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Tinkerer

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  1. Would only be able shorten a few things a few inches, so like 12" instead of 16" on some of the HV900 - leads. The way the boards are laid out necessitate most of those lengths, which are pretty darn long. I might have to try shielding some stuff instead, like the really long transformer leads. The audio input stuff already is and are connected to chassis ground. Any good bulk braid cheap? Heck, I was reading that sort of thing might even be that the diode bridges on the HV900's might be damaged and leaking. They're about the only parts I've never replaced on those things no matter how much they've blown because they still work. Need to check if they're leaking AC I guess. Connections are good. Just rechecked all those from stem to stern.
  2. Link to hum. You'll probably need to turn up the volume a bit since it was recorded with a crappy phone mic. https://www.dropbox.com/s/zomvnhpob9d4dx5/hum.mp3?dl=0 Any help you guys can give hunting this down would be great. If I can just kill this hum and be sure I don't have to reduce the current even further on the Output boards because boy do those things get hot in a hurry then I'm in the clear.
  3. EDIT 3: Fixed the balance problem. It's just the driver board has to warm up all the way for it to get near zero on the right channel. Still need to fix the buzz/hum. Will post a video in a second. Sounds like 60hz to me but you guys will know better. Output stage gets damn toasty though. It's the only thing on the front 12x6x3 heatsink and after less than ten minutes, that is hot to the touch at 38mA. Driver/HV900 sink is warm and GRHV/HV900 rear sinks are stone cold. Lot of mass to those things. EDIT: And current front panel with small variacs mounted. Not the ideal solution but it works and looks pretty spiffy.
  4. and now for something completely different part 3

    I've been using Arrow. They usually ship next day and give you free overnight if you spend more than $20 on an order. And regular shipping is still free on lesser stuff which makes it ideal when I'm repairing something and just need a couple bucks worth of stuff.
  5. Works fine at carbon voltages. Barely any flux but it's also hard to clean off as it had to be soldered with the sockets already mounted inside. But then do the output to socket wires need to be 1kv rated? Because they're just 600VDC teflon insulated.
  6. Yeah. The Output stage stays -12 and gates closed until you start to apply the HV900's. Then moves to about -10 then creeps up steadily with the applied voltage until about -5 where the servo keeps it. Well, I tried a small workaround. Got a couple of old unmounted Superior Electric 120VAC 270VA Variacs for cheap and hooked one up for each channel with a temporary cross bar mount. They're small and good quality. Also swapped completely to nylon screws for the Crees on the Output board and added additional isolators to the current resistors as well as swapped the 4N25's for the newer fairchild 4n25-X001 that handles double the current. Seemed to be working fine, but had one of the HV900's start to smoke after a minute. Nothing actually failed Output board wise. I guess that HV900 was damaged after all from the last time that Output blew. Just couldn't tell until it was under load. Gonna have to rebuild that before I try again. Had another important question that might relate to problems. Are the little Stax jack boards rated for this? Because even when I'm powering up a single channel, the noise from the output board bleeds into both channels, and I don't get if it's the jack or the ground or what. Also, what is the sound of the Output supposed to be like as it's powering up? This is how it seems to me, and was this way when powering from the external big variac. 5VAC, quiet but can hear distortion compared to plain carbon 10VAC, regular 60hz hum, can hear repeating pulses in it 10-40VAC, hum gets louder, pulses closer together until they become a continuous single noise, noise equal in both channels despite power only coming from one 40-50VAC, hum goes mostly away, but still there (this would be when the HV900's are hitting about 450VDC) 50-80VAC, hum returns but not as loud as lower voltages 90VAC+, clear but slight underlying hum (HV900's about at full voltage) Does that line up with you guys at all?
  7. Well, some good news some bad news. Did the left channel and slow powered it as well and it worked fine. Then I got everything all hooked up to mains through the relay. Fired it up two stage like you're supposed to. Main switch in the back powers on the GRHV/GRLV and PSU for the LED's and relay and lets everything warm up for a minute. Front panel engages the HV900's for the Output and lights the LED's up. The left channel struggled a little bit but came around. Right sounded like it was struggling, then went severely out of balance and blew. Looks like the right side opto couldn't take the fast power up. Literally blew its top off. Good news is this is the first time I've ever had an Output board blow where both the HV900's are still perfectly intact and functional. Due to the current limiters I guess? That makes them worth the cash right there, a lot better when you only have to rebuild one board instead of three. Going to try buying higher rated DIP sockets and look if there's more robust 4n25's to pick from. Any other solutions? Should I try a themistor or something to force the Outputs to power up more slowly? Like I said, they did work when it was slow and they had time to warm up and let the servo keep up. I just need something that works for a daily amp. It would be silly to have to power up half the thing with a variac every single time I turn it on, though I guess there's room in the case to panel mount one if it really is the only way. Also, I hadn't realized just how much power this thing eats. I was originally going to run it through my 350watt UPC and it threw that into overload without anything else hooked up. Had to actually run it from the wall.
  8. Holy crap, finally got this thing running right after like two years. My last screwup was actually having the multimeters reading voltage at the test points for the current on the output stage as I turned the supply voltage up. The leads were leaking or something even though they were supposed to be rated for that voltage. So when they were getting close to breakdown is when the noise and meters would start acting up. No multimeters attached except for balance and offset at the jack and it powered up perfectly. 60hz hum was entirely from the variac too. Listened to it for about fifteen minutes, left channel as regular carbon (driver + pair of 5k ballast resistors) and right as circlotron, and was impressed I could actually hear the difference. I was just hoping no noise problems at this point honestly. A couple minor notes on stuff that might be helpful for anyone else. In Soren's servo notes, the 5K resistor is the 500 ohm. Probably a 5000 code RN60 or something was the confusion I guess? I just bent the #2 opto leg up and away from the socket and soldered the 200ohm resistor to it directly so I wouldn't have to cut any traces. Everything else went together easy just as written. Almost everything has an open through hole slot from pulled parts or an easy place to hook up under a terminal. While the servo keeps the driver at about dead 0 balance and offset alone, through the output board it sits at about -5VDC offset and .2VDC imbalance. But it keeps it right there so I haven't fooled with it like Kevin recommended. Other than that, since last time I put new DIP sockets in the Output board, moved the sink mounted current resistors to a bracket on the Output board to shorten the wires and reduce the parasitic capacitance and make the output board easier to pull and service. Heat dissipation isn't as good as being directly on the sink, but still plenty I would think. Should hopefully finish all the stuff for the left channel tomorrow and see how smoothly things go when the output stages are turned on at line voltage from the internal relay instead of slow variac power up.
  9. goldenreference low voltage power supply

    I have one in a separate enclosure earlier in the thread. Two foot power umbilical. No problems. Actually, I think a couple of the GRLV15 runs in my Circlotron are even longer because the case is so damn big. No problems there either.
  10. Changed to local feedback on the driver board and that leveled the current out on the output board. Now sits at 4.7V ( app. 38mA) consistently at lower level on the variac and can be adjusted but that's as low as the pots go. Current still starts jumping around and offset as well, once you bring up the AC into the HV900 transformer up to about 50VAC on the 115 primaries. Current swings are worse at those higher levels with the local feedback. I've seen 12V across the 123ohm resistor for a split second before the current limiters kick in. I was getting serious 60hz hum I think from the variac. I could actually feel the coil vibrating through the case. GRHV/GRLV transformer is dead quiet, so I assume the HV900 toroids should be good too. Couldn't feel or hear any vibration in the amp case. Troubleshooting tips at this point? Output boards have brand new 4N25's from my spares. The Cree's on the output are salvaged from old HV900's that didn't blow them when they died. They showed up fine on my tester but could they be damaged and that's why the current is jumpy at higher voltages? Otherwise, same problem as before. Big static pulses that coincides with a jump in current and offset after output boards are about halfway powered up.
  11. Yeah soren, dialed to ground. And thanks for the advice on the opamp Kevin, makes me feel a lot better. I remember my old KGSSHV servo was kind of similar but with this amp I never knew if a few volts offset away from zero might make it explode. Okay, got some good news. Got some music! Some problems with the sound but will get to that in a minute. Brought the Output V2 stage up slow on the variac to be able to set the current. It started working low level as soon as the variac hit about 10AC and made it to line voltage without anything blowing up or any big changes in behavior. I was kind of worried about how when you power off the driver stage you get +350ish offset until the PSU bleeds down, so I powered off the Output stage first and let the HV900's bleed down before powering off the rest of the amp. But I think that the added diodes in the Output V2 are specifically to counter this, right? So no alterations needed? Here's the thing though, the current keeps skipping around a bit. 30-45mA, continuously, doesn't steady out. You'll also hear some static when it moves and the offset will jump a few volts. Kinda sounds like when I had a leaky resistor in my old SRA-12S through the headphones. Similar symptoms too. Static and a change in offset at the same time. That means the driver local feedback is necessary? And could there be a resistor problem? Could the variation be the resistors bolted to the heat sink not maintaining a steady temperature or not being isolated enough despite being an isolated package Also, more good news. The current limiters work. Any time the board was about to bust 47mA from a current jump, the transistors would close and it would take a second or so for them to open back up all the way.
  12. Got the servo working with Soren's new notes. Tried to run global feedback first and servo is sitting right at -4VDC to -5VDC. It gets exactly to -4 after everything warms up for a few minutes. Can somebody explain why it's at that instead of zero or what I should adjust to fix it? I made sure before I engaged the servo that offset was about +14VDC warmed up with global feedback since you're supposed to have about +10 or a little more to kick the OP27G on right?
  13. Still working on things but had an HV900 question, which soren asked a long time ago, but I didn't see answered. How close do the the paired HV900's have to be to each other and how close do the HV900's have to be to the HV450's +/- together. I only ask because one of the HV900's I built with available Dale resistors (used a CMF604K3200FKR664 at a slightly lower value instead of the Xicon) regulates at +905VDC while the others are at +910VDC. GRHV's are +452VDC and -450VDC respectively.
  14. Technical Assistance/Advice Thread

    I'm looking for a mini panel mount voltmeter so I can have balance and offset readouts all the time on the inside of an electrostatic amp chassis. Needs to run on 15VDC or less. Range to +/- 100 would be nice. I see a ton of them around, but nothing that does negative voltages.
  15. Much appreciated. If I'm lucky, parts will get in Saturday and I can give an update.
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