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The Objective2 (O2) Headphone Amp DIY Project
The Objective2 (O2) Headphone Amp DIY Project
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Old 3rd March 2019, 01:23 PM   #5451
Mooly is offline Mooly  United Kingdom
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The Objective2 (O2) Headphone Amp DIY Project
This has to be something that has gone amiss when you moved the input to the rear panel.

If you quickly link R3 and R7 with a bit of wire you should get either mono sound from both channels if there is a break somewhere or the connection will kill the audio to both if there is a short.

Try that and lets confirm that both channels on the O2 itself are basically OK.
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Old 19th March 2019, 02:19 PM   #5452
rrdio11 is offline rrdio11
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Question New guy

Hi, new guy here. Interested in building O2 for my college project. Already read the original blog and schematics.

Just wondering, is there any newest "official" O2 design out there. The original design I got is in 2011 (a bit outdated I guess?).

read a bit in this forum that the NJM2068 could be "better" with newer LM4562.

and by the way, could you guys tell me how the NJM2903 work in the power management, I mean to control the FET fqpf10n20c right. but on what condition did they turn on or turn off?

Thx beforehand.
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Old 19th March 2019, 07:00 PM   #5453
Mooly is offline Mooly  United Kingdom
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The NJM2068 is an excellent device and I doubt it would be much different in sonics to the LM4562 in this application. The 4562 is also more power hungry which is always important in battery powered equipment.

The first comparator takes an LED as an absolute voltage reference, and by comparing the supply (battery) voltage against this fixed reference allowsthe comparator to flip states when the supply voltage drops below this reference value.

R5 and R9 form a potential divider to 'scale' the supply voltage to a suitable range.

The second comparator is used as invertor to generate effectively generate the two control voltages needed for the FET,s.

When the gate of the upper FET is pulled low the FET turns on and passes the positive supply to the amp. The lower FET needs the gate pulled high to do the same.

This shows the what happens as battery voltage falls:
Attached Images
File Type: png 02_1.png (118.9 KB, 129 views)
File Type: png 02_2.png (99.6 KB, 126 views)
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Old 20th March 2019, 10:20 AM   #5454
rrdio11 is offline rrdio11
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Quote:
Originally Posted by Mooly View Post
The NJM2068 is an excellent device and I doubt it would be much different in sonics to the LM4562 in this application. The 4562 is also more power hungry which is always important in battery powered equipment.

The first comparator takes an LED as an absolute voltage reference, and by comparing the supply (battery) voltage against this fixed reference allowsthe comparator to flip states when the supply voltage drops below this reference value.

R5 and R9 form a potential divider to 'scale' the supply voltage to a suitable range.

The second comparator is used as invertor to generate effectively generate the two control voltages needed for the FET,s.

When the gate of the upper FET is pulled low the FET turns on and passes the positive supply to the amp. The lower FET needs the gate pulled high to do the same.

This shows the what happens as battery voltage falls:

OK, thanks for the explanation. But I still wonder why the FET's gate is connected to rail voltage via R4 & R8. Also why we have R25 as global feedback, we use them as comparator right?
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Old 20th March 2019, 03:41 PM   #5455
Mooly is offline Mooly  United Kingdom
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R 4 and R8 are needed because the comparator has an 'open collector' output stage with no active pull-up.

Open collector - Wikipedia

R25 add hysteresis and ensures that the output switches cleanly by slightly modifying the voltage to be sensed. As the threshold point at which the comparator will switch is approached (when the - and + inputs have identical voltages present) the output of the comparator is unstable and is massively sensitive to the slightest variation in input voltage (uV sensitive). This would mean the output passed through an indeterminate point (unstable and oscillating) and so we artificially add a little extra pull or push to the voltage being sensed by means of the high value resistor. As soon as the comparator flips state, the junction of R5/R9 is pulled a bit a lower or a bit higher depending which 'flip' the comparator is doing.

This shows the output of the two comparators in response to falling battery voltage both with and without hysteresis. You can see how noisy the switching has become. Middle image is the noise in detail.
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Old 20th March 2019, 04:00 PM   #5456
rrdio11 is offline rrdio11
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Quote:
Originally Posted by Mooly View Post
R 4 and R8 are needed because the comparator has an 'open collector' output stage with no active pull-up.

Open collector - Wikipedia

R25 add hysteresis and ensures that the output switches cleanly by slightly modifying the voltage to be sensed. As the threshold point at which the comparator will switch is approached (when the - and + inputs have identical voltages present) the output of the comparator is unstable and is massively sensitive to the slightest variation in input voltage (uV sensitive). This would mean the output passed through an indeterminate point (unstable and oscillating) and so we artificially add a little extra pull or push to the voltage being sensed by means of the high value resistor. As soon as the comparator flips state, the junction of R5/R9 is pulled a bit a lower or a bit higher depending which 'flip' the comparator is doing.

This shows the output of the two comparators in response to falling battery voltage both with and without hysteresis. You can see how noisy the switching has become. Middle image is the noise in detail.
Ahh, I see. Thank you very much
I'm feeling lucky to be in this forum, that help me better understanding electronics device for audio.
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Old 26th March 2019, 02:55 AM   #5457
Fidget is offline Fidget  United States
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Default Thanks for the help!

Mooly, thanks for your troubleshooting guide way back! It helped me find a bad solder joint on U2. Now my O2 amp is working fantastically!

And thanks NwAvGuy for the design! I'm excited to spend some time with it.
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Old 26th March 2019, 07:41 AM   #5458
Mooly is offline Mooly  United Kingdom
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I'm pleased it was helpful, and pleased you have fixed your O2
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Old 6th April 2019, 08:23 PM   #5459
Beetwaaf is offline Beetwaaf
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Heya! Would appreciate some help if anyone would be willing.

I just finished my O2/Odac build buy I'm having a spot of trouble. All of the recommended measurements (from the NwAvGuy website) are as they should but I still can't hear anything on the output jack.
If I plug in headphones into the input jack I can hear some but I realize this is not correct behavior. From my testing the Output jack is shorted to ground but I'm not quite sure where and how to diagnose it. Any help would be much appreciated.
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Old 6th April 2019, 10:56 PM   #5460
Beetwaaf is offline Beetwaaf
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Re: previous post, I forgot it when I was posting but there is an anomalous reading, the Q2 gate is sitting at 8.4 rather than the 9.8 the troubleshooting png tells it should be at.
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