blubliss Posted October 12, 2011 Report Share Posted October 12, 2011 Yeah, PSU repair will cost you extra I think that is the law with Mouser orders, that there is always one more thing which needs to be ordered the day after you've placed a huge order. I truly hope this resistor thing is the problem everyone is having. It was the last thing I replaced (well, excepting the pot) after a month of replacing other parts and pulling my hair out. And I so wanted to keep my pretty PRPs Quote Link to comment Share on other sites More sharing options...
spritzer Posted October 12, 2011 Author Report Share Posted October 12, 2011 (edited) One can always find some other use for those PRP's. Edited October 12, 2011 by spritzer Quote Link to comment Share on other sites More sharing options...
Inu Posted October 12, 2011 Report Share Posted October 12, 2011 I am using T2 three to four times/week since I build it but I have no noise issues after I modified around the pots. I used TAKMAN REY for the most part. Quote Link to comment Share on other sites More sharing options...
blubliss Posted October 12, 2011 Report Share Posted October 12, 2011 Thanks Inu. I seem to recall some early pictures from your build with PRPs in the batteries. Is that not correct or did you change those? Anyways, it seems there are some strange interactions between the resistors and pots in the batteries going on. Quote Link to comment Share on other sites More sharing options...
Kerry Posted October 12, 2011 Report Share Posted October 12, 2011 I tried most of the circuit changes that Inu suggested to the batteries and still had the noise issue (didn't remove the 2K pot, RV1, from the circuit, but i did completely remove RV2 and used fixed values) - I'm using PRP resistors. I've got some GR grade 2SK246 that I'm testing separately first. I'm going to put them in on one channel. If that doesn't work I'm going to get both Dale and and Xicon resistors and replace them out in the batteries. I prefer the Dale as well, but it seems like a bit of experimentation might be in order here. Thanks to Blubliss for posting his results. Quote Link to comment Share on other sites More sharing options...
Kerry Posted October 12, 2011 Report Share Posted October 12, 2011 ...Could be the resistors but Kevin suggested 3675's which were borderline that could be the cause. I checked the 3675's for the batteries before I put them in. I picked ones with higer hfe (70 or so) for the batteries. What were you looking at when you measured these transistors? Quote Link to comment Share on other sites More sharing options...
spritzer Posted October 13, 2011 Author Report Share Posted October 13, 2011 Highest Vbr to make sure the parts weren't marginal. I never tried it though, it just went on my gigantic to-do list. As Kevin pointed out to me, the much higher inductance of the Xicon's (compared to the PRP and Dale's) might help to kill the oscillation causing this noise issue. Quote Link to comment Share on other sites More sharing options...
kevin gilmore Posted October 13, 2011 Report Share Posted October 13, 2011 I am using T2 three to four times/week since I build it but I have no noise issues after I modified around the pots. I used TAKMAN REY for the most part. You are not using it enough. Should be 6 or 7 times a week. Quote Link to comment Share on other sites More sharing options...
chinsettawong Posted October 13, 2011 Report Share Posted October 13, 2011 I just want to reconfirm Andy's solution of solving the noise issue. I've changed out all the PRP resistors in the active batteries and replaced them with 1% Royal resistors (Thai brand). After that is done, there is no more noise. The amp is dead quite. The voltages from all active batteries are very stable, and it is very easy to adjust the output +/- voltages to be close to 0. Wachara C. Quote Link to comment Share on other sites More sharing options...
spritzer Posted October 13, 2011 Author Report Share Posted October 13, 2011 ...goes off to place yet another Mouser order this month... Quote Link to comment Share on other sites More sharing options...
pedefede Posted October 13, 2011 Report Share Posted October 13, 2011 (edited) This week i finally had some time, so i did the last checks - and powerd on the amp!! At first instance, some LEDS didnt wanna light ... and it looked much like Inu's problems described in post 1131. And while debugging, a spark went off ... so it seems like I also failed to face Mekka ... Anyway - checked all semiconducters, - most seemed OK. Replaced a J79, and D6,7,10,11 I fired (the left channel of) the beast up again this evening - and all LEDS light now - except D10 (which is shorted again). - minus side is adjustable - battery adjustable and ok - but plus side cant get above -320V, battery is adjustable and ok (wierd, since its the CCS for EL34 at plus-side thats bugged.) - FETS seems fine ... from a quick check - the 6dj8 cascode stage seems to works nice ok - Q24, J79 only has -485 V (instead of 450) - R56-at -462V and R57 at -307V Will check Qs around D10, - tomorrow. Edited October 13, 2011 by pedefede Quote Link to comment Share on other sites More sharing options...
kevin gilmore Posted October 14, 2011 Report Share Posted October 14, 2011 So i finally had a few minutes to test the prp resistors last night and while you can put 350 volts across them, and they are stable, If you put them very close to the ground plane, they leak current thru the covering on the film. So the prp's probably work if you lift them off the board say .125 inch. But really there is nothing wrong with the xicon's. Quote Link to comment Share on other sites More sharing options...
pedefede Posted October 14, 2011 Report Share Posted October 14, 2011 Replaced the D10 and "rebooted". Same problem, battery adjustable to 740V, but out-minus can only be adjusted up to -320V Everything lights - except now D24 doesnt (but it does work, and have correct Vf). So it seems, that the problem is the CCS around Q30 and Q31. I tried to test it, and it behaves a bit wierd. I put 0,5mA through top of D24 (as R60-61 will do), - but then you only get 1,5mA though Q31. And the voltagedrop across D24 is only around 0,7v instead of 1,8V The other side (Q30) and other channel (not yet powerd up) behaves similar. Any ideas? Quote Link to comment Share on other sites More sharing options...
kevin gilmore Posted October 14, 2011 Report Share Posted October 14, 2011 chinsettawong used the wrong led's the first time. Evidently that makes a huge difference too. The led's need to be 2.1V Quote Link to comment Share on other sites More sharing options...
spritzer Posted October 14, 2011 Author Report Share Posted October 14, 2011 But really there is nothing wrong with the xicon's. ...but... but... they aren't red and purdy... My main issue with them is the max working voltage of 350V. Spend a little more and the Vishay CCF60 have a max working voltage of 500V with almost as many values available. Quote Link to comment Share on other sites More sharing options...
luvdunhill Posted October 14, 2011 Report Share Posted October 14, 2011 ...but... but... they aren't red and purdy... My main issue with them is the max working voltage of 350V. Spend a little more and the Vishay CCF60 have a max working voltage of 500V with almost as many values available. Actually, the max working voltage is <= 500V Quote Link to comment Share on other sites More sharing options...
kevin gilmore Posted October 14, 2011 Report Share Posted October 14, 2011 depends on which of the prp resistors and which wattage size. There is no spec between any wire and the closest possible physical ground. There actually can be up to 540 volts from the one end of the battery resistors to ground. Quote Link to comment Share on other sites More sharing options...
spritzer Posted October 14, 2011 Author Report Share Posted October 14, 2011 Yeah, that's why the 350V spec scares me a bit. Should be fine though but it is certainly worth a try to lift up the PRP resistors and see if that changes anything... Quote Link to comment Share on other sites More sharing options...
Horio Posted October 14, 2011 Report Share Posted October 14, 2011 So i finally had a few minutes to test the prp resistors last night and while you can put 350 volts across them, and they are stable, If you put them very close to the ground plane, they leak current thru the covering on the film. So the prp's probably work if you lift them off the board say .125 inch. But really there is nothing wrong with the xicon's. So is there a possibility of the same noise issues on the KGSSHV if I used PRP resistors mounted flush against the amp boards? Quote Link to comment Share on other sites More sharing options...
Kerry Posted October 14, 2011 Report Share Posted October 14, 2011 Yeah, that's why the 350V spec scares me a bit. Should be fine though but it is certainly worth a try to lift up the PRP resistors and see if that changes anything... I have the PRP resistors lifted by about .05". That's less than half of what Kevin was recommending, but the solder mask should provide a barrier as well. I've ordered the Xicon resistors and will change them out next. So is there a possibility of the same noise issues on the KGSSHV if I used PRP resistors mounted flush against the amp boards? I would always recommend lifting the resistors off the board for high voltage applications. That being said, I believe the noise issue here is very specific since it is amplified by 113 and then again by 1000. Microvolts here become big issues. Quote Link to comment Share on other sites More sharing options...
spritzer Posted October 14, 2011 Author Report Share Posted October 14, 2011 I don't have any noise issues with PRP's in the KGSSHV. My issues are all with using 10M90's in the CCS... Quote Link to comment Share on other sites More sharing options...
Milosz Posted October 14, 2011 Report Share Posted October 14, 2011 I ordered the rest of the stuff -all the passives etc- the other day. The BOM I was working off specified Xicon resistors, I guess this was Kevin Gilmore's BOM. Also, my practice has always been to give parts a little "longer legs" up off the PCB ground plane if voltages are more than, say, 200 V.- unless it's a VHF, UHF or microwave circuit. Insurance. I've got all the parts now except the chassis and the STAX SOCKET. The chassis, I have ideas. But where to get the STAX 5 pin socket? Quote Link to comment Share on other sites More sharing options...
pedefede Posted October 15, 2011 Report Share Posted October 15, 2011 chinsettawong used the wrong led's the first time. Evidently that makes a huge difference too. The led's need to be 2.1V I used the LEDs from the Mouser-BOM: 859-LTL-4213 In the datasheet: http://datasheet.octopart.com/LTL-4213-Lite-On-datasheet-125834.pdf they are indeed specified at 2,1V at 20mA, but the operating voltage in T2, they work at 0,5mA - where Vf is down to around 1,82V (see page 4 on datasheet) Quote Link to comment Share on other sites More sharing options...
kevin gilmore Posted October 15, 2011 Report Share Posted October 15, 2011 Those voltages are correct with those led's. Quote Link to comment Share on other sites More sharing options...
Kerry Posted October 20, 2011 Report Share Posted October 20, 2011 :prettyprincess: I replaced two resistors in the batteries and the noise is almost all gone (very, very slight now). When I originally did the build I used Xicon resistors for R39 (62K), R43 (390K) and R44 (390K) just because I couldn't get the PRP. The rest were all PRP. This setup had a lot of noise. I just replaced R33 (820K) & R34 (820K) with Xicon's (no other change) and the noise is way, way down! I think the relevant resistors are R43, R44 and R33, R34 since they see the highest voltage differential. Seems like the PRP were either leaking or breaking down very slightly. It's odd because the data sheet says they are good to 500V for the 1/2 watt version. Needless to say I am very happy! :prettyprincess: Quote Link to comment Share on other sites More sharing options...
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