Anyone have this turntable issue?

Jim (Jea48), thanks for providing the links.  Not sure if you noticed that the OP is using a step-up transformer between the turntable and the dual chassis Sutherland phono stage, with the phono stage presumably being used in moving magnet mode.  Here is the manual for the step-up:

https://www.ortofon.com/media/148266/ortofon-st-7-userguide01_web01.pdf

It shows that a single ground wire should connect the turntable to the ground terminal on the SUT, and another ground wire should be connected from that terminal to the phono stage.  Which in this case would mean that a single wire should be used to connect that terminal of the SUT to the ground terminals of both phono stage chassis.

Before commenting further I'll await the OP's response to the questions that have been raised since his last post, as well as confirmation of how the ground connections are implemented between the turntable, SUT, and phono stage.

Best regards,

-- Al
 

Thanks Al (almarg).

Here is what the SP3 manual says about the volume control.    
Page 5

D: VOLUME CONTROL / ROTARY ENCODER Continuous rotary optical encoder for determining volume level as well as an input for most variable settings and other selections within both the System and Source menus.

http://www.bryston.com/PDF/Manuals/300024[SP3].pdf
Do you know how those things work?

Is it possible a high level POP voltage spike would cause the circuitry for the volume control to screw up and pass the spike through onto the gain section of the preamp and out the outputs while still maintaining its’ minimum level setting?

Maybe a dumb question I wonder what would happen if the OP set the SP3 to a different Line level input and then conducted the same test. Nothing should happen right? No POPPING sound through the speakers, right?
That is unless somehow the POP voltage spike is traveling on the signal ground. Could that even happen?
The signal ground is not part of the circuitry of the volume control. Correct?

Jim

@jea48 

Hi Jim,

Not a dumb question at all about seeing if the pop occurs when a different input is selected.  That would definitely be of interest, as would the answers to my questions one of which was about whether the pop disappears if the SP3 is muted.  And yes, a grounding issue does seem conceivable.

The fact that the volume control utilizes a rotary optical encoder isn't particularly helpful, though, at least without detailed information on the circuitry that follows its photo-detector, both within the control and externally to it.  That kind of control works by shining a LED near the circumference of a rotatable disk having a large number of radially-oriented slots through which the light can shine.  As the control is rotated a photo-detector produces an output in the form of a pulse each time a slot moves in front of the LED, and subsequent circuitry utilizes the string of pulses to control how much attenuation is introduced, perhaps after first converting the number of pulses into a corresponding change in a DC voltage. 

Best regards,
-- Al
 

Everything is grounded properly as described in the manuals. I believe we have hit on something with the MUTE button though. There is no MUTE button on the front panel of the SP3 processor but when I select MUTE on the SP3 remote, the problem is solved completely. Now the problem is I don't want to have to go to the remote every time I use the turntable. I always thought volume all the way down was the same as mute. Apparently not. Anyone have any idea what is going on here?

Just a guess the mute circuity is ahead of the volume control circuitry section.
You might want to contact Byrston Tech support.  

Just curious did you try setting the SP3 to a different Line Level input and run a test?