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-   -   The Objective2 (O2) Headphone Amp DIY Project (http://www.diyaudio.com/forums/headphone-systems/193977-objective2-o2-headphone-amp-diy-project.html)

qusp 4th August 2011 06:33 PM

one thing, i havent looked up the part numbers for the opamps, because actually its not that easy to read them in the parts list linked to the google docs (pita to navigate too with no quick keys, even space bar doesnt work to create a hand to move the page when zoomed in) but just wondering, i assume the opamps you have used are limited in bandwidth? having a pretty cheap pot in the middle of the feedback loop for volume control doesnt cause any issues with stability?

qusp 4th August 2011 06:39 PM

yeah i know all about the battery issues and comedic videos, just check out the RC forums, ive just started finishing up a lifep04 powered psu for a personal project with charge monitor for low voltage shutdown etc,(not so bad and actually pretty safe, but still subject to the save airfreight limitations as it hasnt been classified on its own, just comes under lithium chemistry)

lion is the worst (but its just so compact with high energy density its appealing), followed by lipoly, but its still manageable with the correct systems in place for protection. possibly still risky for diyers of varying levels though i guess

RocketScientist 4th August 2011 06:41 PM

The volume pot is NOT in the feedback loop. Each stage uses local feedback.

There should be a "-" and "+" button on the left side of the Google Docs viewer. Click the "+" button to zoom in as much as you want. Unless you're using some really weird browser it should work fine.

You can also just download the PDF and use whatever PDF viewer you want.

The gain stage op amp has GBW of 27 Mhz. The output op amps have a GBW of 8 Mhz. They're almost eerily close to the ideal of "fast enough" without having excess bandwidth to create stability issues.

In the first article I show the 10 Khz square response into capacitive loads--there's zero ringing or overshoot. None. I've tried to invoke instability and haven't even seen any hints.

paulb 4th August 2011 06:51 PM

I can't seem to access the documentation package. Google reports "This service is not available"

qusp 4th August 2011 06:56 PM

cool ok, fair enough, at a glance thats how it looked, maybe there is something up with either the pdf, or the viewer on google docs at my end because it wouldnt redraw when i zoomed in, just remained kinda half blurry and aliased, thus not being able to read part numbers or have any patience at all haha. i'll download it and have a look tomorrow. yeah was just asking, given your history i couldnt picture you publishing anything unstable for public scrutiny, but given the inability to read it i thought id ask.

ah IC, had a bit more success, i was reading it wrong, so the pot is wired as 2 shunt volumes in (well on the edge of each) the feedback, loop, but with no feedback currents flowing through the resistive element (only returns),

haha nope right in the middle, just normal pots haha

I withold further comment till i can download it, cant read ****.

RocketScientist 4th August 2011 06:57 PM

Quote:

Originally Posted by paulb (Post 2660786)
I can't seem to access the documentation package. Google reports "This service is not available"

Hmmm... way to go Google! I've had random problems with Google Docs which is sort of amazing when you consider they want companies to run their entire businesses on Google Docs and Google Apps.

But, that said, I just checked and it works for me. Here's the link:

https://docs.google.com/viewer?a=v&p...iOTc4&hl=en_US

qusp 4th August 2011 07:28 PM

1 Attachment(s)
yeah its being really buggy, could be safari or something, dunno, this is what it looks like here and it doesnt improve when i zoom

no excuse for not seeing the separate local loops though, guess i was just seeing what i expected to see, some global feedback.

RocketScientist 4th August 2011 07:30 PM

When I use the Google Docs viewer it takes a second or two after you zoom in to download the hi-res version. Perhaps Australia is connected to the USA via dialup? ;)

agdr 4th August 2011 07:35 PM

2 Attachment(s)
Quote:

Originally Posted by RocketScientist (Post 2660754)
And the half-wave AC supply might seem "cheap and dirty" but properly engineered it works as well as any other AC power supply in this application.

I was wondering about that and just (LT) Spiced it. Linear Tech's model base is pretty devoid of negative regulators so I've substituted in a couple of 100mA units and lowered the load.

Looks good, but 1.9A diode charging current and that's with reduced load... would 1N5402 be more appropriate or am I missing something?

Good work, BTW. :) I'll have to echo qusp's comments about not particularly agreeing with your method or agenda, especially as relates to AMB's mini^3, but you've clearly put in a boatload of work here in actually making an amp and writing it up, rather than just reviewing others. I'm impressed that you open source licensed it, too. Looks like a good solid original build.

RocketScientist 4th August 2011 07:47 PM

Quote:

Originally Posted by agdr (Post 2660844)
Looks good, but 1.9A diode charging current and that's with reduced load... would 1N5204 be more appropriate or am I missing something?

The 1N400x diodes are rated at 30 A of peak current for a half wave cycle (8.3 mS) and don't even get lukewarm in this application under worst case conditions. I don't think it's a problem unless I'm missing something? The diodes are running at 1.9/30 or 6% of their rated current.


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