The Objective2 (O2) Headphone Amp DIY Project

[dewasiuk]

Originally Posted by olli1324

I've been thinking about this since I posted that and I really don't have the time at the moment to organise it. The batteries are on special offer until close of business on Monday so if someone else wants to jump in and buy a bunch you have until then.

Sorry I can't be of more help!

(I can't remember if I have posted the source already but it is: Rechargeable NiMH batteries Hi Watt AA, AAA, C cell, D cell PP3 batteries)

I would be interesting in getting some batteries, unless it's too much of a hassle to get this small battery buy international.

[nezbleu]

On the topic of batteries, it seems "9V" NiMH batteries from "reputable" North American suppliers mostly have capacities on the order of 200mAH, with a few topping 300mAH. But there are eBay sellers from Hong Kong selling batteries rated at 400 and even 450 mAH 4 x 9V 9 Volt 400mAH PP3 NiMH Rechargeable Battery uc | eBay and 2 9V 9 Volt 450mAh Ni-MH 6F22 PP3 Rechargeable Battery Cell Block | eBay .

Does anyone have experience with these? Are these for real? For about $5/battery they seem to be offering almost twice the capacity of name-brand batteries.

[Atilla]

I

[MrSlim]

Originally Posted by Atilla

I

Very Profound....

[tschuss]

Hi guys-
A question for those of you in the US/Canada who have built and are actively testing/using the amp:

Are you all using the recommended Triad WAU12-200 AC adapter?

The reason why I ask is that it seems to me that the listed specs on that particular model are really, really close to the minimum needed to operate the amp. It won't be used with any abnormally high-impedance cans, and will also be used via battery power probably 90% of the time, but I just wanted to make sure that the adapter does indeed work exactly how it should (especially in terms of charging the batteries). I'm giving a couple of these as gifts this year to non-DIYers, and obviously don't want the recipients to worry about the units working correctly.

I trust that NwAvGuy did his homework correctly, but I guess it just makes me a little nervous with only one data point. Is everyone else having good luck with that model too?

Thanks!

[Whdemon]

Originally Posted by NwAvGuy Blog

AC Wall Transformer – There has been some confusion over the wall transformer and it’s a critical component. Most wall transformers put out DC but the O2’s power supply requires at least 13.5 volts AC. The ideal transformer would be rated at 14 - 16 VAC and 400 mA or higher. In North America the Triad WAU12-200 from Mouser is rated at 12 volts but is really about 13.5 VAC with no load, and on normal 120 volt line voltage works fine for anything but full power sine wave testing or driving rare low impedance power hungry cans. If your line voltage is below 117 VAC or 235 VAC, and/or you plan to drive difficult low impedance headpones (i.e. HiFiMan planars), I would suggest a 14+ VAC transformer at 400+ mA. The best Mouser transformers are the WAU16-400, 412-218054 or WAU16-1000 CUI. But those are more expensive than the WAU12-200. The WAU20-200 also works for higher impedance headphones. At least some European 230 volt input 12 VAC output transformers only measure around 11.5 to 12 volts on normal line voltage and won’t work (especially if designed for halogen lights). You can also change the power jack to a 5.5mm x 2.5mm version if needed to match the plug of different wall transformers.

[Atilla]

Originally Posted by MrSlim

Very Profound....

Right, I hit nightly maintenance and somehow only posted 1 letter. What I meant to reply with was:

I'd call this 'Creative twisting of the truth', if anything. The difference in capacities often relates to the number of cells in the battery, for 9V you can have lower nominal voltage and more capacity, or higher voltage with slightly less capacity. I recommend something like Maha Powermax - 300mAh, with low discharge. Reasonable capacity and you don't need to worry about them losing power while you're not using them.

[tinitus]

Whdemon

please, always post a comment, and not only a quote


moderation

[tschuss]

Originally Posted by tinitus

Whdemon

please, always post a comment, and not only a quote


moderation

No doubt.

Thanks Mr Demon, but I have already read that section. I'm looking for others' experience. As a colleague of mine used to say: "You can draw a lot of lines through a single data point"

[sofaspud]

I just received my PCB, so I can't post from a position of experience with the Triad WAU12-200. Personally, if I were buying new from Mouser, I'd probably go with the WAU16-400. I have a couple 5-gallon buckets full of wall warts, and plan to try (in order) three rated at 12VAC 250mA, 12VAC 300mA, and 16VAC 1000mA.
As to working as it should to recharge the batteries, it's only job is to supply power to the cathodes of the Schottky diodes. R1 & R2 do the rest. You could probably use a little bit higher resistor values to limit the current further, at the cost of extending the time needed for full charge. It might not be a bad idea to match the resistor values to the battery used.