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About Tinkerer

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  1. 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.
  2. 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?
  3. 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.
  4. 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.
  5. Much appreciated. If I'm lucky, parts will get in Saturday and I can give an update.
  6. The V2 Output boards don't have servo output. And the mod you made to feed the servo locally with the diodes and 2M resistors way back on page 3 doesn't work. I've tried it before. That's why I've asked three times how to get the servo to work with the V2 boards, and I still haven't gotten an answer. From what you're saying though, it seems like the cleanest solution would probably be to just take some actual Carbon Amp boards and jumper the headphone ballast resistor spots instead of even having specialized driver boards in the first place. The 4N25's in the V2 Output are brand new as well. But I'll pull them and check both them and the sockets.
  7. Yes. You can see the -15 for the output board is that naked green wire that goes to the GRLV in the bottom of the case. The way it's set up is 1.Servo disconnected on driver board (10k resistor and little parallel cap removed from driver) 2.All wires to correct terminals (Output FB to Driver FB) 3.Current limiting transistor setup on the +900 lines of the HV900. (NO and working, haven't pushed them into shutoff yet) 4.120 ohm current resistors on output board replaced with paired noninductive 62ohm resistors on heatsink (unnecessary if number 3 works but had already spent the money on them so figured why not) 5. Driver set to 10mA each side (as low as it will go), offset controls changed to 200 ohm trimmer and 300 ohm tail to make it zero out Interesting thing. The balance and offset measure from the driver board or the jack on the other side of the output stage is exactly the same. I checked it twice to make sure, but measurements are a lot easier that way. What I'm doing is running driver at full mains (GRHV450 and GRLV15 full up, Driver boards full up, -15 to Output boards) and then using a variac to slowly power up the HV900's for the output stage. With the variac at app. 20VAC into the HV900 transformer, which is the HV900 spitting out about 400VDC IIRC (I really need more meters, three is not cutting it), the read voltage from the output stage test points is over 5.3VDC with the V2 current control trimmer pots at maximum resistance. Which is just about 43mA through the Crees on the Output board. And it just keeps scaling straight up. So my guess, based on the driver trimmers that were a little off what they needed to be from what the silk said (no way I could get 8mA or such without swapping some values around), that the Output V2 boards have a similar issue. I just need to know which resistor and what value. Or maybe it's something to do with the old output stage bias trimmer on the driver board that I still don't know what I need to do with if anything. Short it to ground, leave it be, whatever.
  8. Went ahead and gave the circlotron stage a little juice with a variac with the drivers running so I could set the current. With 123 ohm current resistors, it should be 3.075V across for 25mA I think. With the pots maxed out, it was still running up into the low 40's mA with like 20VAC line from the variac. I didn't run it up any higher than that for fear of blowing something. This another case where the resistors are too low? Should I try swapping the 100 ohm cmf60 tail with a 180 I have laying around or something?
  9. So, I got a little impatient and went ahead and hooked up everything for one channel but didn't power up the circlotron stages to see if the feedback would help stabilize the driver boards. It does, best I've seen. After about half an hour, balance had only drifted .5V and offset only 1.0V. Absolute night and day. Even better than the feedback mods to run the driver as a carbon. Might actually be able to power this thing up without a servo. Since this thread hasn't had any good pictures in awhile. I can show how mine stands at least. None of the wiring has been prettied up. All the previous looming minus a couple small runs had to be removed for the new mods, especially with the current limiters. Same with the paste. Will clean it up better once I'm sure everything is good. I've pulled those brackets enough to stop fooling with it for now. You can't see it very well but the transistors bolted to the sink have their legs bent about 45 degrees away from the sink and are mounted on thick ceramic insulators. The 62ohm resistor pairs that replace the 120 on the circlotron board are insulated and ceramic backed so are bolted directly to the heatsink. Their leads are soldered through the test point holes since the 120 resistor holes are too small for the HV wire. Tail resistor for the offset on the driver board was replaced with a 300 ohm and the pot with a 200 ohm for more range. 10mA is also the lowest the current pots would go on the driver board, so anybody that wants lower will probably have to change some bits. Anything that looks completely stupid and any good reasons I shouldn't be able to power up the output stages with a variac next?
  10. I really need to know how to hook the servo up to the V2 Circlotron stage. There's no opto terminal on that.
  11. Still fiddling with this. Here's my issue. The driver board lights up fine, current is set at 10mA (.5V across the 50 ohm both sides). Balance is within .01 volts. But the offset is still giving me fits. EDIT:Got it working but the drift is like 150V every minute up and down as it warms up. That normal without feedback or servo?
  12. The Headcase Stax thread

    Hey coptician, if you still have your old headband, don't toss it out when you get a new one. I need the plastic mounts off of it. Shoot me a PM with what you want for it.
  13. I am. Just wanted to be sure. With all the problems this amp has been, I'm beyond assuming what should be correct until I see it power up completely. Edit:looks like the resistor value should be closer to 300ohm. 115 was with the increased current modification.
  14. Kevin said he set it high intentionally in the original stuff so it would kick over the servo, but I agree that I don't think it was intended to be that high. All I know is a vanilla driver board with no connection to an output board has +455VDC offset with positive probe on O+ and negative probe on ground with a 500ohm (silk value) tail resistor. You can get the offset to 0 with a 120-150ish ohm tail resistor. It was just so far off I had to ask if it was intentional for something in the output stage.
  15. Current is only set at 10mA on mine. Kevin said that as the upper value somewhere I think in here. But I can drop it down if that's the recommended value. I paralleled a resistor to the tail resistor before to fix this offset problem when I ran the driver board as a carbon amp. I can find new value that works based on that. But just to double-check, it is supposed to be 0 offset from the driver board to the output board? There's no other stuff there to fool with? Does the feedback from the output board affect the offset at all? I decided to run it that way instead of locally. What about the output bias pot on the driver board and rigging input to the driver board opto servo from the V2 output board?