current drive with 3886

dewardh · 15th February 2011, 02:49 PM

Any references to actual experience using the 3886 in a (simple) current drive (transconductance) configuration? In theory the feedback modification should be quite simple . . .

Ouroboros · 15th February 2011, 03:03 PM

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.

planet10 · 15th February 2011, 03:53 PM

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.

dave

dewardh · 15th February 2011, 05:50 PM

Quote:

Originally Posted by planet10

We (ie Daniel aka Duo) has a 3875 running as a variable transconductance amplifier.

Link ? ? ?

planet10 · 15th February 2011, 05:55 PM

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.

dave

CharlieLaub · 15th February 2011, 06:10 PM

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

dewardh · 15th February 2011, 06:39 PM

Quote:

Originally Posted by planet10

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).

amt · 15th February 2011, 07:21 PM

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

planet10 · 15th February 2011, 07:43 PM

Quote:

Originally Posted by dewardh

Tried search, didn't find your (looked like something specific, guess not) suggestion.

That curious extra knob, or: "Trans-Amp"
A Transconductance Amplifier

dave

15th February 2011, 02:49 PM	#1
dewardh diyAudio Member Join Date: Dec 2005 Location: Berkeley, CA	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 . . .

15th February 2011, 03:53 PM	#3
planet10 frugal-phile(tm) diyAudio Moderator Join Date: Oct 2001 Location: Victoria, BC, NA, Sol III Blog Entries: 4	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. dave __________________ community sites t-linespeakers.org, frugal-horn.com ........ commercial site planet10-HiFi p10-hifi forum here at diyA

15th February 2011, 05:55 PM	#5
planet10 frugal-phile(tm) diyAudio Moderator Join Date: Oct 2001 Location: Victoria, BC, NA, Sol III Blog Entries: 4	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. dave __________________ community sites t-linespeakers.org, frugal-horn.com ........ commercial site planet10-HiFi p10-hifi forum here at diyA

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15th February 2011, 03:03 PM	#2
Ouroboros diyAudio Member Join Date: Dec 2003 Location: Nottingham UK	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.

15th February 2011, 06:10 PM	#6
CharlieLaub diyAudio Member Join Date: Mar 2007 Location: California	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

15th February 2011, 07:21 PM	#8
amt diyAudio Member Join Date: Feb 2003 Location: oregon	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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