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
