February 25, 201412 yr comment_625086 Nope, no dummy load needed for any adjustment. PSU works just fine without any load and the voltages should stay the same with a load. Report
February 25, 201412 yr comment_625102 Some questions for the experts for the offboard 0.6 amp board. For Q17 and Q18 the PCB shows A970 and ECB (with the flat side facing you). This datasheet http://www.futurlec.com/Transistors/2SA970.shtml gives the orientation as BCE (with the flat side facing you). I'm assuming the datasheet is wrong? I'll be using MPSW56 as a sub for A970. This datasheet http://www.onsemi.com/pub_link/Collateral/MPSW55-D.PDF gives the orientation as EBC (with the flat side facing you). So if I use MPSW56 I'll have to cross 2 of the legs, right? Report
February 25, 201412 yr comment_625104 Nope, no dummy load needed for any adjustment. PSU works just fine without any load and the voltages should stay the same with a load. Thanks. So it is safe to measure at the STAX socket without connecting the headphone? Even with signal feeding to the input? I want to make sure the amp is as close to 100% stable as possible, before connecting my headphone to it. Report
February 26, 201412 yr Author comment_625126 correct data sheet http://gilmore.chem.northwestern.edu/2sa970.pdf safe to measure the voltages at the stax socket. but the bias will be the wrong voltage unless you have a very high impedance voltmeter. Edited February 26, 201412 yr by kevin gilmore Report
February 26, 201412 yr comment_625144 Thanks Kevin. So, it looks like I'll have to de-solder the MPSW56 and cross 2 of the legs. Report
February 26, 201412 yr comment_625186 Thanks. So it is safe to measure at the STAX socket without connecting the headphone? Even with signal feeding to the input? I want to make sure the amp is as close to 100% stable as possible, before connecting my headphone to it. Ditto what Kevin said and it is perfectly fine to have the amp "playing" when testing it. Report
February 26, 201412 yr comment_625191 Will this be the right tool to measure the bias voltage: http://www.fluke.com/fluke/auen/accessories/high-voltage-probes/80k-40.htm?PID=55357 Report
February 26, 201412 yr comment_625265 No need for that, just measure before the ballast resistor i.e. the resistor next to the bias output. Report
February 26, 201412 yr Author comment_625289 but that actually would work other than it divides by 1000 so you have to put it on the millivolt range. and you need to keep it away from steve Report
February 27, 201412 yr comment_625363 One more question for you guys: what is min voltage rating for 5pF comp. cap, C1 & C2? Will 500V good enough? Report
March 3, 201412 yr comment_625950 Guys,Can someone tell me if Kevin's Current Domain Electrostatic Amp that appears on Headwizeis the same as what is known as the KGSS.Les Report
March 3, 201412 yr comment_625974 Thanks Kevin.Can anyone enlighten me in regards to following behaviour of my KGSS. I built this back in2000.All supplies are stable and I carried out Kevin's setup.Set the first pot for zero volts on meter between + and - Outputs.Set second pot for zero output at + and Ground.Reset these after running for 30mins.After doing all of this I watched the both meters and meter between + and - varies between-100mv and 500mv while the other one reads about 1.0v even though both of these were set initiallyat 0.Both channels experience the same effects and both never get greater than 1 volt over 1 hour.Is normal for the amplifier?. It sounds GREAT.Appreciate any comments.ThanksLes Edited March 4, 201412 yr by iwik Report
March 4, 201412 yr comment_626107 Yup, normal drift and warm up found in all circuits. Edited March 4, 201412 yr by spritzer Report
March 4, 201412 yr comment_626156 Got my off-board PCBs back from the fab. Thank you Kerry for sharing your design. I have made a few changes to go with my plan. Actually, I'm making both on-board (standard) and off-board version of the amp. One will stay at home, while the other one may go to my office. Report
March 5, 201412 yr comment_626272 My only problem is the cost... http://www.ebay.com.au/itm/New-High-Voltage-probe-40KV-DC-28KV-AC-1000Mohm-input-1000-1-4-multimeter-warran-/180775974394?pt=AU_B_I_Electrical_Test_Equipment&hash=item2a171675fa Report
March 25, 201412 yr comment_629158 jeebus, that makes me want one. Well this does seem to fit, if a bit cramped... Report
March 25, 201412 yr comment_629160 if you cased the transformer on top that would free up some space, not that you need it Report
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