s_r
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Posts posted by s_r
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Just the right channel, and it's come and gone up until now.
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Your board version is probably older than mine too, right (production v1.07/silkscreen v1.03)? Either way I'll see how it responds once I've added a second 2.2pf cap.
On that note, what about soldering in SIP sockets to make swapping bypass caps easier?
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Seems like oscillation was indeed the cause of the noise & high offset which has been sporadically happening. Happens now with either tube or solid state input. For reference both channels have 15pf bypass caps across the 100k feedback resistors. What about populating both C12 & C13 with 2.2pf caps? Apparently doing this killed the oscillation in pedefede's T2 a few years ago.
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So after setting up my scope to see if there was any oscillation, the distortion and high offset disappeared. Afterwards the distortion would show up after a few hours of it being on, and it's sometimes cured by just unplugging/replugging the headphones. Feels like I'm chasing after Schrodinger's distortion
Whatever the case, I've put heatsinks on both the 3840s and LSK389s now.
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Haven't checked that yet. Where's the best place to measure that? Could try the +200V output of the battery, or the final output, like the measurements I did some months back.
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The batteries measured fine last I checked, the K216s beside the J79s all measure similarly to each other.
Replace the LF353 maybe?No change after swapping out the LF353 either. -
Tried that just now, and the values between all four seem to be within the margin of error. The two on the right channel measure pretty similarly, while the left two differ moreso, strangely enough.
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Guess I spoke too soon. The exact same behavior is happening again (-70V offset, distortion in the right). Something else causing the J79 to have issues?
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With the solid state input, yes. Both tube sets I have, even the 'low noise' philips, are intolerable to me.
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I've replaced the J79 closest to the front panel now. Seems to have done the trick, offset is now normal on the right channel. No extra noise so far either.
Thanks for the help Craig & JoaMat.
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Did some searching of this thread, doesn't seem like you mentioned which J79 it was. Any way to tell which J79 might be bad without pulling them from the board?
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Was it Q24 or Q25 in your case that had blown? Or did you replace both of them?
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On my right channel issue, I've noticed that the right set of EL34's had a bit of 'ringing' noise to them. So I measured the offset which was about -67V (with no headphones plugged in) vs about +2V offset on the left. It wasn't fully warmed up when I measured this though. Balance was close to perfect (0.1V) if that says anything. I tried swapping left & right sets of EL34s, and using 6DJ8s instead of JoaMats solid state input. No change though. Could the sand responsible for handling the offset just be bad? Or something else?
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Beautiful piece of work, Kerry
In the recent months I've been slowly working on my T2, ended up rebuilding the entire amp board with mostly new parts. Just in the off chance that it was something in the board itself which caused the noise I was hearing. Thankfully nothing blew up, the batteries adjusted to 741V, and it plays music. I could still hear a background noise in it though. Having listened to George's T2 as well I was all but convinced this is just the normal noise level for this amp.
I asked JoaMat about his solid state inputs for the T2, and he was kind enough to send them to me to test out (thanks!). Amazingly enough they worked. The amp is still not utterly dead silent, but it's to the point where it's below the background noise level of my room (which is as close to silent as I can make it). I've also ordered some heatsinks for the 2SC3840s so I wouldn't have to worry about them getting too hot.
With either input set though, I've been having some sporadic noise on the right channel. Sometimes it's a random noticeable "pfff", sometimes it gets stuck noticeably louder. The latter is usually solved by unplugging/replugging in the headphones. Very strange. Aside from an overlooked loose connection or a bad solder joint somewhere I'm not sure what it could be. Anyway please excuse my blurry photos.
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Which parts can be left unpopulated on the carbon v5 board if I don't plan on using either servo? From what I remember the 4N25, OP27, 1uf/50V cap, 200ohm, 5kOhm, two .1uf caps, and one PZTA06 are all for the servos. I forget if the two 1N914s in the corner of the board or the 12V zener beside the PZTA06 were necessary though.
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Picked up a minty carrera reissue at a price I couldn't turn down. Debating whether I should put on a deployant strap or keep the tang & buckle.
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Just received my pots & PCBs, thanks again for this GB.
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I think that's how I did it the first time. Just in case I did it that way just now, but no change in the result.
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Payment sent, thanks.
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5 hours ago, Craig Sawyers said:
Yes I can do that. They key is to measure over that audio bandwidth and the A-weight it. I'll give that a bash tomorrow.
Thanks, I should ask if it'd be something I could repeat with my rigol DS1054Z though.
2 hours ago, blubliss said:Mine is very quiet after using the battery adjustment method Craig articulated in this thread. Before that the amp had some consistent background noise which was livable but noticeable.
I tried a while ago to adjust the battery to see if it would have any effect on the noise. It'd sooner go out of whack than change the noise. Unless there's something I'm missing I'm not sure that's the solution.
1 hour ago, GeorgeP said:I have never heard a stat amp where you couldn't tell if it was turned on or off - ie every one, where it is absolutely silent, will give some extremely light background noise - whether it was a Stax, Mjolnir kgsshv, t2 or carbon. The difference is barely perceptible, but is easier to detect if you place your hands over your headphone cups. Like Andy, my experience with the T2 is that it is extremely quiet. The Carbon is a touch more quiet, but not significantly so.
Right, thanks for clarifying. Without another T2 to compare to it's hard to say whether the noise on mine is higher than what's normal. All I can say is that it's high enough to bother me.
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Boards received, thanks!
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Is there some meaningful way to measure the noise at the output with a scope? To compare what I measure with other T2s would probably answer the question.
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So I had another member borrow my T2 to take a look at it. But I was told that the noise is around the normal level for this amp. Am I just the only asshole that finds an audible noise floor to be a dealbreaker? Or are there T2s out there that are actually dead silent (even in a room with no background noise)?
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Remainder paid, thanks again.
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The ultimate DIY? A Stax SRM-T2!
in Do It Yourself
Posted · Edited by s_r
Put in the second 2.2pf cap just now, and the oscillation looks nigh identical as before. Guess I'll try changing the bypass cap value next.
Edit: This is what the oscillation looks like with the bypass cap set to 20pf.