Anyone have this turntable issue?

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?  

In addition to the experiment Jim suggested, did you try this experiment I suggested earlier:

... if you are still using the Plinius Odeon amplifier you mentioned in a post a few months ago you might try changing the setting of its ground-lift switch to the opposite of what it is currently set to. It would be prudent, though, to turn the amp off and wait about 30 to 60 seconds before changing that setting.

While Bryston provides schematics at their website for many of their models, unfortunately they don’t for the SP3. And neither does hifiengine.com. But I took a look at the schematic for the SP1.7:

http://bryston.com/PDF/Schematics/SP1pt7_SCHEMATICS.pdf

As is the case in many designs it appears that the muting function is accomplished with relays that short the various outputs to ground when the mute function is activated. It also appears that the outputs are AC coupled via 100 uF capacitors, which are "ahead" of the relays in the signal path. I would expect that the SP3 is similar in those respects. If perchance you have the ground-lift switch on the amp set to the lift position, while I can’t formulate a complete explanation I’m thinking that the issue might be related to the fact that with the switch in that position and no signal existing within the SP3 the AC coupling would allow the input of the amp to "float" to an uncontrolled and arbitrary level relative to its chassis and to AC safety ground and to the chassis and the circuit ground of the SP3, **if the muting relays are not activated.**

That may or may not have anything to do with the problem, of course, but intuitively it seems to me that it's a possibility. And in any event if you are using the Odeon the experiment I suggested is easy enough to do. Also, as Jim suggested contacting Bryston and describing your findings to them may be worthwhile.

Regards,
-- Al