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Old 2nd November 2011, 05:04 AM   #611
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Okay, so this was my first DIY project and I got down assembling the board. I'm afraid I may have screwed up the MOSFET though. When I was soldering it on, I accidentally bridged the solder between two of the pins.

Now I'm in the testing phase and everything checks out -- except when I check the DC voltage on the output (P2). If I plug into the wall, or if I have both batteries in, the voltage is very low (~3mV). However, when I pull one battery out and check, it is ~200mV). Did I mess up? How can I fix it?

Also, I just tried testing with some sacrificial headphones. There's no loud thump upon turn on/off, just a slight barely-noticeable thud. Also, the amp works when I play through AC-power, or when two batteries are in, but does not play music with only one battery in.

Thanks in advance for any help/advice I can get.

Last edited by Questhate; 2nd November 2011 at 05:27 AM.
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Old 2nd November 2011, 05:25 AM   #612
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Hi, all, First-time DIYer here. I have two questions I'm hoping you'll entertain. First, regarding the transformer: given the two transformers below and the default option on the BOM, which would be the appropriate choice when I'll be driving orthodynamic headphones (50 ohm) and low-impedance dynamic headphones? (Is there any reason for me to upgrade?)

Second, I'd like to be able to adjust the gain, if need be, so I'd like to install the collet sockets mentioned in the BOM, Mouser part 535-10-0518-10. However, this component is on backorder. Is there a Mouser alternative to order?

Thanking you in advance!
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Old 2nd November 2011, 06:23 AM   #613
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@Questhate
You didn't harm the FET. Solder bridges are unavoidable, and common with SMT. You did right by checking your work. Don't, though, turn on the O2 with just one battery. It's not good for any of the equipment. There's even a protection circuit in the O2 to prevent damage.
@Harold
For transformers, I think it comes down to the 12-200 as minimum, the 16-400 as suitable for most phones at most listening levels, and 16-1000 as the "red line it" option.
I don't know much about the gain option sockets. It may have been removed to make room for the gain switch. A look at Mouser only turned up a 575-801010, but at twice the price.
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Old 2nd November 2011, 12:33 PM   #614
MrSlim is offline MrSlim  Canada
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Quote:
Originally Posted by Questhate View Post
Okay, so this was my first DIY project and I got down assembling the board. I'm afraid I may have screwed up the MOSFET though. When I was soldering it on, I accidentally bridged the solder between two of the pins.

Now I'm in the testing phase and everything checks out -- except when I check the DC voltage on the output (P2). If I plug into the wall, or if I have both batteries in, the voltage is very low (~3mV). However, when I pull one battery out and check, it is ~200mV). Did I mess up? How can I fix it?

Also, I just tried testing with some sacrificial headphones. There's no loud thump upon turn on/off, just a slight barely-noticeable thud. Also, the amp works when I play through AC-power, or when two batteries are in, but does not play music with only one battery in.

Thanks in advance for any help/advice I can get.

Did you read Initial DIY Testing (bottom of the page).

A low DC voltage at P2 is good, high voltage is bad. Read the Low Voltage Shutdown section again, you may have a problem with the power management circuit. If it is working properly, pulling either battery should disable the power supply, so that no voltage is on P2.
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Old 2nd November 2011, 02:42 PM   #615
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Where has Rocket Scientist been for the last week?
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Old 2nd November 2011, 03:36 PM   #616
Turbon is online now Turbon  Sweden
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Originally Posted by Speedskater View Post
Where has Rocket Scientist been for the last week?
Hope his building a minidac as I'm looking for one ;-)
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Old 2nd November 2011, 04:37 PM   #617
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Quote:
Originally Posted by sofaspud View Post
@Questhate
You didn't harm the FET. Solder bridges are unavoidable, and common with SMT. You did right by checking your work. Don't, though, turn on the O2 with just one battery. It's not good for any of the equipment. There's even a protection circuit in the O2 to prevent damage.
Quote:
Originally Posted by MrSlim View Post
Did you read Initial DIY Testing (bottom of the page).

A low DC voltage at P2 is good, high voltage is bad. Read the Low Voltage Shutdown section again, you may have a problem with the power management circuit. If it is working properly, pulling either battery should disable the power supply, so that no voltage is on P2.
Thanks guys for the responses so far.

I was running the tests from the Initial DIY Testing section on the blog. What a letdown that the very last test failed.

I tested both the P2 pads, as well as the J3 pins (center pin to the outer pins), and they give the same measurement. Very low DC (~3mV) from the AC or two-battery supply, and a much higher DC (~200mV) from only one battery. So it appears there is something wrong with the power management system.

I'm wondering if anyone knows if there is any way to localize the problem? Did one (or both) of the MOSFETs go bad (and how to measure)? Maybe one of the diodes got ESD damage when I dropped it on the carpet?

And what are the limitations of an amp with a faulty power management system? It appears to work fine with headphones, so I'm assuming that the power management circuit is only there to turn off the board when the battery voltage drops below a certain point? So, assuming I can't fix this problem, would this amp be suitable for desktop-only (no batteries) use without any adverse effects? I'd hate to waste this entire board.

Thanks for all the help guys.
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Old 2nd November 2011, 05:00 PM   #618
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Quote:
Did you read Initial DIY Testing (bottom of the page).
I didn't, and trying to play music with 1 battery I wasn't sure what was going on.
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Old 2nd November 2011, 05:06 PM   #619
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I put one together last night- here are some shots of it if anyone is interested:

O2 Headphone Amplifier - Photography by Travis Dodd

Note: my version does not have the battery mounts or charging circuit. I wanted an A/C only amp.

Super easy to put together and started right up with 3.3mV/2.8mV DC offsets.

Still not sure how I'm going to enclose it...
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Old 2nd November 2011, 05:33 PM   #620
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Where has Rocket Scientist been for the last week?
I received an email from him a couple of days ago...
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