[cmoy]

Hi guys, I heard about this new amp that Apheared built with AD opamps. Where is it?

 

[wab]

Cmoy, I think you're looking for this one:

Apheared's CMoy variant #42: HD600

 

[cmoy]

Thanks Wab. It looks like a loooooong read. Will get to it later today (I hope).

 

[Apheared]

concise: take Elantec EL2001s and stick em in the feedback loop of an Analog AD823, powered via two 9Vs in series, thru a TI TLE2426 rail splitter, with nice system/local bypasses and a Noble AP series pot. Extremely battery friendly for high-ohm cans, and enough swing for a few hundred milliwatts.

Result: Deep & Bright. Much 'hotter' than OPA134/BUF634 pair. Treble will get very agressive on bright headphones or crappy recordings. Actually it's an agressive amp all around. 'Smooth' is not a word you'd use to describe the sound.

As quoted by a friend here who auditioned it for a couple weeks... (paraphrased) "Makes HD600s sound like Grados... too agressive for me. Makes MDR-7506s sing though."

 

[Possum]

Doh, the EL2001's get put INSIDE the feedback loop of the AD823? I have mine outside, at the output of the AD823, separated by a 60+ ohm resistor.

Is this where multiloop comes in? Is there just one loop from the output of the EL2001 to the inverting input of the AD823? Or are there 2 loops: 1) from the output of the AD823 to its inverting input with a feedback resistor; and 2) from the EL2001's output also to the inverting input?

 

[ppl]

Possum: I don't Think Apheared uses a Multiloop on this design but has the EL-2001 inside the Opamp Feedback loop see his orig. Post and the Long Disscutions for futher info.

 

[Possum]

Hmm, looks like I'll have to reroute my feedback loop

I have my EL2001's completely out of the loop, yet the amp still sounds good.

 

[ppl]

Possum: Yes the Articulate and fast response of the EL-2001 along with the Elimination of Crossover Distortion from The Patented Dynamic Signal Biasing allow the Buffer to sound Good outside of the Feedback Loop. But I like to put all output stages within the Feedback Loop, since this reduces Distortion Futher. However alot of Folks like to Use the Output stage of an amp Outsine the Loop. and for stability reasons this can be a good thing. A nte regarding the AD-823: This opamp uses an output stage that hav the Collectors rather than the Emmitters connected to the load. This results in not only the outputstage having voltage gain but results in a rather High output impedaence. This is one Big reason that this opamp Has to be loaded Lightly so the Feedback resistor should be Large in value. like > than 10K and I like to use > than 100K.