[From nobody Sat Aug 16 21:14:28 2008 Return-Path: <wolfgang@openmoko.com> X-Flags: 1001 Delivered-To: GMX delivery to joerg.twinklephone@gmx.de Received: (qmail invoked by alias); 30 Mar 2008 04:16:47 -0000 Received: from aakash.openmoko.org (EHLO aakash.openmoko.org) [124.219.5.209] by mx0.gmx.net (mx080) with SMTP; 30 Mar 2008 06:16:47 +0200 Received: from [222.35.181.223] (helo=[192.168.1.2]) by aakash.openmoko.org with esmtpsa (TLS-1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.63) (envelope-from <wolfgang@openmoko.com>) id 1Jfoy8-0003Ue-8r; Sun, 30 Mar 2008 12:16:42 +0800 Cc: joerg <joerg.twinklephone@gmx.de> Message-Id: <E9817EC7-FA65-4C9E-80F7-9F918988638E@openmoko.com> From: Wolfgang Spraul <wolfgang@openmoko.com> To: "Teenie [?????]" <teenie_hung@fic.com.tw>, Tim Lee <tim_lee@fic.com.tw> Content-Type: multipart/alternative; boundary=Apple-Mail-3-910137442 Mime-Version: 1.0 (Apple Message framework v919.2) Date: Sun, 30 Mar 2008 12:16:43 +0800 References: <200803300446.05576.joerg.twinklephone@gmx.de> X-Mailer: Apple Mail (2.919.2) X-SA-Exim-Connect-IP: 222.35.181.223 X-SA-Exim-Mail-From: wolfgang@openmoko.com X-Spam-Checker-Version: SpamAssassin 3.1.7-deb (2006-10-05) on aakash.openmoko.org X-Spam-Status: No, score=-3.6 required=5.0 tests=ALL_TRUSTED,AWL,BAYES_00, HTML_40_50,HTML_MESSAGE autolearn=ham version=3.1.7-deb Subject: Fwd: GTA02A5: bug in Headset Amp circuitry, max output power to headset X-SA-Exim-Version: 4.2.1 (built Tue, 09 Jan 2007 17:23:22 +0000) X-SA-Exim-Scanned: Yes (on aakash.openmoko.org) X-GMX-Antivirus: -1 (not scanned, may not use virus scanner) X-GMX-Htest: 0.46,0.47 X-GMX-Antispam: 0 (Mail was not recognized as spam) X-GMX-UID: Byzac6t/Rkke+L95UGRq7nRmdWkvKJPI --Apple-Mail-3-910137442 Content-Type: text/plain; charset=UTF-8; format=flowed; delsp=yes Content-Transfer-Encoding: quoted-printable Teenie, Tim Lee - same as before, please look into this. Thanks, Wolfgang Begin forwarded message: > From: joerg <joerg.twinklephone@gmx.de> > Date: March 30, 2008 10:45:59 AM GMT+08:00 > To: openmoko-kernel@lists.openmoko.org > Cc: Andy Green <andy@openmoko.com>, Wolfgang Spraul = <wolfgang@openmoko.com=20 > > > Subject: GTA02A5: bug in Headset Amp circuitry, max output power to =20= > headset > > To make things worse and this a real bug, we have 1kR R4116,R4117 as > additional load after the Cs, in parallel to the speakers of headset. > (No, these Rs are ok, they just make things worse wrt small =20 > capacitors) > >> =46rom datasheet, p5: >>> Output coupling capacitor which blocks the DC voltage at the =20 >>> amplifier=E2=80=99s >>> output. Forms a high pass filter(!!!) with the single-ended load =20 >>> RL at >>> fO =3D 1/(2=CF=80 RLCO). >> With e.g. *typical* (->ds, p.12) 32R-headphones, RL =3D 65 Ohm! Could = =20 >> anybody >> check the Z for OM-headset? >> Please calculate f0 for this value!!!!!! > > So even with some headset with "infinite" Z, my result for above =20 > equation is > f0=3D~160Hz still, which is not acceptable for high quality sound =20 > (IMHO not for > music playback at all!). This means you can't even connect your home =20= > stereo > to the earphone outlet to get usable sound, it also will drop =20 > -3dB@250HZ. > This much for frequency response. Now for volume: > With 3.3V power for amp, we won't even get as few as around 1mW(!) =20 > Po(max) to > the headset speakers for Z(speaker) =3D 1kR, single ended amp. No = matter > whether there is a 33R series resistor, this limits *maximum* volume =20= > to > possibly <80 dB Sound Pressure Level, depending on sensitivity of =20 > headset. > This also isn't acceptable for high quality sound. A headset amp =20 > should be > able to power any headset with at least 10~20mW. > By choosing a headset with even higher Z loudness decreases, with =20 > lower Z low > cutoff frequency increases (-3db@300Hz for 1kR =20 > headset!!!!!!!!!!!!!!!!!!!). > Ergo: this design is definitely broken. There is simply *no* headset =20= > that > yields _good_ sound quality with NEO. The vast majority of > headsets/headphones will probably not work at all. In fact the =20 > headset outlet > itself cuts frequencies below 160Hz, this gets worse when you connect > anything. > > Fix: > O=3D=3D Components we MUST have > 6.8uF C minimum for 1kR internal + highZ(>>1k) external load, like =20 > amp input / > active speakers, so we at least have one chance to get good audio =20 > signal > directly out of Freerunner by any means. > O=3D=3D ...We SHOULD have > For -3dB@50Hz with a load of 65R (internal 33R + std low impedance =20 > headset) we > need 47uF. > For tradeoff power against low cutoff frequency, we should keep the =20= > 33R series > resistors, thus shifting f0 from 100Hz to 50Hz for the usual 32R-=20 > headphone, > and still having a comfortable 20mW for high sensitive earphones =20 > with >80dB > SPL / mW. > O=3D=3D ...nice to have > If we can have C >=3D 100uF, we should use 0R series (1R gets =20 > hot(0.5W) on > short), thus allowing to connect to common passive stereo computer =20 > satelite > speakers, with option active subwoofer, and drive them with a nice =20 > 300mW. > With 32R-HP we really get HiFi with C>100uF. > > > > For a future design i suggest to insert a similar highpass (plus =20 > f0=3D1Hz > lowpass, to compensate offset) to R4112/R4115 feedback path, to =20 > compensate > frequency response. Or switch from U-amp design to I-amp (feedback =20 > current, > not voltage) > > cheers > jOERG --Apple-Mail-3-910137442 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable <html><body style=3D"word-wrap: break-word; -webkit-nbsp-mode: space; = -webkit-line-break: after-white-space; ">Teenie, Tim Lee -<div>same as = before, please look into = this.</div><div>Thanks,</div><div>Wolfgang<br><div><br><html>Begin = forwarded message:</html><br = class=3D"Apple-interchange-newline"><blockquote type=3D"cite"><div><div = style=3D"margin-top: 0px; margin-right: 0px; margin-bottom: 0px; = margin-left: 0px; "><font face=3D"Helvetica" size=3D"3" color=3D"#000000" = style=3D"font: 12.0px Helvetica; color: #000000"><b>From: = </b></font><font face=3D"Helvetica" size=3D"3" style=3D"font: 12.0px = Helvetica">joerg &lt;<a = href=3D"mailto:joerg.twinklephone@gmx.de">joerg.twinklephone@gmx.de</a>></= font></div><div style=3D"margin-top: 0px; margin-right: 0px; = margin-bottom: 0px; margin-left: 0px; "><font face=3D"Helvetica" = size=3D"3" color=3D"#000000" style=3D"font: 12.0px Helvetica; color: = #000000"><b>Date: </b></font><font face=3D"Helvetica" size=3D"3" = style=3D"font: 12.0px Helvetica">March 30, 2008 10:45:59 AM = GMT+08:00</font></div><div style=3D"margin-top: 0px; margin-right: 0px; = margin-bottom: 0px; margin-left: 0px; "><font face=3D"Helvetica" = size=3D"3" color=3D"#000000" style=3D"font: 12.0px Helvetica; color: = #000000"><b>To: </b></font><font face=3D"Helvetica" size=3D"3" = style=3D"font: 12.0px Helvetica"><a = href=3D"mailto:openmoko-kernel@lists.openmoko.org">openmoko-kernel@lists.o= penmoko.org</a></font></div><div style=3D"margin-top: 0px; margin-right: = 0px; margin-bottom: 0px; margin-left: 0px; "><font face=3D"Helvetica" = size=3D"3" color=3D"#000000" style=3D"font: 12.0px Helvetica; color: = #000000"><b>Cc: </b></font><font face=3D"Helvetica" size=3D"3" = style=3D"font: 12.0px Helvetica">Andy Green &lt;<a = href=3D"mailto:andy@openmoko.com">andy@openmoko.com</a>>, Wolfgang = Spraul &lt;<a = href=3D"mailto:wolfgang@openmoko.com">wolfgang@openmoko.com</a>></font></d= iv><div style=3D"margin-top: 0px; margin-right: 0px; margin-bottom: 0px; = margin-left: 0px; "><font face=3D"Helvetica" size=3D"3" color=3D"#000000" = style=3D"font: 12.0px Helvetica; color: #000000"><b>Subject: = </b></font><font face=3D"Helvetica" size=3D"3" style=3D"font: 12.0px = Helvetica"><b>GTA02A5: bug in Headset Amp circuitry, max output power to = headset</b></font></div><div style=3D"margin-top: 0px; margin-right: = 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; = "><br></div> </div>To make things worse and this a real bug, we have 1kR = R4116,R4117 as <br>additional load after the Cs, in parallel to the = speakers of headset.<br>(No, these Rs are ok, they just make things = worse wrt small capacitors)<br><br><blockquote type=3D"cite">=46rom = datasheet, p5:<br></blockquote><blockquote type=3D"cite"><blockquote = type=3D"cite">Output coupling capacitor which blocks the DC voltage at = the amplifier=E2=80=99s<br></blockquote></blockquote><blockquote = type=3D"cite"><blockquote type=3D"cite">output. Forms a high pass = filter(!!!) with the single-ended load RL at = <br></blockquote></blockquote><blockquote type=3D"cite"><blockquote = type=3D"cite">fO =3D 1/(2=CF=80 = RLCO).<br></blockquote></blockquote><blockquote type=3D"cite">With e.g. = *typical* (->ds, p.12) 32R-headphones, RL =3D 65 Ohm! Could anybody = <br></blockquote><blockquote type=3D"cite">check the Z for OM-headset? = <br></blockquote><blockquote type=3D"cite">Please calculate f0 for this = value!!!!!! <br></blockquote><br>So even with some headset with = "infinite" Z, my result for above equation is <br>f0=3D~160Hz still, = which is not acceptable for high quality sound (IMHO not for <br>music = playback at all!). This means you can't even connect your home stereo = <br>to the earphone outlet to get usable sound, it also will drop = -3dB@250HZ.<br>This much for frequency response. Now for volume:<br>With = 3.3V power for amp, we won't even get as few as around 1mW(!) Po(max) to = <br>the headset speakers for Z(speaker) =3D 1kR, single ended amp. No = matter <br>whether there is a 33R series resistor, this limits *maximum* = volume to <br>possibly &lt;80 dB Sound Pressure Level, depending on = sensitivity of headset. <br>This also isn't acceptable for high quality = sound. A headset amp should be <br>able to power any headset with at = least 10~20mW.<br>By choosing a headset with even higher Z loudness = decreases, with lower Z low <br>cutoff frequency increases (-3db@300Hz = for 1kR headset!!!!!!!!!!!!!!!!!!!).<br>Ergo: this design is definitely = broken. There is simply *no* headset that <br>yields _good_ sound = quality with NEO. The vast majority of <br>headsets/headphones will = probably not work at all. In fact the headset outlet <br>itself cuts = frequencies below 160Hz, this gets worse when you connect = <br>anything.<br><br>Fix:<br>O=3D=3D Components we MUST have<br>6.8uF C = minimum for 1kR internal + highZ(>>1k) external load, like amp input / = <br>active speakers, so we at least have one chance to get good audio = signal <br>directly out of Freerunner by any means.<br>O=3D=3D ...We = SHOULD have<br>For -3dB@50Hz with a load of 65R (internal 33R + std low = impedance headset) we <br>need 47uF.<br>For tradeoff power against low = cutoff frequency, we should keep the 33R series <br>resistors, thus = shifting f0 from 100Hz to 50Hz for the usual 32R-headphone, <br>and = still having a comfortable 20mW for high sensitive earphones with >80dB = <br>SPL / mW.<br>O=3D=3D ...nice to have<br>If we can have C >=3D 100uF, = we should use 0R series (1R gets hot(0.5W) on <br>short), thus allowing = to connect to common passive stereo computer satelite <br>speakers, with = option active subwoofer, and drive them with a nice 300mW.<br>With = 32R-HP we really get HiFi with C>100uF.<br><br><br><br>For a future = design i suggest to insert a similar highpass (plus f0=3D1Hz = <br>lowpass, to compensate offset) to R4112/R4115 feedback path, to = compensate <br>frequency response. Or switch from U-amp design to I-amp = (feedback current, <br>not = voltage)<br><br>cheers<br>jOERG<br></blockquote></div><br></div></body></h= tml>= --Apple-Mail-3-910137442-- ]