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Old 15th February 2011, 02:49 PM   #1
dewardh is offline dewardh  United States
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Default current drive with 3886

Any references to actual experience using the 3886 in a (simple) current drive (transconductance) configuration? In theory the feedback modification should be quite simple . . .
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Old 15th February 2011, 03:03 PM   #2
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It might be a question of whether the chip is stable when connected like this. In normal voltage-feedback use Nat Semi state that the minimum gain for stability is x10. What value of current-sense resistor will you be using in series with the speaker load?

I was wondering about trying one of my LM3875 boards to current-drive a speaker, to experiment with using a speaker having low Qe in an open-baffle.
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Old 15th February 2011, 03:53 PM   #3
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We (ie Daniel aka Duo) has a 3875 running as a variable transconductance amplifier. ie turn the knob all the way clockwise it is a current amp.

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Old 15th February 2011, 05:50 PM   #4
dewardh is offline dewardh  United States
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Quote:
Originally Posted by planet10 View Post
We (ie Daniel aka Duo) has a 3875 running as a variable transconductance amplifier.
Link ? ? ?
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Old 15th February 2011, 05:55 PM   #5
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There is a thread where generalities are discussed, youll need to search it down yourself. ETM's book, (thread on Vendor's Bazaar) also has some info on chip amp based current amplifiers.

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Old 15th February 2011, 06:10 PM   #6
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You might find this web page to be a useful guide. Not for the LM3886 in particular, but shows how you can make a current source:

Variable Amplifier Impedance

-Charlie
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Old 15th February 2011, 06:39 PM   #7
dewardh is offline dewardh  United States
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Quote:
Originally Posted by planet10 View Post
There is a thread where generalities are discussed, youll need to search it down yourself.
Tried search, didn't find your (looked like something specific, guess not) suggestion. Read the ETM thread (which seems to have turned into a pi**ing match between Thorstensomebody and the author) and have ordered the book. Also had read the ESP page Charlie linked . . . was hoping for something more specific (actually realized as a working device).
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Old 15th February 2011, 07:21 PM   #8
amt is offline amt  United States
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Do a search on "improved howland current pump" and you will find much to read.

Here is a design Ive been looking at myself just havent had time to try it:

http://www.cabezal.com/~inguz/amp/inguz_amplifier.pdf

And another more complex design"

Transconductance amplifier project - Current-Driving of Loudspeakers


amt
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Old 15th February 2011, 07:43 PM   #9
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Quote:
Originally Posted by dewardh View Post
Tried search, didn't find your (looked like something specific, guess not) suggestion.
That curious extra knob, or: "Trans-Amp"
A Transconductance Amplifier

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