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Old 12th February 2012, 08:49 PM   #5371
ungie is offline ungie  Canada
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Hi ungie... where are those resistors ?
They are the 220 ohm resistors that drop the main +/- 24V rail voltage to the "target" +/- 12V at TP3 and TP4. These nodes are also connected to C14 and C15, respectively.
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Old 12th February 2012, 08:52 PM   #5372
RCruz is offline RCruz  Switzerland
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R27 to R6 node 18.8V
R34 to R29 node -18.6V
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They are the 220 ohm resistors that drop the main +/- 24V rail voltage to the "target" +/- 12V at TP3 and TP4. These nodes are also connected to C14 and C15, respectively.
Done
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Old 12th February 2012, 09:10 PM   #5373
ungie is offline ungie  Canada
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Have you double checked that the six 3v9 zeners are all the correct type and are installed with the correct polarity? To double check you can measure the voltage at the zener side of R10 and R31.
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Old 12th February 2012, 09:14 PM   #5374
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Thanks ungie, I am busy with something quite revolutionary so i can not concentrate on two things at ones. My system sound so nice at the moment that i decided to do a session.
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Old 12th February 2012, 09:18 PM   #5375
ungie is offline ungie  Canada
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Thanks ungie, I am busy with something quite revolutionary so i can not concentrate on two things at ones. My system sound so nice at the moment that i decided to do a session.
I am happy to try and help out Joachim. Enjoy your listening!

Cheers,

Andrew
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Old 12th February 2012, 09:21 PM   #5376
RCruz is offline RCruz  Switzerland
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Node between R31 and ZD4 -12V
Node between R10 and ZD3 +12.3V

Seems ok
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Old 12th February 2012, 09:48 PM   #5377
RCruz is offline RCruz  Switzerland
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Very strange is it not ?
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Old 12th February 2012, 10:08 PM   #5378
ungie is offline ungie  Canada
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Node between R31 and ZD4 -12V
Node between R10 and ZD3 +12.3V

Seems ok
Yes, this seems fine. So something else is causing the current imbalance between the two polarities of the circuit. Because those voltages after the first 220 ohm dropping resistors are very close in magnitude (18.8V, -18.6V), if the current draw was identical in both polarities the values at TP3 and TP4 would be nearly identical. It's actually the current drawn by the positive branch that is slightly low from what it "should" be.
There are a couple of ideas now:

Measure the voltage at the opposite side of each component connected to TP3 and TP4 (emitters of Q4 and Q5 and the non-TP sides of R14, R37, R36, R38, R39, R30).

OR, if you're willing you can lift one side of R34 and insert a ~20 ohm resistor in series with it. This will drop the voltage at TP4 another 0.5V and make sure that Q27 is conducting. If we now have a low DC offset at the input to RIAA we can work through what is the cause of the current imbalance.

Last edited by ungie; 12th February 2012 at 10:10 PM.
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Old 12th February 2012, 10:22 PM   #5379
ungie is offline ungie  Canada
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Ricardo, did you ever mention what op-amp you are using for the servo?

Andrew
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Old 12th February 2012, 10:24 PM   #5380
RCruz is offline RCruz  Switzerland
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But if the intention is to lower voltage on R34, maybe I could reduce Vin a bit and get the same results ?
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