for what it's worth, here's the post that talks about R67/R53 being around 1.0v, as perhaps my last post was too vague to garner a reply.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=19585&perpage=10&pagenumber=7
again, I'm not sure if this value of 1v is needed when the output caps are shorted, or what exactly this is measuring
My values are posted above.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=19585&perpage=10&pagenumber=7
again, I'm not sure if this value of 1v is needed when the output caps are shorted, or what exactly this is measuring
My values are posted above.
ok, so I had a chance to measure all the voltages on each channel, about 30 total measurements per channel and then do some simple calculations and what not. I think that I do need to get the values reported above to around 1.0 V. As I understand it, Q16 and Q17 act as a current source and I'm assuming that R67/R53 are used to set their operation point, and ultimately both of these resistors is controlled by the LED at D5.
Here are some calculations and measurements. I have improvised on the notation, and the _schematic notation refers to the attached schematic (not mine) and these numbers are what I'm using for sanity checks... My goal in choosing a new D5, is to get R67/R53 down to 1v, as recommended in the schematic:
V_R67_R = 2.350 V
V_R67_L = 2.361 V
V_R67_schematic = 1.000 V
V_R53_R = 2.374 V
V_R53_L = 2.373 V
V_R53_schematic = 1.000 V
LED_anode_R = -27.05 V
LED_anode_L = -27.04 V
LED_anode_schematic = -27.60 V
LED_cathode_R = -29.99 V
LED_cathode_L = -29.97 V
LED_cathode_schematic = -29.60 V
V_f_LED_R = (29.99-27.05) = 2.94 V
V_f_LED_L = (29.97-27.04) = 2.93 V
V_f_LED_schematic = (29.60-27.60) = 2.00 V
here are my values for one of the two devices acting as current sources:
Q17_collector_R = -3.90 V
Q17_collector_L = -3.93 V
Q17_collector_schematic = -3.90 V
Q17_emitter_R = -27.62 V
Q17_emitter_L = -27.60 V
Q17_emitter_schematic = -28.00 V
Q17_emitter_current_R = (29.99-27.62) V / 150 ohms = 16mA
Q17_emitter_current_L = (29.97-27.60) V / 150 ohms = 16mA
Q17_emitter_current_schematic= (29.60-28.00) V / 150 ohms = 6.7mA
D5 I am current using has the following specs:
V_f_max = 4.0
V_f_typical = 3.5
so, I'm measuring around 2.9v here, so I got one on the low side.. so, am I safe to assume that all I need to do is replace D5 with a device whose V_f is around 1.5 V to get the voltage across R53/R67 to 1v?
This is my first time troubleshooting a circuit like this, so I'd appreciate all the help I can get!
Thanks in advance for the help!!
Here are some calculations and measurements. I have improvised on the notation, and the _schematic notation refers to the attached schematic (not mine) and these numbers are what I'm using for sanity checks... My goal in choosing a new D5, is to get R67/R53 down to 1v, as recommended in the schematic:
V_R67_R = 2.350 V
V_R67_L = 2.361 V
V_R67_schematic = 1.000 V
V_R53_R = 2.374 V
V_R53_L = 2.373 V
V_R53_schematic = 1.000 V
LED_anode_R = -27.05 V
LED_anode_L = -27.04 V
LED_anode_schematic = -27.60 V
LED_cathode_R = -29.99 V
LED_cathode_L = -29.97 V
LED_cathode_schematic = -29.60 V
V_f_LED_R = (29.99-27.05) = 2.94 V
V_f_LED_L = (29.97-27.04) = 2.93 V
V_f_LED_schematic = (29.60-27.60) = 2.00 V
here are my values for one of the two devices acting as current sources:
Q17_collector_R = -3.90 V
Q17_collector_L = -3.93 V
Q17_collector_schematic = -3.90 V
Q17_emitter_R = -27.62 V
Q17_emitter_L = -27.60 V
Q17_emitter_schematic = -28.00 V
Q17_emitter_current_R = (29.99-27.62) V / 150 ohms = 16mA
Q17_emitter_current_L = (29.97-27.60) V / 150 ohms = 16mA
Q17_emitter_current_schematic= (29.60-28.00) V / 150 ohms = 6.7mA
D5 I am current using has the following specs:
V_f_max = 4.0
V_f_typical = 3.5
so, I'm measuring around 2.9v here, so I got one on the low side.. so, am I safe to assume that all I need to do is replace D5 with a device whose V_f is around 1.5 V to get the voltage across R53/R67 to 1v?
This is my first time troubleshooting a circuit like this, so I'd appreciate all the help I can get!
Thanks in advance for the help!!
in case anyone is following along at home, I got some LEDs that proport to have a V_f_typical of 1.5v today in the mail, and of course they don't... they are measuring around 1.72v... I did pick up some infrared LEDs, but they're measuring way too low, as with these V_R67 / V_R53 is around 0.7v => 4.67mA, and I cannot adjust the trimpot to get V_R28 up to 350mV (well, yet... it takes the circuit about 24 hours to reach equilibrium, so we'll see.. the trimpot is maxed out though) 
So my first question to the audience is does this really matter? Also, it it a problem if V_R67 does not equal V_R53? Since I'm going to be using a really low output MC (0.24mV) all of these things kinda scare me, but perhaps they don't matter at all... I need someone more experience to tell me that!
And for my final question, is this problem related to the fact that I cannot get the junction between Q5,R21,R7,C11 down to 0v, or the junction between R62,Q4,R65,Q19,R13 down to 0v, or do I still have another exciting battle ahead of me!
So my first question to the audience is does this really matter? Also, it it a problem if V_R67 does not equal V_R53? Since I'm going to be using a really low output MC (0.24mV) all of these things kinda scare me, but perhaps they don't matter at all... I need someone more experience to tell me that!
And for my final question, is this problem related to the fact that I cannot get the junction between Q5,R21,R7,C11 down to 0v, or the junction between R62,Q4,R65,Q19,R13 down to 0v, or do I still have another exciting battle ahead of me!
The 1.5V led are indeed difficult to source. I found mine by installing a socket for the led on my PCB, then I collected all the led types that I had at home, then I tried all of them. The one I found at exactly 1.5V are small (3mm) red diodes. They are coming from an old PCB that I salvaged years ago. Then I found some more on an other old PCB. It seems that the 1.5V are from old circuits. Maybe the new led design, with higher intensity probably, are using a different junction that is producing a higher voltage. Try to find old PCB with small leds in a surplus store. It may be your solution. Good luck.
Leds in this application are used as low noise zener diode. Normal diode forward voltage are more noisy and less stable. I think the noise issue of the led was really a design criteria to get the preamp noise floor as low as possible. At least this is what I guest from the designer intentions.
Algar_emi said:
Here's a good link on the diode versus LED noise:
http://www.diyaudio.com/forums/showthread.php?threadid=35821
I am pretty much giving up on this, I cannot find anything that will work. V_R67/V_R53 is now down to 1.11 V on both channels and this is as low as I could get. There is a .01mV discrepancy between V_R67 and V_R53 in each channel as well.
Do you think this will matter at all?! If anyone has any suggestions at all, I'm all ears!
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
enjoy your Ono
mlloyd1
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...
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...
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.
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.
luvdunhill said:
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?
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?
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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