The Objective2 (O2) Headphone Amp DIY Project

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Mooly

Mooly

Administrator
Joined 2007
Paid Member
If the pins were touching it is more likely something in front of the regulators has been damaged. Check the voltage across these caps first. You need at least 18 volts DC across each.

Screenshot 2022-08-01 133046.jpg
 
K

ktre

Member
Joined 2020
Mooly said:
If the pins were touching it is more likely something in front of the regulators has been damaged. Check the voltage across these caps first. You need at least 18 volts DC across each.

View attachment 1076995
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Unfortunately I already desoldered them but I am relatively sure that we (a friend of mine) checked it before.

So long story short, I could use those others regulators from the link, one positive one negative?
 
availlyrics

availlyrics

Member
Joined 2011
ktre said:
Anyone knows something about headnhifi shop? It just says that Stefan is on longer vacation (good for him :)) but I would need a new power adapter and as far I understood it, the one the o2 is using is a "special"one?
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"special" means, AC to AC stepdown transformer, which has no rectifier and is not SMPS based (obviously). Hint- Transformer based adapter is heavier than SMPS based.
So, anything above 12V AC min. to 20V AC max. with current capacity of 500mA or above will do. Higher voltages will result in higher heat dissipation across 7812 /7912 regulator
One can also "remove or desolder" rectifier /filter section from any AC to DC transformer-based adapter and then use it .
CAUTION -USE DMM TO CHECK EVERYTHING, DC ADAPTER WILL DESTROY O2!
I use 12V AC adapter salvaged from old an Creative speaker.
 

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S

schmalgausen

Member
Joined 2013
availlyrics said:
12V AC after rectification and filter gives 12X1.41 gives approx 16.91-0.8 = 16.11V DC which is well above the 2V drop requirement of regulators. Usually, 12VAC gives output above 13V AC at no load. O2 presents a very light load to any transformer
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http://nwavguy.blogspot.com/2011/08/o2-details.html

  • Power Jack – For AC line power or charging, connect the AC wall transformer to this jack. The standard plug is 5.5mm outside and 2.1mm inside. The transformer output can be anywhere from 14 VAC to 20 VAC and at least 200 mA. Don’t use more than 20 VAC or less than 14 VAC (except for the 12 VAC transformers listed in the parts list). Do not try to use a DC adapter. A DC adapter may appear to work if batteries are installed, but the amp will be at least partly running off the batteries.
 
K

ktre

Member
Joined 2020
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K

ktre

Member
Joined 2020
schmalgausen said:
At first, you need power adapter. Then a socket. What is actual problem with your O2?
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I know but just in that moment I broke the socket :) So I need a new socket as well.

The problem is:
It was actually on my desk, I built it but it was only working with the batteries so I never used it and forgot about it. After picking up again (a year or so) I realized that the power supply was broken. (I measured it but it is 0)
I checked in the meantime a different power supply in an audio shop but it still didn't work without the batteries. So I checked everything again with a friend which has an actual idea about electronics (I don't, obviously) and we came to this conculsion:
ktre said:
I think I destroyed my "fixed regulators" MC7812ACTG and MC7912ACTG...My Objective o2 desktop kit is only working with the batteries included. The 15V AC is not showing any signs of current at all. I tried in an audio shop another 15V AC power adapter, also nothing.

Long story short: I want to replace the fixed regulators, can I use those from the links:

https://www.conrad.at/de/p/stmicroe...linear-to-220-positiv-fest-1-5-a-1184699.html
https://www.conrad.at/de/p/stmicroe...-negativ-fest-12-v-1-5-a-to-220-3-156077.html

Or anyone knows another source in EU? (I'm also asking at head n hifi but I have a Conrad store nearby)
Click to expand...

Fast forward: I also realized that the end of the cables (right beside R6) that goes to the socket were broken at the socket. While desoldering I got stock in the hole of the socket and melted it...
NOW I hope that: With the new fixed regulators (which I just put in) and a new, working power supply and the socket (that have to order now) it should finally work as a desktop version.
 
availlyrics

availlyrics

Member
Joined 2011
schmalgausen said:
http://nwavguy.blogspot.com/2011/08/o2-details.html

  • Power Jack – For AC line power or charging, connect the AC wall transformer to this jack. The standard plug is 5.5mm outside and 2.1mm inside. The transformer output can be anywhere from 14 VAC to 20 VAC and at least 200 mA. Don’t use more than 20 VAC or less than 14 VAC (except for the 12 VAC transformers listed in the parts list). Do not try to use a DC adapter. A DC adapter may appear to work if batteries are installed, but the amp will be at least partly running off the batteries.
Click to expand...
I had raised my concerns with NWAVGUY back in 2011, when he was active, regarding running O2 on higher AC voltage, overheating of regulators and lack of protection diodes. But he replied that he had very little space to adjust for heatsinks or diodes. His opinion was that as per datasheets, those regulators can handle that kind of heat dissipations.
Please see attch., 11.5V AC old dusty Creative adaptor, but actual measured voltage is 14.2V AC. I have many such salvaged 12V AC trannies with o/p no-load voltage between 13-15VAC. 230V AC is standard in our country, but actual measured voltage is between 235-240V AC
 

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