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

Status
Not open for further replies.
Jump to Latest
#2
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:

An externally hosted image should be here but it was not working when we last tested it.
 
#4
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
 
#5
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.
 
#7
redrabbit said:
background:
In Jung's "Composite Current Boosted Line Driver II"....
(page 22)
http://waltjung.org/PDFs/ADI_2002_Seminar_Ch6_Audio_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=
Click to expand...
Have you done any calculations about how much current you really need? (not much :nod: ). The TPA6120 is rather capable with extremely low distortion values.
 
#9
funny ideas in my head?

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
 
#10
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.
 
#14
bear said:
Why 811s?
They were faster than the preceeding opamp and available?

My personal experience with 811s is that they sound a bit hard and mechanic, subjectively speaking...

I'd pick other opamps myself...

_-_-bear
Click to expand...

If you found the ad811 to sound hard and mechanic Im not sure that they were used beneficially. In a composite opamp they do there part well, and sound absolutely musical, i use them at unity gain as a buffer with a fet front end and so far it has beat every discreet linestagei have built up to this point...


Colin
 
Status
Not open for further replies.
Top Bottom