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jwzhan

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Everything posted by jwzhan

  1. jwzhan

    Deals

    http://www.tempoelectric.com/azl_sale.htm this guy has some interesting things (mostly audio related) for sale at fairly low price... definitely worth checking out.
  2. well... I'll get back to you on the actual value in a bit when I get home.. Yes, I did measure with the input shorted to ground.
  3. Measuring across the 2*20ohm resistors, at stable temp, they are all around 900mV. This is the lowest value I can get without changing 500ohm to a higher value.
  4. I tried to get it as low as possible but it drifts quite a bit... by quite a bit.. I mean 50~100mV at stable temp... Balance between the channels would drift by about 10mV as well... so achieving 1~2mV without opamp is very difficult on the balanced version to say the least.. Yeah 4 pots. 2 off voltage rails controlling dc offset and bias voltage somewhat..For every turn, the bias voltage would change by about 2mV or so.... and at 0.9V, I'm already very close to the max resistance of the pot.. 2 after JFETs. These controll the balance between the channels and the distribution of the over all bias voltage... both of my amp boards have around 1.8V, so 0.9V/0.9V is about the best I can do... I'm using the default 500ohm with the pots. 0.9V seems to be fine for me... the off board heatsinks are capable of handling the heat.. runs about 45C at stable temp. irrc, using a DMM, the voltage ramps up to something like 1.2V at shut down for both boards.. Also.. I've been using single ended headphones on the amp... haven't tested with balanced headphones yet..
  5. I just powered up my dynahi and used cheap apple buds for testing... The result is... weird... There is a somewhat loud weird inconsistent crackling/humming noise for a brief 1 or 2 seconds immediatly following turn on when the earbud is plugged in.. and there is a sharp pitched noise about 1 second after turning off (not immediately, but occurs after 1 sec. as DC offset ramps up assumably.) There is also a consistent light humming noise in the background which is likely due to how the amp is setup and wired at the moment. Well... I dared to plug my DT880 250ohm (which is probably not a smart move) in there given the above result since the apple earbuds didn't blow up on me, and did play music when the amp was on. The initial crackling/humming noise is still there with similar volume. But the turn-off pitch is not there or lessened by a significant amount. I have adjusted the amps so that DC offsets are under 100mV without the OPAMP in warm state. With OPAMP, the DC Offset is ±10mV. The voltages across the 2*20ohm resistors in all channels are 0.9V, which doesn't really matter.... I know that it takes time for the OPAMP (445) to start working, could it be the cause? It occurs in both amp boards. I'll have more detail tonight if I have more time to work on the amp.
  6. Is the DIY Audio person not selling it anymore? I recall he was selling the GR grade 10 for $15... Or is GR grade hfe not high enough? (didn't read the entire thread.)
  7. jwzhan

    AKG K812

    I'm sure there is a Chinese buyer out there who will beg you for it if you are good at BSing. The Chinese HiFi community is still raving about rudi and ultrasone after all, not to mention Lehmann, Graham Slee, hedgehog SAC KK and the sorts. Many even still think D7100 is a worthy successor of D7K... All thanks to some douchebag bloggers...
  8. that's no joke at all.... I've seen some chinese meet where people pull lines straight out of the transformer box to the equipments... they claim it produce the cleanest sound...
  9. I agree that the filtered outlet is mostly maketing, but at least it has some effect.... unlike the furutech rare metal plated stuff... I believe a well designed PSU should be able to get rid of a reasonable amount of noise from the AC line, but the sometimes.... a reasonbale amount is not good enough... I have experienced it first hand when I was living in the college dorm where a whole bunch of microwave, air conditioner and refrigerators are plugged into the same AC line and there was a shit ton of noise... I remember being able to hear them through ESP950 and CKKIII... a $50 APC surge suppressor that did -45dB on EMI/RFI help a lot but still didn't get rid of the noise entirely... I doubt that any household AC line will get that bad.. but filtering noise from AC line never hurts... and as I stated.. the $400 price tag is on the high side. I'll never buy it at that price, but I might buy it if it were $100, which will never happen...
  10. These might make a difference. I remember looking at them awhile back and saw someone testing these using a AC line noise sniffer thingy. They did find that the AC line noise is reduced through these. I've always wanted to try the filtered AC outlet.. but the price is just way too high to justify any possible improvement... EDIT: here is the video...
  11. the new hifiman electrostatic prototype
  12. finally got off my butt and fixed the PSU. It's making music now, and I hope it will continue do so... I'm now using the trafo Palchiu gave me... loaded, the voltage drops to 460VAC, so I guess it's fine. That trafo weighes about 0.3lb heavier than the SumR one while with the same output current at 150mA. eggil, that sucks... I'm sure RIchard will replace yours. He did replace mine, but took around 1 month. I still have the SumR raplcement on hand, if you need it, I can send it to you now while you wait for your replacement. Just PM me. That's at least the 4th one that KGSSHV has killed... maybe 150mA is not enough...
  13. yup... either that or they have really bad eyes and as long as they send me the wrong set that they are looking at which doesn't have problems, I might still be fine... That thing came up a few times during some conversations... don't exactly know what it is but the description claims "its design is as good as 717/727 and uses better material, so it should beat them with ease..." which is the description every taobao crap amp uses... I can't find any internal photo which is not surprising given that the person hasn't sold any...
  14. well... after sending PJ the photo, he, his dealer and STAX still insist that the scratches are made up and want to send back my 009. I agreed. I surely hope that STAX has done something to the phone and claimed to not have. I'll be looking over them with a magnifying glass this time... if those scratches are still there... I will probably just call my CC and try to get a charge back... (got scammed similarly to this about 3 years ago and my CC honored the charge back.) And apparently removing the earpad will void the warranty... WTF.... that's a first for me... We will see if STAX's and PJ's reputation still hold up next week...
  15. UPS charged me around 10% import tax one time. That's only 1 out of 3 shipments that got charged, but you might still want to keep that in mind. Other than that, the cases are great.
  16. this. Although its value is questionable, it's a good attempt, much better than other completely subjective evaluation. It's a broad brush evaluation, but similar to how I check if the headphone is worth the price tag in general.
  17. can't check right now. but the difference is most likely whether it's insulated or not. use the insulated one, especially if you are using the mini board.
  18. almost 2 months after my RMA, PJ sent me an e-mail telling me that STAX and PJ did not find ANY problem with the 009, including the scratches. They told me that my 009 has no imbalance issue... which I did not claim it to have... I think this is one of those template replies they have set up for RMAed 009s... After I saw their reply, I was like WTF, are those guys completely blind?! Luckily I took some photos before sending them off, otherwise I would've been completely fucked. These are the two scratches that they claim to not exist.. The not so obvious one actually runs about 1/5 of the circumference of the cup, which is a HUGE scratch. Thank god I did not wire transfer the money to them; instead, I used credit card. Worst case, I'll just call my CC and get a charge back, which I'm very inclined to do given that they are trying to deny any wrong doing.
  19. what are you saying? what does the number of customers have anything to do with the fact they only have some "preliminary" measurements which can be easily fudged?
  20. yep... the same group.... Those people (backers) are going nuts on this thing... some probably spent close to $1000: [email protected] 300, [email protected] 250, [email protected] 150, [email protected] 170, and the new 120 clock thing (using their cheapest options.) That's a whole lot to pay for something that's almost still completely preliminary... no internal pic, no final case design, nothing at all, in fact it seems like LHL isn't even sure what it will be.... The only thing they have so far, is the measurements that , as far as I know, can be easily made up... With the (IMO) grossly overpriced power supply and that clock thing, they collected about $150K in 3 days, which is quite stunning but also worrisome. Yeah... everything added together just seems like a train headed for disaster, but I'm still keeping my order just because it's not that much at 199, and I'm looking at it more like a toy than a serious piece of equipment, which is the way many of the backers are thinking... They are likely to find themselves disappointed...
  21. yeah... I laughed when I saw that thing... utter BS... I guess they really want attention from the mainstream... And the Pulse X special edition? All they said is they are replacing about $100 worth of parts and adding some magical tunning... which they are charging $600 MSRP for... Yet they still claim they would lose money on making too many of these SE-X... This just sounds like marketing BS.. I don't think they are going to skip town with all the money, but there is the chance that their final product doesn't live up to the expectations... who knows... that's why I didn't want to pay $299 for this. Too many uncertainties with this thing, but I guess I'll just have to wait and see...
  22. jwzhan

    AKG K812

    "the cavity in here is really wide, so it should give you a really spacious sound."
  23. That's the e-mail I received as well. After a few exchanges, they agreed to let me just contribute $10 to get the pulse after I mentioned blessingx's ID. Thank you. You are a true blesser (if that's a word.)
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