestage, finished my FE87e Fullrangers, so what's left?
Right: A (power)amp!
I've read about tubebufferd gainClones, but I don't want to something like that: My linestage will be to far away to implement series feedback, and:
My linestage has a (voltage)gain of about +26dB....
That is: 1v in, 20v out...
I don't want to keep the linestage's inputs verrrrry low, so I end up having 2v output (and a lot of noise... :-( ), so my question is:

How can I build a gainclone thinggy that accepts some 20V input?
(I thought of a simpel voltage divider, but there must be some more elegant way)

Hint welcome!

Cheers, Paul

ReidK · 11th October 2006, 10:09 PM

You don't want to attenuate (reduce) the level only to amplify it again. That will do nothing but increase the noise level.

The LM3886 can handle input voltages in that range (20V). You just need to adjust the gain to a low value (like 1 or 2). Gain, which is the factor by which the amplifier multiplies the input voltage, is set with external resistors.

There's one potential problem - like many op-amps, the 3886 has stability problems at low gain levels. In other words, it tries to stop being an amplifier and become an oscillator (tone generator). At best, this makes the amp useless. At worst, the chip can burn up, though the 3886's substantial protection circuitry would probably preven that. This thread had a good discussion of how to make a low-gain gainclone: Gainclone...No gain, YES pain.

Good luck.

Reid

juma · 13th October 2006, 07:13 PM

Hi bibster,
use OPA549 - there are some people who prefer it to LM38xx chips. It is known that it works better in low gain configurations (G=1 or 2) - it has wider bandwith when configured that way. No stability problems at all, other specs also very good. Take a look at:
http://focus.ti.com/docs/prod/folders/print/opa549.html
http://www-s.ti.com/sc/ds/opa549.pdf

11th October 2006, 07:07 PM	#1
bibster diyAudio Member Join Date: Aug 2004 Location: Lasbordes, 11400	High input level LM3886 amp ? Hi all, I've about completed my 5687 based linestage, finished my FE87e Fullrangers, so what's left? Right: A (power)amp! I've read about tubebufferd gainClones, but I don't want to something like that: My linestage will be to far away to implement series feedback, and: My linestage has a (voltage)gain of about +26dB.... That is: 1v in, 20v out... I don't want to keep the linestage's inputs verrrrry low, so I end up having 2v output (and a lot of noise... :-( ), so my question is: How can I build a gainclone thinggy that accepts some 20V input? (I thought of a simpel voltage divider, but there must be some more elegant way) Hint welcome! Cheers, Paul __________________ Demagogue: One who preaches a doctrine he knows to be untrue to men he knows to be idiots. H.L. Mencken

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11th October 2006, 10:09 PM	#2
ReidK diyAudio Member Join Date: Jan 2006 Location: Los Angeles (a.k.a. Hell on Earth)	You don't want to attenuate (reduce) the level only to amplify it again. That will do nothing but increase the noise level. The LM3886 can handle input voltages in that range (20V). You just need to adjust the gain to a low value (like 1 or 2). Gain, which is the factor by which the amplifier multiplies the input voltage, is set with external resistors. There's one potential problem - like many op-amps, the 3886 has stability problems at low gain levels. In other words, it tries to stop being an amplifier and become an oscillator (tone generator). At best, this makes the amp useless. At worst, the chip can burn up, though the 3886's substantial protection circuitry would probably preven that. This thread had a good discussion of how to make a low-gain gainclone: Gainclone...No gain, YES pain. Good luck. Reid

13th October 2006, 07:13 PM	#3
juma diyAudio Member Join Date: Nov 2005 Location: Zemun	Hi bibster, use OPA549 - there are some people who prefer it to LM38xx chips. It is known that it works better in low gain configurations (G=1 or 2) - it has wider bandwith when configured that way. No stability problems at all, other specs also very good. Take a look at: http://focus.ti.com/docs/prod/folders/print/opa549.html http://www-s.ti.com/sc/ds/opa549.pdf

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