powertoold
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Posts posted by powertoold
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Hopefully this helps someone in the future.
My 500V offboard KGSSHV (running at ~10mA, 100R for the current adjusting resistors) developed some grainy distortion on the left channel (only with some low bass reverb frequencies). After replacing all sorts of parts, I found that the distortion was due to the IXYS transistors.
I had bought 2x IXTP01N100D from Mouser in June 2020 and 4x in Jan 2021. It turns out both of these sets were "bad" parts, symptoms below:
1) Offset voltage on left channel started at around +35V and drift upwards to around +70V
2) There was no way to lower the offset voltage, as the trimpot was maxed out
3) The sound was a bit metallic from the left channel
4) The volume was a bit lower than normal
Fortunately, spritzer sold me some of his old stock IXTP01N100D, and after replacing the new IXYSes with spritzer's old stock IXYS, all of the symptoms went away, and the amp sounded "normal" again.
With the old stock IXYS:
1) My offset voltage started around -35V and then drifted towards 0V
2) Amp seemed cooler to the touch
BTW, I think the 500V KGSSHV offboard at 10mA is the best pairing for the 007 mk1.
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Just in case anyone needs this for future reference, I've posted the tracings of the 0.4 and 0.5 offboards. The difference is shown near the purple dot.
The front side of the boards are identical to me. Also, there's no need to cross the diodes or the 50K resistors on the 0.5. This means there's no need to flip the 0+ and O- as well.
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1 hour ago, hhobeika said:
I am not sure if it was corrected in rev 0.5 but it should be easy enough to check by comparing the PCB traces between rev 0.4 and rev 0.5 if you have both.
I see, thanks! I'm not very knowledgeable with circuits, so I'm just making sure my thoughts are correct before something blows 😅
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My 500V offboard kgsshv currently has two rev 0.4 amp boards and a rev 0.6 power board.
I am looking to swap one of the rev 0.4 amp boards to a rev 0.5 board.
When I change from a rev 0.4 to a rev 0.5 amp board, I will need to:
1) Not cross the 50K resistors
2) Not cross the 1n914 diodes
3) Not flip the O+ and O- bias outputs
Is this correct and also is there anything else I need to do when going from rev 0.4 to rev 0.5 boards?
Thanks y'all!
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Just to update anyone who happens on my issue in the future:
I wasn't satisfied with the new C4686s from eBay (sound seemed a little more "metallic" and the transistors have questionable authenticity), so I took a risk and switched back to the old C4686s, and the initial distortion problem is now gone. So I'm not exactly sure what was the cause. The only new part on the board is the Offset Trim Pot.
Now, the sound is back to its former glory, and I'm very happy.
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9 hours ago, Pars said:
Lots of peeps have had problems with Dalbani selling fake shit. I'm not so sure I would be so quick to think the Mouser IXYS parts are your problem... possible, but not likely.
Thanks. Yes, what I ended up doing was mix and match older looking C4686s with "real" looking Dalbani C4686s, lol.
The reason I think the IXYSes were the culprit was that I tried old C4686s + old pot + new IXYSs and wasn't able to get the offset bias below 60V. Only after using the old IXYS was I able to, regardless of old or new C4686s.
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13 hours ago, kevin gilmore said:
if the thermal grease really is the color of artic silver, that stuff is electrically conductive. causes all sorts of problems.
I took a picture of it here. You can see the contact isn't that great either.
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On 6/15/2020 at 9:06 AM, mwl168 said:
IIRC, significant voltage is dropped in the chain of R26 and VR1 and I am wondering, depending on where VR1 value is set, if one of them is overly stressed beyond its rating and causing some issues.
Just wanted to update everyone on the amp.
About 2 weeks ago, I started trying to replace the MOSFETs and c4686 transistors on the left channel. I also bought a new 1K pot and 2 ixys chips from mouser.
When I initially removed the amp board from the case and looked at the existing c4686 transistors, it seems like the heat conducting material (looks like Arctic silver) was lightly applied to the back of the transistors and was therefore not dissipating the heat well. This led me to speculate that overheated c4686 transistors were the culprit for my left channel distortion.
I also bought some new c4686 transistors off dalbani on eBay. I don't know the authenticity of these transistors. When I received the transistors, they had different fonts on some of the transistors, so I wasn't very confident.
When I started replacing the parts on the left channel, I replaced both the MOSFETs and all of the c4686 transistors along with the 1K pot. Unfortunately, after doing this, the left channel offset bias couldn't get under 70 or 80 volts no matter how much I adjusted the 1K pot. This led me to believe that maybe the transistors I got off of eBay were fakes.
Long story short, I made all manner of component replacements and configurations in order to troubleshoot this issue. After about seven or eight attempts at replacing various components with new versus old parts, I finally found that the IXYS MOSFETs I got from mooser were the culprit for the bias offset voltage problem. This was very bad luck because I hadn't expected that I would be getting a bad part from mouser.
I was lucky in that I was about to give up on the amplifier because having to solder and desolder off-board transistors is a PITA.
Tldr: mouser sent me some bad ixys MOSFETs, leading me to try all sorts of component replacements in order to resolve the problem. The irony is that I actually liked the semi-distorted sound more than the clean sound I have now.
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11 hours ago, mwl168 said:
Hmm, what’s the voltage drop and dissipation on R26 and VR1 when you adjusted the offset to 0V?
I'm not really comfortable working with a live circuit right now, as I don't have any experience building amps 😅
I have the tools necessary to replace parts, so I'm trying to go that route first. I'm fairly certain that my issue is related to a failed or overheated component, as the amp was working fine until a month ago. Also, my right channel has no issues.
As for R26, are you implying that it's necessary to make changes or check on R26 when changing R5/R6? I've searched this thread about changing R5/R6, and other than your post, I didn't see anyone else talking about R26.
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41 minutes ago, mwl168 said:
Ok, that makes sense.
When you increase the output device bias current, you need to tweak the offset adjustment chain (R26 and VR1 - 2K and 1K respectively in the schematic) so you can adjust the offset close to 0V. The easiest thing to do is to decrease R26 but make sure the voltage drop is somewhat even between R26 and VR1 so they are not stressed.
I posted earlier in this thread of a similar effort I made on my build: https://www.head-case.org/forums/topic/8327-im-on-a-roll-the-kgsshv/page/187/
The goal is to get the offset and balance close to 0V as possible. They will drift a bit and that's normal.
Perhaps there is some misunderstanding here. With 100R on R5/R6, I am able to adjust my balance and offset close to 0V. However, if I do so, there is some distortion in the 20-200hz low frequency region (only in the left channel, right channel is perfect). Also, the amp sounded great for 2 years with 100R and only started developing this distortion in the last month.
To reduce this distortion, I would have to adjust the offset voltage to around +70V on the left channel.
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12 hours ago, mwl168 said:
I've asked this question before - what's the lowest offset voltage you can adjust to with the higher bias current of the output devices (lower R5, R6 values)?
I would first get the offset and balance to reasonable range and see if that affects the distortion issue you are experiencing. If the amp is set up properly you should be able to get both to below 1V easily.
If the amp was originally set for lower bias, increasing the bias current may cause the amp to run out of offset adjustment range without making change to the offset adjustment circuit.
With 100R, the lowest offset voltage I can adjust to is +70V. At this voltage, the distortion is barely audible. With 180R, I can set the offset and balance as close to zero as possible, and there’s no audible distortion. Using a trimpot adjustment tool, I’ve adjusted the offset voltage while music is playing and didn’t hear any static while adjusting the pot, so it doesn’t seem like the distortion originates from a noisy pot?
The distortion is also reduced when I adjust the balance voltage (although I forget if more positive or negative).
I’m willing to replace whatever parts would be likely causing this problem. I hope to narrow it down, so I don’t have to replace everything on the amp board 😅
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Hi everyone,
I originally posted about this issue in the Carbon thread, but it's more appropriate here.
After 2 years, my 500V off-board kgsshv started developing left-channel distortion (sounds like sand in a cardboard box) with certain frequencies (only audible when music is playing and more audible with higher volume). I believe this is a result of increased current (100R in R5/R6) and overheating (for a short time, I had kgsshv sideways with the left channel board on top).
The distortion is reduced with any of the following steps:
1) Increase left-channel offset bias voltage to ~70V or higher
2) Change R5/R6 back to 180R
The distortion is present immediately at power on (cold), and doesn't get much worse with warm amp.
My issue now is that the higher current sounds much better (microdynamics and "thickness") to me (100R at R5/R6), so I'd like to figure out how to fix the distortion by replacing components. I can't live with the stock current, and this kgsshv has sentimental value to me and some others on this forum
My question is
1) What are the most likely components causing the distortion? I was thinking the resistors or the IXYS mosfets.
2) When the amp is warmed up, I notice that the heatsinks near the right channel are warmer (2x by feel) than the left channel. Is it possible that the thermal interface between the left-channel mosfets and heatsink is compromised?
Thanks all!
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This is regarding the KGSSHV (non-Carbon) issue above:
I think I resolved the static / distortion issue. I had essentially doubled the current to ~10mA by adding a parallel 200R resistor to the 180R. I removed the parallel resistor, so the amp is now "stock." After I removed the parallel resistor, static / distortion isn't audible (yet). Thanks all.
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17 hours ago, jose said:
What have you used as input devices?, Were they macheted? do you have the transformer near the inputs? ....
I've used 2 different DACs and also played from several different source files. The static increases with higher volumes and is only audible during "difficult" resonant frequencies (such as reverb from guitar strings).
19 hours ago, Pars said:From the schematic I have, the 500K resistors are from the inputs to ground, so would be in parallel with the volume pot. See if that value changes as you move the pot from 0 volume to full.
That said, measuring resistors in circuit will give you sometimes strange results as you don't know the exact interactions with connected components. Also, ohming out resistors for what is suspected to be a leakage problem won't really tell you anything.
Can you post detailed pics of the amp boards? Are the resistors lifted off of the board, or installed right on the surface? And what is the origin of this KGSSHV? i.e. who built it?
As far as I know, the resistors are installed on the board's surface. This KGSSHV (non-Carbon) was made by Horio / TMoney I believe. Everything seems well-built, and the heatsink is massive.
It'd be great if there was something I could try that doesn't involve replacing components (to troubleshoot or eliminate the static).
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I tested almost all the resistors on both channel boards, and the resistance on both channels are similar. However, there were some odd measurements:
The 500k resistors were each measuring 1k on both boards.
One set of 175k resistors (sorry I don't have a diagram of the R numbers) start measuring at around 100k and slowly drift to 120k. This was true for both boards.
Overall, the measurements were essentially identical on both boards. I'm using a Klein Tools M400 DMM. At this point, I'm setting the offset on both channels at around 100V and just using the amp that way, since at 100V the static isn't audible so far 😅
I just don't have the tools or know-how to replace those odd-measuring resistors, since it's an off-board KGSSHV with the amp boards glued to the heatsinks.
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Thanks all,
I can hear this type of static with both my 007 and LNS, so the problem likely originates from the KGSSHV.
I'll try to check the resistors that sorenb mentioned. I'm assuming this sort of issue isn't likely to originate from the power supply board.
My KGSSHV uses PRP metal film resistors. I don't think they have a good reputation on this board 😅
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Hi all,
I have a KGSSHV (not carbon) 500V that has developed some low-level static / distortion with certain resonant frequencies on the left channel. I'm fairly certain it's caused by the KGSSHV since the static is reduced when I adjust the offset voltage to be more positive (currently at 40V offset; I believe ideal is 0V offset and 0V balance).
Would anyone have any insight into what is causing this static / distortion, especially since it is reduced when I make the offset voltage more positive?
Thanks!
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In my experience (could be placebo), even correcting the voltage balance and offset, a warmed up 500V KGSSHV will sound better compared to cold.
That is to say, a servo wouldn't improve the sound much if the amp is cold.
Does that sound about right in your experiences?
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At lower volumes, do balance and offset voltages that are farther away from zero make a bigger difference vs higher volumes?
For example, my 500v kgsshv is usually ~2v away from 0 for balance and offset. If the left channel is negative 2v and right channel is positive 2v, would that be audible at low volume and not higher volumes, or is it always 4v/500v difference at any volume, which is less than 1% between the channels?
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It'd be great if someone with a 007mk1 can compare the subbass quantity vs the 009S with dance music. I can't live without the 007mk1's bass
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This has been addressed before, but for the YOLO types, if you take off the black cloth debris cover on your 007, the clarity improves by 10-15%, which is very significant. Do it at your own risk though.
I love my kgsshv + 007mk1 so much. I can't thank Stax and KG and spritzer and the community enough. My system has become my most cherished possession by far. It's been a long journey where I didn't believe perfection existed, until now
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In my experience, channel imbalance has been a problem predominantly with the Omega type drivers. Stax and channel imbalance seem to go hand in hand unfortunately.
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It's quite a shame, considering the Stax high end sound is basically "perfect" and "worth it" if you take care of the equipment to last 10-20 years. You can spend ~$6k on a system that provides 15 years of enjoyment, granted no technical issues appear with the headphones heh
I guess headphones will always be niche because it messes up your hair
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I was surprised when I saw Stax's sales numbers, assuming they are true. $1.3 million a year is only 325 SR-009.
i'm on a roll... the kgsshv
in Do It Yourself
Posted · Edited by powertoold
I don't have a means to test the IXYS transistors I got from Mouser. The Jan 2021 ones I got from Mouser are lot TS1811 S23728.
If y'all got a 500V with IXYS and offset voltage problems, perhaps you have these problematic transistors as well. The amp works and all. It just doesn't sound or measure like what it's supposed to.
Edit: on closer inspection, it seems the parts I bought in June 2020 and Jan 2021 are the same lot number.