bui501 Posted July 19, 2016 Report Share Posted July 19, 2016 6 hours ago, chinsettawong said: Hi Vinh, I'm also in Bangkok. If you need any help, just let me know. Wachara C. Hi, Wachara! Thank you for the help offer. I can use your advice on potential sources for case and hardware once the electronics work is done, especially if you know if local vendors. One thing to consider if you have not already is to elevate the resistors and diodes slightly off the board by 3mm or so. It's a practice used by many (myself included) to prevent leakage or arcing due to the high voltage involved in this amp. Ah... (Light bulb moment). When I took apart my Stax srm-1/mk2, the first thing that struck me was why the heck the resistors were so high off the board and taking up so much space, so I almost took them off to remount because they were making it difficult for me to mount the pro mod board I was trying to install! :-D I've done a lot of DIY, but this is my first time with high voltage circuitry. Sent from my iPhone using Tapatalk Quote Link to comment Share on other sites More sharing options...
bui501 Posted July 19, 2016 Report Share Posted July 19, 2016 Just wanted to thank everybody for the support and advice I've received in my short time in this forum. This is better than I had hoped for! Sent from my iPhone using Tapatalk Quote Link to comment Share on other sites More sharing options...
bui501 Posted July 23, 2016 Report Share Posted July 23, 2016 2 hours ago, mwl168 said: One thing to consider if you have not already is to elevate the resistors and diodes slightly off the board by 3mm or so. It's a practice used by many (myself included) to prevent leakage or arcing due to the high voltage involved in this amp. Good advise. I use those wooden coffee stirrers at Starbucks as spacers while soldering the resistors to the boards. When done, pull 'em out. Gives a nice uniform outcome. Thanks again for the great tips. I started populating the boards this morning. Took your advice to use pieces of coffee stirrers as spacers to get the resistors and diodes off the board... Sent from my iPhone using Tapatalk Quote Link to comment Share on other sites More sharing options...
cheshirecats Posted July 28, 2016 Report Share Posted July 28, 2016 Hi everyone. A few questions: (1) Regarding the input JFET (lsk389), what will be the best Idss (for reducing THD)? i.e. Shall we use lsk389a or b or c. I remember reading somewhere that larger Idss = less distortion, but then it's a bit strange that lsk389a is more expensive than lsk389b/c. (2) Can we use BF862 (lower noise, more available, higher gfs, lower ciss, higher idss) instead? Currently the gate resistor is 100ohm, so probably one shall increase it to 470ohm for BF862? (3) Can we reduce the gain of the amplifier? (since my DAC can output quite high levels (+24dBu), and I usually listen at low volume). Moreover, will this leads to lower THD? It will be great if someone can do a LTSpice simulation... Thanks. Quote Link to comment Share on other sites More sharing options...
bui501 Posted August 7, 2016 Report Share Posted August 7, 2016 I finished populating all the components on the three boards for my KGSSHV build late last night. I've tested the voltages from the mains line, transformer, and the PSU board and got the measurements below. Everything "seems" to be working correctly EXCEPT that I'm not sure if the differences between the actual and rated voltages coming off the PSU board for the +/-450V and the Bias output is OK or Not. The Bias TP on the PSU Board measures +580 VDC, but then the two terminals labeled "Bias" on the board both measure only 400 VDC or so. (It measures 385 VDC when I first turn on the power and then slowly rises to about 404 VDC after running for several minutes.) Can you guys help me? Are my voltage measuresments within acceptable specs for the PSU board? BTW, I decided to use Molex 2- and 3-pin connectors so I could connect and disconnect the various interconnections quickly and easily. If anybody sees a potential problem with that, let me know. The connectors are rated for lower voltages but much, much higher currents than I suspect would run through the power supply board. Mains Voltage directly from wall outlet: Rated at 220VAC, Measured Actual 230VAC on Fluke Multimeter Measurements from Transformer: AC420, AC420: both measured 470VAC Actual AC15, AC15: both measured 16VAC Actual Measurements from terminals coming off PSU Board: Terminal Name - Actual Measurement +450 +500 VDC -450 -500 VDC +15 +15 VDC (we seem to be Golden here) -15 -15 VDC Bias Terminal (two pins both seem to be tied together on the board): +404 VDC Actual Measurement on Fluke Multimeter Bias TP +580 VDC Actual measurement <photo deleted to offset attachment quota> 1 Quote Link to comment Share on other sites More sharing options...
Kerry Posted August 7, 2016 Report Share Posted August 7, 2016 Looks nice. The bias voltage is fine. The TP is before the 5M resistor and directly reads 580V. Most multimeters have a 10M resistance on the print probes when testing voltage. This causes the drop. I'm assuming you wanted the 450V outputs to be 500V. I like the idea of the connectors but you have to make sure they have the proper voltage ratings. Quote Link to comment Share on other sites More sharing options...
joehpj Posted August 7, 2016 Report Share Posted August 7, 2016 470VAC is even way too high for 500V. Where did you get your trafo? Quote Link to comment Share on other sites More sharing options...
spritzer Posted August 7, 2016 Report Share Posted August 7, 2016 It's one of my transformers and it is rated for 450VAC when loaded. It all measures just fine. 1 Quote Link to comment Share on other sites More sharing options...
bui501 Posted August 7, 2016 Report Share Posted August 7, 2016 Awesome! Thanks everybody. I'll start testing the amp boards as soon as I get back home later this week... Sent from my iPhone using Tapatalk Quote Link to comment Share on other sites More sharing options...
bui501 Posted August 8, 2016 Report Share Posted August 8, 2016 Looks nice. The bias voltage is fine. The TP is before the 5M resistor and directly reads 580V. Most multimeters have a 10M resistance on the print probes when testing voltage. This causes the drop. I'm assuming you wanted the 450V outputs to be 500V. I like the idea of the connectors but you have to make sure they have the proper voltage ratings. Forgot about the voltage drops through the resistors... I need to go back to engineering school... ( Sent from my iPhone using Tapatalk Quote Link to comment Share on other sites More sharing options...
joehpj Posted August 8, 2016 Report Share Posted August 8, 2016 bui501 said AC420. And I thought 470V is way too high for rated 420V. Unloaded 470V for 450V rated is indeed just fine. Any reason for using 450V as sec? I thought 400-420V was already enough. How much voltage drop should I consider when ordering transformers? Quote Link to comment Share on other sites More sharing options...
bui501 Posted August 9, 2016 Report Share Posted August 9, 2016 bui501 said AC420. And I thought 470V is way too high for rated 420V. Unloaded 470V for 450V rated is indeed just fine. Any reason for using 450V as sec? I thought 400-420V was already enough. How much voltage drop should I consider when ordering transformers? Spritzer will have to answer that one. The transformer I have was custom ordered by him for the kit he sells with the KGSSHV boards. The xformer looks really well made, and the output voltages are very stable. Sent from my iPhone using Tapatalk Quote Link to comment Share on other sites More sharing options...
mypasswordis Posted August 9, 2016 Report Share Posted August 9, 2016 Joe, the input zener string is set to 50V above output VDC so 400VAC could be cutting it close for 500VDC output depending on your primary voltage. ~420VAC is probably the best compromise. The reason it's measuring 450 is the primary voltage is 10V above 220V. Quote Link to comment Share on other sites More sharing options...
bui501 Posted August 10, 2016 Report Share Posted August 10, 2016 Wow! What a roller coaster ride of a day... I woke up early this morning to test the amp boards. Plugged them into the PSU, turned on the power, and all LEDs lit up. I thought I was golden... For about 2 seconds before there was a bright spark accompanied by a loud "POP" from one of the IXTP01s on one of the amp boards. The first pop was quickly followed by a second pop before I could yank the power cord from the wall. I was initially too embarrassed to post this in this forum: The sparks resulted in scorch marks on the IXTPs on the one board. Spritzer confirmed to me that I should have used aluminum oxide isolators instead of just plain heatsink paste between those high-power mosfets and their heatsinks. Fortunately, the damage was on only one of the boards. I created some space between the IXTPs and heatsinks and cleaned off the heatsink paste on the second board and plugged it in. The LEDs came on and stayed on with no sparking from the board, and everything was stable enough for me to adjust the balance and offset pots on the board. By the end of the day, I was able to hook up a phone as a source and my beat up pair of Stax 303s. The result was loud, distortion-free music from the one board. I screamed so loudly with joy, my wife got pissed off at me... Back in the dog house again. Hopefully, the only damage on the first amp board is only in the scorched IXTP01s and nothing else... I have some replacement IXTPs along with proper aluminum oxide isolators on order from Mouser... Damn these long waiting spells for replacement parts. At least the first board is working. Sent from my iPhone using Tapatalk 4 Quote Link to comment Share on other sites More sharing options...
Kerry Posted August 10, 2016 Report Share Posted August 10, 2016 (edited) What couplers are you using between the PS and amp boards? I like those. Edited August 10, 2016 by Kerry Quote Link to comment Share on other sites More sharing options...
bui501 Posted August 10, 2016 Report Share Posted August 10, 2016 What couplers are you using between the PS and amp boards? I like those. The white ones coming off the PSU are Molex power connectors; the green ones on the amp boards are Phoenix connectors, but to be honest, I looked up the specs, and the white molex connectors are rated for only 250 v at 5amps... I need to switch to higher voltage ones to be safe. They just happen to be what I had in my parts bin from a former project. Sent from my iPhone using Tapatalk Quote Link to comment Share on other sites More sharing options...
bui501 Posted October 16, 2016 Report Share Posted October 16, 2016 After almost 4 months of learning and building, an exciting spark from one of the amp boards, and lots and lots of advice from Spritzer, I finally finished up my KGSSHV last night. I've posted photos of my build below. I know the electrical build can't compare with those by other members here, but I'm rather proud of the case work. I purchased a generic aluminum case from an eBay seller in China and spent the last couple of months learning to use CAD CAM software along with some machine shop equipment to customize the case for my build. The red and black anodizing was done by a local shop (in Bangkok). I did all the customized mill work. I etched all the text on the front and back panels using a laser that burned the text directly onto the anodized aluminum. (I put the "BuiAudio" logo on the front just to impress my little sons. :-) The amp sounds wonderful -- no noise at all and dramatically better (and louder) than my STAX SRM-1/MK-2 with my stax SR-303 and SR-407. Now for the next phase... To build a pair of DIY electrostatic headphones like the ones inspired by chinsettawong on head-fi.org... 9 Quote Link to comment Share on other sites More sharing options...
johnwmclean Posted October 16, 2016 Report Share Posted October 16, 2016 That really impressive work, especially milling your own panels. Quote Link to comment Share on other sites More sharing options...
bui501 Posted October 16, 2016 Report Share Posted October 16, 2016 12 minutes ago, johnwmclean said: That really impressive work, especially milling your own panels. Thanks, John. I've been following your work on head-case.org and that means a lot to me coming from you. -vinh Quote Link to comment Share on other sites More sharing options...
chinsettawong Posted October 16, 2016 Report Share Posted October 16, 2016 Nice work Bui501. Really like you case work. About the DIY headphones, I'm always around if you should need any help. Wachara C. 1 Quote Link to comment Share on other sites More sharing options...
GeorgeP Posted October 16, 2016 Report Share Posted October 16, 2016 Nice work! What did you use for the etching? And do you have a link to the case? Quote Link to comment Share on other sites More sharing options...
bui501 Posted October 16, 2016 Report Share Posted October 16, 2016 Nice work Bui501. Really like you case work. About the DIY headphones, I'm always around if you should need any help. Wachara C.Thanks, Chinsettawong. It was your DIY electrostatic headphones that got me rolling down this path.Sent from my iPhone using Tapatalk 1 Quote Link to comment Share on other sites More sharing options...
bui501 Posted October 16, 2016 Report Share Posted October 16, 2016 1 hour ago, GeorgeP said: Nice work! What did you use for the etching? And do you have a link to the case? George, This is the link for the case I purchased from eBay; the seller is located in China:http://www.ebay.com/itm/New-aluminum-amp-chassis-home-audio-amplifier-case-size-340-430-92MM-/322291438722?hash=item4b0a111482:g:zQ0AAOSwyLlXo3Qc The seller charged me a reasonable price for 3-day DHL shipping from China. I didn't like the plastic feet that came with the case, so I purchased these aluminum feet:http://www.ebay.com/itm/321374671507 And the handles on the front plate came from this seller on aliexpress (also located in China or Hong Kong):https://www.aliexpress.com/store/product/Breeze-audio-handle-for-chassis-82type/331129_32718799987.html For the etching, I simply used a laser engraver and etched directly on the anodized aluminum. I just used a low power (100mW) laser engraver; normal anodized aluminum (not the hard-anodized version) engraves really well with a laser. Any spot that's hit by the laser turns a white color. 1 Quote Link to comment Share on other sites More sharing options...
JoaMat Posted October 16, 2016 Report Share Posted October 16, 2016 Indeed a most elegant amplifier. Impressive chassis work - like a Maserati. Quote Link to comment Share on other sites More sharing options...
Kerry Posted October 16, 2016 Report Share Posted October 16, 2016 Very nice chassis work. I like the red anodized face. Welcome to the wonderful world is milling. It really is very rewarding Quote Link to comment Share on other sites More sharing options...
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