tag:blogger.com,1999:blog-6890046273025265768.post1315039423477159604..comments2024-03-18T03:10:30.572-07:00Comments on NwAvGuy: QRV09 DIY Headphone AmpNwAvGuyhttp://www.blogger.com/profile/00309644608738074125noreply@blogger.comBlogger13125tag:blogger.com,1999:blog-6890046273025265768.post-72845950337591480302012-05-10T12:20:55.573-07:002012-05-10T12:20:55.573-07:00I meant similar to a 5 ohm load with the original ...I meant similar to a 5 ohm load with the original 10 ohm serial resistor, so the TPA6120 sees a total of 15 ohms in the audio band in either case.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-6890046273025265768.post-2637526326072120852012-05-10T11:14:54.299-07:002012-05-10T11:14:54.299-07:00The LF distortion is odd and a serious weakness of...The LF distortion is odd and a serious weakness of the TPA6120 (along with the 10 ohm series resistance requirement). I don't, however, agree a 15 ohm resistive load with the series ferrite is "similar to a 5 ohm load". At low frequencies the ferrite isn't adding significant reactance and, regardless, its effects are in <i>series</i> with the 15 ohm resistive load.NwAvGuyhttps://www.blogger.com/profile/00309644608738074125noreply@blogger.comtag:blogger.com,1999:blog-6890046273025265768.post-858741059481966262012-05-10T10:41:28.207-07:002012-05-10T10:41:28.207-07:00Low frequency distortion with low impedance loads,...Low frequency distortion with low impedance loads, even at relatively low output levels, is a common problem in TPA6120 based amplifiers, including the FiiO E9, the QRV09 measured here, and the Xonar Essence ST and STX sound cards. All of these are quite similar in this regard.<br /><br />A load of 15 ohms with the ferrite is similar to 5 ohms without the serial resistor being bypassed, so the Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-6890046273025265768.post-62457109228729148352012-05-09T18:41:05.135-07:002012-05-09T18:41:05.135-07:00No, it's mainly the ferrite. I've seen the...No, it's mainly the ferrite. I've seen the same issue with other amps, even without any series resistance involved. Plus the TPA6120 has very good low impedance drive and current capability.NwAvGuyhttps://www.blogger.com/profile/00309644608738074125noreply@blogger.comtag:blogger.com,1999:blog-6890046273025265768.post-90604526699297587982012-05-09T09:33:07.182-07:002012-05-09T09:33:07.182-07:00Regarding the increased distortion with the ferrit...Regarding the increased distortion with the ferrite and 15 Ohm load, isn't it largely because the amplifier then needs to drive a more difficult load of 15 Ohms only instead of 25 total ?Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-6890046273025265768.post-19418423822854588902011-07-17T12:20:38.220-07:002011-07-17T12:20:38.220-07:00Another great in-depth article. I'm rapidly be...Another great in-depth article. I'm rapidly becoming addicted to your site and I've started playing with op-amps again which is fun. Something I would like to see is a large photo (under good lighting) showing each side of the full PCB for any equipment you mention. Thanks for all the work you put into organizing and presenting these investigations.DiamondGezanoreply@blogger.comtag:blogger.com,1999:blog-6890046273025265768.post-87879365549746309452011-07-02T12:43:43.753-07:002011-07-02T12:43:43.753-07:00"And, unlike some of the Asian design boards ..."And, unlike some of the Asian design boards I've seen, Per-Anders seemed to optimize the layout for best performance rather than nice aesthetics."<br /><br />That sound like a premise for another article all by itself.maverickroninnoreply@blogger.comtag:blogger.com,1999:blog-6890046273025265768.post-76358362375927822572011-07-01T15:11:05.454-07:002011-07-01T15:11:05.454-07:00Mike, the channel balance is indeed up to the resi...Mike, the channel balance is indeed up to the resistor tolerances and the relative gain. But it's also part luck. Some resistors are machine graded into tolerance categories during manufacturing. If you're buying the tightest tolerance for that particular series of graded resistors some of the values will be almost perfect. But, if you buy one of the lesser tolerances, <i>none</i> of themNwAvGuyhttps://www.blogger.com/profile/00309644608738074125noreply@blogger.comtag:blogger.com,1999:blog-6890046273025265768.post-35573629806774553762011-07-01T13:27:52.089-07:002011-07-01T13:27:52.089-07:00Oh whoops, I meant to write difference "for t...Oh whoops, I meant to write difference "for the better."<br /><br />About the 0.004 dB channel balance error on the QRV09: this is primarily the result of individual component tolerances on each side of the circuit? i.e. actual resistance values of parts being +- 1% or whatever of the nominal value. <br /><br />I didn't look at the circuit other than the photograph displaying howMikenoreply@blogger.comtag:blogger.com,1999:blog-6890046273025265768.post-6314787499504995852011-07-01T09:23:27.661-07:002011-07-01T09:23:27.661-07:00Mike, thanks for the comments. There are some exam...Mike, thanks for the comments. There are some examples where "upgrading" op amps does change the sound in audible ways--sometimes for the worse. I'll be covering that in the future article. <br /><br />For the QRV09 I think there are several less expensive op amps that would deliver sonically identical performance. So, in this case, it's not about better sound but saving money. NwAvGuyhttps://www.blogger.com/profile/00309644608738074125noreply@blogger.comtag:blogger.com,1999:blog-6890046273025265768.post-85160083936158103452011-07-01T09:08:05.215-07:002011-07-01T09:08:05.215-07:00When there are no revolts over product reviews, it...When there are no revolts over product reviews, it looks like you get a lot less comments, heh.<br /><br />I'm looking forward to the entry on op amp swaps for sure. It always seemed dubious to me.<br /><br />If you're modifying a relatively high-end design, you're probably not going to get significantly better performance by using something else, and you might end up with something Mikenoreply@blogger.comtag:blogger.com,1999:blog-6890046273025265768.post-13038687813893257312011-06-29T16:10:49.627-07:002011-06-29T16:10:49.627-07:00Another great article. To bad I'm way too clu...Another great article. To bad I'm way too clumsy to something like that together<br /><br />I like the idea of building a clone of the Benchmark's amp. I'd especially love it if there were no SMDs so I could do it myself.maverickroninnoreply@blogger.comtag:blogger.com,1999:blog-6890046273025265768.post-28510925107531163742011-06-29T15:49:08.710-07:002011-06-29T15:49:08.710-07:00Another fine entry. I feel you re: small parts. I&...Another fine entry. I feel you re: small parts. I'm working on a USB audio dongle for a buddy that has developed a weird RF pickup issue. Christ - I'm too old and shaky to fiddle with such tiny parts...<br /><br />Robheycarnuthttps://www.blogger.com/profile/02046373294198981949noreply@blogger.com