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-   -   The Objective2 (O2) Headphone Amp DIY Project (

mikeaj 1st December 2011 02:56 AM

I think the grooves seem better on bottom rather than top. It's everybody else mounting theirs upside-down! :usd:

sgrossklass 1st December 2011 03:09 AM


Originally Posted by agdr (
RocketScientist - good find on those Lelon 470uF caps in the new spreadsheet BOM! 50% higher ripple current rating and 50% more rated life for 1/2 the cost. I had missed those.

Now of course specs are one thing and real-life performance is another. Not too many free lunches out there. That's one thing people should have learned from Capacitor Plague.

Nikon1975 1st December 2011 04:14 AM

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Just wanted to post some pictures. I find it cute, considering that is done by hand. I would comment that this is really an easy project, I did it, no brainer in two hours, ordering parts from Mouser. Case was purchased locally, and needed a bit of filing to allow the connectors in.

If you are wondering why you should not DC couple a battery operated preamp with something is not battery operated, look at the other picture. Still not sure what happened, but no other damage than what you see.
I had the signal generator of the pico tech 4262 connected to the O2 and the output of the O2 connected to a test channel of the F5.

I also did some measurement with my limited instrument, and this thing behaves really well. I also like the sound with my Audio Technica ATH-900 (40 ohm).



Nikon1975 1st December 2011 04:16 AM

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I think picture got deleted when I edited the post.


RocketScientist 1st December 2011 04:30 AM


Originally Posted by sgrossklass (
Now of course specs are one thing and real-life performance is another. Not too many free lunches out there. That's one thing people should have learned from Capacitor Plague.

For what it's worth, I've used 3 different caps on the unregulated side of the supply in the O2, including the Lelons, and have not been able to measure any difference in the ripple performance, etc. Compared to many applications, the caps run cool (especially the pair closer to the power jack). And it's not a demanding application.

Electrolytic capacitor death is most famous on PC motherboards. The caps in the 40 - 150 amp CPU core power supply, that sit right next to the hot CPU heatsink and MOSFETs, are famous for dying after 3 - 5 years. If those motherboard caps can last that long with 7x24 use in a 45C+ environment with extreme ripple currents, I think the O2 is on solid ground to outlive many of the people who build one.

For those who don't have one, it's worth pointing the entire O2 runs far cooler than lots of other headphone amps that don't perform as well--most notably tube amps, single-ended MOSFET amps, and various Class-A amps. Despite everything being a snug fit, the B2-080 enclosure never gets more than lukewarm (and then only over the regulators) on AC power and is stone cold on battery power.

Component costs fluctuate wildly even month-to-month based on inventory levels and other factors. The original Nichicon 470 uF caps were $0.08 each and went up to over $0.40 each--same part. So based on price alone do you think they're better or worse than the $0.25 Lelon caps?

The more critical power supply caps in the O2 are the 220 uF C8 and C9. They're special low impedance types chosen specifically for their specs. Unlike the 470uf caps, C8 and C9 do have a measurable effect on the audio performance.

RocketScientist 1st December 2011 04:55 AM

@Nikon1975 if you put enough of those NJM chips in a pan with some hot oil, and add some butter and salt after they've all popped, them are good eatin'! ;)

I'm guessing you created some sort of ugly ground loop with your test equipment. If both channels were connected you might want to replace the other 4556 as well just in case.

Nice looking amp! I like the rounded case!

Nikon1975 1st December 2011 06:58 AM



No, only one channel was connected. My scope has a generator that can give only 1V output, and I was thinking of using the O2 to have a bit more voltage to test amps with not much gain. Maybe I have to think it better, probably putting coupling caps on the cable I use for testing would make.


RocketScientist 1st December 2011 07:49 AM

Unlike amps with virtual grounds, the O2 has all the grounds at the same "true ground" potential (assuming you're not using a bench DC supply to run it). So there shouldn't be any DC risk with ground loops--i.e. coupling caps may not help. And you can safely put up to +/- 7 volts of DC into the input of the O2 without harm and none of it will make it to the 4556 op amps or output. So DC on the input is not a problem.

One big problem with Pico's instruments is most of them share the instrument ground with the PC's USB ground. And you mentioned other test equipment as well. If whatever was hooked to the O2's output was in any way connected to the PC or back to AC-line ground, you created a mammoth ground loop and all bets are off. You might have made it self oscillate that way.

It's also possible the input of the O2 was grounded back through the USB connection and whatever was on the output had significant AC leakage current (that "fuzzy" feeling when you touch something running on AC power that's not grounded). If you measure from such equipment to ground it's not uncommon to find 60+ volts of AC but at a high impedance so it's not actually dangerous to humans, but it can be to electronic gear caught in the middle.

That's why I use isolated scope inputs, isolated generator outputs, and why the dScope has fully isolated inputs and outputs not just from ground but from each other. Oftenn with grounded equipment like the Picoscope, the only way to break that loop is to use an audio ground loop isolator with a transformer in it (which will somewhat degrade the signal) or, and this is pretty cheesy, run the Picoscope from a battery powered laptop.

And, just an FYI, the same thing can happen with much more spectacular results when testing audio power amps using USB grounded test equipment.

qusp 1st December 2011 08:51 AM

yeah thats pretty useless isnt it? sharing usb ground along with its infamous switching spikes, with sensitive instrumentation? is that for real? could you use something like an ASDL driver, LVDS, or some other type of active BALUN in the middle rather than a transformer similar to what TP is using for the teleporter i2s transceiver? i know to some extent you will end up measuring that, but if its a known quantity perhaps you could adjust to it?

thats not a suggestion btw, but a real query as i'm looking into measurement equipment for the next round of tools purchases along with a variac

btw Davide: is that little case from that local mob i linked you the other day? i just recieved their catalogue and theyve got some pretty cool stuff and a massive range!! i wonder what sort of quality their custom milling/CNC services are

agdr 1st December 2011 09:04 AM


Originally Posted by RocketScientist (
For what it's worth, I've used 3 different caps on the unregulated side of the supply in the O2, including the Lelons, and have not been able to measure any difference in the ripple performance, etc.

Lol - yeah those beefed up parameters of the Lelons are not "needed" in any way for this particular circuit. I'm mainly impressed with the price. That is some smart shopping. :)

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