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Old 8th November 2011, 05:13 PM   #661
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I got My board from the main group buy, I thought that was the newest revision? Mine does say sept 2011 on it.
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Old 8th November 2011, 05:25 PM   #662
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That should work as long as significant EMI/RFI from the DC-DC converter doesn't find its way into the audio circuitry by other means (inductive, capacitive and ground system coupling). The best would be to have the DC-DC circuitry in a different enclosure. The pre-packaged DC-DC modules tend to have much lower EMI than discrete/DIY DC-DC designs.
Thanks, RS. This add-on is mainly aimed at charge options rather than supplemental play power. I have in mind an external Murata NDTD0515C converter, but would appreciate anyone's advice on a 3-way connector that can be located on the B2 back panel.
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Old 8th November 2011, 05:54 PM   #663
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IMPORTANT! As reported by Schmidtc89 and forsakenrider, the front right corner of the gain switch, S2, can possibly touch the via (hole in the PCB) located next to R21. This will cause problems with one channel of the amp but won't cause any harm. It would seem most boards are not having the problem but it's worth taking some precautions.

I should have caught this, but it's the sort of risk one runs in ordering a large batch of PCBs before hardly anyone has built amps. The via used to be under the "foot" towards the middle of the switch so I moved it up close to the edge of R21 thinking it was out of the way (it looks fine in the overlay view of the board in software). But looking at my assembled board, I can see it's too close to the corner "foot" of S1. It's not shorting on my my board but I could see how it could. At least the short won't harm any components, put DC on the output, or do anything else dangerous.

The solder mask registration on boards tends to vary a bit from board to board. The solder mask on a given board, how the switch is installed with the bit of play present in the holes, and if it's fully seated down on the board, will determine if it could short.

THE FIX FOR ASSEMBLED BOARDS: If you have a board with a shorting gain switch, the easiest way to fix it is to use a small flat screwdriver or similar under that corner of the switch and heat the pin, or pins, in that corner of the switch (closest to R21) while prying up on the switch. It should move enough to lift the "foot" off the via. You can easily test with a DMM or just pry it up until you can see a sliver of "daylight" under the foot.

FOR THOSE WHO HAVEN'T YET BUILT THEIR BOARD: If you have some fairly beefy diagonal cutting pliars you can trim the leg on that corner of the switch. Don't try to use "precision" cutters as you may damage them. The other option is to bend the foot inward slightly or simply install the switch with that corner raised up slightly.

I'll put a note right now in the assembly instructions and, ideally, I should also revise the artwork to move the via but I'll wait for some more feedback from O2 builds to see if anyone discovers anything else that needs tweaking. Sorry for any hassles and thanks for bringing this to my attention. Please feel free to pass this along in other forum threads, etc. Thanks.
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Last edited by RocketScientist; 8th November 2011 at 06:14 PM.
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Old 8th November 2011, 06:04 PM   #664
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Originally Posted by sofaspud View Post
Thanks, RS. This add-on is mainly aimed at charge options rather than supplemental play power. I have in mind an external Murata NDTD0515C converter, but would appreciate anyone's advice on a 3-way connector that can be located on the B2 back panel.
If your goal is only charging, you can save some money and hassle and use a single 24 volt DC-DC converter with a series diode and resistor connected directly across both batteries. The resistor should be in the range of 270 - 390 ohms depending on if you plan to leave the supply connected for extended periods. The diode should be a 1N5818. That way you could use a panel mount regular coaxial DC power jack for the charging input. The downside to this approach is the external supply (using the back panel connector) will not run the amp and charge the batteries at the same time like the AC power supply will. This will also work with any 24 VDC wall transformer.

I'm not sure what to suggest for a small inexpensive 3 pin panel mount connector that won't short out the DC-DC converter (like a 3.5mm plug would). There might be room for a Mini DIN jack but I'm not sure. The other small multipin connectors tend to get expensive, require crimped pins, etc.
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Old 8th November 2011, 07:35 PM   #665
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Thanks, everyone, for the heads-up on S2. I planned a mod that make it a virtual non-issue, but it's good to know.
The 24V recharge is something I hadn't thought of. It's an option to be considered. I'd like to include a fused USB charge option, so I'm not sure how workable that is from 5V. Like the OPA2277, I already have the Murata converters. Mini-DIN or a FILO 3.5mm jack were the best I had come up with. I don't want a makeshift solution in case there's enough interest to post it for the DiyAudio gang.
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Old 8th November 2011, 08:52 PM   #666
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What do you guys recommend for the soldering iron heat setting? I have access to an iron with a heat control from 350 to 850 degrees F.
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Old 8th November 2011, 09:12 PM   #667
MrSlim is offline MrSlim  Canada
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I have one like this My Soldering Iron that I usually use around the 1:30 - 2:00 position, so around 700 degrees? Although I have no idea if it's a linear adjustment..
I'll have to see if the IR temp sensor I just ordered can tell me what the tip temp is..
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Old 8th November 2011, 11:00 PM   #668
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What do you guys recommend for the soldering iron heat setting? I have access to an iron with a heat control from 350 to 850 degrees F.
It's trial and error as few irons have a very accurate calibrated scale (assuming they don't have a digital temp readout). Around 650 is hot enough for most connections and helps keep the tip from turning black just sitting in the holder. 700 is better for really big connections (like the battery connectors on the O2) where you need lots of heat. But the tip will oxidize faster if you run at 700 all the time. Anything much over 700 will really shorten the tip life and is too hot for delicate connections.

It also depends if your iron has true closed loop feedback and how fast it corrects the tip temp. 650 is plenty on a pro-grade iron as it will maintain that temp even when soldering very large connections. But cheaper irons will "lag" and it will take much longer to solder big connections at 650.

If you're going to take break you can turn the iron down to the minimum setting (rather than turning it off) for faster warm up when you come back. Some pro irons do that automatically. They can tell when you haven't soldered anything in a while and they go into standby.
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Old 8th November 2011, 11:11 PM   #669
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All things considered, I still use a soldering "gun". One of those gun-shaped soldering irons, with no temp control but the trigger. And I solder anything from SMD to really large joints with it.

What I'm saying is, don't be *too* fussy about it. If you notice you're turning black and oxidizing too fast, lower it a bit. If it doesn't melt solder *instantly*, raise it up a bit. After a few tries you'll know how to tune it for what you want.

Anyone wants to buy me a closed-loop feedback soldering station for Chrstmas?
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Old 8th November 2011, 11:31 PM   #670
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Originally Posted by dewasiuk View Post
What do you guys recommend for the soldering iron heat setting? I have access to an iron with a heat control from 350 to 850 degrees F.
I used a cheapo radio shack soldering iron and didn't have any major problems. The only time I had difficulty was when I as trying to solder the MOSFET, the MOSFET heat-sinks would pull the heat away almost too fast, so getting the solder to stick to the board and pins was "fun".
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