Jung's line drvr, use parallel AD811's?

[redrabbit]

background:
In Jung's "Composite Current Boosted Line Driver II"....
(page 22)
http://waltjung.org/PDFs/ADI_2002_Se..._Drivers_I.pdf
......uses a single AD811 as a buffer-in-a-opamp-loop(per channel) to boost current, which will drive +100 ohm headphones.
_____

question:
Can I parallel more 811's, for more output current?...to drive 32ohm headphones.

=RR=

[jackinnj]

I cobbled together this -- the idea for the AD811 surfaced in the 2003 remake of the Adcom GFP565 preamplifier from AudioXpress -- the AD826 dual VFB opamp (contrast with the CFB AD811) is supposedly very well matched and seemed, at least from the figures in Walt Jung's "OpAmp Applications Handbook" to offer a couple of gnat-whiskers better performance -- this replaces the opampcumbuffer in the GFP-565.

needless to say, I am going to burn some boards this morning and check it out -- it's mostly surface mount, save for the RN55D resistors. I have a vintage preamp with a socketed LM301 which I will try it out on:

[redrabbit]

Alrighty.
I migh have those parts too.
I'm a point-to-point only guy, but I might give it a go, if you get good results.
Thx.

=RR=

[jcx]

AD811 isn't particularly magical to my knowledge, so many substitue options are available today - with greater output current so that paralleling isn't necessary

as long as the output amp is faster than the input op amp the frequency compensation isn't too difficult

I have used the 1A output current LT1210 in a multiloop similar to this, with the TO-220 packaged 1210 in point-to-point on a gnd plane + plated through hole prototyping pcb

in smt there are many high speed DSL driver options with >300mA output rating - LT1795, AD8397, TPA6120

[vynuhl.addict]

The ad744/ad811 combo sounds killer!. I use this combo at the output of my pre-amp in a gain of 3 and it would take a very well worked out discreet design to better sonically and especially considering with the dc offset as low as 1/10th of a millivolt you can eliminate ac output coupling and use it dc coupled. Just dont turn on your power amp first..


Colin.

[vynuhl.addict]

http://www.analog.com/en/prod/0,,759_786_AD815,00.html


The ad815 is a dual op amp capable of up to 500ma output current, need good heatsinking or it will get very hot...


Colin

[peranders]

Originally posted by redrabbit
background:
In Jung's "Composite Current Boosted Line Driver II"....
(page 22)
http://waltjung.org/PDFs/ADI_2002_Se..._Drivers_I.pdf
......uses a single AD811 as a buffer-in-a-opamp-loop(per channel) to boost current, which will drive +100 ohm headphones.
_____

question:
Can I parallel more 811's, for more output current?...to drive 32ohm headphones.

=RR=

Have you done any calculations about how much current you really need? (not much ). The TPA6120 is rather capable with extremely low distortion values.

[jackinnj]

I forgot about the TPA6120 -- I have a pair of these somewhere -- on both National and TexInstr websites there are guidelines for babysitting the thermal properties of these devices --

[bear]

Ok, so I am an idiot and have soft gummy brain tissue... and I haven't read the .pdf because I'm impatient, on a dial up and it is still downloading...

But what about taking one of these super composite fedback opamp thingies, and dumping a high current SE class A follower or a PP one at the outpoot and wrapping the feedback around it... to drive those pesky headfunes??

<sound of laughter...?>

_-_-bear

[peranders]

You must separate the minimum specification and what you actually want to build. A normal opamp can drive a headphone rather good and if you connect them in parallel the result will be even better. The next option is to and a simple output buffer of a BUF634. The next step is some overkill. You could check my designs, from the rather simple one to the real overkill.