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Old 12th June 2007, 12:12 AM   #111
mlloyd1 is offline mlloyd1  United States
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i'm just butting in here, but the real issue you're making are current sources. once you get a reference voltage, whatever it happens to be, based on whatever LED you happen to pick, you choose the resistor to give you the desired current (after subtracting the VBE voltage, of course). That being said, as long as your current source transistors are working fine, I wouldn't sweat about about 100mV.



enjoy your Ono

mlloyd1
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Old 16th July 2007, 02:42 PM   #112
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so, it seems that I have my fuse delimma worked out for the time being and am using a 3A fuse. I don't get a bunch of warm fuzzys about this, but it will suffice for now.

Now that my Xono actually runs for an extended period of time, I ran into another issue that I'm still in the processing of debugging. I was listening to my 3rd or 4th LP side with the amp all cased up and sitting on top of my record rack and the left channel went out. Strange I thought, so I took the top of and measured a few of the DC values, such as the rail voltages and the bias points, and the JFET drain resistors, etc. and everything looked good. I made sure all the input and output connections were okay and verified that the left channel worked on another phono preamp. All seemed fine. So, I shut the thing off and waited for the LEDs to go out (about 30 seconds maybe) and then I turned it back on and everything worked!

So, I'm confused. If it was a thermal issue, I wouldn't have expected it to work after I restarted it, as it didn't have that much time to cool down! I didn't have time to stress test it much, but I listened to it for 5 minutes or so with no problems. I decided to put the case back together, then leave it running (no signal) overnight and this morning I tried it again and both channels were (still) working.

So, my guess at this point is maybe is that I have to have an input signal to trigger the problem? The way I figure is either one of the devices is having thermal issues (seems unlikely to me at this point), or perhaps some capacitor is going to zero and never charging back up (this is a shot in the dark).

Any ideas on how to troubleshoot this, other than first looking for a way to repeat the problem and then after it happens measure as many of the DC values as possible? What devices would you focus on? I don't have an easy way to bypass the balanced portion of the curcuit, as I didn't add the single ended output connections, but it seems that this would be an easy way to rule out those devices...
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Old 16th July 2007, 04:47 PM   #113
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Speaking about shoot:

Sylvain,
i've got the caps i talked about (actually i have a suitcase of them)

Either Siemens, the later S+M series(is same production but with Siemens-Matsushita print), or ITT labelled ones.
For C4 i have a 10,000pF cap.
For C4+C5 it would be a sextet of 5 times 6490pF and one 3280pF, makes a total of 35730pF instead of 35700pF.
All 1% accurate, comparable sizes to the blackbox RelCap RTEs.

If you're interested in giving them a try, i can lettermail you the values.
On the house, of course.
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Old 17th July 2007, 01:34 PM   #114
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Quote:
Originally posted by luvdunhill
So, I'm confused. If it was a thermal issue, I wouldn't have expected it to work after I restarted it, as it didn't have that much time to cool down! I didn't have time to stress test it much, but I listened to it for 5 minutes or so with no problems. I decided to put the case back together, then leave it running (no signal) overnight and this morning I tried it again and both channels were (still) working.
just another update. I've had it on and cased up for another 24 hours and checked it every 6 hours or so and it everything was fine in both channels using a listening check. Later tonite I'll try putting a test tone through it for a few hours and see if that triggers the problems. Until then, any ideas or other things I should try?
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Old 18th July 2007, 02:54 PM   #115
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well, more strangeness... so, my Ono seems to be rock stable when there is only an occasional signal... I put on a Cardas test LP that has a locked groove with vertical modulation and this played for about 6 hours fine. Before this, the unit had been turned on for 16 or so hours. I then put on another LP (Mahler's 1st, 3rd movement) and the left channel shut off in about 3 minutes. I turned it off and on and then I listened to the same LP for 30 minutes or so with no problems.

The only difference I can see in these two channels is that the turntable ground is connected to the channel that isn't exhibiting problems and there seems to be a lot of static electricity on my LPs these days, due to the weather.

Another observation, that may not be related is that the bass seems to be a bit rolled off... I'm not sure if this is lack of break-in or perhaps the fact that this preamp has a bit less gain than my previous one? The bass is very extended mind you ...

Is there anything else I can try / measure to track this down?
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Old 28th October 2008, 11:33 AM   #116
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Hi, I'm a new member, pls send me the project files, thanks!
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