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Old 11th September 2010, 08:42 PM   #4851
Salas is offline Salas  Greece
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I would try play the Mosfet's stopper value up too, afterwards. Some nH resonates with some base or gate. Could be originating in the error amp's layout too, you are right.
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Old 11th September 2010, 09:04 PM   #4852
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While I was pulling the 60R out, I installed 330R. Steady State oscillation has stopped. I now get periodic blips. Not a solid line by any means but a HUGE improvement. I will do the same for the error amp as well.

Note that the vertical scale is now 2mV/div
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Old 11th September 2010, 09:16 PM   #4853
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How does it show if your time scale is 10us? Does it change by clipping elsewhere the gnd crock of the probe? Because it looks more like noise now.
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Old 11th September 2010, 09:36 PM   #4854
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Get much of the same when moving the gnd of the probe around. Attached is the 50ns and 10us with 47R as base stopper on error amp.

I am wondering if I should move the gate stopper back to 120R on the 9140 to see if oscillation resides in error amp or shunt.

The attached look more like noise to me now.
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Old 11th September 2010, 09:42 PM   #4855
Salas is offline Salas  Greece
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At 10us should be cool if it was something with the probing only. They look the same at both time settings. Like noise indeed. But playing with the stoppers you change things. From there you will see where it likely comes from.
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Old 11th September 2010, 09:47 PM   #4856
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I get the same noise with the power disconnected and the probe hooked up.
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Old 11th September 2010, 09:48 PM   #4857
Salas is offline Salas  Greece
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Ooops, it may be working OK now and the noise is not the shunt. Because periods vanished. To be sure, a test is if it has something bad it will make the phono's FFT full of harmonic grass all over. If its as clean as with the other channel on original reg its not its own noise.

P.S. Catch you later.
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Old 11th September 2010, 10:02 PM   #4858
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Good Night and Thanks. Need to clean up my mess now.

P.S. Couldn't resist but replace 330R gate stopper with 120R on 9140 and oscillation returned. Replaced back to 330R and oscillation stopped.
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Old 12th September 2010, 01:24 AM   #4859
Salas is offline Salas  Greece
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This is 9140 with almost double Crss than 9240, and your first iteration proprietary layout, so when it works, it works with what stoppers it needs. Maybe a 220R test at a point for the sake of it. It is not the phase margin bcs both doubling the Ccomp and changing the step network's place did not change it at all, nor the termination from film Zobel to 10x value lytic did. Actually it loses margin with more base and gate stopping. Some layout inductance talked to some base and gate and it had a certain period resonance its the most probable. Watch that FFT noise floor VS other channel with V1, its tell tale on a 58dB phono. If it will feed even 1-2mV of noise, the first stage cascode will catch it. No PSRR to speak off. I wonder where the scope gets that noise when the reg is powered off though. Can it be doing something with the bench DVM which is also across the output or is there some emitting equipment near? Also does it start fast now, so there is nothing left to see about in the main CCS part? Will be nice if its fully OK and you will not have to bother with layout experiments.
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Old 12th September 2010, 02:06 AM   #4860
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Help me explain this. That noise was read across a 5W 700R DALE wire wound resistor. If I read across a 510R 1/4 watt carbon or metal film I don't see the noise. Even with DVM attached.

The regulator picks up instantly when hooked up to the RIAA. It takes its time when hooked up to 700R resistor.

I will try 243R (since I have one) as gate stopper on other channel. If it works I will install in both channels. I ran a quick scan on the noise floor of the riaa and it was same as V1.0 (or very close). I will do a more detailed analysis later when I get my work bench cleaned up. It showed absolutley no 60,120,.... Hz peaks. I still have not gotten my measured noise floor to your levels though.
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