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AD815

post #1 of 21
Thread Starter 
Hi,

I have a spare AD815AY and wondered if theres any nice headphone amp circuits floating around I could try out using this chip.
I've already built this guys pre-amp http://www.diyaudio.com/forums/showt...594#post831594
The sound is very good when used as a pre-amp, much better than various other op-amp based pre-amps using OPA627 etc
post #2 of 21
Have you seen this updated version:
http://www.diyhifi.org/forums/viewto...er=asc&start=0
post #3 of 21
Thread Starter 
I have thank you
Just wondering if this pre could be converted to be suitable as a head amp, I like the idea of not needing coupling caps and this circuit works great as a pre-amp but would it be safe to use with headphones if not is there another way which would make it safe
post #4 of 21
I've never tried it as a headamp driver but keep in mind that the folks at diyaudio can be very quirky, unconventional, and subject to illogical conclusions like saying "X" is better than "Y" when there were more variables that differed than just X and Y. If you find no posts on head-fi about using it, be a pioneer and tell us how it does...
post #5 of 21

AD815 for headphone amp

Hello

I’m using the AD815 as a headphone amp with the koss ksc75 (unmod). The thing with using the 815 is the high offset (up to 50mv or more). I use Carlos FM voltage injection circuit to deal with the offset. It might be better to use Walter Jung composite amp circuit with the 815 in a FET opamp feedback loop (my next project). Or use a servo circuit (I will try this too!). One thing I can say It sound great
post #6 of 21
I am building one of Carlos' preamps right now. I just got the main board etched and populated and fired it up with no servos or DC compensation whatsoever this afternoon (am planning on doing a servo circuit after I figure out which one; will also build Carlos' trimmer). Looks pretty good initially with offsets at full pot rotation less than 20mV; no signs of oscillation and the chip runs cool. From what I have read, it can be used as a headphone amp also.

As far as folks on diyaudio being quirky, yeah you are probably right, but it depends on which folks, etc. It always takes time to weed out the reliable info posts from the others. And its not like we don't have some quirky folks here either... now please excuse me while I go wrap my board in ERS paper...
post #7 of 21
Here is the original Walt Jung article describing the AD815, and it's use for headphones.
http://waltjung.org/PDFs/Composite_L...Distortion.pdf

I am ordering two 815's from digikey....they only offer the 24 pin SOIC type....so....I guess I'll try that circuit out.
I wonder if I should try ordering the 815 from Analog, as it comes in these packages: DDPAK, SIP, SOIC.
(SIP yes!! )

I have built a few of his other published "Composite Line Drivers" with excellent results. I imagine there are other "modern" chips, as substitutes these days, but I wonder how much improvement there can be???
Currently on my bench is a GainClone amp, being fed by Jung's "Composite Line Driver #1" (AD744 with AD811 (or 812, dual)).
found here (page 20):
http://waltjung.org/PDFs/ADI_2002_Se..._Drivers_I.pdf




=FB=
post #8 of 21
post #9 of 21

Cheap!!!

OK, besides B.G.Micro being incredibly inexpensive... ,
I did not expect to see a package for a week. Two days after I called, it arrived.......and I sent them a Money Order! They may not have even received my check, before they sent the goods!!!!! That, is service, my friend. (I doubt they will admit they did that, maybe to please a first-time customer like me).

Anyway, I bought 10 AD815AY for $15.
I built the Jung circuit, but leaving out the bandwidth cap(s). All point-to-point soldererd. Also, my stock of 3.9 uH (or 4.0) inductors is nill, so that's an add-on, later.
http://waltjung.org/PDFs/Composite_L...Distortion.pdf
Even still, I fired it up for an ear-peak ....very nice indeed.
It's not in a case, and it wouldn't be fair to compare it yet to my other good ones: (AVA buffered LH0002, Tori amp, Macura 634 buffered Amp).

Bypass caps: 470uf and 0.1uf
Those yellow things are 10meg resistors.
The clear parts are hermetic resistors, military surplus.

(edit: here it tells you how to make your own 3.9uH inductor:
http://headwize.com/projects/showfil...mhagen_prj.htm )
=FB=
post #10 of 21
Quote:
Originally Posted by Freq Band View Post
OK, besides B.G.Micro being incredibly inexpensive... ,

http://waltjung.org/PDFs/Composite_L...Distortion.pdf
Even still, I fired it up for an ear-peak ....very nice indeed.
It's not in a case, and it wouldn't be fair to compare it yet to my other good ones: (AVA buffered LH0002, Tori amp, Macura 634 buffered Amp).


Have you compared amps yet? I just finished my Walt jung composite amp,I really like the sound. What headphones are you using?
post #11 of 21
I'm having AD815. But i don't have a headamp schematic . I also have PCB(Carlos pre), so can't I use this pre to driver headphone(100ohm) without modding or how to mod this pre.

Thanks.
post #12 of 21
post #13 of 21
It's not easy to tell without a schematic, but of course you can use a properly implemented AD815 to drive headphones.
post #14 of 21
If you are talking about carlosfm's preamp, then he just answered that question elsewhere.
post #15 of 21
OK, so the schematic is the "Carlosfm preamp"?

In the schematic it says that the output caps are 33uF/0.1uF, but there's also a direct output. 33 uF output caps are too small for a 100R phone. The bass will be cut off. If you use the direct out you get around this problem.

Maybe the 33R output resistor is needed for stability, I don't know since I have no experience from AD815, but it's highish with regards to the 100R load you want to use it with. The frequency response will vary with the headphone's impedance, the crosstalk and damping factor will be affected too. When used as a preamp, driving something like a 10k load, this resistor is adequate.

AD815 has very high input bias currents and it has to be balanced. Carlos has solved this (the way I like it) by adding a current source (he calls it voltage) on the input pin. This could be a resistor in the 100k plus region or a constant current source. If this is done properly there's no need for output capacitors.

Nota bene! Never plug in the phones without checking for DC-offset on the output with theese kind of opamps.

I think this could be a fine sounding headphone amp. Please report back if you give it a try.
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