Hi Valery,
When I first disconnected R36/R37 on the one board worked flawlessly. I then disconnected it and hooked up the other board and it didn't work with the same modifications. When I hooked the first board back up it no longer worked.
Looking at the circuit, removing R36 & R37 just puts C23 and C15 in series and well as C24 and C26. Could it be that these are now of improper values?
When I first disconnected R36/R37 on the one board worked flawlessly. I then disconnected it and hooked up the other board and it didn't work with the same modifications. When I hooked the first board back up it no longer worked.
Looking at the circuit, removing R36 & R37 just puts C23 and C15 in series and well as C24 and C26. Could it be that these are now of improper values?
You can actually jamper C25, C26 and try using 22pF for C23, C24.
I have tried to switched the OPS to slewmaster-based 3-pairs IRFP here again - it works flawlessly. It's a mystery. I continue researching it...
This doesn't make sense. If yours works I need to get mine set up exactly the same as yours. I must have something wrong on my board. I am going to pull all the caps and replace them. Those are the only components I can't verify in circuit and I want to be sure about them before I make any more changes. I had a really hard time identifying part numbers when I first populated these boards because the screen print was so hard to read. Now that I have a better one to go by I'm going to go ahead and replace them.
I'll report back once that's done.
Thanks, Terry
I'll report back once that's done.
Thanks, Terry
Hi Valery
I also find the custom components awkward, not very portable so I have not studied them much.
To make this work I would need some sub-circuit information, also an entry in the symbol file I think, I will check exactly what I need.
In the mean time, it is possible to look at the main TMC loop, if you move the probe to the NFB line before the TMC resistors.
That is, in the NFB line on the other side of the junction of R36 and R37 to where you have it.
The altered position shows the effective Return Ratio around the OPS.
This will be informative for the simple case with no C27 and C28 (Miller Input Compensation).
Once they are added then you need a balun and Tian probe.
Best wishes
David
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Valery,
I've looked at Bimo's LTspice files and I think the only non-stock element is the potentiometer. He probably used the symbol and subcircuit from the Yahoo LTspice users group. Attached in a ZIP file are the symbol (potentiometer.asy) and subcircuit (potentiometer.sub) files. These should be copied into the default LTspice folders lib/sym and lib/sub respectively. Then you can attach the potentiometer part to the .asc file.
I hope this helps.
Ray
EDIT: You can also place the symbol file into one of the lib/sym subfolders, like the lib/sym/Misc folder. You can then find the potentiometer part in that folder. Misc is also where the LTspice triode symbol is located.
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I was just playing with my Krypton-V IPS through the lateral OPS and I'm seeing a similar oscillation so now I'm wondering if some of this oscillation issue I'm having may be OPS. I don't have time tonight but I'm going to investigate some more tomorrow with some different OPS to see if I get the same results. I'll report back.
Thanks, Terry
Thanks, Terry
Hi Terry, also, one of my thoughts with regards to this was an idea to increase the 2SK1058 gate-drain caps from 220pF to, let say, 330pF, and/or adding some 100pF caps to the opposite side (2SJ162 gate-drain).
We've got some difference in the output transistors (slightly different biasing), so maybe their input capacitance is also slightly different...
Cheers,
Valery
Hi David,
We can actually drop TMC for now, just removing those 1K resistors. I mean - it increases performance at the higher end of the audio frequency range, but we can try to simulate the circuit stability-wise without it first.
My prototype stays stable with or without TMC. I only get some low-level (1V RMS) oscillation if I remove the gate-drain caps from 2SK1058, but this one seems to be a local OPS issue. With the caps in place - no problem.
I'm puzzled trying to understand the difference between my build and Terry's build...
Cheers,
Valery
I need to do some more investigation. I will try a few more IPS with this OPS. I'm getting too many variables. I need to do this a little more scientifically. I hate to think I have been doing all these changes to the Tubsumo only to find it is the OPS.
I'll report back in the morning.
I'll report back in the morning.
I just looked back through the Slewmaster thread where I was testing the small lateral MOSFET OPS that Jason was helping me design. I looked at the screenshots of the oscillation I was seeing on my scope and it looks almost exactly like what I have been dealing with here. On the little OPS I ended up with 470R on the 2SK and 330R on the 2SJ. IIRC, I removed the 330pf cap.
I'm going to try the offset in Gate resistors and see what happens.
Blessings, Terry
I'm going to try the offset in Gate resistors and see what happens.
Blessings, Terry
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Hi Valery,
I know we're 13 hours apart so you are probably sleeping right now but I thought I would give an update. I hooked up a CFA-XH IPS to this OPS today and it played perfectly. No oscillation. I played it for about 3 hours and it sounds great. I just went back out and hooked up a Symasui IPS and what do you know, oscillation. Not quite as pronounced as with the Tubsumo but definitely there. So I'm thinking I need to start there before I try anything else with the Tubsumo IPS. I didn't realize that we had used different MOSFETS. On the mini lateral OPS, adding the 330p caps to the 2SK channel worked, but I ended up removing that and changing the gate stoppers to 330R on the 2SJ channel and 470 on the 2SK channel. Since we already have the 330pf on the 2SKs and that doesn't seem to be enough, would you suggest different caps or should I try upping the gate stoppers on the 2Sk1058 side?
Thanks, Terry
I know we're 13 hours apart so you are probably sleeping right now but I thought I would give an update. I hooked up a CFA-XH IPS to this OPS today and it played perfectly. No oscillation. I played it for about 3 hours and it sounds great. I just went back out and hooked up a Symasui IPS and what do you know, oscillation. Not quite as pronounced as with the Tubsumo but definitely there. So I'm thinking I need to start there before I try anything else with the Tubsumo IPS. I didn't realize that we had used different MOSFETS. On the mini lateral OPS, adding the 330p caps to the 2SK channel worked, but I ended up removing that and changing the gate stoppers to 330R on the 2SJ channel and 470 on the 2SK channel. Since we already have the 330pf on the 2SKs and that doesn't seem to be enough, would you suggest different caps or should I try upping the gate stoppers on the 2Sk1058 side?
Thanks, Terry
Hi Terry,
Woke up early today 🙂
The difference in input capacitance we are trying to balance out is around 300pF, however, it may vary to one or the other side, so you can try to increase/decrease the caps value in the range of 220pF - 680pF. On the other side, p-channel (SJ) may also come up with some local oscillation, although its input capacitance is higher, so you can try to add some 47pF - 100pF gate-drain right on its pins.
With my particular transistors 220pF on the n-channel (SK) side work very well, but it looks like it may vary and I don't have more clever method of determining the right values except just trying them out, adjusting to one side or the other 🙂
The gate stoppers increase also worth trying, although I would use 680R as a maximum value.
I have tried this OPS with Low TIM hybrid IPS - no problem, just had to slightly increase the VAS current - at 7.8mA it did not even require re-biasing.
Cheers,
Valery
Woke up early today 🙂
The difference in input capacitance we are trying to balance out is around 300pF, however, it may vary to one or the other side, so you can try to increase/decrease the caps value in the range of 220pF - 680pF. On the other side, p-channel (SJ) may also come up with some local oscillation, although its input capacitance is higher, so you can try to add some 47pF - 100pF gate-drain right on its pins.
With my particular transistors 220pF on the n-channel (SK) side work very well, but it looks like it may vary and I don't have more clever method of determining the right values except just trying them out, adjusting to one side or the other 🙂
The gate stoppers increase also worth trying, although I would use 680R as a maximum value.
I have tried this OPS with Low TIM hybrid IPS - no problem, just had to slightly increase the VAS current - at 7.8mA it did not even require re-biasing.
Cheers,
Valery
Hi Valery,
Obviously, the outputs you used are closer to the 330p difference than mine. I think tomorrow I'll try the gate resistor change and see how that goes. On the mini I used 330R and 470R. Since these are 220R I'll try increasing to 330R on the 2SK channel and see how that goes. Do you think I should have some capacitance, maybe the same on each side, along with the resistor change?
Thanks, Terry
Obviously, the outputs you used are closer to the 330p difference than mine. I think tomorrow I'll try the gate resistor change and see how that goes. On the mini I used 330R and 470R. Since these are 220R I'll try increasing to 330R on the 2SK channel and see how that goes. Do you think I should have some capacitance, maybe the same on each side, along with the resistor change?
Thanks, Terry
You're mentioning 220R - just to clarify, I'm using 470R for all the stoppers (and 220pF G-D caps om N side). Is this what you started with?
With regards to the different stopper R values for N and P - I would first start with no caps at all and then try adding to N and then to P side...
With regards to the different stopper R values for N and P - I would first start with no caps at all and then try adding to N and then to P side...
Sorry, you're right, they are 470R. I was looking at the screen print on an empty board. Would you go up to 680R and K channel or down to 330 on the J channel?
Thanks, Terry
Thanks, Terry