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Old 28th March 2013, 12:45 PM   #1931
FdW is offline FdW  Netherlands
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Originally Posted by studiostevus View Post
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[5mV/0.1us/div]

Same tune, different dance I'm afraid.... Vgs=3.51 and 2.95

Both channels show the same behavior, which is suspicious....
That is real strange, if you are using SK170's and 390 Ohm, then at 1mA you should see an Vgs of 390mV. As the Vgs of the mosfet's should be around 4Volt, you are expected to see a Vds (on the NJF) of about 4V-390mV. Are you sure that you are reporting Vgs on the NJF's (not the mosfet's)?
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Old 28th March 2013, 01:02 PM   #1932
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Originally Posted by FdW View Post
That is real strange, if you are using SK170's and 390 Ohm, then at 1mA you should see an Vgs of 390mV. As the Vgs of the mosfet's should be around 4Volt, you are expected to see a Vds (on the NJF) of about 4V-390mV. Are you sure that you are reporting Vgs on the NJF's (not the mosfet's)?
1. Wait a second, now I am confused. NJF = N-channel JFet = 2SK170 ?

2. IF indeed I am measuring the right device, I still may have mixed up the bloody datasheet pinouts (I hate that drawing, wrong for the 10th time). So IF I was measuring the right device, the Vgs on the 2SK170 is 0.00.

Edit: forgot to thank you again for putting up with this....!
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Old 28th March 2013, 02:11 PM   #1933
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Alright, after realizing I read the datasheet wrongly, I also realized that the pinouts of the 2sk170 are different from the j310. So I bent the legs of the 2sk170, and indeed now there is a 'realistic' Vgs. Unfortunately with 390R the Vgs is too low, so I increased to 470R.

This increased Vgs to 339mV and 290mV, which makes me think there is something else wrong (as it should work with 390R already). Q105 , Q206 ???

Any suggestions?
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Old 28th March 2013, 02:35 PM   #1934
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Originally Posted by sq225917 View Post
Sandro, thanks for the parts, they arrived safe and sound. I'll save them for my second build from the most recent GB.
You are welcome Simon I got your nice RIAA caps for mine still waiting for a bit
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Old 28th March 2013, 02:39 PM   #1935
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Both channels show the same behavior, which is suspicious....
Sorry for my probably stupid question;
But do you hook up & measure both Boards @ the same time.
Is there a possible chance both are playing games
with each other ?
Just an idea...
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Old 28th March 2013, 02:55 PM   #1936
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Quote:
Originally Posted by studiostevus View Post
Alright, after realizing I read the datasheet wrongly, I also realized that the pinouts of the 2sk170 are different from the j310. So I bent the legs of the 2sk170, and indeed now there is a 'realistic' Vgs. Unfortunately with 390R the Vgs is too low, so I increased to 470R.

This increased Vgs to 339mV and 290mV, which makes me think there is something else wrong (as it should work with 390R already). Q105 , Q206 ???

Any suggestions?
If the PSU gives out +/- 18 Volt then Q106/206 (the mosfet's) are o.k.

If you have 2sk170's as Q107/207 and 390 Ohm in R108/R208, and then measure 390 mV across R108/208 (e.g. Vgs of the NJF's) then the whole shunt is o.k.

If there is +- 18 Volt and there is 390 mV then the problem is, as before, in the CVS and or the CCS (e.g. the 'top'/'input' halve of the PSU). Can you confirm the above Q107/Q207 and R108/208 values and measurements ?
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Old 28th March 2013, 02:57 PM   #1937
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Quote:
Originally Posted by Benedetto View Post
Sorry for my probably stupid question;
But do you hook up & measure both Boards @ the same time.
Is there a possible chance both are playing games
with each other ?
Just an idea...
For testing I am only using one now
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Old 28th March 2013, 03:06 PM   #1938
FdW is offline FdW  Netherlands
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Quote:
Originally Posted by studiostevus View Post
Alright, after realizing I read the datasheet wrongly, I also realized that the pinouts of the 2sk170 are different from the j310. So I bent the legs of the 2sk170, and indeed now there is a 'realistic' Vgs. Unfortunately with 390R the Vgs is too low, so I increased to 470R.

This increased Vgs to 339mV and 290mV, which makes me think there is something else wrong (as it should work with 390R already). Q105 , Q206 ???

Any suggestions?
The point is, not the voltage, but the current. There should be a Ids of about 1mA (any value between 0.5mA and 2.0mA is fine with me at this point).

This current can be confirmed by I? = Vgs / Rgs. So my questions may have been, what is Ids of the NJF's and what is Vds of the NJF's.

The mark of an correctly operating PSU is
Ids (e.g. I R108) = 0.5 to 2.0 mA.
Vds = 0.5 to 3.0 Volt (while the PSU output is 18V).

And that is what I am trying to confirm (it takes a while to get there sorry for that).
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Old 28th March 2013, 03:09 PM   #1939
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Originally Posted by FdW View Post
If the PSU gives out +/- 18 Volt then Q106/206 (the mosfet's) are o.k.
Yes, that's the case

Quote:
If you have 2sk170's as Q107/207 and 390 Ohm in R108/R208, and then measure 390 mV across R108/208 (e.g. Vgs of the NJF's) then the whole shunt is o.k.
Nope, that's not ok. I am using 2sk170bl and 390r for r108/208 and had less than 390mV (something like 288mV and 329mV).

I considered increasing r108/208, but I guess the problem lies elsewhere...

Quote:
If there is +- 18 Volt and there is 390 mV then the problem is, as before, in the CVS and or the CCS (e.g. the 'top'/'input' halve of the PSU). Can you confirm the above Q107/Q207 and R108/208 values and measurements ?
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Old 28th March 2013, 03:40 PM   #1940
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Quote:
Originally Posted by studiostevus View Post
Yes, that's the case



Nope, that's not ok. I am using 2sk170bl and 390r for r108/208 and had less than 390mV (something like 288mV and 329mV).

I considered increasing r108/208, but I guess the problem lies elsewhere...
So the currents are 783 and 843 mA, that is fine and verifies that the shunt is operating nicely. Also the CCS must be operating, otherwise there would be no 18V or the thing (heat sink) would be cooking.

First suspect should be the CVS (where the external power enters the PSU). If possible replace Q104/204 (BC337/327) with lower gain versions (say Hfe 300 or less) also replace R100/200 with 68 Ohm or parallel the 330 with 100 Ohm and see what happens if this does not help let me know.

(p.s. I will not be able to answer until tomorrow morning )
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