The Objective2 (O2) Headphone Amp DIY Project

[qusp]

Originally Posted by RocketScientist

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?

hehe, nope, its still like that now, i'm on a 10mbit cable line too, i refreshed this page to see this post, but the google page is still craptastic

[RocketScientist]

If anyone else is having trouble with fuzzy Google Docs results please let me know and I'll have to give my friends at Google a call. Several good friends work for them and even if it's not their responsibility they usually know who to prod. Google employees tend to be a rather proud bunch and quick to defend their honor.

[agdr]

Originally Posted by RocketScientist

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.

30A non-repetitive peak. I just found my mistake - forgot to add series resistance to the voltage source. That drops it down below 1A peak.

[qusp]

I have a boatload of windows open in safari which does tend to bog it down memory wise, but all the same there does seem to be something a miss.

just went to download it and couldnt (see below), looks like theyve got some honorable defending to do

[RocketScientist]

Originally Posted by agdr

30A non-repetitive peak. I just found my mistake - forgot to add series resistance to the voltage source. That drops it down below 1A continuous.

It's the duty cycle that ultimately matters. The "non-repetitive" issue, AFAIK, is mostly related to thermal issues. And if the diode is staying very close to ambient what matters are what sorts of other harm peak currents can cause. If the 1N400x can handle peaks of 30A without such harm, brief repetitive spikes of 1.9A should be a walk in the park.

But, it's good to know it's theoretically below 1A . I never attempted a simulation on the power supply. The only simulation I ran for the entire O2 was was the power management circuit. I've mostly not had good luck with simulation representing the real world due to all the things it normally doesn't account for. And when I try to crank in all the parasitics etc., almost without fail, it fails to converge at all. But I'm sure others are better at it than I am. I'm a math and hands on guy mostly.

[RocketScientist]

Originally Posted by qusp

I have a boatload of windows open in safari

Well THERE'S YOUR PROBLEM! Try using a well designed browser, like Chrome, Firefox or IE9 Safari is largely a half baked cousin to iTunes. Seriously, it loses nearly every browser comparison lately.

[agdr]

Diodes are so cheap I always spec them so that repetitive peaks stay under the rating. Probably over-enginering, but it has never done me wrong.

I've actually tried spice-ing the comparator circuit too, but no luck. I'm sure its on my end though. I've subbed in a LT comparator and I don't have models for the mosfets. Time permitting I may try adding the appropriate models in if I can find them.

A few months ago I was pondering a dual-battery protection circuits and was thinking about comparators on the rails. Never did design anything. But I more or less decided that any such circuit would be best as "supervisory", powered by a separate supply with a separate battery. Seemed that collapsing rails during a fault condition would produce random results with the protection circuit unless powered by something else.

But it looks like you've used comparators good down to 2V, and the LED reference is probably around 2V - haven't looked it up yet - so that likely long before the rail caps have discharged in a fault condition the protection circuit would have kicked in. I'm assuming you probably have designed in some hysteresis so the protection circuit doesn't bounce around the trip point. Haven't read through your ckt description yet.

Also during my past ponderings it seemed like a latching protection circuit would be a good idea, something that alerted the user a fault had occurred by a LED and required manual (power cycle) action to reset. Given that if the protection circuit ever operated then by definition it needs user attention..

bat A low
bat B low
bat A and B low
bat contact A disconnect
bat contact B disconnnect
both batt contacts disconnect

[Earfanatic]

The O2 is very interesting. Well done.
And thanks for the answer in the other thread too.

[RocketScientist]

@agdr: I've tested the power management circuit every way I know how and, it took a few tweaks, but it works very well. It shuts down around 13- 14 volts (6.5-7 volts per battery) so there's no issue of the circuit itself not having enough power. I have a bipolar bench supply and have fed the O2 even conditions of extreme battery imbalance and it shuts down flawlessly every time. The trick is minimizing any transients at the headphone output due to asymmetrical rail conditions and I think I've done that. Yes it has hysteresis.

Please let me know if you have further comments after you read through the Circuit Description at the end of the article? It's always good to have another set of eyes or two checking for errors and if anything needs correcting I'll fix it ASAP.

[agdr]

I just made it back to the computer. Well congratulations on the protection circuit. Sounds like a very good design. A good protection circuit is really the special sauce to making a dual battery design safe and reliable.

I'm most useful with power supplies and other things close to DC. Hopefully someone here will eventually run a group buy of O2 boards.