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Old 23rd July 2012, 06:30 PM   #2671
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Were those the measurements you got when you first built the amp? Or did it originally test fine, and measures that way now?
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Old 24th July 2012, 12:38 AM   #2672
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I only measured resistances when I first built it, because it worked straight away with junk headphones and batteries. They are the measurements from now.

It works with batteries. And when I test ground+the power jack I get the right voltage. So according to the O2 docs, that means the problem is in between the power jack and U5, right?
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Old 24th July 2012, 03:28 AM   #2673
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Yes, if your O2 works on batteries but not AC power, the problem must be from the wall outlet to D1 & D5 inclusive. With the O2 switched off, make voltage measurements along those paths (AC, and DC positive & negative). If you've verified the AC voltage is correct at J1, you can start at the DC side of D3 & D4. When you get the regulator outputs fixed, continue with the voltage checks from the O2 docs.
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Old 24th July 2012, 05:37 AM   #2674
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Quote:
Originally Posted by sofaspud View Post
Yes, if your O2 works on batteries but not AC power, the problem must be from the wall outlet to D1 & D5 inclusive. With the O2 switched off, make voltage measurements along those paths (AC, and DC positive & negative). If you've verified the AC voltage is correct at J1, you can start at the DC side of D3 & D4. When you get the regulator outputs fixed, continue with the voltage checks from the O2 docs.
Okay, at J1 I get 16V AC. +- 20.85V at D4 and D3. Then when I measure U6, starting from the pin the pin closest to J1 is 0V, 20V, then 0. U5 is 20v, 0, then 0.4V.

Should the last one be 8V?
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Old 24th July 2012, 06:24 AM   #2675
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No, it should be +12VDC. The U6 output should be -12VDC. It seems you have good regulator input (20V), but no regulator output.
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Old 24th July 2012, 06:39 AM   #2676
Splatem is offline Splatem  New Zealand
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I replaced Q2 and solved the DC output problem I was having (thanks Swalter). Now it seems I'm getting a loud turn on transient, it makes a big pop when I turn it on (AC power, batteries not in use). It sounds very loud, unlike the earlier O2 amps I have built. I double checked component values, and reflowed the solder several times around the board. All my voltages seem within acceptable range of the troubleshooting values. The power rails are not quite balanced at +11.8V and -11.6V on U2 pins 8 & 4, but this should be ok?

There is something I can't get my head around, when I look at the "Power Management" section of O2 Circuit Description on the nwavguy blog, it says that the output of U2B goes high in order to turn on Q2. I'm seeing something different to this behaviour. When I removed U2 (and U1,U3,U4) from the board I am still seeing 8.4V on the Q2 gate, which causes Q2 to be operational and pass voltage to the drain pin. At the same time, Q1 is not sending voltage to the drain pin, because it requires a gate pull down from U2. When I look at the circuit diagram, it seems R8, R25 and R9 would provide about 8.3V on Q2 gate without even needing U2 to be present? This would seem to go against the purpose of U2, which should turn on both Q1 and Q2 at the same time. I must be missing something, or is Q2 not under the control of U2 when running on AC power?
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Old 24th July 2012, 08:52 AM   #2677
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Quote:
When I look at the circuit diagram, it seems R8, R25 and R9 would provide about 8.3V on Q2 gate without even needing U2 to be present?
I'm not sure how you arrived at that voltage. My rough calculations show it to be a little less than that. Either way, I'm not sure how relevant voltage readings are for an un-stuffed board. You're measuring a voltage divider made up of the series pair R8 and R25 in parallel with R5. This in series with R9. Remember also that the power management circuitry is not referenced to circuit GND.
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Old 24th July 2012, 11:27 AM   #2678
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Hi All,

Successfully build an O2 + Odac. Lows and mids sound fine, but there is a strong emphasize on high frequencies (sibilance). No obvious distortion. Both line in and Odac show similar sound in the highs. Can this be caused by some high frequency (<20khz) oscilation? If so, how could I measure this without an oscilloscoop? Or are the other things to check out first?

Thanks for any advice.
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Old 24th July 2012, 07:58 PM   #2679
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Originally Posted by Francois G View Post
Question for the designer; he mentioned PCB layout is critical to the DAC performance and especially noise.
Of course, but this is something I would merely be fooling around with(no official releasing or claims of good design), but if I do feel okay about the finished product, I may post the designs just for critiquing and for anybody to do whatever they wish with them.
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Old 25th July 2012, 01:07 AM   #2680
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Originally Posted by dewasiuk View Post
Of course, but this is something I would merely be fooling around with(no official releasing or claims of good design), but if I do feel okay about the finished product, I may post the designs just for critiquing and for anybody to do whatever they wish with them.
Thanks, I follow you reasoning. Best wishes and do share if all works out well.
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