I think I understand. I built one 10µF capacitor into the adapter (at the mass), so the problem with the headphones should be fixed. I also measured a 1,59V current at the capacitor when plugged in and silent. Sound is good as before.
Unfortunately, the internal speaker sounds really bad now (distorted). So I think i'll remove the silver again and find somebody who can help me with the soldering... Al Johnson wrote: > > On Wednesday 26 November 2008, zerghase wrote: >> Thank you for your advice. >> An adapter with an additional power source is out of the question for me. >> I >> do have a USB-headset, but that's out of the question, too, because I >> want >> to be able to play music while charging the Freerunner. >> So, I disassembled my Freerunner, and shorted the two caps you were >> talking >> about in the other thread[1][2]. I used conductive silver, because I >> don't >> own the equip that is needed for SMD soldering, and the danger of >> destroying something without heat is minor. Then I built an adapter for >> my >> headphones, and tested it with different capacitors. With 1µF, the bass >> was >> cut off just as with the internal 1µF caps. Then I tried 10µF, 100µF and >> even without any capacitor, and I had always a good sound with full bass, >> and there was absolutely no difference between the three solutions. >> I have no clue why the capacitor is needed (or why it's needed at all), >> but >> for me it works great without it. Maybe it is handled already inside the >> IC? Is this possible? > > It's good to hear someone's actually tried a mod :-) > > Caps in that position are usually to block dc on the output, especially > with a > single sided power supply. You may want to check for dc on the output > before > running without caps for an extended period if you value your headphones. > I > haven't checked the datasheet for this amp so it's possible it's handled > by > the chip already, but I would be surprised. Bigger caps will give a lower > cutoff frequency, but if 10uF sounds good you may as well stick with it as > they'll be physically smaller. > >> It would be great if there were no objections. Then everybody could do >> the >> HW fix for the sound issue, even without soldering skills and without >> risking damage. >> >> [1] >> http://lists.openmoko.org/pipermail/hardware/2008-September/000558.html >> [2] http://www.die-informatiker.eu/zerghase/capacitors.jpg >> >> Sincerely, >> zerghase >> >> Al Johnson wrote: >> > On Wednesday 26 November 2008, zerghase wrote: >> >> Can someone please explain, how such an adapter had to look like >> (maybe >> >> a circuit diagram), because I'd like to build one. >> > >> > It'll be an active circuit so will need power. That means batteries, or >> > getting power from USB. Most likely it'll use an opamp or headphone amp >> > chip >> > in an active filter arrangement. It's almost a textbook case of a bass >> > boost >> > circuit - just pick the frequency so the boost starts at the same >> > frequency >> > as the bass rolloff starts on the Freerunner. This should give you some >> > ideas: >> > http://headwize.com/projects/showfile.php?file=equal_prj.htm >> > >> > Having said that it'll be quicker, cheaper and easier to buy a usb >> > headset. >> > You can always cut off its headphones and solder on a 3.5mm socket >> > instead. >> > >> >> I think in most cases, people will use an adapter >> >> from the 2.5mm to a 3.5mm jack anyway. >> >> Will the audio quality be equal with an adapter to the hw fix? >> > >> > It'll be close if you do it well. >> > >> >> If not, is there a description >> >> of a hw fix for it (Joerg, you say there are different ways, so i >> assume >> >> you have already >> >> done or at least designed one)? >> > >> > This thread is the closest so far AFAIK. I haven't actually tried it >> yet. >> > http://lists.openmoko.org/pipermail/hardware/2008-September/000558.html >> > >> >> Sincerely, >> >> zerghase >> >> >> >> Joerg Reisenweber wrote: >> >> > Yes, sounds like a good idea (input impedance should be (much) > >> [>] >> >> > 1000Ohm >> >> > though, not <1k) >> >> > This adapter also could implement some hw-equalization for the >> >> > highpass-filter >> >> > created by the 1uF*(1/(1/1k + 1/(33R + adapter-impedance)). (where, >> in >> >> > sequence, values are from: C4111:1u, R4117:1k, R4407:33R. Right >> >> > channel analogue) >> >> > >> >> > Requests for assistance welcome. >> >> > cheers >> >> > jOERG >> >> > >> >> > Am So 16. November 2008 schrieb Scott Carlson: >> >> >> Would also be possible to create a small inline adapter for head >> set >> >> >> that have <1k input impedance? It may be convenient to make a batch >> >> >> >> and >> >> >> >> >> sell them >> >> >> cheap? (As a non-intrusive) hw fix.? >> >> >> >> >> >> SCarlson >> >> >> >> >> >> > Sorry the audio is definitively broken due to the capacitor issue >> >> >> >> >> >> you're >> >> >> >> >> >> > mentioning. There is no sw-fix either. >> >> >> > You may get (semi)decent audio by: >> >> >> > o- using a home-stereo line in, which has >1k input impedance >> >> >> > o- using high impedance headphone (>600 Ohm) >> >> >> > o- do a rework on the capacitors (there are different ways to do >> >> >> >> that, >> >> >> >> >> all >> >> >> >> >> >> > need excellent soldering skills) >> >> >> > o- use a bt-headset >> >> >> > >> >> >> > very sorry I didn't achieve to fix this for MP yet >> >> >> > cheers >> >> >> > jOERG >> > >> > _______________________________________________ >> > hardware mailing list >> > [email protected] >> > http://lists.openmoko.org/mailman/listinfo/hardware > > > > _______________________________________________ > hardware mailing list > [email protected] > http://lists.openmoko.org/mailman/listinfo/hardware > > -- View this message in context: http://n2.nabble.com/-sound-%3A-capacitor-that-act-like-a-high-pass-filter-and-so-removes--the-bass-on-the-headphones-jack-tp1502610p1583669.html Sent from the Openmoko Hardware mailing list archive at Nabble.com. _______________________________________________ hardware mailing list [email protected] http://lists.openmoko.org/mailman/listinfo/hardware
