June 14, 201511 yr Author board picture updated, please check with this http://gilmore.chem.northwestern.edu/goldenreferencehvsic.pdf
June 14, 201511 yr Is the filename of the schematic supposed to be "goldenreference"? Edited June 14, 201511 yr by gepardcv
June 14, 201511 yr Insanity said: "Ok I did the following test. When I removed the input wires from both boards, without grounding the inputs, the sizzling channel started sizzling well noticeable, whereas the other channel remained almost silent. Interestingly, when I grounded the inputs from the sizzling channel it was almost quiet, with the sizzling being barely noticeable to unnoticeable. This seems to rule out the elma as a source of the problem. Does this sound more like a problem of the first amplifier stage or another stage? What parts would you start working at? lsk389 and mpsw06? below it? I don't have a scope..." I think the most likely thing is that you have a noisy or leaky input transistor. Here is what I think is happening. Remember that there is a 500k resistor between the input gate and ground. Any current leak into the gate will flow through the resistor to ground, causing noise that will be amplified. When you turn down the volume or short the input to ground that shorts the noise. As you turn up the volume that increases the resistance between the gate and ground which increases the resistor noise. Allen Wright mentioned a similar problem he had with a tube preamp design where the grid current running through the input pot produced noise. The only thing is, if this is the cause, I'm not sure why it is intermittent rather than continuous. However, I would replace the input transistor and see if that solves the problem.
June 14, 201511 yr No, there is one more 100 ohms resistor that goes to the gate of C2M1000... Also, stn9360 base and emitter flipped? Seems true on both of those. From the schematic R1 could go higher to 4K (reduces heat from Q6), R6 could go to 50K, C7 should be as low as possible (5pF) provided it doesn't oscillate. Also, D1 could go higher (100V - 200V). It reduces the noise floor a bit. We might need to add a protection diode across Q6 if you raise D1 to protect on Q6 power off.
June 14, 201511 yr Author fixed the board and the schematic. the 100 ohm gate resistor is a cheat. that and the winding ground on the +/-15 so that it is easier for joamat to make a single sided board without any feedthru's but really the board should be double sided and plated thru holes.
June 15, 201511 yr I was also thinking it might be nice to have more room (larger diameter) for the C4. If we go with a higher value for D1. Maybe slide Q8/9 over to the right a bit. Also, the labels for AC In are set to AC360. This would work good for a 450VDC supply. I think we could use AC325 for the 400VDC supply. Antec makes some nice ones that are inexpensive.
June 15, 201511 yr Ok Jim that sounded plausible. Here is what I did. I stepwise replaced all the transistors that are not mounted on heatsinks, but the problem has not changed. Could a resistor be causing the problem? Or maybe on of the diodes? I cannot imagine how a problem with the 3rd and 4th stage could be so dependent on the volume control/grounding of the inputs. I am confused. Help? Insanity said: "Ok I did the following test. When I removed the input wires from both boards, without grounding the inputs, the sizzling channel started sizzling well noticeable, whereas the other channel remained almost silent. Interestingly, when I grounded the inputs from the sizzling channel it was almost quiet, with the sizzling being barely noticeable to unnoticeable. This seems to rule out the elma as a source of the problem. Does this sound more like a problem of the first amplifier stage or another stage? What parts would you start working at? lsk389 and mpsw06? below it? I don't have a scope..." I think the most likely thing is that you have a noisy or leaky input transistor. Here is what I think is happening. Remember that there is a 500k resistor between the input gate and ground. Any current leak into the gate will flow through the resistor to ground, causing noise that will be amplified. When you turn down the volume or short the input to ground that shorts the noise. As you turn up the volume that increases the resistance between the gate and ground which increases the resistor noise. Allen Wright mentioned a similar problem he had with a tube preamp design where the grid current running through the input pot produced noise. The only thing is, if this is the cause, I'm not sure why it is intermittent rather than continuous. However, I would replace the input transistor and see if that solves the problem.
June 15, 201511 yr Have you swapped the amp boards around? I can’t help thinking this an external issue with the proximity of the amp board.
June 15, 201511 yr I swapped the boards and the problem persists on the same board. I also changed the 1n914 diodes after the lsk389 and the 500k input resistors. No change. Any other ideas where to look? Slowly I am starting to think that this problem has been there all the time since I built the amp, but I have only noticed it when I started turning up the volume a bit, because of my new 007s (which was not necessary on the 009). I initally built the amp with all ixys parts and a few month ago I switched to 4686. Only the current source is still ixys. Unfortunately I cannot tell (as mentioned before) if the problem was already there with the all ixys build. If you recommend replacing the remaining transistors (on the heatsink) I guess I would start with the remaining ixys pair... Have you swapped the amp boards around? I can’t help thinking this an external issue with the proximity of the amp board.
June 15, 201511 yr Author the idea with the new supply is to be able to supply more current for things like the megatron. so for the current limiter to work, that 10 ohm resistor would have to be something like 5 ohms. will look into it later.
June 15, 201511 yr Author no room, but 5.1 ohm resistors are available in 5 watt, so thats about 135ma updated picture, smaller for now, bigger later Edited June 15, 201511 yr by kevin gilmore
June 15, 201511 yr The problem has been solved by replacing the two 100ohm resistors and the 6.8k inbetween. Looks like they may have shorted to ground. Replaced them and mounted them a bit elevated. The smoke took one mpsw56 with it, which has replaced too. Seems to work fine again. No more sizzling...
June 15, 201511 yr Glad to hear you sorted out the issue. As a general rule is important to lift the resistors off the board. This had caused all kind of mischief on these HV builds. Enjoy
June 22, 201511 yr From a thermal and technical point of view, would it be possible to make kgsic boards with onboard heatsinks such as this? FA-T220-64E
June 22, 201511 yr Author the cree part is a to246, so no. besides which people want to run at 20ma or more, and at 450V power supplies that is 9 watts no onboard heatsink I know of is more than about 4 watts
June 23, 201511 yr You can lower the current and the amp performs well at 10mA but it's still a lot of heat. Now we could to a board which would fit some larger heatsink which could be mounted to a board (like the 717/727) but it would be pretty esoteric.
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