Re: no-cap bass fix
This is *STRONGLY DISCOURAGED* and will break quite a couple of things. Details see inline below [Stefano Cavallari Di 23. März 2010]: Yesterday night I was going to fix the poor audio response of the Freerunner. Just before starting to solder (having opened the phone and the metallic plate) I discovered the caps I got were the wrong ones. So I looked at the scheme for an alternative solution, and I decided to try to replace the audio caps with 0R, thus losing DC blocking. You're not only losing the DC-decoupling, you're also losing the negative half of the sine wave, when amp is basically shorting output to GND to create the negative current by discharging the coupling capacitor. See operation principles of analog bridge amp outputs in some good book about electronics. This is NOT a class-A amp (http://en.wikipedia.org/wiki/Electronic_amplifier#Class_A ), means it never opens both the pullup and pulldown transistor concurrently. The LM4853 is a class-B push-pull bridge. The plan was to measure the DC component and if low enough, leave it as it. If not, putting the DC filter in the minijack adapter. This is basically feasible, but will most surely break JACK_INSERT logic, by applying a voltage 0V to the GPIO detecting if a jack is inserted or not. Each time you enable the amp to output some sound the headphones, it will latch up and not detect jack removal. And it's quite unlikely jack insertion is correctly detected each time as well, there also might be both false positives and false negatives. So I did that, and it seem to work. I tried first with a multimeter. It reads 0.2 V DC, but I have to confirm it with an oscilloscope. This reading probably is with headset amp disabled. Correct reading should be Vmid, i.e. ~1.6V I tried the audio with very cheap headphones first (I was afraid of burning them), Chances are you actually will end up with broken headset speakers, just because of this then with decent ones. It seems to work way better! Now I just need a better adapter cable (mine need to be inserted middle way, it's not the right one), and then I have usable audio :) Don't you think, if this was a viable workaround for the problem, we at OM (particularly me in this case) came up with this suggestion some 1.5 .. 2 years ago? cheers jOERG signature.asc Description: This is a digitally signed message part. ___ Openmoko community mailing list community@lists.openmoko.org http://lists.openmoko.org/mailman/listinfo/community
Re: no-cap bass fix
On Wednesday 24 March 2010 16:22:15 Joerg Reisenweber wrote: This is *STRONGLY DISCOURAGED* and will break quite a couple of things. Details see inline below [Stefano Cavallari Di 23. März 2010]: Yesterday night I was going to fix the poor audio response of the Freerunner. Just before starting to solder (having opened the phone and the metallic plate) I discovered the caps I got were the wrong ones. So I looked at the scheme for an alternative solution, and I decided to try to replace the audio caps with 0R, thus losing DC blocking. You're not only losing the DC-decoupling, you're also losing the negative half of the sine wave, when amp is basically shorting output to GND to create the negative current by discharging the coupling capacitor. See operation principles of analog bridge amp outputs in some good book about electronics. This is NOT a class-A amp (http://en.wikipedia.org/wiki/Electronic_amplifier#Class_A ), means it never opens both the pullup and pulldown transistor concurrently. The LM4853 is a class-B push-pull bridge. I should have read the data sheet. Audio does not seem distorted though, except at high gains. There is a some white noise in the background, not noticeable when music is running though. Anyway I was ready to use external capacitors in the adapter cable. The plan was to measure the DC component and if low enough, leave it as it. If not, putting the DC filter in the minijack adapter. This is basically feasible, but will most surely break JACK_INSERT logic, by applying a voltage 0V to the GPIO detecting if a jack is inserted or not. Each time you enable the amp to output some sound the headphones, it will latch up and not detect jack removal. And it's quite unlikely jack insertion is correctly detected each time as well, there also might be both false positives and false negatives. Jack sensing still works and seems reliable. Anyway if it stop working or it proves to be not reliable I can just disable it. I'll never use an headset, just headphones for playing music. I can force the output to the jack when starting the player. So I did that, and it seem to work. I tried first with a multimeter. It reads 0.2 V DC, but I have to confirm it with an oscilloscope. This reading probably is with headset amp disabled. Correct reading should be Vmid, i.e. ~1.6V I tried the audio with very cheap headphones first (I was afraid of burning them), Chances are you actually will end up with broken headset speakers, just because of this then with decent ones. It seems to work way better! Now I just need a better adapter cable (mine need to be inserted middle way, it's not the right one), and then I have usable audio :) Don't you think, if this was a viable workaround for the problem, we at OM (particularly me in this case) came up with this suggestion some 1.5 .. 2 years ago? It depends on what you mean for viable. It is not something correct, and I was aware of that. Building a custom cable with non-SMD capacitors is easier than finding right capacitors. Risking some cheap headphones that will sound way better than good headphones on a unfixed phone is even easier. I just wanted to share my experience, maybe someone finds this compromise useful. -- () ascii ribbon campaign - against html e-mail /\ www.asciiribbon.org - against proprietary attachments signature.asc Description: This is a digitally signed message part. ___ Openmoko community mailing list community@lists.openmoko.org http://lists.openmoko.org/mailman/listinfo/community
no-cap bass fix
Yesterday night I was going to fix the poor audio response of the Freerunner. Just before starting to solder (having opened the phone and the metallic plate) I discovered the caps I got were the wrong ones. So I looked at the scheme for an alternative solution, and I decided to try to replace the audio caps with 0R, thus losing DC blocking. The plan was to measure the DC component and if low enough, leave it as it. If not, putting the DC filter in the minijack adapter. So I did that, and it seem to work. I tried first with a multimeter. It reads 0.2 V DC, but I have to confirm it with an oscilloscope. I tried the audio with very cheap headphones first (I was afraid of burning them), then with decent ones. It seems to work way better! Now I just need a better adapter cable (mine need to be inserted middle way, it's not the right one), and then I have usable audio :) -- () ascii ribbon campaign - against html e-mail /\ www.asciiribbon.org - against proprietary attachments signature.asc Description: This is a digitally signed message part. ___ Openmoko community mailing list community@lists.openmoko.org http://lists.openmoko.org/mailman/listinfo/community
